Loading...
HomeMy WebLinkAboutSWP2702817_4FINAL TECHNICAL APPENDICES CEDAR RIVER SECTION 205 STUDY RENT ON, WA Seattle District, Army Carps of Engineers June, 1997 TABLE OF CONTENTS APPENDIX B - HYDROLOGIC APPENDIX APPENDIX C - HYDRAULIC DESIGN APPENDIX D - PROJECT FEATURES APPENDIX E - PROJECT COSTS APPENDIX F - FISH AND WILDLIFE COORDINATION ACT REPORT e APPENDIX B HYDROLOGIC APPENDIX CEDAR RIVER AT RENTON FLOOD DAMAGE REDUCTION SECTION 205 FEASIBILITY STUDY APPENDIX B TABLE OF CONTENTS Paragraph Page SECTION 1: HYDROLOGY 1.01 WATERSHED a. Drainage Basin 1 b. Principal Tributaries 3 C. Reservoir and Storage Projects 4 1.02 CLIMATOLOGY a. Climate 8 b. Climatological Records 8 C. Temperature 9 d. Precipitation 9 e. Snowfall 10 f. Storm Analysis 11 g. December 1933 Storm 11 h. December 1975 Storm 12 i. December 1977 Storm 13 1.03 STREAMFLOW CHARACTERISTICS a. Discharge Records 14 b. Runoff Characteristics 15 C. Flood Characteristics 16 d. Flood History 17 1.04 FLOOD FLOW ANALYSIS a. Previous Studies 20 b. Routing Model 20 C. Cedar River at Renton Frequency and Flow Duration Curve 22 d. Design Floods 23 1.05 REFERENCES 27 LIST OF TABLES Table No. Title Page 1 Cedar River Basin Summary of Temperature Data 28 2 Cedar River Basin Normal Monthly Temperatures 29 3 Cedar River Basin Summary of Precipitation Data 30 4 Lake Washington Basin Normal Monthly Precipitation 31 5 Cedar River Basin Ten Largest Peaks of Record 32 6 Peak Flows at Renton for 5, 10, 20 and 100 Year 33 Return Periods 7 Peak Flows at Renton for 200 and 500 Year 33 Return Periods Exhibit No. LIST OF EXHIBITS Title Page 1 Cedar River Basin Map 34 2 Cedar River at Renton Frequency Curve 35 3 Cedar River at Renton Flow Duration Curve 36 4 5 Year Cedar River at Renton Hypothetical Hydrograph 37 5 10 Year Cedar River at Renton Hypothetical Hydrograph 38 6 20 Year Cedar River at Renton Hypothetical Hydrograph 39 7 100 Year Cedar River at Renton Hypothetical Hydrograph 40 8 200 Year Chester Morse Lake and Masonry Pool 41 9 200 Year Cedar River at Renton Hypothetical Hydrograph 42 10 500 Year Chester Morse Lake and Masonry Pool 43 11 500 Year Cedar River at Renton Hypothetical Hydrograph 44 SECTION 1. HYDROLOGY 1.01 WATERSHED a. Drainage Basin The 188 square mile Cedar River Basin is located southeast of the city of Seattle and is a major tributary to the 606 square mile Lake Washington Basin (Exhibit 1). The Cedar River originates in the Cascade Mountains just south of the Snoqualmie Pass and flows in a westerly direction until it enters Lake Washington at the city of Renton. Lake Washington empties into Puget Sound at Seattle through the Lake Washington Ship Canal and the Hiram M. Chittenden Locks. The river itself is one of the main sources of supply for Lake Washington which replenishes water lost in the lake every year through evaporation and operation of locks. The Cedar River watershed is bounded by the Snohomish and Sammamish River Basins in the north and Green River Basin in the south. The environment within the basin ranges from wilderness to heavy industrial. The Cedar River is used for recreation, hydropower, and municipal water supply. The entire basin above Landsburg is within the city of Seattle watershed which is closed to development and recreational activities. The river below Landsburg is a major salmon -spawning area. Currently, 67 percent of Seattle's municipal water supply is drawn from the Cedar River at Landsburg. Chester Morse Lake (Cedar Lake) effectively divides the basin into upper and lower subbasins. The upper Cedar subbasin has a drainage area of about 81 square miles. This area is rough and mountainous with a stream gradient averaging about 300 feet per mile. Elevations range from 5,500 feet (National Geodetic Vertical Datum - NGVD) at the crest of the Cascade range to about 1,600 feet near the outlet 1 of Chester Morse Lake. Two dams built by the city of Seattle for water supply and hydropower control the level of Chester Morse Lake which is about 3-1/2 miles long and 1/2 mile wide. The lower Cedar subbasin is about 107 square miles in area with elevations ranging between 20 and 4,100 feet. This subbasin includes some high elevation hills in the upper reach and relatively flat plateau areas in the lower reach. The Cedar River in the upper reach of this subbasin flows generally westward through a relatively narrow valley ending a few miles below Landsburg. Stream gradients through this reach average around 200 feet per mile for the first 3 miles and about 35 feet per mile for the last 14 miles. From this point the river flows northwesterly for 19 miles before emptying into Lake Washington. Stream gradients in this lower reach average about 21 feet per mile. The river in this reach occupies a braided channel in a widening flood plain with streambanks that are easily eroded during high -flow conditions. The lower 5 miles of the Cedar River through the city of Renton has been channelized and stabilized to some extent. In the past, much of the flood plain below Landsburg was farmland, but urbanization is now occurring in much of this area. As a result, an increase in flood damages will likely occur in the coming years. The natural vegetation pattern within the basin has been considerably modified by man. Most of the areas along mountain slopes were formerly covered with dense stands of conifers. The areas downstream of Chester Morse Lake were logged in the early 1900's and are now covered with second -growth timber. Logging now takes place above Chester Morse Lake, and the only remaining, K untouched timber stands are above 3,000 feet in the headwaters area. Most of the flood plain has been logged, and this has eliminated or altered the natural vegetation in this area. Undeveloped land has been disappearing gradually in recent years under the pressure of urbanization and development. b. Principal Tributaries The major tributaries to Chester Morse Lake are the Cedar River itself and the Rex River. The Cedar River enters the lake from the southeastern extremity and has a drainage area of approximately 41 square miles. The Rex River which flows in a northwesterly direction has a drainage area of 13.4 square miles and drains the southern part of the basin above the lake. There are also several small creeks that empty directly into Chester Morse Lake. Taylor Creek, a major tributary between Landsburg and Chester Morse Lake flows northward to join the Cedar River near Selleck. Taylor Creek has a drainage area of 17.2 square miles and is located in the southeastern portion of the Cedar River. On the opposite or north side of the river, Rock Creek (drainage area 11.1 sq. mi.) drains the area around Walsh Lake. For water quality reasons, this creek has been diverted by the Seattle dater Department so that it now enters the Cedar River below Landsburg during normal flow conditions. From this point downstream to Lake Washington, the only tributaries are some minor creeks and storm drain outlets except for Rock Creek near Maple Valley (drainage area 12.6 sq. mi.) located on the south side of the Cedar River. The geology of the basin causes some unique hydrologic behavior. The Cedar River basin, from Chester Morse Lake downstream, contains glacial deposits. This material can be highly permeable to groundwater. The right abutment of 3 the Masonry Dam, just downstream from the Crib Dam at Chester Morse Lake, is an ancient, glacial moraine formed from these deposits. Whenever the pool rises behind the Masonry Dam, seepage into the abutment occurs; and the amount of seepage seems to be related to the Masonry Pool elevation. This resulting groundwater splits the seepage and some of it eventually finds its way back to the Cedar River above Landsburg and some of it into the Snoqualmie River. The timing of the groundwater travel to the Cedar River above Landsburg results in a substantial increase in the river's base flow during the summer months. c. Reservoir and Storage Projects The principal storage reservoir in the Cedar River basin is Chester Morse Lake, a water supply and power project owned and operated by the city of Seattle Water Department and Seattle City Light. Two other storage impoundments, Lake Washington and Lake Youngs, effect flows on the Cedar River but to a much lesser extent. Considerable pressure to increase the municipal and industrial (M&I) water supply storage in the Cedar River Basin is expected in the future to cope with an unprecedented amount of population growth in the region. Lake Washington, located at the mouth of the Cedar River, is regulated by the Corps of Engineers principally to supply water for operating a set of navigation locks. A 2-foot draft limit of the lake between 20 and 22 ft (Corps of Engineers' datum) or about 13.2 and 15.2 feet NGVD, respectively, during the winter provides some erosion protection around the shoreline of the lake. About 217 million gallons per day (m.g.d.) or 335 cubic feet per second (c.f.s.) is required on an average annual basis to operate the locks without drawing the lake below the authorized limits. The discharge capacity of the spillway at the Locks is 18,200 c.f.s.. The fish ladder and saltwater return 4 systems have a combined discharge capability of approximately 385 c.f.s. During periods of high runoff, Lake Washington can produce a backwater effect on Cedar River streamflows below Renton which must be considered in hydraulic computer model studies. Historically, regulation of Cedar River flood flows has not significantly affected Lake Washington in an adverse manner. Lake Youngs, located in the Cedar River Basin southeast of Renton, has a capacity of 11,000 AF and is used as an equalization reservoir in the city of Seattle's water supply system. Water from a diversion facility at Landsburg, which averages about 113 m.g.d. or 175 c.f.s. on an average annual basis, may either enter directly into Seattle's water supply or into Lake Youngs. During floodflow conditions on the Cedar, the Landsburg diversion is shut off and all of Seattle's water is drawn from Lake Youngs. Seattle's development of the Chester Morse Lake project initially began in 1905 with the first hydroelectric power delivered to the city of Seattle from the Cedar River. The head required for this plant was provided by a Crib Dam constructed about 1904 just downstream of the natural outlet to Chester Morse Lake. This raised the natural level of the lake 18 feet to elevation 1,548 feet (approximately NGVD datum). The Crib Dam spillway crest (top of flashboards) was lowered after a failure in 1911 and maintained at varying elevations between 1,546 and 1,548 feet until about 1936 at which time it was permanently held at elevation 1,546 during the non -conservation period. Width of the Crib Dam spillway crest was constructed to a length of about 108 feet. Reconstruction of the Crib Dam occurred in 1988 with the new facility called the overflow dike (described later in this section). Construction of the Masonry Dam was initiated by Seattle in 1913 and completed in 1914. The initial design called for the top of dam to be at 1,615 feet and the spillway crest to be at 1,605 feet. An ungated notch 39.5 feet wide with a bottom elevation of 1,554.5 feet was left in the dam pending construction of a retaining dike near the northeast end of the dam. Because of the serious seepage problems that were later encountered, this dike was never constructed and the notch (service spillway) served as the permanent spillway for the Masonry Dam until 1988 when the emergency and service spillways were constructed (described later in this section). The current asbuilt top of dam is at elevation 1,600 feet. Stoplogs were installed in the notch at varying heights to 6 feet on a year round basis between 1922 and 1957. Between 1957 and 1988, stoplogs were removed during the winter flood season. In order to minimize seepage, especially during the summer and fall conservation period, the Masonry pool (between Masonry dam and overflow dike) is drafted once the lake recedes below elevation 1,546 where Chester Morse Lake becomes independent of Masonry Pool and can be controlled by the overflow dike exclusively. The principal low level outlets for Masonry Dam are the powerhouse penstocks which have a maximum combined discharge capacity of 750 c.f.s. at pool elevation 1,570 feet and an invert elevation at about 1,500 feet. The powerhouse has a tailwater elevation of about 930 feet and discharges to the Cedar River above the Cedar River at Cedar Falls streamgage. A single Howell- Bunger valve through Masonry Dam at approximately elevation 1,498 feet, with a discharge capacity of about 600 c.f.s. at pool elevation 1,570 feet is used to evacuate water during operation and maintenance activities. C In 1988, the Masonry Dam was reconstructed to provide a second and much larger emergency spillway on the north side cf the dam primarily to improve dam safety. Reconstruction also resulted in some modification of the service spillway. The new emergency spillway has three 40-foot bays with radial gates. The crest elevation of the emergency spillway is at elevation 1,538 feet and top of the gate is at elevation 1,570 feet. Total discharge capacity of the emergency spillway at elevation 1,570 feet is 70,000 c.f.s. The service spillway crest was raised to elevation 1,557 feet and a 13 foot gate added with a top elevation at 1,570 feet. Maximum discharge capacity of the service spillway at elevation 1,570 feet is 4,400 c.f.s. The combination of the emergency and service spillway was designed to pass the spillway design flood. Additionally, during this reconstruction, the upstream Crib Dam was removed and replaced with a concrete Overflow Dike. The spillway section in the Overflow Dike has a crest elevation of 1,546 feet (same as the top of the original Crib Dam)and a width of 100 feet. Top of the Overflow Dike was built to elevation 1,550 feet. Two low level outlets are provided in the Overflow Dike: the original 69-inch diameter woodstove conduit with an invert elevation of roughly 1,524 feet and discharge capacity of about 420 c.f.s.; and a new 78-foot diameter conduit with an invert elevation of 1,526 feet and discharge capacity of about 800 c.f.s. Flow from Chester Morse Lake to the Overflow Dike is limited by the approach channel which has a bottom elevation of about 1,528 feet. 7 1.02 CLIMATOLOGY a. Climate The climate of the Puget Sound area is quite mild when compared to other regions at the same latitude because of the moderating influence of the prevailing circulation from the Pacific Ocean. The Cedar River Basin climate is characterized by heavy rainfall, particularly at higher elevations, moderate humidity, wet winters, dry summers, and a comparatively narrow temperature range. b. Climatological Records Only two climatological stations are located within the Cedar River drainage basin: the Landsburg station at elevation 535 feet and the Cedar Lake station at elevation 1,560 feet. Each station has accumulated over 75 years of independent temperature and precipitation records and reflects the climatologic conditions occurring in the middle segment of the basin. Stampede Pass, a National Weather Service (NWS) station with about 50 years of record, is located near the head of the adjoining Green River Basin and is considered to be reflective of conditions near the headlands of the Cedar River basin. The NWS station Seattle -Tacoma WSO-AP located about 5 miles southwest of Renton has nearly 50 years of record and is considered to be representative of conditions in the lower segment of the Cedar River Basin near the mouth. c. Temperature The mean annual temperature of the Cedar River Basin ranges from 390F at the upper elevations to 490F near the mouth. Summertime temperatures within the basin average between 45OF at night to 70OF in the afternoon; wintertime temperatures average between 240F at night to 35OF in the afternoons. Temperature extremes recorded in or near the Cedar River Basin are 101OF at Landsburg and -21OF at Stampede Pass. A summary of H. temperature averages and extremes and normal monthly temperatures for stations in or near the Cedar River Basin are shown in Tables 1 and 2, respectively. d. Precipitation Orographic lifting and cooling as the air mass moves inland from the Pacific Ocean and results in persistent cloudiness and widespread precipitation patterns in the Puget Sound area. Precipitation is generally light in summer, increasing in the fall, reaching a peak in winter, and then decreasing in spring. Generally, 50 percent of the annual precipitation falls in the 4-month period from October through January, 75 percent occurs in the 6 months from October through March, and less than 5 percent during July and August. In the Cedar River Basin, annual precipitation averages about 86 inches, ranging from approximately 66 inches in the lower Cedar basin to about Ill inches in the upper Cedar basin. Normal monthly precipitation at stations in or near the basin ranges from 14.3 inches in December at Stampede Pass to only 0.7 inch in July at Seattle -Tacoma WSO-AP. Maximum recorded monthly precipitation was 46.80 inches at Cedar Lake in December 1917. A maximum 24-hour precipitation of 7.94 inches was recorded at Stampede Pass in November 1962, and the maximum 1-hour precipitation recorded during this period was 0.61 inch. A summary of precipitation averages and extremes and normal monthly precipitation for stations in or near the Cedar River Basin are provided in Tables 3 and 4. e. Snowfall The percent of precipitation that falls as snow depends largely upon elevation. Mean annual snowfall varies from about 13 inches near G the mouth of the basin to almost 450 inches in the higher elevations. Snow surveys are routinely made at 9 snow courses in or rear the Cedar River Basin. f. Storm Analyses The Cedar River Basin on the western slopes and foothills of the Cascade range lies directly in the path of cyclonic disturbances rising inland from the Pacific Ocean from October through March. Nearly all major floods in the basin are produced by severe storms which occur mainly during the winter months and produce gale force winds and heavy precipitation. Storm precipitation varies over the basin, with greatest amounts falling at the highest elevations in the upper Cedar River basin where precipitation is generally orographic in nature. It is not unusual for a major storm to occur in the upper Cedar River Basin with only moderate precipitation falling in the lower basin as in December 1977. The reverse situation can also occur but usually produces less severe flooding due to the attenuating effect of Chester Morse Lake on reservoir inflows. The most common pattern of winter precipitation is a period of steady rain and warm temperatures for 8 to 12 hours followed by a cooler showery period. These storms often occur as a series of waves passing in rapid succession at intervals of 24 to 36 hours and can produce large volumes of precipitation and significant flooding as in December 1975. A critical storm situation from a reservoir regulation standpoint can occur when several major events occur within 7 to 12 days of one another potentially preventing storage evacuation between events, such as in December 1933. Freezing levels during major storm events typically rise above 8,000 feet as the first storm approaches and remains high until the last of the series of storms passes through the area. Snowmelt resulting from warm temperatures can average more than 5 to 10 10 percent of the total storm precipitation and as much as 50 percent of the daily total for some events. The storms of December 1933, 1975 and 1977, discussed further in the following paragraphs are characteristic of the different meteorological conditions producing major flood events. g. December 1933 Storm The month of December 1933 was one of unprecedented rainfall over western Washington, including the entire Cascade Mountains. The total monthly precipitation was greater than for any month of record at the majority of stations. A pronounced high pressure cell of polar air stagnated in a position from central Alaska southeastward over Canada during the entire month, forcing the low pressure storms from the Gulf of Alaska to go southward and progress across British Columbia and Washington. Moderate precipitation was general over western Washington, starting on the 2d and increasing in intensity as a storm center developed in the Gulf of Alaska on the 4th, increasing in magnitude and starting a southward movement on the 7th. After 8 December, this storm center stagnated with only minor shiftings off the Washington coast, and secondary lows with frontal waves moved eastward over Washington or southern British Columbia. This situation resulted in steady rains over the western portion of the State for about 28 days with two distinct storm fronts and periods of concentrated rain occurring about 12 days apart. Due to a lack of snow measurement stations in the Cedar River or adjacent basins in 1933, little is known about the actual contribution of snowmelt to this flood event. However, based on a study of snow depths at climatological _1 stations in the White River Basin about 20 miles south, snowmelt may have been only a small portion of the total runoff volume. The study indicates that at the beginning of the storm the snow line was at approximately 2,000 feet, which indicates that 60 percent of the basin was snow-covered. During the storm, however, the snow line apparently receded only a few hundred feet, as the stations at Parkway (elevation 2,628 feet) and Longmire (elevation 2,762 feet) were still snow-covered at the end of the storm. The snow depth at Parkway decreased from 13.5 inches on the 7th to 2.1 inches on the llth, and at Longmire from 9.0 inches on the 8th to 1.0 inch on the llth. Perhaps 5 to 10 percent of the flood volume was the result of snow melt. h. December 1975 Storm By 29 November, the high-pressure ridge protecting the Pacific Northwest from more intense storms had flattened out and moved eastward to be replaced by a strong inflow of warm, saturated air. Heavy rain began over western Washington late on the 29th and early 30 November. It did not moderate at most stations until near midnight on 30 November, after which the rate of fall became increasingly heavy as the warmer air arrived. Snowfall in the mountains had changed to heavy rain by the afternoon of 30 November. Precipitation at Stampede Pass began early on 30 November, with more than half the 4 inches of rain on that day falling as snow. Much of the rain was retained within the snowpack. As the warm air mass arrived at Stampede Pass, the temperature rose about 250F in a few hours to near 40°F. The wet snowpack was estimated to be completely conditioned and yielding runoff by the end of 30 November. During to next 24 hours to midnight on 1 December, a near -record 6.9 inches of rain fell at Stampede Pass. This was augmented by about 2 inches of snow melt for an estimated combined 24-hour contribution to runoff of 8 inches. Rainfall and snowmelt 12 continued through 3 December. Precipitation diminished the morning of 4 December, and the temperature dropped to below freezing, reducing snowmelt. Rainfall and snowmelt contributed to a total storm runoff at Stampede Pass estimated at 21.6 inches. The storm period from 0000 hours on 30 November to 0600 hours on 4 December included three distinct storms following each other in close succession. i. December 1977 Storm For several days prior to the onset of the heavy precipitation in western Washington, a protective ridge of high pressure shunted the more intense Pacific storms to the north of Washington. By the morning of 1 December 1977, the high-pressure ridge had flattened sufficiently to allow the Pacific storm track to be depressed south, bringing a series of intense short -wave storm systems into Washington and northern Oregon. Very heavy rains were encountered on the westerly orographic slopes of the Cascade and Olympic Mountains. Temperatures rose 100 to 150F following the passage of the first warm wave, and the freezing level remained between 5,000 and 10,000 feet during the first and second days of the storm period. Snowmelt estimated in excess of 5.9 inches, the majority of which occurred between 2 and 3 December after the flood had peaked, added to the total storm runoff. Stampede Pass recorded over 13 inches of precipitation during the 3-day storm, 5.93 inches of which was recorded in one 24-hour period. 13 1.03 STREAMFLOW CHARACTERISTICS a. Discharge Records Most of the major streams and tributaries within the Cedar River Basin have one or more recording streamgages. The Landsburg and Cedar at Cedar Falls gages on the Cedar River have the longest records of any station in the Puget Sound area with streamflow records dating back to 1895 and 1914, respectively. Records for most of the remaining gage stations date back to 1946. Streamgage records for the Cedar River stations below Chester Morse Lake are significantly affected by project regulation. Records of daily (and some limited hourly) Chester Morse Lake elevations, power production, and other pertinent project data have been maintained by City Light since about 1905 and Chester Morse Lake elevations have been published by the USGS since 1977. The Corps of Engineers has maintained a record of Lake Washington elevations since 1901. The streamgage location at Renton has a tendency to aggrade which affects the observed flow rate during periods of high runoff on the river. During the December 1975 flood, the rating at Renton shifted by 0.15 foot or 170 c.f.s. The average shift in the rating or loss in channel capacity since 4 December 1968 when the rating began to shift has been about 0.22 feet or 350 c.f.s. per year. The continued aggredation is causing a loss in channel capacity and is significantly affecting the flood situation at Renton. b. Runoff Characteristics Streamflows typically follow the general rainfall pattern in the area, with highest runoff occurring in the rainy fall and winter months. Winter flows are characterized by frequent rises resulting from storms or series of storms; however, not all rises reach flood proportions. Runoff gradually decreases as rainfall diminishes in the spring 14 and summer dry months. Lowest flows occur in August and September, although low flow conditions can extend into November or December. Occasionally, above -normal spring precipitation from a heavy storm in March or April will produce periods of high runoff and cause the annual peak to occur during this period (e.g., March 1972). The seasonal rise in temperatures during the spring and early summer months frequently produces a period of high snowmelt runoff from the upper Cedar basin. This snowmelt runoff is not as significant in the lower Cedar basin where snowpack is generally light and does not last long into the spring months. Snowmelt runoff into Chester Morse Lake during the spring period is typically stored for summer conservation. Inflow to Chester Morse Lake is affected by seepage from the reservoir, which can range from about 50 c.f.s. to over 400 c.f.s. during low and high reservoir levels, respectively. Return flow from reservoir seepage causes the streamgages Cedar River at Cedar Falls and at Landsburg to show a somewhat higher base flow during late summer and early fall than other nearby streams. This flow augmentation from seepage return to the river above Landsburg is estimated to be roughly 75 percent of the reservoir seepage lagged 60 days. Flow augmentation at Renton is not as obvious since streamflows are reduced because of Seattle Water Department's diversion below Landsburg which averages about 159 m.g.d. or 245 c.f.s during July and August and 92 m.g.d. or 142 c.f.s. during the winter. A high base flow condition is also noticeable on Taylor Creek, a tributary to the Cedar above Landsburg, but the source is unknown. All three streamgages on the Cedar River below Chester Morse Lake are affected by project regulation and releases for power production which can be as great as 750 c.f.3. 15 c. Flood Characteristics Flood flows of significant magnitude on the Cedar River are caused by concentrated 2-to 5-day rainstorms or series of storms with intense periods of rainfall that usually last less than 24 hours. Flood runoff to Chester Morse Lake is characterized by sharply rising hydrographs with peak discharges maintained for only a few hours and followed by recessions almost as rapid. The natural rate of rise in the inflow to Chester Morse Lake is estimated at approximately 560 c.f.s. per hour and the. rate of fall above the base flow inflection point at about 480 c.f.s. per hour based on the December 1977 flood which is representative of most large flood events. Air temperature during these storms is usually warm enough to melt a significant amount of the snowpack as the freezing level will typically rise above 8-10,000 feet. Flood flows below the dam are generally a result of spill from Masonry Dam combined with local runoff. Induced storage in Chester Morse Lake and the small dimensions of the service spillway significantly dampens the reservoir inflow and resulting spill thereby diminishing the flood impact in the downstream reach. In rare instances these storms occur in a critical sequence such that the timing of the local runoff and dam release combine to produce the most severe level of flood damage in the lower basin as in December 1933 and December 1975. These long duration, high volume floods, rather than those with higher peaks but less volume, produce the most critical runoff sequences for downstream flood control. Local runoff from the flatter terrain of the lower elevation subbasins below Masonry Dam is characterized by a relatively slow rise and long flow duration. On the average, local runoff will peak about 5 hours after Chester Morse Lake inflow peaks, although this can vary significantly depending on the regional extent of the storm and meteorologic conditions. In addition, considerable variation can exist in the relative magnitudes of the local runoff peak and reservoir inflow peak from W event to event. The effect of Lake Washington on flood flows in the Cedar River below Renton has not been a significant problem historically. d. Flood History Reports of flooding along the Cedar River in the reach below Landsburg can be traced through newspaper articles back to 1850. Flood damages prior to construction of the Masonry Dam were primarily concentrated in the Renton area. Since that time, channelization work in the lower 1 mile of the Cedar River around 1912 and development upstream of Renton has been such that the upstream area now experiences flood damage before Renton. The current Corps of Engineers zero damage level at Renton is 4,000 c.f.s., although this can vary with the amount of aggradation (see Section 1.03a). The National Weather Service in December 1983 established flood stage for the lower valley based on the Landsburg gage at 5 feet or about 3,500 c.f.s. (NWS flood stage is usually set lower than USACE zero damage stage to provide a warning period). The maximum recorded level of Lake Washington during the winter due to high inflow occurred in December 1975 and was 20.6 feet (COE datum) which is 1.4 feet below the normal maximum lake level. The level of Lake Washington during the December 1977 flood was 20.1 feet but this was forced due to project operations. No significant damage was incurred or induced around the lake at Renton from the December 1975 event. The greatest floods of record on the Cedar River from a damage standpoint occurred in December 1933, December 1975 and November 1990. All of these floods were large volume events, with the December 1933 flood having the greatest volume and longest duration. A tabulation of the ten greatest observed and natural (deregulated) discharges at the Renton and Landsburg 17 gages and inflows to Chester Morse Lake are provided in table 5. The following paragraphs provide a general description of the flooding associated with several of the largest events of record in the Cedar River Basin. (1) The flood of December 1933 was the result of a combination of heavy precipitation and snowmelt. This particular flood affected the entire basin. Some inundation occurred in the town of Renton, and severe flooding occurred along the river between Landsburg and Renton. Reported logjams that formed in the channel during this flood may have induced some of the damage. (2) The flood peak in February 1951 was the result of some very heavy rains that occurred from B to 11 February. Flooding occurred in the river valley upstream of Renton, but no inundation took place within the city itself. (3) The high water of March 1972 was the result of some very heavy rainfall that occurred mostly on 5 March. Local inflow between Cedar Falls and Renton was particularly high. (4) The flood peak in December 1975 was similar to that which occurred in 1933 but of slightly higher magnitude and shorter duration. A ripe snowpack, combined with heavy rainfall, produced optimum yield which aggravated flood conditions. At Renton, the river was above the major -damage level for 79 hours. Many residential areas had between 3 and 4 feet of floodwaters. An estimated $2,350,000 of damage at 1975 prices and conditions was experienced by this flood in the Cedar Valley. 1p (5) The high flows of Decetber 1977 were the result of high - intensity precipitation falling on =:e Cascades above about 1,500 feet. Flows at Renton were relatively low because of a lack of significant local flow between Cedar Falls and Renton and flood peak storage in Chester Morse Lake. (6) The storms of November 1990 produced two large flood events; the first occurring around Veterans Day and the second just after Thanksgiving. Continuous warm heavy rainfall along with a melting snowpack characterized the weather conditions throughout November. Flooding on the Cedar River on November 24-26 was a new record maximum and lead to the closure of the Renton Municipal Airport adjacent to a Boeing Company complex that includes the 737 and 757 jet factories. The recurrence interval of the Thanksgiving flood has been estimated from gages on the Cedar River at about a 50-year event. 11K 1.04 FLOOD FLOW ANALYSIS a. Previous Studies Much of the work described in this section was based on the Corps of Engineers, Seattle District, 1988 Cedar River Flood Control Study. The work performed in the 1988 study was used to construct the previously adopted Cedar River at Renton frequency curve dated July 1989. The 1989 Cedar River at Renton frequency curve was developed using the Corps of Engineers SSARR (Streamflow Synthesis and Reservoir Regulation) flood routing model. It was preferred to route Chester Morse Lake inflow using SSARR as opposed to using observed gage readings at Renton when producing the frequency curve. This would produce somewhat different flows at Renton than the observed gage record, but would provide a common reservoir operating scheme for the entire period of record. b. Routing Model The SSARR computer model was used to route observed flood hydrographs from Chester Morse Lake to Renton and develop coincident local inflows for each historic flood event analyzed. The model was calibrated to the December 1975 and 1977 floods by routing project inflows through Chester Morse Lake to the downstream streamgages at Cedar Falls, Landsburg and Renton and adding an estimate of the local inflow between the gage. Routing parameters (time of storage and routing phases) were adjusted for each routing reach until the timing and attenuation of the routed hydrograph reconstituted the observed hydrograph. Project releases and downstream flows in the calibration effort were adjusted to include an estimate of the powerhouse discharge, seepage from the Masonry pool, and seepage return flows above Cedar Falls and Landsburg. Landsburg M&I diversions were reduced to zero when the flow at Landsburg exceeded about 2,000 c.f.s. as agreed r_o by the Seattle Water Department. 20 Observed flow data from 30 large flood everts from 1906-1986 was applied to SSARR to obtain the peak flow at Renton under current City of Seattle flood regulation procedures (City of Seattle, Chester Morse Lake Operation and Maintenance Manual). Historical inflows to Chester Morse Lake were calculated by several methods depending on the availability of hourly streamflow and reservoir elevation data. For each method, the inflow was calculated using the continuity equation from an estimate of the dam outflow including spill, powerhouse discharge and seepage from the Masonry pool and change in reservoir storage. In some cases where hourly streamflow data but not reservoir elevations were available and spill was known to have occurred, the hourly reservoir levels were back -calculated from the spillway rating curve. If hourly data was limited, the computed inflow hydrographs were reshaped to more accurately define the timing and magnitude of the flows using regression and other transfer techniques and comparison with tributary streams. Local inflow hydrographs below the dam for each historic event were determined by subtracting the routed observed hydrograph at an upstream gage from the observed hydrograph at a downstream gage. The Landsburg local was adjusted to exclude seepage return flow. The Renton local was adjusted to include M&I diversion at Landsburg. Cedar Falls local (between the dam and the gage at Cedar Falls) was estimated to be 10 percent of the Landsburg local based on a ratio of the drainage areas. Renton local inflow prior to 1945 was estimated as 60 percent of the Landsburg local based on regression analysis of the peak discharges between the Renton and Landsburg locals and routings of hypothetical floods. 21 Initial reservoir elevations were set at either the historic elevation if no spill occurred for a period of time prior to onset of the flood or at an elevation commensurate with the service spillway crest if spill had occurred on the beginning of the flood. In cases where bulkheads were installed in the service spillway (prior to 1957), an appropriate adjustment was made in the starting reservoir elevation based on the volume of inflow. Outflow from Chester Morse Lake was modeled through level pool routing and was determined by a rating table that included discharge from the power tunnel and flow over the service spillway. The outlet rating was adjusted to reflect maximum power release even through the peak of each flood event which is the historical practice to limit the pool rise. Seepage and seepage return were assumed to be equal which produces a slight but acceptable increase in Cedar River flows of less than 200 c.f.s. C. Cedar River at Renton Frequency and Flow Duration Curves Computed peak flows obtained by SSARR were used to develop the Cedar River at Renton frequency curve (Exhibit 2) following the methodology discussed in U.S. Army Corps of Engineers (1993), and U.S. Department of the Interior (1981). The frequency curve was produced using median plotting positions and assuming a zero skew which is consistent with skew values for similar natural watersheds in the region. Graphical curve fitting methods were applied to the peak flows since analytic fitting methods are not recommended for developing regulated flow frequency curves (U.S. Army Corps of Engineers, 1993). To update the 1989 frequency curve, data from the November 1990 flood was routed through SSARR to produce a peak flow at Renton. The computed peak flow was found to be 9,520 cLs and this was applied to the output of the previous 22 30 SSARR runs to produce a new frequency curve. When comparing the 1989 curve with the new curve it was discovered that the November 1990 event increased the 100 year peak flow by less than 5%. Due to model and gage inaccuracies it was deemed unnecessary to abandon the 1989 frequency curve. It should be noted that the flow gages at Cedar Falls, Landsburg and Renton were all known to have failed during various periods on the 24th and 25th of November 1990. An additional frequency curve was developed to reflect future development in Renton (see Exhibit 2). Future condition flows were taken to be an additional 8% over present condition flows as stated by King County Department of Public Works (1993). A summary of peak flow values at Renton for various return periods is given in Tables 6 and 7. A Cedar River at Renton flow duration curve (Exhibit 3) was developed using USGS mean daily flow data and the STATS (HEC, 1987) computer program. The period of record for the flow duration curve is from water year 1946 to 1993. d. Design Floods Hypothetical hydrographs of local inflow below the dam and reservoir inflow were constructed based on observed floods and regression analysis between peak discharges and coincident 1-, 3-, and 5-day maximum average flows. Reservoir inflow was determined by regression analysis between the peak at Renton and the 3-day (critical duration) inflow to Chester Morse Lake. Coincident local inflow hydrographs below the dam were developed based on regression between the peak at Renton and the peak of the local inflows for Renton and Landsburg. The local inflow was adjusted within acceptable limits in the SSARR routing model to reproduce the design flood at Renton. For inflows with 100 years return period or less, the discharge from the Masonry Dam consists of flow through the powerhouse and flow over the service spillway. Outflow from the dam was modeled through level pool routing and was determined by a discharge rating table in the SSARR model. Starting 23 lake levels for the 5, 10 and 20 year events were taken to be the normal winter flood control pool (elevation 1546 ft). For events 100 years or greater the initial lake elevation was taken to be 1560 ft based on the assumption that antecedent conditions would cause tie higher elevation. The 5, 10, 20 and 100 year hypothetical hydrographs for Renton are displayed in Exhibits 4 to 7, respectively. Hypothetical hydrographs for the 200 and 500 year floods were developed through SSARR runs and simulate the opening of the 3 emergency gates. According to the Chester Morse Lake Operations and Maintenance Handbook, the current plan of operation for Chester Morse Lake with the emergency spillway gates requires these gates to remain closed at all times except in the case where an inflow greater than a 100-year event would cause the reservoir to exceed the maximum flood pool at elevation 1,570 ft. A 100-year inflow is defined when the flow exceeds 15,000 c.f.s. which is indicated by a specified rate of rise in pool elevation. Emergency gate openings were determined according to a rate -of -rise table and emergency gate schedule given in the handbook. Opening of the emergency gates can occur at any elevation beyond 1560 ft as long as the rate of rise is satisfied, but must be opened at elevation 1568 ft. This procedure allows for a considerable amount of latitude in emergency gate operation. For the purpose of this analysis, a conservative operation was chosen to estimate the maximum discharge from Chester Morse Lake. Other flood control operations are possible which could produce lower maximum outflows from Chester Morse Lake. For example, an operation designed to optimize available storage could reduce outflows by up to 26 and 14 percent respectively for the 200 and 500 year floods. However, since the actual operation for a given flood event is unknown, this analysis assumed a conservative operation in that the rate-o'-rise criteria and gate schedule would be rigidly adhered to. For both the 200 and 500 year floods, the following operational assumptions were made: 24 1. The emergency gates will not be opened un=i1 the rate of rise in pool elevation equal or exceeds the values in the rate of rise table. For the 200 and 500 year floods analyzed in this study, the rate -of -rise did not necessita=e opening the emergency gates until elevation 1567.ft. 2. Gate openings are made in accords with the Masonry Dam emergency gate schedule while adhering to an opening constraint of 2 ft/hour. 3. The emergency gates will not pass more than current inflow on the climbing side of the inflow hydrograph. 4. It was assumed that all three emergency gates would be utilized and opened in unison. Evacuation of the Masonry Pool can be performed in many different manners and is not prescribed in the Operation and Maintenance Handbook. Both the 200 year and 500 year floods were evacuated using the following procedure: 1. As the reservoir pool falls below elevation 1568 ft, the emergency gates are closed to 4.0 ft and maintained until elevation 1562 ft with the goal of attaining 1560 ft (the initial pool elevation)by the end of the 6-day simulation. 2. At elevation 1562 ft, outflows are gradually ramped down to begin a transition back to the service spillway at elevation 1560 ft. The reservoir regulation applied to the 200 and 500 year floods rigidly followed the emergency gate schedule and made all the specified gate changes according to pool elevation. An exception was taken for the specified gate opening of 5.6 ft when the pool elevation reached 1568 ft. A 5.6 ft gate opening would discharge roughly 19,400 cfs which is more than the peak inflow for both the 200 and 500 year floods. Therefore, the gates were only opened enough to pass the current inflow while also adhering to the 2.0 ft/hour gate opening constraint. The gate opening was then increased or held depending on whether inflows were climbing or falling. Evacuation of the reservoir was performed as described above. 25 For the 200 year flood (Exhibits 8 and 9), a first emergency gate opening of 2.0 ft was made at 14:00 on Day 2 producing a discharge of 7,440 cfs by elevation 1567.5 ft. Two hours later, at elevation 1568 feet, z,e emergency gates were opened to 4.0 ft producing a discharge of 14,300 cfs. On Day 2, 17:00 it was observed that the inflow had peaked two hours earlier at 16,100 cfs and was receding. Therefore, the gates were only opened enough to pass the current inflow of 15,600 and were held at that gate setting until the pool fell below 1568 ft. The 500 year flood (Exhibits 10 and 11) was regulated similar to the 200 year flood. An initial emergency gate opening of 2.0 ft was made at elevation 1567.5 (Day 2, 12:00) producing a discharge of 7,440 cfs. Two hours later, at elevation 1568 ft, the emergency gates were opened an additional 2.0 ft yielding 14,300 cfs. At 15:00 hours the emergency gates were opened to pass the current inflow of 17,900 cfs. The following hour it was observed that inflows had peaked at 17,900 cfs, therefore the gate opening from the previous hour was maintained until the pool elevation reached 1568 ft. W 1.05 REFERENCES City of Seattle, Seattle City Light, Seattle Water Department (1986), Cedar Falls Improvement Project, Final Environmental Impac= Statement, pg 2-12, 3-8, 3-9. City of Seattle, Seattle City Light, Seattle Water Department (unknown date), Operations and Maintenance Handbook, Cedar Falls Headworks and Overflow Dike. Hydrologic Engineering Center (1975), Hydrologic Frequency Analysis, U.S. Army Corps of Engineers, 609 Second Street, Davis, CA 95616, pg 4-28. Hydrologic Engineering Center (1987), Statistical Analysis of Time Series Data (STATS), U.S. Army Corps of Engineers, U.S. Army, 609 Second Street, Davis, CA 95616, pg 4-28. King County Dept. of Public Works Surface Water Management Division (1993), Cedar River Current and Future Conditions, pg 3-35. U.S. Army Corps of Engineers (1988), Cedar River Flood Control Study 1988 (Hydrol), Wrap-up Rpt and Draft Hydrol App. Report # 1110-2-1403b, Lk Wash R. Basin - Invest, Seattle District. U.S. Army Corps of Engineers (1993), Hydrologic Frequency Analysis, Engineering Manual 1110-2-1415 U.S. Department of the Interior (1981), Guidelines For Determining Flood Flow Frequency, Bulletin #17B, U.S. Department of the Interior, Geological Survey, Office of Water Data Coordination, Reston, Virginia. 27 TABLE 1 CEDAR RIVER BASIN SUMMARY 0= TEMPERATURE DATZ (THROUGH 1994) Temperat,-re (OF) Period Climatological Elevation of Mean Record Extreme Extreme Station (Feet) Record Annual Years Maximum Minimum Bothell 2N 100 1931-1959 49.9 29 100 -10 Cedar Lake 1,560 1912- 47.6 83 98 -16 Kent 30 1913- 51.06 82 101 - 5 Landsburg 535 1916- 49.04 79 101 0 Seattle -Tacoma WSCMO AP 400 1945- 52.0 50 100 0 Seattle WBAP 14 1928-1964 52.3 33 100 0 Seattle WB City 14 1878-1971 52.4 81 100 3 Stampede Pass WSCMO 3,958 1944- 39.3 51 91 -21 M TABLE 2 CEDAR RIVER BASIN NORMAL MONTHLY TEMPERATURES (°F) (1961-1990) Station Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual Cedar Lake 34.4 37.0 39.9 45.8 51.7 55.6 60.7 60.2 56.7 49.9 41.7 37.6 47.6 Landsburg 36.9 39.8 43.3 48.4 53.8 57.9 61.9 61.3 57.4 50.3 42.6 39.3 49.4 Seattle -Tacoma WSOAP 40.1 43.5 45.6 49.2 55.1 60.9 65.2 65.5 60.6 52.8 45.3 40.5 52.0 Stampede Pass WSMO 24.1 28.1 30.1 35.3 42.5 49.2 56.1 55.6 51.1 42.1 30.9 20.5 39.3 29 Station Bothell 2N Elevation (Feet) 100 TABLE 3 CEDAR RIVER BASIN SUMMARY OF PRECIPITATION DATA (Through 1994) Precipitation (Inches) Period of Mean Record Greatest 1-Day Greatest 1-Mo Record Annual Years 1/ Amount Date Amount Date 1931-1959 39.46 29 2.80 Dec 37 14.35 Dec 33 Cedar Lake 1,560 1899- 102.50 80 6.16 Nov 06 46.80 Dec 17 Kent 30 1912- 38.48 62 3.00 Jan 35 16.99 Dec 33 Landsburg 535 1903- 56.37 77 4.05 Feb 51 22.63 Dec 33 Seattle -Tacoma WSCMO AP 400 1944- 37.19 44 3.74 Sep 91 12.92 Jan 53 Seattle WBAP?/ 14 1928-1964 36.08 34 3.02 Feb 45 10.93 Jan 53 Seattle WB City2/ 14 1878-1971 34.01 94 3.52 Dec 21 29.06 Jan 53 Stampede Pass WSCMO 3,958 1944- 92.57 45 7.94 Nov 62 30.42 Jan 69 1/ Record years reflects only those years in which the gage was active 21 Record included for extension of Seattle -Tacoma WSCMOAP 30 TABLE 4 LAKE WASHINGTON BASIN NORMAL MONTHLY PRECIPITATION (INCHES) (1961-1990) Stations Jan Feb Mar Air May Jun Jul Aug Sip Oct Nov Cedar Lake 13.31 10.55 10.04 8.38 5.82 5.51 2.12 2.89 5.63 10.29 13.4 Landsburg 7.24 5.66 5.20 4.46 3.31 3.14 1.33 1.82 3.32 5.53 7.45 Seattle -Tacoma 5.38 3.99 3.54 2.33 1.70 1.50 0.76 1.14 1.88 3.23 5.83 WSCMO AP Stampede Pass 14.59 10.19 8.88 6.28 3.97 3.84 1.56 2.85 4.65 7.74 12.1 WSCMO 31 TABLE 5 CEDAR RIVER BASIN TEN LARGEST PEAKS OF RECORD (C.F.S.) CHESTER MORSE LAKE RENTON (1933, 1945-1993) LANDSBURG (1903-1993) (1906-1993) Recorded Natural (deregulated)1/ Recorded Natural (deregulated)1/ Date Discharge2/ Date Discharge Date Discharge Date Discharge Date Inflow Nov 1990 10,600 Nov 1990 15,300 Nov 1911 14,2003/ Dec 1977 13,900 Dec 1977 13,500 Dec 1975 8,5004/ Dec 1977 13,800 Nov 1906 12,400 Nov 1990 13,700 Jan 1923 12,800 Dec 1933 8,100 (est) Jan 1984 13,700 Nov 1990 10,800 Jan 1923 13,400 Nov 1990 12,500 Feb 1951 7,100 Nov 1959 11,900 Jan 1903 10,400 Feb 1924 13,400 Nov 1911 12,000 Mar 1972 G,200 Dec 1975 11,800 Nov 1909 8,370 Dec 1917 13,300 Dec 1917 11,700 Dec 1977 5,700 Mar 1972 11,700 Dec 1917 8,150 Jan 1984 12,600 Nov 1959 11,700 Nov 1959 5,600 Feb 1951 11,600 Dec 1975 81000 Nov 1906 12,100 Dec 1943 11,300 Jan 1984 5,600 Nov 1959 11,400 Dec 1933 7,520 Nov 1959 12,100 Dec 1975 10,600 Dec 1946 5,500 Dec 1933 11,120(est) Feb 1951 6,100 Dec 1943 11,700 Jan 1984 10,500 Jan 1965 5,250 Dec 1955 i1,100 Dec 1921 5,960 Nov 1911 11,400 Dec 1924 10,350 1/ Flows developed from SSARR routing model. Natural flows are without Cedar Lake. 2/ Does not include floods of 1906 and 1911 with an estimated peak at Renton of 13,000 cfs and 11,100 cfs respectively. These two events were used to construct the frequency curve. 3/ Landsburg November 1911 high flow caused by failure of flashboards. The estimated flow without flashboard failure is 8,740 c.f.s. 4/ The USGS estimated the December 1975 peak at 8800 c.f.s. USACE used 8,500 c.f.s based on routing and backwater studies. 32 TABLE 6 " PEAK FLOWS AT RENTON FOR 5, 10, 20 and 100 YEAR RETURN PERIODS Return Period Peak Flow (years) (cfs) 5 4,900 10 6,300 20 7,900 100 12,000 1/ The regulation for up to a 100 year event assumes: a. all inflows will pass through the power tunnel and over the service spillway. b. the gates for the service spillway will be at full open. TABLE 7 " PEAK FLOWS AT RENTON FOR 200 AND 500 YEAR RETURN PERIODS Return Period Peak Flow (years) (cfs) 200 18,200 500 21,500 1/ For the 200 and 500 year floods analyzed in this study, the following reservoir operation assumptions were made: a. rate -of -rise did not necessitate opening the emergency gates until elevation 1567 ft. b. Gate openings are made in accords with the Masonry Dam emergency gate schedule while adhering to an opening constraint of 2 ft/hour. C. The emergency gates will not pass more than current inflow on the climbing side of the inflow hydrograph. d. It was assumed that all three emergency gates would be utilized and opened in unison. Tr u0 FAI IIIy L'uIpb ul GIIJInuuts -➢• - —w— — i^1O^""°" Seattle District °°`" 1 " w ,.Wn i M � ' � , , T E :rm..c.. in i.iom.:on bMrtMp. THE CORPS AND ITS SUPPLIERS MAKE NO REPRESENTATION OF ANY IOND, INCLUDING aUT MDT LIMITED TO Date: 4r1a1s7 allCHWAPJWMESARR TI METO BE IMPUE / IT FITNESS FOR A PARTICULAR USE, NOT{ ARE ANY C r River Preparer LDD �/ WARRANTIES H BE IMPLIED WITH RESPECT ro THE INFORMATION, DATA OR p BERVICE FURNISHED HEREIN. i j<0E PROBABILITY X 2 LOG CYCLES 4G 8043� KEUFFEL & ESSER CO. NA6r 1s USA. 100 9: 9.999.8 99 98 95 90 80 70 60 40 30 20 10 5 2 _.-._.. .. .._i Exceedance Frequency in Percent U.J v.t v.0 VA,_ U.Ut �_ j NOTES: . 1. This verve was originally developed for the 1988 Cedar River Flood Control Study. The i i i ! I ! - ! I I i - 1 November 1990 storm was applied to this curve and it was found that the 100 year peak differed by Icss than S%. Due to inaccuracies model and gage it was deemed unneca�sary to redraw the 1988 curve. 2. Peak flown were generated with the oomputer model SSARR so that all events would have a common +.. ' ! i ! ! i ` I-j_l- 'r�;- f .4-�... replationplarL-;i--I—=- !.j- 3. lice regulation for up to a 100 year event asaurnes:_L!— Will! pan the Power tunnel and over the service spillway. _ I -1.1-- I I b. the��f the nernhrough gates spillway will be at full open 4. The regulation for larger than i ! ! - ; A-! events 100 assume: I I _ ; • j a. The emergency Bales will not IN opened wrtil the rate of rise in 1 elevation 1 pool equal or exceeds the values in the rate of rise tabled . For the 200 and S00 year floods analyzed this study, the in! rate-oftise did not necessitate o the Pon�B �BeaY B+�s until elevation 1367 ft. b. Gate openings are made in a000rds with the Masonry Dien emergency gate scheduled ! while adhering °_a i . I I ! : I ! ' ! I , i ' ' ! I ' 17— ' . ; .. I ' ': _ i 7 — to an opening constraint of 2111hour. G The emhydroergency gates will not psss more than curmrt inflow on the climbing the inflow ! - ! j - „! _ _r G:'I = _ . _�.. __ side of _ _..:� ! , I i ► ; ! : • d. Itwas assumed that all throe emergency gates would be utilized and opened in unison. - l.f_ S. Median plotting positions were determined using an N value representing the period of record. The N value used was 81 yeas (1906-1994 6. Future condition flows were taken to be VA greater than present condition flows as stated by King County Department of Public Works d7 Fadsting send future condition curve appear to converge at roughly the 1.23 percent moeedaooe &eWaw7 (80 year return period). ! ! I I I. I 1 i I ! � . - i� p] MY of Seattle, Seattle City Light, Seattle Water Dgw6nent (unknown date), operations and Matntsna ncsHandboo� CtdarFa!lsXtadwlorkscnd thrylow m King County Department of Pubfic Warty. Surfaoa Water Management Division (M9 Cedar River— Curra t and Future Conditions Report FREQUENCY STATISTICS _ Log --- TratuformofFlow ofi tt 1 - Mean 3.4908 - - _:};. - :1. t- 4 ' .1. l i Variance 0.0572 _ Standard Deviation 0.2392 - - - - - !- t i -1- . i'. - - _ O Mediae Plotting Position - I -!- _ - , - - — CUMULATIVE FREQUENCY CURVE -- , k.i.- _ Existing Condition. — ;_ I = ' _ ' - - = Maximum Annual Peak Rainflood Events - �. --- Future Conditions- (Including the November 24 26, 1990 Flood) . CEDAR RIVER AT RENTON j - - — — — sx and 9Ssc Confidence Interv.ls - — - - - - _ _;....... _ GS Station Number 12119000 St ; i 1 I ; it 1 .. .. _ _ Drainage Area =186 sq. mi. Computed by: K Yoko yams Ol March 1995 • Checked by. G. Singleton D. Hareey •. ; � �' I • I .. If _ _ Rt 4 3 OQ 9 1 6 5 4 3 7 i0a 100 7 4 3 N ra 99.9 99.8 PROBABILI l'y,.X .! L (is, f Y! I L� KEUFFEL & ES5% 94 CU 46 8043 99 98 95 90 !0 GO 50 40 30 10 5 1 0.5 0.2 0.1 0.05 0.01 1 " 000 NMI mum nm�fflufilll M =mMuffm MHE lam Holm -0 HM 111 nil =BMW a 11MINUMPA m min 11MIM-1111-11-1111EN ME MHM�� WdMIMM mmmfflfi� Masi pm=ffzmfl� MNM= N E MEEMI M -UMMEM MEE= MN Bull FLOW DURATION CURVE 7 MIS a t MN 11 0 MAR RIVER AT RENTON USGS Station Number 12119000 Ira in I M P111 I Drainage Area = 186 sq. mi. 111 Based on USGS observed data from 1947-1992 Y— yokoyamn 12 December 1994 5 10 20 30 40 50 60 70 80 90 95 96 99 Exhibit 3 Cedar River at Renton Flow Duration Curve ic 99.8 99.9 99.99 5000 4500 4000 3500 _ 3000 N ti- U 3 2500 0 EZ 2000 1500 1000 500 0 0 O O CEDAR RIVER AT RENTON 5 Year Hypothetical Hydrograph 0 0 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 o 0 o S 8 t0 N 00 O t0 N 00 O t0 N 00 O to N 00 O m N 00 O t0 tV 00 O DAY 1 k DAY 2� DAY 3 DAY 4 DAY 5 DAY 6 Exhibit 4 5 Year Cedar River at Renton Hypothetical Hydrograph 7000 6000 5000 w 4000 U O 3000 2000 1000 0 0 0 O CEDAR RIVER AT RENTON 10 Year Hypothetical Hydrograph 0 0 0 0 0 0 0 0 0 0 0 0 0 0 $ 0 0 0 0 0 O 0 $ o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 t0 N 00 O OJ N c0 O c0 N 00 O co N co O co N 00 O c0 N co O DAY 1 DAY 2 DAY 3 DAY 4 DAY 5 DAY 6 Ex 10 Year Cedar River at R( ypothetical Hydrograph 9000 8000 7000 6000 h 5000 U 3 4000 3000 2000 1000 0 CEDAR RIVER AT RENTON 20 Year Hypothetical Hydrograph 0 0 0 o O 0 0 0 0 0 O o 0 0 O o 0 0 0 O O 0 0 0 0 0 0 9 9 0 9 9 9 O 9 0 0 0 0 0 0 9 0 0 9 9 0 0 0 9 0 tD N 00 O m N 00 O to N 00 O tD N 00 O to N 00 O CD N 00 O DAY 1 DAY 2 DAY 3 DAY 4 DAY 5 DAY 6 Exhibit 6 20 Year Cedar River at Renton Hypothetical Hydrograph CEDAR RIVER AT RENTON 100 Year Hypothetical Hydrograph 13000 12000 11000 10000 9000 8000 u� i� 7000 0 6000 ii. 5000 4000 3000 2000 1000 0 i O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O (D C14 co 0 to C14 ap 0 0 ^ 00 O 6 .4 W 0 z6 �,i a6 O t6 i� oD O DAY 1 DAY 2 DAY 3 DAY 4 DAY 5 DAY 6 Ex 100 Year Cedar River at P iypothetical Hydrograph CHESTER MORSE LAKE AND MASONRY POOL 200 Year Flood 18000 0 16000 14000 12000 10000 U 3 0 8000 IZ 6000 4000 2000 0 2 Exhibit 8 200 Year Chester Morse Lake and Masonry Pool CEDAR RIVER AT RENTON 200 Year Hypothetical Hydrograph noon 20000 16000 16000 14000 u 12000 0 10000 8000 6000 4000 2000 0 p p p p p 8 8 8 S 8 8 8 S 8 8 8 8 8 8 8 8 8 8 8 O (O fV 6 O (D fV !7D O fLl N m O 6 6 6 O 6 (V DAY 1 DAY 2 DAY 3 DAY 4 DAY 6 Exhibit 9 200 Year Cedar River ai n Hypothetical Hydrograph �$ �$ 6 25 25 25 0o O 6 (V c0 O DAY 6 CHESTER MORSE LAKE AND MASONRY POOL 500 Year flood 20000 18000 16000 14000 -- _ 12000 — a U 3 10000 0 8000 6000 i 4000 2000 - ------------------ 04 --r_ I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O I? O O O O O O O O O O O O O O O O O O O O p f0 N co O (O CA 00 O to N aD O to N 00 O to 00 O to N 00 O DAY 1 DAY 2 DAY 3 DAY 4 DAY 5 DAY 6 —CIVIL Inflow CIVIL Outflow -- - - - - CIVIL Elev Exhibit 10 500 Year Chester Morse Lake and Masonry Pool 1572 1570 1568 1566 > a2 w 1564 1562 1560 CEDAR RIVER AT RENTON 500 Year Hypothetical Hydrograph 24000 22000 20000 — 18000 I 16000 14000 I r U 3 12000 0 10000 8000 — 6" 77 4000 2000 — 0 $ 8 S 8 $ 81 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 p (D (V a0 O tD N CO O fD N i6 O 6 e4 i6 O 6 N co O i6 N 6O O DAY 1 DAY 2 DAY 3 DAY 4 DAY 6 DAY 6 Exhibit 11 500 Year Cedar River — on Hypothetical Hydrograph APPENDIX C HYDRAULIC DESIGN APPENDIX C HYDRAULIC DESIGN APPENDIX SECTION 1. HYDRAULIC DESIGN 1.01 SUMMARY The original scope of this project as proposed in the reconnaissance phase included a sediment capture basin located within the study reach, combined with initial dredging to establish the desired channel bed elevation. Proposed hydraulic evaluation included the assembly and application of a sediment transport computer model (HEC-6) to assess dredging and sediment trap success, and a steady state, one dimensional water surface profile computer model (HEC-2) to evaluate flood water surface profile reduction with the proposed project. During the course of the study, the ground and channel survey data was converted to HEC-RAS (a Windows -based one-dimensional water surface profile computer model) format to facilitate project evaluation and organization of alternatives. Additionally, the SAM sediment computer model was applied at the preliminary evaluation stage to improve the assumptions taken in the HEC-6 model. 1.02 General Description of study reach The study reach of the Cedar River is about 9000 ft in length, extending from the I-405 freeway overpass in Renton, Washington at the upstream end to Lake Washington at the downstream end. The prehistorical Cedar River channel did not flow into Lake Washington at the time settlers of European descent arrived at what is now the city of Renton. The lake was at that time nine feet higher in elevation, and flowed out through the Black River into the Duwamish, then into Puget Sound near present day Harbor Island. The Black River was a sluggish, deep, slow -moving slough with a fairly stable channel. The Cedar River is a steep gradient, gravel bed stream flowing from a fairly confined narrow valley. The present day city of Renton is founded on an historical alluvial fan at the mouth of the Cedar. At times the Cedar River may have alternately flowed into the lake or into the Black River, or into both. Flood flows historically inundated large portions of the active alluvial fan. In the early 1900's, an artificial channel was dredged from about the location of the present day I-405 overpass to the lake, and the Cedar was permanently diverted into Lake Washington. Early accounts of flooding prior to the construction of the artificial channel indicate that the river overflowed its banks frequently and floodwaters flowed down random channels over the area now occupied by the city of Renton (Ref #1). Around the same time period the Hiram Chittendon Locks and the Lake Washington Ship Canal were constructed, and the level of the lake was permanently lowered nine feet. The dredged channel was extended, and the left bank area was developed into the present day Renton airfield. Extensive manufacturing facilities were constructed on the right bank by the Boeing company to support production of aircraft. 1.02 Available data a. Hydraulic model data The City of Renton provided a copy of the study report documenting Northwest Hydraulic Consultants' (NHC) limited flood analysis study of the lower two miles of the Cedar River completed in 1991 (Ref #2). NHC provided electronic copies of the HEC-2 input and output files for the subject report as well. The report compared the channel conditions from 1986 to 1991, and calibrated the model to the recent estimated 50-year recurrence interval flood event in 1990. Cross sections for part of the historically dredged channel were evaluated as well, including a limited set from 1954, and several limited sets from the 1960's and 19701s. Twenty-six cross sections were surveyed in 1994 of the channel and overbanks (Fig 7), and channel sections were surveyed again at the accessible bridge locations following the December 1995 flood event. Observed high water marks were available for the November 1990 flood event (an estimated 50 yr recurrence interval event), and the December 1995 and February 1996 flood events (both about 15 to 20 yr recurrence interval events). Calibration of the study hydraulic models was made with the 1995 and 1996 events only, since historical bed elevation changes suggest that any other than the most recent data are not applicable for calibration purposes. b. Sediment model data The City of Renton provided estimates of total past expenditures on delta and channel dredging activities. Dredging volume records were not available, though. Anecdotal information regarding the average annual volume of sediment extracted from the river just upstream of the study reach was obtained from the Stoneway sand and gravel mining company. The Stoneway company mined gravel from the river bed upstream of the study reach for many years, up until the 19601s. Little observed sediment transport data is available for the Cedar River. King County has performed a fairly extensive literature search as part of their comprehensive plan for flood damage reduction throughout the entire Cedar River basin, and have cited what little observed data is available (Ref #3). The Corps of Engineers, as part of this study, conducted a very limited sampling program to determine preliminary bedload transport estimates within the study reach. 1.03 Hydraulic and Sediment Analysis a. General description of hydraulic model The NHC HEC-2 model was used to establish general cross section locations so that results could be compared to those provided in the 1991 NHC report. An HEC-2 model was developed for the study reach from the I-405 overpass to the mouth of the river and beyond to the extent of the delta formation in the lake. The HEC-2 model format was modified thereafter to HEC-RAS format to facilitate the presentation of data and results. Because the flow characteristics of the channel and overbanks varies significantly between relatively low flows and higher out -of -bank flows, model flow data input was primarily separated into low flow and high flow computation runs. Manning's n values for the channel and overbanks were selected by calibration to the December 1995 and February 1996 flood events, and compared with those used in the NHC study several years prior. The selected n values compared favorably with those used in the previous model and were generally within the expected range for channels similar to the study reach. Channel n values ranged from 0.022 to 0.040 throughout the study reach, with a value of 0.03 to 0.035 for most cross sections. Overbank n values were much more difficult to assign, and 7 generally ranged from about 0.045 to about 0.12, with a value of about 0.05 to 0.06 for most left bank sections along the Renton airfield, and 0.075 to 0.12 for left bank sections where structures and vegetation restricted conveyance. Right bank n values varied from about 0.045 to about 0.1, with most sections including the Boeing manufacturing plant using n values from 0.045 to 0.06 and sections with heavier vegetation along the city park upstream of the Boeing plant using n values from 0.07 to 0.1. Upstream of the Logan Street bridge, overbank n values ranged from 0.05 to 0.085, depending on the vegetation and obstruction density. The following table shows a comparison of computed versus observed highwater for the February 8, 1996 flood. The discharge used for the simulation was 8,000 cfs. Cedar River high water marks Sect. ID Observed Computed 16.12 19.4 20.3 25.32 20.9 21.2 33.82 22.2 22.5 39.64 23.5 24.0 41.14 23.6 24.0 46.54 25.2 24.9 52.44 26.9 26.9 56.43 28.5 28.0 Manning's n value selection for the overbanks was difficult, and probably does not accurately represent the true roughness characteristics of these areas. They were selected in order that the amount of flow in the channel and along the left and right banks could be properly distributed. The nature of flood overflows along the left bank through the Renton airfield is such that a one dimensional steady state model is difficult to apply. Flood overflows do not pond on the airfield or flow downstream uniformly with the channel flow, rather they flow downstream and away from the river channel under rapidly varied conditions. The left bank upstream and downstream of the South Boeing bridge behaves as an overflow weir, with overflows flowing along the landing strip or across the strip centerline. Flow passing over the centerline of the strip is lost directly to the lake without returning to the river, while flow along the right side of the strip returns to the river downstream of the South Boeing bridge. Observed water surface elevations are not uniform across the cross sections. Bridge flow characteristics were similar for all spans crossing the Cedar River upstream of and including the Logan Street bridge. Bridges at Logan Street, Wells Avenue, Williams Avenue, Bronson Way, and Houser Way all have abutments supporting the left bank bridge deck and intermediate near -bank piers and abutments supporting the right bank bridge deck. Logan Street has both left and right bank abutments and an intermediate pier near each abutment. Houser Way has a right bank abutment and left bank abutment and intermediate pier near the left bank. The Renton City Library is constructed over the river and is supported by two concrete pile bents (multiple piles aligned parallel to flow direction) centered roughly near the low water line along each bank. Upstream bridges were analyzed with pressure flow and weir overflow for higher discharges. The South Boeing bridge is supported by left and right bank abutments and intermediate piers located near each bank. Riverbank elevations upstream of the bridge are lower than the top of bridge deck elevation. Some left bank locations upstream are as low as the bottom chord steel on the bridge. The South Boeing bridge was analyzed with pressure flow, and approach roads were analyzed with weir flow for higher discharges. Head loss coefficient for the bridge and piers are in reality highly variable, since debris blockage greatly varies the characteristics of flow under the bridge, as observed during past flood events. The North Boeing bridge is supported by two pile bents (row of piles aligned parallel to flow direction) at each end of the span, located near the bank. It was analyzed with pressure and weir flow for higher discharges. With project conditions consisted of raising the South Boeing Bridge therefore allowing all debris that accumulated on the South Bridge to flow downstream to the North Boeing Bridge. HEC-RAS analysis of the North Boeing bridge was conducted with a 20% debris blockage to determine the effects on WSEL. The worst case scenario for the blockage, 3 year sediment accumulation, resulted in increasing the upstream WSEL by 0.9 feet. This increase continued upstream for 200 feet. Levee heights in this area were raised to contain the possibility of debris blockage at the North Boeing Bridge. To duplicate the varied flow observed in the overflow area on the left bank required an iterative process of adjusting model discharge distribution values at each cross section and corresponding computation of weir flow over the centerline of the airstrip to account for that portion of flood discharge lost directly to the lake without returning to the channel. Each run of the model was compared to the observed field data and to a best guess estimate of flow distribution based on engineering judgment and cursory computation, then the process was repeated until satisfactory agreement between observed conditions and computed results was reached. The calibrated model was used as the base input file for all project alternatives analysis and for the HEC-6 sediment transport analysis. b. General description of sediment model The sediment transport modeling analysis was conducted with the HEC-6 computer model, developed by the Waterways Experiment Station (WES). A recently upgraded version of the model prepared by WES hydraulic modeling group staff to address gravel bed rivers like the Cedar was used for this study. b.l SAM computer model Prior to application of the HEC-6 sediment transport model, a preliminary assessment of the sediment transport characteristics of the river was conducted with the SAM computer model developed by WES. SAM computes the sediment transport capacity of a cross section using any one of about nineteen transport equations based on hydraulic characteristics computed from normal depth computations at the cross section being analyzed. Input data includes the annual flow duration curve, the bed material sediment gradation at the cross section of interest, the river channel cross section water depth, width, discharge, and water velocity, the energy slope at various discharges, and the sediment inflow load curves developed from observed bed load and suspended load data, and the roughness coefficients for the channel as provided in the calibrated HEC-6 model. SAM aids the engineer in selecting the most appropriate transport equation, the most appropriate sediment inflow load curve, and the most appropriate sediment inflow gradation curves for application in the HEC-6 model. rd Observed sediment transport data for the Cedar River is not extensive. Some data has been collected in the past by King County's Surface Water Management division, and is documented in a literature review presented in the County's Current and Future Conditions Report for the Cedar River Basin (Ref #3). Most sediment transport capacity estimates have been made by indirect means, such as bed elevation surveys, channel meander analysis, discharge capacity changes, specific gage analysis for the lower basin flow gage, previous lower channel dredging records, and other methods. Northwest Hydraulic Consultants Inc. (NHC), under contract to the City of Renton, collected suspended load and bedload transport measurements during the course of this study (Ref #4). NHC collected additional sediment data during the December 1995 and February 1996 flood events (Ref #5). Both of these events were of about 15 to 20 year recurrence interval. The Corps and NHC also extracted a number of bed material samples from the channel at low flow throughout the length of the study reach (Figure #1). Gradation analysis of the samples was conducted by NHC and by staff at Seattle District in the District's geotechnical laboratory (also in Ref #4). Observed suspended and bed load transport data are very limited throughout the basin, with no observed data available for large flood events. In addition, the unstable, aggrading nature of the channel bed - in the study reach did not provide a means of accurately calibrating the HEC-6 sediment transport model for application within the study reach. SAM was also used in this study to estimate the average annual sediment yield, to develop the sediment discharge rating curve (sediment discharge vs. water discharge), to develop the most appropriate sediment inflow gradation curve, and to determine the most appropriate sediment transport equation to be used in the HEC-6 model. Observed bed load and suspended load data was analyzed and an approximate sediment transport relationship was developed. This relationship was compared to predicted sediment transport in the SAM model using four of the most appropriate transport equations, given the channel geometry, bed material gradation, flow conditions, and sediment inflow gradation. None of the four equations provided clear agreement with the observed data and derived equation at lower discharges (below about 7500 cfs). However, minor manipulation of sediment inflow load curve and inflow load gradations in the SAM input provided the best fit between the sediment rating curve and sediment inflow gradations predicted by the Meyer -Peter Muller equation (MPM) and the curve derived from observed data. Shown below are the sediment transport rating curves predicted by the four transport equations plotted along with the curve derived from the observed data (Equation 1.03-b.1 above). 5 T R b L 0 1000 t= O a N C w 10 E d 0.1 Sediment Discharge Rating Curve Cross Section 74.83 100 10000 1000000 Water Discharge (cfs) Although the Schocklitsch equation more closely matches the observed data curve, we felt that it might lead to less conservative design conclusions by under -predicting sediment accumulation in the project reach. The MPM equation, although over -predicting transport capacity at lower discharges, predicts transport capacity at higher discharges quite similar to the other two applicable formulas (Einstein and Parker). The MPM formula is also perhaps more applicable in this case because it predicts transport capacity based on excess bed shear stress, rather than excess bed velocity exposure above critical bed velocity as in the Schocklitsch formula. In gravel bed rivers such as_ theCedar, bedload transport increases as discharge increases at a -- greater rate than in sand bed streams. Shear stress -based transport relationships more accurately predict transport capacity than critical bed velocity -based transport relationships. The sediment discharge rating curve predicted by the MPM method was separated into particle size classes and plotted with the observed sediment load data. In this way, the MPM-predicted sediment inflow could be compared to observed data by particle size gradation to assess the ability of the MPM method to predict which grain sizes would be transported at the appropriate discharges. The figures below show comparative sediment inflow curves by particle size gradation for the observed data and for the predicted sediment inflow. Sediment Inflow by Size Gradation Observed versus Predicted 109.20 93.60 c 0 62.40 .75 mm Coarse Sand, Predicted 01a 46.80 d io • —+—.75 mm Coarse Sand, Obser%ed 31.20 E I v 15.60 i 0.00 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 Discharge (cis) By integrating the annual flow duration curve (shown below) developed from historical hydrologic data with the computed sediment rating curve, an estimate of the average annual sediment yield was predicted with SAM. Annual Flow Duration Cedar River 25000 200 150 100 Discha 50 01 0.0001 0.001 0.01 0.1 1 10 100 Percent of Time Equaled or Exceeded) Predicted annual yield from the SAM model analysis was compared to data collected for other Puget Sound and Pacific Northwest area streams with similar watershed characteristics and was determined through engineering judgment to be an adequate representation of the actual yield. The table shown below tabulates annual yield figures for several similar basins (Ref #7-12). Basin Name Drainage Area Annual bedload Annual total (mil) sediment yield sediment yield ( tons /mi' ) ( tons /mil ) Cedar River, WA 110 (below 50 (estimated) 500 (estimated) (estimated) Masonry Dam) Cedar River 110 -40 430 (predicted MPM) White River, WA 400 (above Mud 50 to 125 1250 to 3125 Mtn. Dam) (glacially fed, high suspended load) Snohomish River, - 20 to 100 200 to 1000 WA (various (various (various tributaries) tributaries) tributaries) Bogachiel River, 287 55 (approx.) 1390 WA Soleduck River, 226 21 (approx.) 531 WA Quillayute 629 33 835 River, WA By manipulating slightly the sediment inflow load curve and the inflowing load gradation curve and selecting from the two or three different transport equations most appropriate for gravel bed rivers, a fair estimate of annual yield was obtained with the MPM equation. MPM predicted more reasonable annual sediment yield than the other three formulas, all of which significantly overpredicted yield by as much as an order of magnitude. Additionally, the MPM formula provided the better channel bed response when utilized as developed in the HEC-6 model simulation, as discussed in Section 1.03.b.2 below. Agreement with annual yield estimates between the predictive method and the observed data and data for similar watersheds was considered to be more important in this study than other comparative measures, since the primary focus would be estimation of future dredging requirements. b.2 HEC-6 Model The HEC-6 model used the HEC-2 cross sections and n-values calibrated for the December 1995 and February 1996 flood events. Some closely spaced cross sections were removed from the input file to obtain better model stability. Bridge cross sections also are not analyzed as in HEC-2. No pressure flow condition is allowed in HEC-6. To compensate for this the channel `n' values for the bridge section are artificially raised to reflect appropriate bridge head losses. HEC-6 application requires first the calibration of the steady state hydraulics of the model. The model was calibrated to the HEC-RAS model for bankfull flows in the lower reach of the study area (about 3500 cfs) and for the February 1996 flood event (about 8000 cfs). As discussed above, n-values were increased as appropriate for the cross sections representing bridges, to reflect the observed head loss through the bridge (measured during February 96 event). Following satisfactory calibration of the steady state hydraulics, the sediment inflow load curve and gradations were added. The Meyer -Peter Muller sediment transport relationship was selected for use in this HEC-6 simulation, based on evaluation of transport characteristics with the SAM computer model. As a test of sediment transport calibration, the historical hydrologic data from the period from 1991 to 1994 were parsed and input with proper time step. Minor modifications to the sediment inflow load curve and inflow gradations were made until the model predicted with some agreement the observed bed elevation changes over that time period. The adopted sediment load versus water discharge relationship is shown below. Additionally, the model was run with the historical hydrologic data for the week or so surrounding the December 1995 flood event, using 1994 cross section geometry and the above -developed sediment inflow load curve and gradations. Field surveys of the bridge cross sections immediately following the December 1995 event were compared against the predicted bed elevation changes from the HEC-6 model and found to be in fair agreement. 9 goes • • ------- s e g e • ■ --- ---- ---- tt�tt■•.■tu �Wv111���8---MIMS-- gee•--___._.___ .. • Obserye• / ����Il���fd111�■____ J�W��■■■. t■ttl■��.■t■t�■tttl■t.�w■■■tt■■�ttl�tl�.si �.W_ �y��lill�������ll��>•■■Aillw.�■�_II��y■■��I_ as ••>•Ne�ee�//eNNe.�.e1MN�g� Vlel/Nl���N///Ne�e��N. ww���w■�■nww���w■■■.����r �u��Jw■t.�■ww���p■■u ��:y1�W���������������U�■11� • am 09NWi�W�M�i./uNeeN�y./ �ww�w■■■u���w■�■/ew�•��wwe ��p�/.N�wINt■\ ���■11111�o■�IIII�I��■■/.Ily�■■�Iil��■11111 ���■�IIIIy��.11U�I■■■lllly�■��ill�y■ HU e y!•■��III�y��11�!•�llf�ll�■■1111���■�IIII ME■■II111IENIEW■11111ME MISS■■I11IINIME III g •g gee •e1• •gee• Cursory analysis of historical aggradation of the channel within the study reach was conducted using cross section surveyed in 1986, 1991, and 1994. During that time period, no dredging activity within the channel occurred, and no upstream extraction of sediment was conducted at the Stoneway gravel mining site. Computation of channel bed volume changes from the mouth to I-405 over that eight year period from 1986 to 1994 showed an average sediment accumulation of about 5,150 cubic yards per year. Several moderate sized flood events occurred during that period, including an estimated 50 year recurrence interval event in November 1990, a 15 to 20 year recurrence interval event in December 1995, and a 15 to 20 year recurrence interval event in February 1996. Based on the observed data, the predicted channel bed aggradation and predicted maintenance dredge average annual volumes based on the HEC-6 model simulation were considered to be conservative. The calibrated sediment transport model was then used to predict the future condition of the channel for the no -action alternative by simulating a computational hydrograph represented by the annual flow duration curve. The computational hydrograph, shown below, was developed by partitioning the annual flow duration curve into a series of discrete steady flows, each having a specified duration. For a 20 year simulation, this computational hydrograph is repeated 20 times. 10 Disci Annual Computational Hydrograph Cedar River 0 50 100 150 200 250 300 350 400 Duration (days) The HEC-6 model aborted -at about 20 years in the future during a 50 year simulation because the predicted channel bed had aggraded to such a degree that insufficient effective -flow capacity remained within the channel boundary. The future without -project condition assumed, then, that the channel was no longer viable at 20 years in the future if no action is taken. The predicted bed elevation was input into the HEC- RAS hydraulic model and used to predict water surface profiles for the without -project condition. Several channel dredging scenarios were evaluated with the HEC-6 model. Detailed description of the various alternatives studied are discussed in Section 1.04 below. In general, the HEC-6 model results provided conservative estimates of average dredge volumes and dredge cycle frequency required to maintain the desired channel flow capacity within the study reach. Maintenance dredging intervals of from two to five years were evaluated for the alternatives by simulating a 20 year series of computational hydrographs and developing average maintenance dredge volumes over the period of simulation. 1.04. Alternatives Analysis Alternatives consisted of levees and/or floodwalls, dredging to various depths, narrowed low flow channels, sediment trap, raising the South Boeing bridge, widening the existing channel, and constructing an overflow channel, as well as combinations thereof. The no -action alternative was also evaluated to show the potential reduction in channel capacity if nothing is done to alleviate the continuing aggradation of the channel bed. Hydraulic analysis of water surface 11 profiles for a range of anticipated discharges was performed for each alternative using HEC-RAS. Sediment transport analysis using HEC-6 was performed for alternatives requiring initial and/or maintenance dredging to provide desired level of flood protection to the project study area. The selected alternative was based on the NED plan determination, using Corps economic guidelines, with some minor changes to accommodate the desires of the local sponsor. a. No -action alternative The no -action alternative was first analyzed with the sediment transport model to determine the extent of future aggradation and its effects on channel capacity. Simulation of future aggradation with the sediment model was performed for a fifty year period. However, the predicted bed aggradation reduced the channel capacity within about 20 years to such a degree that the flow distribution between overbanks and channel no longer met computational criteria for the HEC-6 model and the computation aborted each time the run was made. The HEC-RAS model geometry was adjusted to reflect the bed elevations predicted by the HEC-6 model after 20-years of simulation to compute the future condition water surface profiles. This predicted estimate can be compared to the aggradational trend shown in a specific gage analysis of the U.S.G.S. gage at Bronson Way (shown below). Rating Curve @ USGS gage site Cross Section 7483 nhc 1991 model 34 32 30 28 26 24 StaK VD) 20 18 0 2000 4000 6000 8000 10000 12000 Discharge (cfs) b. Bypass channel alternative 14-Dec-94 24-Nov-86 - A 18-Feb-8 1-0c;-79 X 16-Jan-7 23-Sep-7 This alternative included a diversion structure to carry discharges in excess of the existing channel capacity to Lake Washington through an artificial channel. Upon cursory examination it became obvious that there existed no shorter or more efficient route to the lake than the existing channel, and that any such bypass channel sized to carry even the discharge in excess of channel capacity for a 100 yr flood would have to be very large. Such a channel would require large 12 real estate investment and high construction costs, and cause disruption to the operation of the airfield. FAA restrictions would very likely also require that the bypass channel be covered at least partially throughout the entire length. Preliminary investigation of a constructed bypass channel showed that an overflow weir would have to be constructed along the left bank of the existing channel over about 1000 ft of length, which would pass flow directly into the bypass channel. The overflow channel would be designed to carry up to about 8500 cfs (100 yr flow of 12,000 cfs minus existing river channel capacity of about 3500 cfs) about 4000 ft to the lake, roughly alongside the existing river channel. Assuming a concrete lined channel with slope approximately equal to the river (So = .0023) and a maximum depth of about 8 ft, design width would be at least 200 ft. The high construction costs and failure of this alternative to address the aggradation problem in the existing river channel eliminated it from further consideration. A system of closed conduits of similar capacity would require higher construction costs and thus was also eliminated from further consideration. c. Sediment trap alternative This alternative, originally selected during the reconnaissance phase, considered several locations for a trap, or over excavation, within the existing river channel. Primary concerns with this alternative focused on the potential for reduced maintenance dredge requirements for portions of the channel not within the trap area. Most sections of the river upstream of the study reach were eliminated from further consideration for trap locations due to environmental concerns with disturbance of very productive sockeye spawning areas. Real estate concerns favored trap siting within the study reach, as the entire length of the artificial channel from I-405 to the mouth is wholly owned by the City. Three sites were proposed as potential trap locations. The old Stoneway plant extraction area is upstream of the study reach, but would provide sufficient channel length and depth for as much as 10,000 cubic yards of sediment storage. The existing river channel from the South Boeing bridge to Logan Street bridge provides sufficient length and depth for as much as 25,000 cubic yards of sediment storage. The existing river channel from the South Boeing bridge to the mouth provides sufficient channel length and depth for as much as 70,000 cubic yards of sediment storage. Construction access limitations and construction equipment bridge clearance issues ruled out trap locations from Logan Street bridge upstream to I-405. Sediment transport analysis of the proposed Logan Street -to - South Boeing bridge location with the HEC-6 model showed that the trap could fill quickly with smaller sized sediment particles that may have flushed out to the delta if the trap were not constructed rather than depositing in the channel. This effect would increase dredge requirements unnecessarily. Periodic excavation of the trap area to the initial geometry would provide renewed sediment storage capacity. Concerns with the sediment trap concept were voiced by the local sponsor when results showed possible filling of the sediment trap during a single large flood event and subsequent loss of channel capacity for short term future flood events during the same flood season. Should such a series of events occur, it would not be possible to remove sediment from the trap area safely between consecutive events during the flood season, and therefore the project would not provide the design level of protection. 13 Environmental concerns with the channel bed configuration upstream and downstream of the sediment trap resulted in less favorable standing of this alternative. An effective sediment trap design would result in significant modification of the existing character of the river through the trap reach by making it deeper and slow moving. Sediment transport analysis showed that regular dredging of the entire project reach was more efficient at removing only those sediments which would normally accumulate in the channel and would reduce the overall annual dredging equivalent volume. Further consideration of the sediment trap alternative was eliminated. d. Channel widening The existing 100 to 110 foot wide channel would be widened to 150 feet upstream of the South Boeing Bridge and to 250 feet from the South Boeing bridge to the mouth. However, widening alternatives seriously impacted the City of Renton's Riverside Park along the entire right bank by removing most of the park area. High construction costs, park impacts, and limited effective reduction in flood profiles eliminated this alternative from further consideration. Additional investigation included widening the channel to 250 feet from Logan Street bridge to the mouth and adding an additional span to the South Boeing bridge. Minimal reduction in flood water surface elevations were provided by this alternative. In addition, this alternative did not address continued channel bed aggradation. e. Narrow low flow channel Wingwalls or riprap would confine a narrow channel excavated six feet below existing grade roughly in the center of the existing channel bed from I-405 to the mouth of the river. This alternative was proposed as a means of increasing bed shear and thus transport capacity for flows below about 1000 cfs (the flow at which the most sediment is transported through the reach over long periods of time). However, simulation of this alternative with HEC-6 over a 20 year period showed no significant reduction in average maintenance dredging volumes for the study reach over that provided by regular dredging of the entire width of the existing channel. Additionally, large construction costs for this alternative would also be required, therefore it was eliminated from further consideration. f. Dredging alternatives Channel and/or delta dredging alternatives were evaluated with the HEC-RAS steady state hydraulic model and with the HEC-6 sediment transport computer model. Dredge channel configuration generally considered excavation of the entire width of the existing channel bed down to the desired depth. Excavated side slopes were assumed to be 1V:3H in all cases; a reasonable assumption for in -water excavation of gravels with relatively stable slopes. The hydraulic model predicted that critical depth control for all alternatives except the deep dredge alternative occurred near the downstream face of the North Boeing bridge. The critical depth hydraulic control was clearly indicated by the two to three foot head drop through and downstream of the North Boeing bridge observed during the Dec 95 and Feb 96 floods. Alternatives including delta and channel dredging were evaluated against alternatives including only channel dredging. The additional reduction in flood water surface profiles attributed to delta dredging 14 was not significant in all but the 10 feet deep channel dredge alternative. For this reason, delta dredging was not included in three of the four channel dredging alternatives. The rate at which the delta builds is dependent on the available sediment storage volume available in the lake near the delta. Lake Washington is quite deep, well over 100 ft, immediately outboard from the delta, with very large capacity for additional sediment deposition. Thus the rate of outward delta growth has been, and would be expected to remain, quite slow. With this natural limit to delta growth, and consequent limit to delta subchannel length increase, the effect of the delta on flood water surface profiles would be expected to remain fairly constant over the expected life of the project. However, significant coverage of the delta with permanent vegetation would be expected to increase the potential for backwater effects to extend into the project channel. f.l. Existing channel dredge to existing thalweg This alternative consisted of initial excavation of the existing channel to a uniform width at the existing thalweg elevation, and regular maintenance dredging every 2, 3, or 5 years thereafter. Hydraulic analysis of this alternative showed that no significant reduction in flood profiles would be realized (Figure #3). Sediment transport analysis of this alternative showed the following dredge quantities required to maintain the desired channel geometry: Alternative RI: Year (Beginning of year) 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Existing channel thalweg, maintain at existing channel bottom 2 Year 3 Year 5 Year Malnt. Malnt. Malnt. Dredge Dredge Dredge Volumes Volumes Volumes (cy) (Cy) (Cy) 31067 31067 31067 91943 114828 91278 133856 91139 111403 93870 113750 93684 109170 93999 114058 93950 113813 136548 93987 93885 114232 15 19 20 93710 137485 21 114335 f.2. Existina channel dredge 4 ft below existina thalwe This alternative consisted of initial excavation of the existing channel bed approximately 4 feet below the existing channel thalweg from cross section 56.43 (d/s face Logan Street bridge) to cross section 16.12, and to uniform elevation 8.0 from cross section 16.12 to just downstream of the river mouth (cross section 0.08), and tapering up to the existing thalweg elevation at cross section 65.01 (d/s face of Wells Avenue bridge). Regular dredging to the initial bed profile every 2, 3, or 5 years thereafter would maintain the desired level of protection within the study reach. Hydraulic analysis of this alternative showed that a reduction in flood profiles would be realized (Figure #4). Sediment transport analysis of this alternative showed the following dredge quantities required to maintain the desired channel geometry: Alternative F,2: 4 foot dredge below existing channel thalweg, maintain at 4 foot 2 Year 3 Year 5 Year Maint. Maint. Maint. Dredge Dredge Dredge Volumes Volumes Volumes (cy) (cy) (cy) Year 0 158420 158420 158677 (Beginning 1 of year) 2 109415 3 154403 4 117006 5 243989 6 119637 171192 7 8 124258 9 172946 10 11 124480 264124 12 124435 173899 i3 14 123941 15 173967 272486 16 124421 17 18 124278 174178 19 20 122996 270199 16 21 174140 f . 3 . Existina channel dredge 6 ft below existing thalwe This alternative consisted of initial excavation of the existing channel bed approximately 6 feet below the existing channel thalweg from cross section 56.43 (d/s face Logan Street bridge) to cross section 25.32, and to uniform elevation 8.0 from cross section 25.32 to just downstream of the river mouth (cross section 0.08), and tapering up to the existing thalweg elevation at cross section 76.82 (d/s face of Bronson Way bridge). Regular dredging to the initial bed profile every 2, 3, or 5 years thereafter would maintain the desired level of protection within the study reach. Hydraulic analysis of this alternative showed that a reduction in flood profiles would be realized (Figure #5). Sediment transport analysis of this alternative showed the following dredge quantities required to maintain the desired channel geometry: Alternative F.3: 6 foot dredge below existing channel thalweg, maintain at 6 foot 2 Year 3 Year 5 Year Maint. Maint. Maint. Dredge Dredge Dredge Volumes Volumes Volumes (cy) (cy) (cy) Year 0 194394 194394 195952 (Beginning 1 of year) 2 113774 3 159988 4 123099 5 252420 6 124262 176764 7 8 124634 9 178660 10 11 124769 279309 12 125119 179273 13 14 124879 15 180027 288229 16 124934 17 18 124932 179810 19 20 125062 288088 21 179884 17 f.4. Existing channel dredge loft below existing thalweg This alternative consisted of initial excavation of the existing channel bed approximately 10 feet below the existing channel thalweg from cross section 56.43 (d/s face Logan Street bridge) to cross section 46.54, and to uniform elevation 7.0 from cross section 46.54 to just downstream of the river mouth (cross section 0.08), and tapering up to the existing thalweg elevation at cross section 76.82 (d/s face of Wells Avenue bridge). This alternative approximately duplicates the historical dredge profile the City of Renton maintained prior to the 1980's. Regular dredging to the initial bed profile every 2, 3, or 5 years thereafter would maintain the desired level of protection within the study reach. Hydraulic analysis of this alternative showed that a reduction in flood profiles would be realized (Figure #6). Sediment transport analysis of this alternative showed the following dredge quantities required to maintain the desired channel geometry: Alternative FA: 10 foot dredge below existing channel thalweg, maintain at 10 foot 2 Year 3 Year 5 Year Maint. Maint. Maint. Dredge Dredge Dredge Volumes Volumes Volumes (cy) (cy) (cy) Year 0 260462 260462 260235 (Beginning 1 of year) 2 119604 3 173731 4 124836 5 265879 6 126041 183964 7 8 127406 9 185209 10 11 127971 288400 12 128224 185602 13 14 128088 15 186339 291226 16 128024 17 18 127848 187600 19 20 127879 297554 21 190664 IN g. Modification to South Boeing Bridge This alternative considered raising the South Boeing bridge to an elevation above the design flood water surface. Permanent raising of the bridge by more than just a few feet also required significant regrading of the bridge approach roadways to accommodate the shallow grades required to tow aircraft across the bridge. High costs and very limited amount of elevation gain of the bridge afforded in this concept eliminated it from further consideration. Temporary jacking systems for lifting the bridge only during floods were evaluated instead. The bridge structure would be lifted only during the flood event above the flood water surface to sufficient height that debris would no longer impact the low chord steel. This alternative considered alone reduces debris impact damage to the bridge deck during floods, but does not significantly reduce overall flood damages within the study area. However, the bridge jacking concept was used in combination with other alternatives to provide reduction of debris impact damage, reduced levels of induced flooding from bridge blockage by debris, and overall reduction in flood water surface profiles. Temporary jacking systems for the bridge were required for all levee alternatives to eliminate excessive levee height requirements upstream of the bridge which would result if the bridge were not raised. h. Levee and/or floodwall This alternative considered levees and/or floodwalls to provide the desired level of protection for the study area. However, this alternative was not effective in significantly reducing flood damage over the life of the project unless combined with a dredging program. Without dredging, the initial level of protection would be reduced over time as a result of continued aggradation of the channel bed. In addition, without dredging, the bridges crossing the river throughout the study reach would eventually be rendered impassable under all flow conditions by sediment and debris deposition. HEC-RAS was utilized to evaluate the height of levees necessary to contain events of various recurrence intervals for each dredging depth scenario. In addition, some alternatives included an intentional overflow section levee designed to withstand overtopping for the duration of the flood event during events larger than the design level of protection. The purpose of the overflow section would be to limit flooding to an area not seriously at risk of large damages, thereby preserving the rest of the levee system intact and effective in preventing damage to higher valued areas. However, during some very large events greater than the design level of protection, the entire levee system would be overtopped. 1.05. Selected alternative The selected alternative (Alt. F-2) was one of four combination alternatives, all of which included channel dredging to various depths, a South Boeing bridge jacking system, levees/floodwalls on both banks extending up to Williams Avenue, and an overflow levee/floodwall section on the left bank from the South Boeing bridge to the mouth of the river. These combination alternatives were analyzed in detail following the first round of elimination during the early part of the study. The selected alternative provides greater than a 90% chance of containing the 100-yr flood, slightly less protection than the NED- recommended plan, because the local sponsor chose not to increase the 19 level of protection for the upstream portion of the study reach. It includes initial dredging of the channel to a depth of about four feet below existing thalweg and maintenance dredging to the initial dredge bed elevation every three years or as necessary to provide the desired level of protection or greater, levees and floodwall sections extending from the mouth up to the Williams Avenue bridge, a jacking system for the South Boeing bridge, an overflow levee and floodwall section extending from the South Boeing bridge to the mouth of the river, and closure panels for the section of levee on each end of the South Boeing bridge. A complicated procedure for determining required levee elevation for the desired level of protection was used. The local sponsor requested that the completed project provide sufficient level of protection for FEMA to re -designate the protected area as outside the 100 year floodplain limits. This criteria required that the project provide protection to at least the 100 year recurrence interval event with 90 percent reliability. Recent COE guidance on the application of risk and uncertainty analysis to levee projects was used to determine the 90 percent reliability level of protection (Ref #6). The 90 percent reliability water surface profiles were determined by using the HEC-FDA program. This model combines the discharge frequency curves with uncertainty and the hydraulic stage - discharge rating curves with uncertainty. The HEC-FDA model was constructed and a Monte Carlo simulation was conducted. The proposed levee elevations were found to have a greater than 90% chance of containing the 100 year flood. The overflow levee section was designed to contain at least the 90 percent reliability 100 year frequency water surface profile (i.e., design water surface profile)for the four foot dredge channel with three years of predicted sediment accumulation, immediately before a maintenance dredging cycle. Levees on the right bank throughout the study reach and on the left bank upstream of the overflow section were designed to provide a minimum of one foot of freeboard above the design water surface profile. The South Boeing bridge jacking system would be designed to lift the low chord of the bridge at least one foot clear of the maximum water surface elevation which could be contained by the overbuilt levees upstream of the bridge. The recurrence interval of an event which would overtop the overbuilt levees upstream of the bridge was determined to be in excess of 100 years, and perhaps as much as 150 years. Overflow upstream of the upstream end of the overbuilt levees (Williams Avenue) occurs during events larger than 100 year recurrence interval (90 percent reliability). Levees on the right bank downstream of the South Boeing bridge are set back 60 to 100 feet with velocities in the overbank ranging from 2 to 4 fps. Therefore no bank protection is required for the right bank. Levees on the left bank are adjacent to the river with average channel velocities ranging from 8.5 to 10 fps. An 18' thick layer of Class I riprap with toe protection is required to protect the lower 2000 feet of levee. 20 References Reference #1 - "One Hundred Years on the Cedar". Margeret Slauson. 1967. Reference #2 - Lower Cedar River HEC-2 Model and Evaluation of Flood Relief Alternatives. Northwest Hydraulic Consultants Inc. February 1992. Reference #3 - Current and Future Conditions Report - Cedar River, Appendix B: Addendum to Bedload Analysis. King County Department of - Public Works. Surface Water Management Division. November 1993. Reference #4 - Cedar River Sediment Data Collection and Analysis. Northwest Hydraulic Consultants. July 1995. Reference #5 - NHC additional sediment data from December 1995 and February 1996 events. Reference #6 - Guidelines for risk and uncertainty analysis in water resources planning, Vol. I and II. March 1992. IWR Report 92-R-2. Reference #7 - Nelson, L.M., 1971, Sediment Transport By Streams in The Snohomish River Basin, Washington, October 1967 - June 1969 U.S. Geological Survey Open -file Report, 44p. Reference #8 - Nelson, L.M., 1974, Sediment Transport By Streams in The Deschutes and Nisqually River Basins, Washington, November 1971-june 1973 U.S. Geological Survey Open -file Report, 37p. Reference #9 - Nelson, L.M., 1979, Sediment Transport By The White River Into Mud Mountain Reservoir, Washington, June 1974-june 1976 U.S. Geological Survey Water -resources Investigations 78-133, 26p. Reference #10 - Nelson, L.M., 1982, Streamflow and Sediment Transport in The Quillayute River Basin, Washington: U.S. Geological Survey Open - file Report 82-627, 29p. Reference #11 - Glancy, P.A., Sediment Transport By Streams in The Chehalis River Basin, Washington, October 1961 - September 1965 U.S. Geological Survey Water -supply Paper 1798-h, P.hl-h53, 1971. Reference #12 - Sikonia, W.G., Sediment Transport in The Lower Puyallup, White, and Carbon Rivers of Western Washington U.S. Geological Survey Water Resources Investigations Report 89-4112, 2001990. 21 FIGURES Figure #1 - Bed material sample location plan map Figure #2 - Bed material gradation by distance from mouth Figure #3 - Existing channel dredge w/out delta dredge w.s Figure #4 - 4 ft dredge w/out delta dredge w.s. profiles Figure #5 - 6 ft dredge w/out delta dredge w.s. profiles Figure #6 - 10 ft dredge w/out delta dredge w.s. profiles Figure #7 - Cedar River Cross Section Locations (1994 COE profiles Survey) • 14 •• . •• t' t ' �! • � mar. w � � �' At . '1 - • y 1 : A• � •,i �: • 'f 11 � 1N � •I r `[r3, c. , ff • 16 51 .7 6 , .t,t.f '' •r j .:'.{�. Y J • ` ' � _.r � s,F �-•1 � _n � i : i•S � ■ ' ` -v '. ,••i }fist. •:/. •} 4 ,j. '�.: '• 1 � • .^. t -� ` ��•► - . 11 - �j � t;' @.0 •� 1 r• j '�{ r• • :fn a., j i� � ��.n. . •' r• 'ai' • �+ E, . A _ •• •'•p Spr`ir •� .h�i;• _,� il.f � .J� I•�•,- :.? � w t`.�� r• .�)■ • 1. i :•1s7�' � r.7C7r1' '.Y'f w � � i �' �S' u. a .I'l . •^ � �`, _ , jryai. , }I w, :z1as. ti �:•:.! i� ... � ' :F`• .+^' �-- ' r. „q .• M .• ..� � .. �ii: ���L .. • r • •c - it jt".616 ILI .?R•_ • r i►'s �r, s•�< �" -.- • • ` f -•tea. 1 AAMr ff ,• ..., � ••'• * Alt - t aL t,- - .q • As .� �' f}�S did +1, - `' �.• . .5''. � �`' �, �•� — a -' r' � . }q :'-j' •� t •f � � •fir . {% •n •\r -! �L 'M7 _ .�j *• �?.:. ;. �. � �ti i a�•i' o. '�i:• • �vt %"• � .•. It— �� ^y.„i -' ^ rt''t�ct��•..� f�rr � � •*, y.t iF �. / tt f :�� ��• 'e� �,r. ' �• `.;�• � •' � •� a' f/' .7a+Y'• '^ 1 R �� ry � _ .... •� •w� ,w '.♦yt ,� _ f y�` ;�7i � w .� a' nl ■ � 7 .� r i ia+• -i ,�?, r� , �t S �_ r �'�A/ i .�,� "F4.0,., � T' +�-. •�riY .! �' `ry •�.�:� • �� .F __ t �l i 6N , •� `•� w = :. ,, - •� ram` �'•' • 4 , � ,v,:� ..'. ���, irk 'i /. rf ,. �. •�j •• � �' w ..+!Y �� r 7�•A # �{, �� 1.• jl, . ` , v ^ ice. `'Ur 1- �st`••y,•�e+Wt+"*'S.�y. �'!r .}: f'•' `• U�. • 1-t'' L...r��{t ,` •:?:t �:/. ��,r jai.£`-'�� :.S'•. re.� s F•�� .yl:� �i:.'w,c'r• t+�1\• t•���i �•t t{ ]' • ^ :��=Ely�t }+�., !�•. n"r,�.� '.jl �. tll 1^_J :� ; • a�.• ., �+,%►R y,, ,:,�� , J .ip t 9i t�1'7L1 • , •`!—,�t� :��. � �- ,i �i�• '.1 Yf .1 JIM, . y i','t�.r ` ♦:: � C .� • .t 1 j, f- .- 'iFt!1iT?!Y•�i%i'�k 't'. e • }.a :��_ TT3r a •' :�'`ejt•l:..i .,.rAlXAIT ., t •e.; � Ij"'i f • . it tA t • 14 Ll . 1.', c,57' rf .. , �• •, •�,5� ��. Jacr■ •1••+.''�* �3 tii{. `\ �" �� �j•{T ���t�l , \/\ 3 ■ .}1 * !r, fit' ; y� ti '�.-4 �))� C�"•1 {• ��. (a l.t �i •;rtii,1 �;� �Iil 1 r 0.2000 0.100 Bad gradation variation upstream by distance upstream from mouth Cedar River 1000 ouOU 3000 4000 5000 OOOV 7000 DOoo Distance upstream oyMouth Very Coarse Gravel —i Coarse Gravel --*—Medium Gravel —wFine Gravel —+^—' Very Fine Gravel -Very Coarse tond Coarse Sand Medium Sand —Fine Sand —Very Fine Sand � m �� 45 40 35 Ce 15 10 5 Existing Thalweg Dredge . -. Delta Dredge 3 yr predredge 100 Year profiles .O -•-. d , �x x � x x o ,. x o, +F 0 +Thalweg Elev. (ft) —x-100 yr Levee profile —)K-100 yr WSEL, proposed 0 100 yr WSEL, exisiting 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 Distance ups' rom mouth, (feet) C m 2 1 1 Q C ,I 45 40 35 30 0 25 z c 0 :r > 20 a� w 15 10 5 0 4 Ft Dredge no Del, , 3 yr Predredge 100 year Profiles 11- i T- Existing Thalweg - - - - - -4 ft Dredge Channel Thalweg - - - 3 yr Predredge Thalweg --100 yr Levee Profile -- — ---- - _ - — -—)c-100 yr WSEL, proposed —100 yr WSEL, existing 0 1000 2000 3000 4000 5000 6000 7000 8000 Distance upstream form mouth, feet FIGURE 4 us We 6 ft Dredge no Del, edge 3 yr predredge 100 year profiles 45 40 35 30 0 25 z C O > 20 a� w 15 10 5 0 + 0 i —i Existing Thalweg - - - - - - 6 ft Dredge Channel Thalweg r --------- ------- — — — 3 yr Predredge Thalweg —X 100 yr Levee Profile —X-100 yr WSEL, proposed e 100 yr WSEL, existing 1000 2000 3000 4000 5000 6000 7000 Distance upstri rm mouth, feet Fir„Rs 8000 9000 45 40 35 30 0 25 z r- c 0 :r > 20 m w 15 10 5 0 10 ft Dredge no Del :! 3 yr predredge 100 year profiles X � X X Existing Thalweg - - - - - - 4 ft Dredge Channel Thalweg —X-100 yr Levee Profile -- -- - - - •------ —)K— 100 yr WSEL, proposed -------------------------- —e-100 yr WSEL, existing 0 1000 2000 3000 4000 5000 6000 7000 8000 Distance upstream form mouth, feet FIGURE 6 9000 11� APPENDIX D PROJECT FEATURES APPENDIX D ANALYSIS OF DESIGN TABLE OF CONTENTS Paragraph Page SECTION 1. DESIGN CONSIDERATIONS 1.01 Site Description D-1 a. Left Bank Description D-1 b. Right Bank Description D-2 1.02 Existing Condition D-2 SECTION 2. DESIGN FEATURES AND ANALYSIS OF THE RECOMMENDED PLAN 2.01 General D-2 2.02 Final Variations Considered D-2 2.03 Proposed Project D-3 2.04 Design Length and Layout D-3 2.05 Details of Flood Protection Features D-4 a. Levees D-4 b. Floodwalls D-5 c. Closure Structures D-5 d. Erosion Control D-8 e. Utilities D-8 2.06 Bridge Jacking Details D-9 2.07 Operation and Maintenance D-9 a. Operation D-9 b. Maintenance D-9 TABLES TABLE D-1 Project Feature vs. Rivermile D-1 TABLE D-2 Levee Configuration D-4 FIGURES FIGURE D-1 Typical Levee Sections D-6 FIGURE D-2 Typical Floodwall Sections D-7 FIGURE D-3 Site Plan 1 D-10 FIGURE D-4 Site Plan 2 D-11 FIGURE D-5 Site Plan 3 D-12 FIGURE D-6 Site Plan 4 D-13 FIGURED-7 Site Plan 5 D-14 FIGURE D-8 Jacking Option Structural Plan D-15 FIGURE D-9 Jacking Option Bridge Elevation D-16 FIGURE D-10 Jacking Option Truss Elevation D-17 FIGURE D-I I Jacking Option Upstream Pile Cap Plan D-18 FIGURE D-12 Jacking Option Pile Cap Elevation D-19 FIGURE D-13 Jacking Option Lifting Jack Collar Details D-20 1. Design Considerations 1.01 Site Description. The Cedar River is located entirely within the boundaries of . King County Washington. The proposed project lies on the final 1 1/4 miles of the Cedar River before it empties into Lake Washington. Both banks of the river in the vicinity of the proposed project are highly developed with The Boeing Company on the right bank and the City of Renton's Municipal Airport on the left bank. A narrow riverside park owned by the City of Renton runs along the lower 1+ miles of the right bank downstream of the Logan Avenue bridge. Features along the river that will be referred to throughout this report are listed below along with their corresponding rivermile. TABLE D-1. PROJECT FEATURE VS. RIVERMILE PROJECT FEATURE RIVERMILE Mouth of Cedar River at Lake Washington 0.00 North Boeing Bridge 0.01 Boat Ramp on Right Bank 0.14 Gazebo on Right Bank 0.37 Hangars on Left Bank 0.41 Hangars on Left Bank 0.52 Park Access Via N. 6`h Street on Right Bank 0.60 Compass Rose on Left Bank 0.63 South Boeing Bridge 0.74 Logan Ave Bridge 1.07 Williams Ave Bridge 1.23 Wells Ave Bridge 1.31 City of Renton Public Library 1.50 Interstate Highway 405 1.64 a. Left Bank Description. The left bank project area begins at Williams Avenue Bridge, the next bridge upstream of Logan Avenue. The area between Logan and Williams Avenues is a city park which has a riverside trail and some trees planted along the rivers edge. Adjacent to the park are a couple of buildings and parking lots. Downstream of the Logan Avenue Bridge the left bank area is used for the airport and related businesses including The Boeing Company operations. An airport perimeter road begins just downstream of Logan Avenue and travels the length of the left bank to the mouth of the river. The edge of this road generally stays within 15 feet of the river bank until the small -plane hangars are reached where the road moves inland. Buildings, airplane hangars, and vehicle and airplane parking areas are scattered throughout this stretch until downstream of the hangers where FAA restrictions prohibit objects in the safety zone of the runway. Utilities include electrical (overhead and buried), natural gas, water, sanitary sewer, and storm drainage lines. D-1 b. Right Bank Description. The right bank project area also begins at Williams Avenue. Two trails parrallel the river at different elevations between Williams Avenue and Logan Avenue. The two levels converge above Logan Avenue and traverse a semi- circular path in front of the Renton Senior Center. Downstream of Logan Avenue lies a riverside park that averages 200 feet wide and runs the remainder of the right bank to the mouth. The park has a'bike and pedestrian trail that meanders its length and is landscaped with planted mounds and numerous trees. An access road leading off of Logan Avenue at North 6`h Street provides vehicle access to the northern end of the park. Parking is provided along the access road and there is a ramp for non -motorized boats. The park also has a covered gazebo and a public restroom. Utilities include trail side lighting, underground irrigation, sanitary sewer, and storm drainage lines. 1.02 Existing Condition. The existing left bank profile averages several feet lower than the corresponding location accross the river on the right bank. This allows for frequent overtopping of the left bank (presently estimated at a 2 year event) while the right bank experiences little flood damage. The lowest spot along the left bank is immediately downstream of the South Boeing Bridge. The natural slope of the land is to the north, towards Lake Washington, with the runway centerline preventing further advancement west of the water flowing over the left river bank. The lower left bank prevents the right bank from having much inundation from river water and keeps the South Boeing Bridge from being threatened by high flood waters. Inland areas along both banks have interior runoff back flooding caused by clogged storm drainage outfalls. Most of the storm drainage lines outfalls have become plugged with river sediments as the river channel has filled in over the years when regular dredging of the channel was stopped. 2. Design Features and Analysis of the Recommended Plan 2.01 General. This section presents features and analysis of constructing flood protection measures along both banks of the lower Cedar River. Present conditions allow for frequent flooding of the Renton Municipal Airport along the left bank causing property damage, extensive cleanup, and delays for the users of the airport. 2.02 Final Variations Considered. During the design process several alternatives were considered. All alternatives were to contain the 100 year flood event through the construction of levees and floodwalls, and all involved some dredging both initially and as part of a maintenance program. The different dredge depths considered were 10 feet (the historic dredge depth), 6 feet, 4 feet, and 0 feet. Dredge depths are in reference to the survey of the river channel completed in 1995. Differing height levees were computed for each of these dredge depths. The layout of the levees and floodwall for each of the four alternatives was similar to that of the rccommended plan with the only difference being the upstream extent. The 0 foot dredge alternative used levees that extended to rivermile 1.6. Maintenance dredging frequency and quantities were also developed. (See Appendix A. Hydrology and Hydraulics.) Cost comparisons were prepared and the four alternatives weighed against each other using environmental impacts and construction cost criteria as well as the desires of the local sponsor and users of the facility. For the IsO South Boeing bridge the alternatives considered included permenantly raising the bridge in place, bracing the bridge against flood flows and letting it overtop, and hydraulically j acking the bridge above flood levels only when needed. Permenantly raising the bridge was not considered further because The Boeing Company's criteria for pulling large commercial airplanes over the bridge requires a shallow slope up to and down from the bridge deck. There was not enough physical space to fit in the long approach ramps required to meet the new bridge height. Bracing the bridge against flood flows meant assuming it would become blocked with debris and cause backwater affects upstream requiring even higher levees'and floodwall sections be constructed. Additionally it was determined that the existing bridge could not withstand the horizontal loads applied to it and a new bridge would have to be constructed. 2.03 Proposed Project. The main design features of the project include: dredging of the river channel to an average depth of 4 feet below the 1995 surveyed river thalwag, construction of flood control features along both banks to contain the 100 year flood event in the present river channel, hydraulically jacking the South Boeing Bridge above the contained flood water surface profiles, and providing closure structures to span the approach roads to the bridge. Additionally the left bank will incorporate an overtopping section of both levee and floodwall downstream of the South Boeing Bridge. The remaining floodwall and levee sections will be constructed with a top elevation that is one foot above the 100 year event water surface profile. This overbuilding of levee and floodwall sections will provide the right bank with greater than 100 year flood protection. See figures D-3 through D-7 for locations of levees and floodwalls and overtopping sections. The recommended plan provides for federal construction and local maintenance of all project features. 2.04 Design Length and Layout. The flood control features will include both earth embankment levees and steel sheetpile floodwalls. In areas of the riverside park the bike and pedestrian trail will be raised or realigned to accommodate the levees while preserving the aspects of the original park. For the Left Bank beginning at the upstream extent of the proposed project: *The riverside trail between Williams Avenue and Logan Avenue will be raised in its present alignment an average of 3 feet. •A steel sheetpile floodwall will be erected along the rivers edge between Logan Avenue and the South Boeing Bridge. Average height of this section is 8 feet above the existing ground line. *An 80 foot long removable closure structure will be provided to span the approach road leading to the South Boeing Bridge. •A steel sheetpile floodwall will be erected along the rivers edge between the South Boeing Bridge and the downstream extent of the small -plane hangers. This section of floodwall will be designed to overtop and averages 7 feet high. •An overtopping levee 4 feet high will be constructed from the end of the flood wall to the North Boeing Bridge and the end of the project. D-3 The right bank project layout will be: •The riverside trail between Williams Avenue and Logan Avenue will be raised in its present alignment an average of 3 feet. *The trail in the park will be realigned and raised and average of 3 feet between Logan Avenue and the South Boeing Bridge. •An 80 foot long removable closure structure will be provided to span the approach road leading to the South Boeing Bridge. •The trail in the park will be raised 4.5 feet to the top of the levee alignment from the South Boeing Bridge to the park access road from North 6`h street. •A short floodwall section will be constructed where North 6th street enters and space constraints do not allow for continuation of the levee. •A series of short levee sections will be constructed to join existing areas of high ground in the park. Sections of the park trail will be realigned and raised to accommodate the levee. Levee height varies between 3 and 6 feet. *An 80 foot long removable closure structure will be provided at the gazebo location. •The levee sections will continue through the park to the North Boeing Bridge and the end of the project. Various utilities will need to be relocated along both banks. Figures C-3 through C-7 show the levee and floodwall footprints for both banks. 2.05 Details of Flood Protection Features. a. Levees. Several variations of levee configuration were necessary due to widely differing uses of the land where the levees will be constructed. Generally all levees will be constructed out of compacted fill with a three foot top width and no steeper than 2H:1 V side slopes. The side slopes and top will be covered with a layer of topsoil and seeded. Variations of this include; having one side of the levee slope at 4H:1 V to meet FAA restrictions on slope, increasing both side slopes to 3H:1 V to allow for maintenance mowing and pedestrian use in areas of the park, and constructing an 8 foot wide asphalt trail on top of the levee in other areas of the park. The top elevation of the levee was determined using the water surface profiles developed by Hydraulics (See Appendix A. Hydrology and Hydraulics.) and adding a settlement allowance of 1 inch for every foot of levee height. See figure D-1 for typical levee sections. Ie� TABLE D-2 LEVEE CONFIGURATION Levee Type Description Type I 3' top width; 2H:1 V side slopes. Type Ia 3' top width; 3H:1V side slopes. Type II 8' wide Asphalt trail on top of levee section; 3H:1V side slopes for maintenance mowing and use in park setting. Type III Landward side slope flattened to 4H:1 V to meet FAA restrictions; levee designed to overtop when flows in river are greater than 100 year event. Backside of levee strengthened against scour with 18" layer of rock. b. Floodwalls. Where the width of the alignment is restricted due to existing development, roads, topographic features, or geotechnical concerns, a floodwall will be constructed. The floodwall will be composed of interlocked steel sheetpile 18 to 26 feet in length. The sheetpile joints will be sealed relatively watertight with a mastic joint sealer. The sheetpile will be capped with a continuous steel channel section welded in place. The floodwall height will be between 6 and 9 feet above the ground surface. The steel sheetpile wall will be allowed to rust becoming a brownish -copper color. Areas of sheetpile floodwall that are highly visible can be partially hidden using landscaping. The sheetpile floodwall sections downstream of the South Boeing Bridge will be designed to overtop when flows in the river exceed the 100 year event. These sections will have a rock splash apron installed at the landward toe to prevent undermining. Typical sections for the floodwall can be seen in figure D-2. c. Closure Structures. Three removable closure structures are required along the alignment, two at the South Boeing Bridge, and one at the gazebo location on the right bank. The South Boeing Bridge closure structures had to be designed to pass aircraft through with enough vertical and horizontal clearance. They will be 80 feet long and 3.5 feet high. The closure structure for the gazebo location will be 80 feet long and 6 feet high. The closure structures will consist of a concrete bottom sill that has a rubber seal and pre -formed slots that W8x15 structural steel sections can be inserted vertically into. The slots will be spaced on 8 foot centers. The vertical steel sections allow for fabricated treated wood sections to span the distance between them to form a wall. Seals along the backside and between the wood sections will minimize leakage. The terminal ends of the closure structures will have the same steel section formed into a concrete wall from which the levee or floodwall will continue. D-5 E ALIGNMENT 2" MIN. TOPSOIL 1.5' 1 1.5' AND SEEDING ' IDO YEAR WATER C7 SURFACE ELEVATION EXISTING GROUND i LEVEE EMBANKMENT MATERIAL I� SURFACE 20R 3 I 20R3 STRIP 6" AND REMOVE UNSATISFACTORY MATERIAL NOTE: LEVEE TYPE I HAS 2H:IV SIDE SLOPES, LEVEE TYPE Ic HAS 3H:IV SIDE SLOPES. LEVEE TYPE I & TYPE la NOT TO SCALE E ALIGNMENT L Y 2" MIN. TOPS AND SEEDING 1 L_� 3" AC PAVEMENT I' 100 YEAR WATER 4" GRAVEL BASE 3 LEVEE EMBANKMENT I� MATERIAL _ _ 3 STRIP 6' AND REMOVE UNSATISFACTORY MATERIAL LEVEE TYPE II NOT TO SCALE E ALIGNMENT 100 YEAR WATER RIVER SIDE I • AIRPORT SIDE SURFACE ELEVATION V 24' OF CLASS II RIAP PR1 2 LEVEE EMBANKMENT I� MATERIAL — - -ems^ STRIP 6" AND REMOVE UNSATISFACTORY MATERIAL LEVEE TYPE III NOT TO SCALE 16' OF CLASS I RIPRAP SLOPE PROTECTION 4" OF GRAVEL FILTER 4' OF TOPSOIL AND SEEDING 4 I F- 8' FIGURE D-1 TYPICAL LEVEE SECTIONS I L � I � 1 I � 1 < EXISTING VEGETATION. 1 REMOVE LARGE TREES I AND REPLACE WITH SHRUBS / AND WILLOW SHOOTS. � l / I 1 1 t ALIGNMENT / 1 I STEEL CHANNEL 1 1 I 100 YEAR WATER - A I SURFACE ELEVATION I �] - 1 I I I I I I I 8' TO 9' 24' OF CLASS 11 1 I RIPRAP ON BANK I I STATION L 59+00 1 TO L 64+00 - I WILLOW v pr-STEEL SHE PILE EXISTING GROUND LINE VARI S 5' TO I ' FLOODWALL TYPE I NOT TO SCALE E ALIGNMENT 100 YEAR WATER - STEEL CHANNEL SURFACE ELE'ATION�I TEEL SHEETPILE TO 7' ROAD SEEDING OVERNRIPRAP EXISTING , POF CLASS I GROUND LINE RIPIPRAP SPLASH APRON GEOTEXTILE 10, FLOODWALL TYPE II NOT TO SCALE FIGURE D-2 TYPICAL FLOODWALL SECTIONS D-7 d. Erosion Control. For the right bank in the park the grassed side slopes of the proposed levees will provide adequate erosion protection due to low water velocities. The levee sections on the right bank can be set back from the rivers edge and will not have the main flow of the river against them. The outside of the river bend downstream of the Logan Avenue bridge on the left bank will be riprapped for approximately 400 feet. There is evidence of erosion along this portion of the river and some existing rock is already in place. The riprap will extend up to the base of the sheetpile floodwall to be constructed along this reach. Riprap will also be used on the riverside of the levees downstream of the small plane hangers on the left bank along the overtopping levee section. The levees here must be located in close proximity to the rivers edge due to safety clearances for the airport runway.. A rock splash apron will be provided on the landward side of the sheetpile floodwall where it is part of the overtopping section. The overtopping portions of levee, downstream of the small -plane hangers, will have a protective rock layer placed below the seeded topsoil layer on the landward side to prevent scour of the levee material when it overtops. e. Utilities. Several utilities will be impacted by construction of the proposed project. The storm drainage system for the airport currently has outfalls that drain to the river. The ends of the pipes have become plugged with river sediments* since the river was last dredged by the City of Renton. The proposed plan calls for exposing the ends of the pipes by dredging or excavating and installing a backflow preventor. Where the pipes must pass through the sheetpile floodwall the pipe will be exposed on both sides of the alignment, shut off, and a section of the pipe removed so that the sheet pile maybe driven. After the sheetpile has been driven a hole will be cut through the steel sheetpile centered on the axis of the pipe. A 1'/z foot long steel sleeve with an inside diameter 2 inches larger than the outside diameter of the existing pipe will be inserted into the hole and welded to the sheetpile. The existing pipe will be passed through the sleeve and reconnected to the ends of the existing pipe left in place. The space between the pipe and the sleeve will'be filled with an asphaltic mastic to provide a watertight seal. The excavation will be backfilled with suitable material and properly compacted. The existing storm drainage system on the right bank also drains to the river. The Boeing Company has definite plans to install an interceptor that will take the flows from all but one of the outfalls on the right bank and carry them to Lake Washington. The proposed plan assumes that this work will be completed before construction of the proposed project. The remaining outfall will be retrofitted with a backflow preventor. An existing water line and an existing sewer line cross the river via the South Boeing Bridge. The proposed jacking of the bridge will require that these lines be re-routed. Both lines will be re-routed under the river 3 feet below the historic dredge depth of 10 feet. The sewer line is a pressure system so no siphon is required. The re-routed lines will be encased in concrete to prevent accidental damage during subsequent maintenance dredging operations and to prevent the lines from floating. Trail side overhead lights will be moved to new locations in areas where the existing trail is re -aligned. The underground irrigation system for the park will need to be modified after completion of levee construction. M 2.06 Bridge Jacking Details. The south Boeing bridge will be jacked clear of the water surface of the design flood event. The concept involves unbolting the existing bridge from its current foundations and jacking the bridge intact to a sufficient height to prevent debris in the river from snagging the under side if the bridge. Four hydraulic jacks of approximately 175 tons capacity each will be positioned on new foundations at each of the four corners of the bridge. The foundations will be concrete pile caps on nine to 12 deep piles. Based on the design of the original foundations, the new piles will be more than 80 feet long. The pile caps will also serve as guides for the jacks and protection from debris for the jacks. One new steel lifting truss, 66 feet long and 6'/z feet deep, will be installed at each end of the bridge and attached to the new hydraulic jacks. In order to clear debris in the flood waters, the bridge will be jacked to a height of seven feet. Boeing can expect to operate the bridge until the water reaches the bottom of the bridge, then the bridge will be raised and the closures for the bridge approaches will be sealed. Figures D-8 through D-13 show details of the bridge jacking plan. 2.07 Operation and Maintenance. Following construction, the completed project will be transferred to the local sponsor for operation and maintenance (0&M). The Seattle District will prepare an 0&M manual and famish copies to the local sponsor. The local sponsor will then be responsible for operating and maintaining the project as described in the O&M manual to ensure serviceability against floods at all times including levees, floodwalls, closure structures, dredging, and bridge jacking operations a. Operation. Operation of the project during flood events will require the monitoring of river levels, installation of the closure structures, raising of the South Boeing Bridge, and verification that the project is operating as designed. All equipment and supplies required to operate the project will be stored close by. Flood exercises will be required periodically to train local sponsor personnel in the proper operation of project features. Removal of debris will be required throughout the year to ensure proper operation of drain pipes, the South Boeing Bridge jacking mechanisms, and installation of the closure structures. b.. Maintenance. Maintenance of the project is required to ensure that the project will provide the designed protection during floods. The major maintenance feature of the proposed project is the periodic redredging of the river channel. See Appendix A - Hydrology and Hydraulics for a discussion of redredge frequency and amount. General project maintenance will include mowing the grassed levees, removing undesirable vegetation from the embankment side slopes, removal of debris from levee slopes and structures, trimming and pruning of trees and shrubs along with monitoring survival of planted materials, correction of all types of animal burrows and, if required, restoring the embankment to the design grade and section. As the age of the project increases, maintenance of the project will include replacing deteriorated and damaged equipment. Particular attention to closure structures and jacking machinery will be required. The local sponsor will prevent encroachment on the rights -of -way that would interfere with project operation and maintenance. An inspection program will be developed by the local sponsor to recognize and correct any conditions that could adversely affect the project. lwl '------------------------_----_------------------------_----_---_--_---_-------------------------------------_------------------------- / / / / / / U / / / / ~ / / - . / �' [�-�-- �--,---cl- / RE 5TR-yCTURE ......... Ej . / / 10 / �[ / �� / �-n ( / ~� N"�g�g�U������� l[l�J�� / n -- / ' .^~. / / / / / / / PE I Fc / U - -/ K-------� `-TRA|L --� / -- / . - / ' / °� "~~�� / / ' / /XX/ / / / / / / FIGURE D5 / / | / |° |00~ / / U. S. ARMY ENGINEER DISTRICT, SEATTLE CORPS OF ENGINEERS / / ` / / U / USITE PLAN 3CEDAR RIVER WASHINGTON / / / / / / / / / om/E AND TIME nm//ux "-JuN-n,' .wu mS/ow FILE: /.*uevonv*o fc*°.*c,/dp,zdgp SCALE: / ^ ^ /mr / ILrn Lli •f'rra ..'"' ?j % •tititi \:; __~ ..._v�_.......... ....—^........... .....__.i......_.. f y;f r?; : r1+�{ :r.'.-.•• `% •/ ° f .Y.��...:••�' ...... �,w••_.�.....�.........`_.�.:.i._.„»:.....�•..�..-roi:em•+•...nrml:w;�+::� A� r+•`2 _ _ ..-.L...i..1r F: . ..." -.. A ... • - Y' ram,„... -.r•� �.......• .. ._ .... .......��:..... __. .-c Go . - i ..40 O \ :. j } .r i"':--' ...r...,sr•_"'" _ _..� _ _ �"—•„___.'• ''..a.�'"'""'^�`�.. .+�ti;..� ':.„ ^: -y/ .. /..•' % f'/„„�f.• ' a• fir` ;;�.:- � W .r•"r""' -.-•-' �.-�_... ....-' ....... y��'•w•..+�.... ::� ' :" ' �,-,-N-.�'. '•Y�� �`„V`:` t � �� ��p / ©T�/�'" /" /r��..-•• � .."... :..„ { ..t; , it-S •l, ./ ..••"Q x� `I ., P r ..Pr ,,i..Mri •--•" -....•-._••• 7.r I rT % ��1 ta3Yc5 1 -. ^.`i � i :.` ..-'•..•'Y J �` jl-- _ ._..... _ '..:_ •. i r f � -` '• .-f -_., '" _._._ _.:.::..w•^c>'-' � •l.4-' ,.,.--•^"' • t t ' ��� '•r*• `� \ .a :.::v �' rr � .'r':•� �' :. �: .—_ - htyr" /�f -..-per.. 't � t ^-y ; �,'�i j 1'. O _,Yt.-._ .•., -•r••` ;: ...... R:..'^"''v- e-..' ! 1..: i fr.••.w,la.i : : tr , vX �. `', �~ ._ � / ;. '1''j ' �+�'.' Y:"'>Y. .. - ._�fd�� -'!'� .. % r .."I •�'•'•".,„,n.,r•�.,r...... ,�'•• ..t"1 •.� t •r '`t'-+�...: ti.r•.:.i.-._.. r' '+•*.c%c'..� i i ti•T;rr�.fr "_•. '� , � � � •- !'. "-- .:+. t t :ram., f •^-'w:.c'� L'f� � yFI FIGURE D-6 100' 50' 0 100, 200' I " = 100' U. S. ARMY ENGINEER DISTRICT, SEATTLE CORPS OF ENGINEERS SEATTLE, WASHINGTON SITE PLAN 4 CEDAR RIVER WASHINGTON SIZE INVITATION NO. FILE NO. PLATE B C1.4 OSCN: BRANDT CHK: SHEET D-13 DATE AND TIME PLOTTED: 17-JLIN-1997 10.34 nccicu ❑11 r. ,,.,-e _ .. NEW LIFTING TRUSS NEW 10'X 10' PILE CAP TYP EXISTING STEEL GIRDERS c c : Af I I I I I I I I I I I I I I I i I I I I I I I I I I I I I I I I I I I I I I I I i I I I I I I I I I I I I i I I I I i I I I I I I I - - C C EXISTING PIER I c ,. BRIDGE DECK c o I c c c 80' PILE, 12" DIAMETER TYP EXISTING ABUTMENT NEW 10'X 13' PILE CAP j SEE PLATES S3.4 & S3.5 I TYP I FIGURE D-8 NOTES: 10' 0 10' 2 0' 3 0' I' - o" I. ONE HYDRAULIC JACK WILL BE INSTALLED ON EACH NEW PILE CAP. U. S. ARMY ENGINEER DISTRICT. SEATTLE CORPS OF ENGINEERS 2. THE BRIDGE WILL BE UNBOLTED FROM ITS SEATTLE, WASHINGTON CURRENT FOOTINGS. JACKING OPTION 3. THE BRIDGE WILL BE BOLTED TO THE NEW STRUCTURAL PLAN LIFTING TRUSSES. CEDAR RIVER WASHINGTON SIZE INVITATION NO. FILE NO. PLATE B SI.I DESIGN FILE: I:OdesignsOcrfc0strOcrfcsa0a.dgn DSGN: SHAW CHK: SHEET D-15 DATE AND TIME PLOTTED: 09-MAY-1997 09:28 DESIGN FILE: I:OdesignsOcrfc0strOcrfcsa0a.d9n SCALE: %i6" EXISTING ABUTMENT PPROXIMATE EXISTING GROUND EVEL. EXCAVATE AS REQUIRED FOR TRUSS, AND SHOTCRETE NEW SURFACE UNDER BRIDGE. NEW LIFTING TRUSS TYP ----------------- --------------------------------------- t EXISTING PIER EXISTING GROUND LINE NEW GROUND LINE FIGURE D-9 ,• _ 10, 0 10, 20' 30' Y16 I' - 0„ U. S. ARMY ENGINEER DISTRICT, SEATTLE I CORPS OF ENGINEERS SEATTLE, WASHINGTON JACKING OPTION BRIDGE ELEVATION CEDAR RIVR WASHINGTON SIZE INVITATION N0, FILE NO. PLATE B ISI.2 DESIGN FILE: i:Odes ignsOcrfc0strOcrfcso0b.dgn OSGN: TMS I CHK: SHEET D-16 ATTACH TO JACK COLLAR AT EACH END OF TRUSS •• • 4'-6" 6'-0" W8X40 VERTICAL TYP ELEMENT, TYP W 18X 175 1 _ _ _ _ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ _ _ _ _ _1 2L 5X3X1/2 TYP NOTES: I. THE EXISTING BRIDGE GIRDERS WILL REST ON THE VERTICAL TRUSS MEMBERS. 2. ALL STEEL IS A36. 3. THE ENTIRE TRUSS MUST BE PAINTED OR GALVANIZED FOR CORROSION PROTECTION. DESIGN FILE: i:OdesignsOcrfc0strOcrfcso0c.dgn W 18X 175 0 FIGURE D-10 5' 0 5' 10, 15' U. S. ARMY ENGINEER DISTRICT, SEATTLE CORPS OF ENGINEERS SEATTLE, WASHINGTON JACKING OPTION TRUSS ELEVATION CEDAR RIVER WASHINGTON SIZE INVITATION NO. FILE NO. PLATE B S1.3 DSGN: TMS CHK: SHEET D- 17 NOTE: EXACT LOCA OF THESE TWO SURI WILL BE DETERMINE DESIGN OF GUIDE W FOR THE JACKS. TF SURFACES RESIST L LOADS WHILE BRIDG NOTE: CONSTRUCTION OF DOWNSTREAM PILE CAP SIMILAR. DOWNSTREAM PILE CAP IS 3' SHORTER IN DIRECTION OF FLOW, BUT OTHERWISE IS IDENTICAL. MGM r FIGURE D-II U. S. ARMY ENGINEER DISTRICT, SEATTLE CORPS OF ENGINEERS SEATTLE, WASHINGTON JACKING OPTION UPSTREAM PILE CAP PLAN CEDAR RIVER WASHINGTON SIZE INVITATION NO. FILE NO. PLATE B 51.4 DESIGN FILE: i:0designsOcrfc0strOcrfcsa0d.dgn OSGN: TMS I CHK: SHEET D-18 NOTE: CONSTRUCTION OF DOWNS - SIMILAR. DOWNSTREAM PILE CAP IS 3' SHORTER IN DIRECTION OF FLOW, BUT OTHERWISE IS IDENTICAL. 13' - 0" RADIUS CORNER FIGURE D-12 U. S. ARMY ENGINEER DISTRICT, SEATTLE CORPS OF ENGINEERS SEATTLE, WASHINGTON JACKING OPTION PILE CAP ELEVATION CEDAR RIVER WASHIN"PLATE SIZE INVITATION N0. FILE NO. DESIGN FILE: i:OdesignsOcrfc0strocrfcso0f.dgn DSGN: TMS I CHK: SHEET D— 19 i9/ WELD ATE I J I LL.L I-VLLHI\ COLLAR SECTION SCALE: 3" = 1'-0" ASSEMBLY NOTES: 1. BOLT THE WEB OF THE TOP W 18 OF THE LIFTING TRUSS TO THE SHEAR PLATE SHOWN HERE. 2. WELD THE FLANGES OF THE W18 TO THE WELD PLATES SHOW HERE. 3. THE WHEELS SHOWN HERE ARE TO GUIDE THE JACK ALONG THE NOTCH IN THE CONCRETE PILE CAP. 4. THE WHEELS MUST SUPPORT A FORCE OF 12 KIPS. " SHEAR PLATE 'ENTERL I NE OF N18 MEMBER 3 HYDRAULIC JACK COLLAR ELEVATION SCALE: 3" = 1'-0" FIGURE D-13 AR PLATE 1,, 0 3" 6" 9" 12" 3" - I' - 0" U. S. ARMY ENGINEER DISTRICT, SEATTLE CORPS OF ENGINEERS SEATTLE, WASHINGTON JACKING OPTION LIFTING JACK COLLAR DETAILS CEDAR RIVER WASHINGTON SIZE INVITATION NO. FILE NO. PLATE B S 1.6 DESIGN FILE: i:OdesignsOcrfc0sfrOcrfcsc0g.dgn OSGN: TMS CHK: SHEET D-20 APPENDIX E PROJECT COSTS I OI AL ALL CONTRACTS TOTAL PROJECT COST SUMMARY PAGE 1 OF 2 - —BASED ON THE DETAILED PROJECT REPORT DATUMARZTT-1-997- I'l-'()JI:CT CEDAR RIVER SEC110N 205 FLOOD DAMAGE REDUCTION STUDY DISTRICT: SEATTLE I ()(!A I ION. RENTON. WASI IING1 ON POC: OLTON SWANSON. CHIEF, COST ENGINEERING _ EPJun EFFECTIVE PRICING LEVEL: Oct 1997 EFFECTIVE PRICING LEVEL: ACCOUNT COST CNTG CNTG TOTAL COST CNTG TOTAL COST CNTG FULL NUMBER FEATURE DESCRIPTION ($K) ($K) (%) ($K) ($K) ($K) ($K) ($K) ($K) ($K) 9 C)1ANNELS AND CANALS 5,272 1.054 20% 6.326 5.408 1.082 6,490 TOTAL,2 2 $1.054 20% $6,326 $5,408 $1,082 $6.490 O1 LANDS AND DAMAGES 803 161 20% 964 803 161 964 30 PLANNING, ENGINEERING AND DESIGN 516 104 20% 620 522 105 627 31 CONSTRUCTION MANAGEMENT 422 84 20% 506 442 88 530 TOTAL PROJECT COSTS 0 3 $1,403 0 $8,416 _37J75 $1,436 $8.611 TOTAL FEDERAL COSTS THIS TPCS REFLECTS A PROJECT COST CHANGE OF TOTAL NON-FEDERAL COSTS DISTRICT APPROVED: THE MAXIMUM PROJECT COST IS %� /GdGlri�G",)y1 CHIEF, COST ENGINEERING CHIEF, REAL ESTATE DIVISION APPROVED: CHIEF. PLANNING CHIEF, COST ENGINEERING CHIEF, ENGINEERING DIRECTOR, REAL ESTATE CHIEF, CONSTRUCTION CHIEF, PROGAMS MANAGEMENT CHIEF, OPERATIONS DIRECTOR OF PPMD CHIEF, PROGRAMS MANAGEMENT APPROVED DATE: PROJECT MANAGER DDE (PM) FULLFUND2.zls 6/15/97 TOTAL CONTRACT COST SUMMARY PAGE 2 OF 2 BASED ON THE DETAILED PROJECT REPORT DATED MARCH 1997 PROJECT CEDAR RIVER SECTION 205 FLOOD DAMAGE REDUCTION STUDY DISTRICT: SEATTLE LOCATION: RENTON. WASHINGTON POC: OLTON SWANSON, CHIEF, COST ENGINEERING T-W-AC7=7MATE-PREPARED:Jun 97 AUTHORIZLL)113U[5GET YEAR: FULLY FUNDED ESTIMATE --- EFFECTIVE PRICING LEVEL: Oct 1997 EFFECTIVE PRICING LEVEL: ACCOUNT COST CNTG CNTG TOTAL COST CNTG TOTAL FEATURE OMB COST CNTG FULL NUMBER FEATURE DESCRIPTION ($K) ($K) N ($K) ($K) ($K) ($K) MIDPT (%) ($K) ($K) ($K) 9 CHANNELS AND CANALS 09.01 CHANNELS 09.01.01 MOB, DEMOB & PREPARATORY WORK 132 26 20% 158 OCT 98 2.6% 135 27 162 09.01.14 SIDECASTER/SPECIAL PURPOSE DREDGING 1.480 296 20% 1,776 OCT 98 2.6% 1,518 304 1,822 09.01.30 BANK STABILIZE, DIKES AND JETTIES 2,541 508 20% 3,049 OCT 98 2.6% 2.607 521 3,128 09.01.99 ASSOCIATED GENERAL ITEMS 1.119 224 20% 1,343 OCT 98 2.6% 1.148 230 1,378 TOTAL CONSTRUCTION COST $5.272 Si.054 0 61 ,408 $1.082 6,490 O1 LANDS AND DAMAGES 803 161 20% 964 OCT 97 0.0% 803 161 964 30 PLANNING, ENGINEERING AND DESIGN 478 90 20% 574 OCT 97 0.0% 478 96 574 MONITORING 38 8 21% 46 OCT 01 16.8% 44 9 53 31 CONSTRUCTION MANAGEMENT 422 84 20% 506 OCT 98 4.7% 442 88 530 TOTAL PROJECT COSTS 013 $1.403 20% $8,416 $7,175 $1.436 $8,611 FULLFUND2.xls 6115/97 CEDAR RIVER SECTION 205 FLOOD DAMAGE REDUCTION STUDY NARRATIVE 1. To reduce flood damages on the Cedar river in Renton several flood control measures will be implemented. The flow capacity of the river will be increased by dredging to a depth of four feet below 1995 conditions conditions from the mouth of the river to the South Logan Avenue bridge, gradually sloping to existing gradient at Williams Avenue. Dredging will be accomplished by dragline and hydraulic excavator. The dredged materials will be disposed of near the intersection of Interstate 405 and Highway 169. 3600 LF of levees will be constructed as space allows and 3620 LF of sheetpile floodwalls will be driven where space is limited. Temporary closure structures will be provided for the south Boeing bridge and for the rest room at City park. The south Boeing bridge will be modified to allow it to raise during a flood event. Hydraulic cylinders will jack the bridge evenly from all four corners. Mitigation features include construction of a salmon spawning channel and plantings along levees in the Cedar River Trail Park. 2. The basis of the estimate is the detailed project report dated March 1997. 3a. The need for overtime for any of the construction activities has not yet been determined. 3b. The construction window for working in the river is June 15 through August 31. A. The only assumed subcontractor identified at this time is for the truck hauling of the dredged materials. Three separate contracts may be used for the major types of work which include bridge acking, dredging, and levee and floodwall construction. 5a. Site access will include City of Renton Parks parking lots and access roads, Renton Airport access road, the Renton Boeing Plant access roads and bridges, Williams Avenue and Wills Avenue. 5b. The nearest borrow areas are located approximately 2 miles away in' Renton, WA. 5c. All construction methods are assumed to be conventional at this time. 5d. Salmon migration periods and the potential for flooding are the only factors anticipated to affect construction. 5e. Availability of labor and equipment is not foreseen as a problem. The project site is centrally located in the Puget Sound urban corridor. 6. Contingencies are set at 20% for all features including construction and in-house labor. Inflation factors used in full funded summary according to EC 1-2-169 dated March 31, 1996. Labor rates are based on October 1997 King County union wages. Equipment rates are effective )ctober 1995 and material prices are effective October 1995. All MCACES database materials and naterial quotes are effective October 1997. 6/15/97 .1111 1" Jun 1997 Tri-Service Automated Cost Engineering System (TRACES) TIME 10:49:45 fl. (late 10/01/97 PROJECT CEDAR2: Four Foot Dredge Alternative - Cedar River Section 205 DPR Estimate TITLE PAGE 1 .....---------------------------------------------------------------------------------------------------------------------------------------------------------------------- Four Foot Dredge Alternative Cedar River Section 205 Flood Damage Reduction Study Detailed Project Report Renton, Washington Designed By: Seattle District Design Branch Estimated By: U.S. Army Corps of Engineers Prepared By: Cost Engineering Branch William Garrott/Stephen Pierce Preparation Date: 03/17/97 Effective Date of Pricing: 10/01/97 Est Construction Time: 426 Days Sales Tax: 8.20% This report is not copyrighted, but the information contained herein.is For Official Use Only. M C A C E S F O R W I N D O W S Software Copyright (c) 1985-1996 by Building Systems Design, Inc. Release 1.10 LABOR ID: Kit"" EQUIP ID: NAT95A Curren— +- nOLLARS CREW ID• NAT9S° "1" 10: NAT95A " 1'. J,m 1997 Tri-Service Automated Cost Engineering System (TRACES) TIME 10:49:45 ff. Oote 10/01/97 PROJECT CEDAR2: Four Foot Dredge Alternative - Cedar River Section 205 fAflfl OF CONTENTS DPR Estimate CONTENTS PAGE 1 -------------------------------------------------------------------------------------------------------------------------------------------------------------------- No Backup Reports... SUMMARY REPORTS SUMMARY PAGE PROJECT INDIRECT SUMMARY - system.........................................1 PROJECT DIRECT SUMMARY - system...........................................2 DETAILED ESTIMATE DETAIL PAGE 10. General Overhead 0. Overhead Items A. Supervision and Management................................1 B. Administration Job Office.................................1 D. Engineering and Surveying.................................2 E. Quality Control and Testing...............................3 F. Safety, Trfc Cntrl, Fst Aid,Fire..........................3 G. Sanitation Fac & Temp Bldgs...............................4 I. Miscellaneous Project Expenses ............................4 09. Channels and Canals 01. Channels 01. Mob, Demob & Preparatory Work 01. Mobilization and Demobilization ...........................5 03. Preparatory Work..........................................5 it.. Sidecaster/Special Purpose Dredg 02. Sitework.................................................5 30. Bank Stabilize, Dikes & Jetties 02. Civil.....................................................6 04. Structural...............................................11 06. Demolition...............................................11 08. Relocations..............................................12 99. Associated General Items 02. Structural..............................................14 99. Mitigation (Salmon Spawning..............................14 * * * END TABLE OF CONTENTS * * * ;tu, li Jun 1997 Tri-Service Automated Cost Engineering System (TRACES) TIME 10:49:45 1.11. Date 10/01/97 PROJECT CEDAR2: Four Foot Dredge Alternative - Cedar River Section 205 DPR Estimate SUMMARY PAGE 1 ** PROJECT INDIRECT SUMMARY - system ** --------------------------------------------------------------------------------------------------------------------------------------------------------------------------- QUANTITY UOM DIRECT OVERHEAD HOME OFC PROFIT INS/BOND 090 Tax TOTAL COST UNIT COST ----------------------- -------------------------------------------------------------------------------------------------------------------------------------------------- 09 Channels and Canals 0901 Channels 090101 Mob, Demob & Preparatory Work 110,000 8,378 4,427 6,140 1,934 654 131,533 090114 Sidecaster/Special Purpose Dredg 158500.00 CY 1,237,746 94,266 49,817 69,091 21,764 7,363 1,480,047 9.34 090130 .Bank Stabilize, Dikes & Jetties 6920.00 LF 2,124,863 161,828 85,522 118,611 37,362 12,641 2,540,827 367.17 090199 Associated General Items 935,399 71,239 37,648 52,214 16,448 5,565 1,118,513 ----------------------------------------------- --------- ----------- TOTAL Channels 4,408,007 335,711 177,415 246,057 77,508 26,223 5,270,921 ------------------------------------------------------------------- TOTAL Channels and Canals 4,408,007 335,711 177,415 246,057 77,508 26,223 5,270,921 ------------------------------------------------------------------- TOTAL Four Foot Dredge Alternative 4,408,007 335,711 177,415 246,057 77,508 26,223 5,270,921 LABOR ID: K--_--- EQUIP ID: NAT95A Curre --_ ^OLLARS CREW ID: NATO-- -"` TD: NAT95A 1" 19W Tri-Service Automated Cost Engineering System (TRACES) TIME 10:49:45 !i. 0.1 10/01/97 PROJECT CEDAR2: four Foot Dredge Alternative - Cedar River Section 205 DPR Estimate SUMMARY PAGE 2 PROJECT DIRECT SUMMARY - system ** ---------- --------------------------------------------------------------------------------------------------------------------------------------------------------- QUANTITY UOM MANHRS LABOR EQUIPMNT MATERIAL OTHER TOTAL COST UNIT COST ............... . ...------------------------------------------------------------------------------------------------------------------------------------------ 09 Channels and Canals 0901 Channels 090101 Mob, Demob & Preparatory Work 090114 Sidecaster/Special Purpose Dredg 158500.00 CY 090130 Bank Stabilize, Dikes & Jetties 6920.00 LF 090199 Associated General Items TOTAL Channels TOTAL Channels and Canals TOTAL Four Foot Dredge Alternative OVERHEAD SUBTOTAL HOME OFC SUBTOTAL PROFIT SUBTOTAL BOND SUBTOTAL B&O Tax TOTAL INCL INDIRECTS 1,680 54,000 50,000 6,000 0 110,000 15,365 587,577 650,168 0 0 1,237,746 7.81 11,970 684,430 591,387 736,790 112,255 2,124,863 307.06 7,736 250,187 215,592 469,621 0 935,399 ---------------- --------- ----------------------------- 36,751 1,576,195 1,507,147 1,212,410 112,255 4,408,007 ------- --------- ------------------ -------------------- 36,751 1,576,195 1,507,147 1,212,410 112,255 4,408,007 ------- --------- -------------------------------------- 36,751 1,576,195 1,507,147 1,212,410 112,255 4,408,007 335,711 4,743,718 177,415 4,921,133 246,057 5,167,190 77,508 5,244,698 26,223 5,270,921 LABOR ID: KI""' EQUIP I0: NAT95A Currer -QLLARS CREW 1D• NAT9 '): NAT95A APPENDIX F FISH AND WILDLIFE COORDINATION ACT REPORT CEDAR RIVER SECTION 205 DREDGING PROJECT U. S. FISH AND WILDLIFE COORDINATION ACT REPORT U.S. Fish and Wildlife Service North Pacific Coast Ecoregion Western Washington Office Olympia, Washington I 'A .'. February 1997 U.S. Fish and Wildlife Final Coordination Act Report CEDAR RIVER SECTION 205 DREDGING PROJECT Prepared for U.S. Army Corps Of Engineers Seattle District Prepared by Gene Stagner, Biologist U.S. Fish and Wildlife Service North Pacific Coast Ecoregion Western Washington Office Olympia, Washington February, 1997 LIST OF TABLES Table...................................................................7 Birds observed in the vicinity of the lower Cedar River Table2..................................................................10 Resident and anadromous fish species utilizing the Cedar River Table..................................................................11 Sockeye Salmon redds observed in the lower Cedar River, 1994 and 1995 Table4..................................................................16 Smelt egg distribution in Lake Washington tributaries LIST OF FIGURES Figure...................................................................3 Lower Cedar River Section 205 Project Vicinity Map, City of Renton, King County, Washington Figure2...................................................................4 Lower Cedar River Section 205 Project Location Figure..................................................................11 Cedar River Salmon and Steelhead Periodicity Chart Figure4..................................................................13 Cedar River Sockeye Escapement Figure..................................................................15 Anadromous Fish Returns to the Lake Washington Basin and Cedar River Historically, the lower Cedar River was dredged periodically to a depth of >10 feet. This was expensive and created a need to dredge the delta area. The delta created the control level for water flow into the lake and therefore limited flow if it was not dredged to an equal depth as the channel. Due to the recent flooding along the lower Cedar and the significant damage incurred, alternative methods for flood control are being investigated by the City of Renton and the Corps of Engineers. An interagency scoping meeting was conducted on June 12, 1996, to discuss the latest flood control alternatives and solicit agency issues. These issues should be addressed in the Environmental Impact Statement (EIS) and in the design report. The discussions focused on fish and wildlife resource studies, and impacts of the projects on these resources. Sediment traps and transport were discussed and five (5) alternatives were presented. The no action alternative will be evaluated in context during the EIS. Consequent phone discussions with the Corps indicated that the sediment traps would not significantly delay the frequency of lower channel dredging so that alternative will likely be dropped from future consideration. The remaining alternatives with various permutations are discussed below. PROJECT LOCATION AND DESCRIPTION LOCATION This proposed project involves the Cedar River from the mouth at Lake Washington upstream approximately one mile. It is entirely within the city limits of Renton. The Cedar River watershed is located about 16 miles southeast of Seattle entirely within King County (See Figure 1). The headwaters begin within the boundaries of the Mt. Baker - Snoqualmie National Forest. The drainage basin is about 50 miles long and encompasses an area of approximately 186 square miles. The Cedar River cuts a canyon through steep mountain terrain from its source to Chester Morse Lake at about rivermile (RM) 37.2. This relatively small reservoir angles west about 1.5 miles to Masonry Dam (RM 35.9). From Masonry Dam, flow is diverted through penstocks to Seattle's Cedar Falls Power DI—+ 1—+-A nn„+ Z 5 , fles west. !�t this point, the entire flow returns to the main Cedar River 1 1411t. 1V Vated abo— 3 5 channel. Downstream to Landsburg, the river channel initially occupies a steep, well-defined channel that gradually widens and moderates in steepness. At Landsburg, water is diverted into a pipeline which transports it to Lake Young Reservoir southeast of Renton. The diversion dam at Landsburg (RM 21.8) blocks anadromous fish runs from using the upper basin. A Habitat Conservation Plan (HCP) is currently being negotiated for lands owned by the City of Seattle in the upper Cedar River. If this plan is implemented, Seattle has agreed to fund fish passage around the Landsburg dam for Chinook salmon, coho salmon, and steelhead trout. Sockeye salmon will not be allowed passage above the dam due to a concern for water quality given the larger number of adult fish. Steelhead trout were hauled around the dam historically but this has not happened in the last few years. 1) this section with a few channel splits and bends with sand and gravel bars. Rural areas exist on both sides of the river valley floor with higher urban densities nearer the population center of Renton. In this section, river banks have received extensive bank protection work, primarily riprapping. The lower 3 miles of the river flow through a heavily industrialized area of Renton. The last 1.25 miles of the river flow through a channelized segment before emptying into Lake Washington (See Figure 2). The effects of development in the lower Cedar River are most apparent from the increased rates and volume of storm water discharge caused by the extensive impervious surface areas of buildings, highways, and parking lots. This has resulted in substantial bank erosion, increased siltation, and frequent floods in the vicinity of Renton. Water quality and fish habitat have deteriorated as a result. Figure 2 Lower Cedar River Section 205 Project Location (Not to Scale) KI The proposed levees would consist of filling in between the existing mounds on the right bank. The levees would not encroach on the river and would be set back from the river's edge to allow for riparian zone planting. On the left bank (the airport side), sheet piling combined with raising the roadway to form a berm would be used to protect the airport. The south Boeing bridge creates a debris trap during floods and would require higher levees upstream of the bridge to accommodate the backwater effect caused by debris blockage. The proposed solution to this is to constnact hydraulic jacks under the bridge and jack the bridge up during flood events to reduce the potential for debris blockages. This feature is included with each alternative. Two dredging methods have teen proposed for this project. A barge mounted clamshell dredge could be used since the water depth is adequate to float the barge. In conjunction with the clamshell a barge mounted dragline could be used in the lower portion of the project area. The other method considered is to divert the water by coffer dams and remove the gravel from the contained area by excavator. FISH AND WILDLIFE RESOURCES WILDLIFE RESOURCES Terrestrial wildlife species and wildlife habitat in the study area are limited due to the amount of industrial and commercial development. However, many different wildlife species can adapt to these environments. In fact, the diversity of bird species in the project area is significant. A narrow band of riparian vegetation occurs discontinuously at the w•ater's edge. Bird species are the most prevalent wildlife using these areas. The lower Cedar River is used by several groups of bird species such as songbirds, waterfowl, shorebirds, wading birds, gulls, hawks, and eagles. Gulls are probably the most abundant group of birds in the area. One of the reasons for dredging the Cedar River delta in 1994 was to reduce the risk of aircraft and bird collisions at the Renton airport. The shallow gravel bar areas attract many birds, primarily gulls. These birds were presumed to increase the risk of collision with aircraft landing or taking off at the airport (COE 1993). Sixty-four different bird species were recorded during surveys completed by Service, Corps and Harza Northwest biologists (Table 1). These surveys were completed between March, 1992 and September, 1995. Many of these birds were using the project area for breeding and rearing. Smaller birds breeding in the area included bushtits, swallows, red -winged blackbirds and hairy woodpeckers. A male woodpecker, accompanied by a female, was observed excavating a hole in one of the few alder snags in the area. The number of broods and young of the year observed indicated that this area is getting substantial use for nesting and/or rearing. Juvenile gulls, mallards, common mergansers, and Canada geese were observed in the project during most of the spring and summer. Bushtits, hairy on Riparian areas also maintain the health of the stream by providing large woody debris to the stream, creating storage for overbank flood flows, trapping sediments and pollutants, moderating temperature extremes, and providing organic material. Even small areas of riparian zone habitat are important to a stream's health. This important habitat has been greatly reduced on many of the Lake Washington basin rivers as the area becomes more urban. Pressure will continue to be exerted on riparian zone habitat as the Cedar River basin is developed. Since the riparian zone in the project area is greatly reduced from its historical extent, the remaining riparian zone is even more valuable. Riparian vegetation in the project area is very limited on the west or left bank, especially adjacent to the airport. Willows, a few short alders, and a mix of non-native weedy species, mainly blackberry, account for most of the vegetation. The east or right bank is more diverse with scattered overstory tree species such as alder, willow, and cottonwood. Cultivated trees such as oaks, maples, and conifers have been planted along the trail system. These trees provide perching, nesting and foraging habitat for birds. Many bird species were observed foraging in the trees and shrubs near the river. A few areas contained a mix of trees, shrubs and herbaceous vegetation. These areas provide the greatest wildlife habitat value in the area. Overhanging vegetation is limited, but furnishes a small amount of cover for duck broods and aquatic furbearers. Grazing habitat is provided to ducks and geese in the form of cultivated and mowed grass associated with the trail/park system. Neotropical migrants are land birds that breed in Washington yet migrate to the neotropics, like Mexico and Greater Antilles, during the winter. Over one half of our breeding birds are neotropical migrants (Morton and Greenberg 1989). Passerines (perching or songbirds) make up the largest group of these birds and include birds like flycatchers, thrushes, sparrows, waxwings, and warblers. Many of these birds rely on the riparian areas by the river for breeding. Fifty-three percent of all neotropical migrants are associated with these riparian areas and 67 percent of the species with known declines use these habitats. A recent review of Washington's neotropical migrants by Andelman and Stock (1993), supports the need to concentrate our efforts on preserving or restoring habitats for these birds. Riparian habitats were identified as a priority habitat for species with known population declines. Sixty-eight of the 120 bird species breeding in Washington use riparian areas. Thirty-one percent of these species are habitat specialists and depend on only one or two habitats for breeding. Andelman and Stock (1993) found severe long-term population declines in several of these riparian species that include the gray catbird; the Wilson's, yellow, and orange -crowned warblers; eastern kingbird; solitary vireo; rufous hummingbird; barn swallow; and song sparrow. They also identified several species that are habitat specialists (i.e., use two or fewer habitats) and have localized breeding populations. The species that use the riparian zone heavily include Vaux's swift and MacGillivray's warbler. Andelman and Stock (1993) identified riparian zone habitat as one of the highest priority habitats to protect. Table 2. Resident and anadromous fish species utilizing the Cedar River or south end of Lake Washington as observed by Service and Corp biologist in 1994 and 1995 studies Mountain whitefish' Yellow perch ' Bull trout Longfin smelt ' Dolly Varden Lar escale sucker' Sockeye salmon' Northern s uawfish Kokanee Lon nose dace ' Coastal Cutthroat trout ' Torrent scul in ' Steelhead trout ' Coast range scul in ' Rainbow trout ' Reticulated scul in ' Coho salmon' Prickly scul in ' Chinook salmon Blue ill Peamouth chub Brown bullhead ` Smallmouth bass' Brook lamprey' Largemouth bass ' Atlantic salmon ' Pumpkinseed ' Tench Three-s ined stickleback ` Warmouth ` These species were actually found in the Cedar River during studies for this'Sec. 205 project Sockeye salmon spend one year in Lake Washington as pre-smolts before migrating through the Ballard Locks to the ocean. They spend two years in the ocean and then return as adults to spawn. The adults enter Lake Washington as early as July and may begin spawning as early as August. Most spawners, however, enter the Cedar beginning in early September and continue through mid - December with peak spawning occurring in mid -October. A few fish may be found spawning as late as February (See Figure 3). Escapement levels to the Cedar River have ranged from 107,000 to 383,000 adults, with an average of 226,827 between 1964 and 1989. Stober and Graybill (1974) showed that the heaviest spawning activity on the river occurs in the higher quality habitat of the upper and middle river reaches above RM 5.3. The largest concentrations of spawners were consistently observed above RM 11.5. The lower reach below RM 5.3 was the least utilized section of the river. Stober (1975) found no spawners below RM 5.3 during spawner counts of the same study area. Stober and Graybill (1974) also discovered that the early spawners used the upper accessible reaches of the Cedar while the later spawners used the middle and then the lower reach toward the end of the spawning period. This trend seems to be apparent during the December 1994 spawning survey in which twenty-eight (28) redds were located below the south Boeing bridge (See Table 3). 10 hundred thirty-two (432) redds located on November 16, 1994. Most of these redds were located between the Wells Avenue bridge and just below the Logan Avenue bridge. Seventy six (76) of these redds were located in the proposed project section below reference point (RP) 16 near the Logan Avenue Bridge. Redds observed downstream of the Logan Avenue bridge were confined to the riffle -like areas along the left bank. Only one survey was completed in 1995 (November 3), due to high water and poor observation conditions. In the 1995 survey, eighty-one (81) redds were within the proposed dredging area located downstream of RP 16. The results of these two years indicate a significant usage of the lower Cedar by sockeye salmon. A more extensive discussion of the spawning surveys can be found under the Habitat Survey/Studies section. The lower section, from RP 14 to the mouth, is characterized by deeper water and slower velocities. This type of habitat was not being used by sockeye salmon for spawning. Upstream in the area where spawning was concentrated, the water is faster and more shallow. Observations during the spawning survey indicated that redds were being constructed in less than 2 feet of water with obvious velocity. This corresponds to documented preferred spawning habitat for sockeye in streams. Reiser and Bjomn, (1979) report sockeye salmon preferences for spawning velocities of 4 - 21 feet per second (fps) and depths of z6 inches. Velocities and depths in this range were measured over redds by Chambers et al. (1955. cited in Reiser and Bjornn 1979). These measurements indicated a velocity of 11 fps over each redd with depths from 12 - 18 inches. These values fall within the depth and velocity preference curves developed by the Cedar River Committee Curve Report (Seattle Water Department 1991). In recent years there has been a significant downward trend of the sockeye salmon population. In 1988, the total run size to the Lake Washington/Cedar River basin was the largest on record with an estimated 640,000 adult fish. About 376,000 adults escaped to spawn in the Cedar River that year. Since 1988, escapement to the Cedar has declined dramatically with escapement estimates in the range of 38 percent to 44 percent of the pre-1989 26-year historic average, and with no indications that this trend will change. The 1992 Washington State salmon and steelhead stock inventory (WDFW 1992) listed this population as "depressed". The escapement for 1996 was an exception to this downward trend and was large enough to support a Lake Washington fishing season for sockeye (See Figure 4). Approximately 500,000 adult sockeye returned to the Lake Washington basin during the summer of 1996. A combination of a high fry count entering the lake and excellent ocean feeding conditions is credited with this record run. Over 28 million fry entered the lake from this year class. Whether this is an upward trend is very much open for conjecture. With the exception of this year class, the overall trend is still downward. The 26,000 sockeye escapement in 1995 was the lowest since at least 1970. It is most likely that the 1996 escapement is an aberration common to anadromous fish populations. The escapement goal for the Cedar River is 350,000 adult spawners. 12 Utilization of the project area is primarily for transportation with some possible, although limited, rearing for juveniles. Coho spawning occurs predominantly in the small tributaries of the Cedar River, although some probably occurs in the mainstem, from mid -October through February. Coho rear in the Cedar River one year before migrating out from March through June. Similar to chinook, use of the project area is largely for transportation and limited rearing. The wild winter run of adult steelhead enters Lake Washington between mid -December and mid -May with a peak during late January through early February. Peak spawning in the river can vary from year to year, but generally begins in mid -March and continues into mid -June with a peak during mid - April to mid -May. Spawning of most wild steelhead in the Cedar occurs from RM 1.6 to 21.8 with spawning densities being relatively uniform from RIM 5.2 to 21.8. The project area is used by steelhead primarily for transportation, although some limited rearing may occur. A stream -side steelhead culture program using captured wild brood stock provides 40,000 to 80,000 fry that are planted in the Cedar annually. Predation by California sea lions has caused an estimated 50 percent mortality on the returning winter run of Lake Washington bound wild steelhead. Healthy populations of bull trout, a federally listed candidate species, are known to occur in the upper Cedar River watershed above Masonry Dam (RM 35.9). It is unknown whether bull trout reside in the reach between Landsburg Dam (RM 21.8) and Masonry Dam (RM 35.9). A char was recently caught off of the mouth of the Cedar in Lake Washington. This may have been a Dolly Vanden or a bull trout. Fluvial populations of bull trout are not uncommon in adjacent drainages. It is possible that bull trout could use the project reach during their spawning migration. However, poor water quality and habitat conditions in the lower river make it unlikely that the project reach is used extensively by bull trout. Longfin smelt are a key species in the Lake Washington fish community and the species which is likely to be affected to the greatest extent by the proposed project. They may compete with juvenile sockeye for the same food resources in the lake (Chigbu and Sibley 1992). This may have contributed to the decline of the sockeye population. Other information shows a concurrent population expansion of longfin smelt and sockeye during the raid 1960s (Edmondson and Abella 1988). This would indicate that at most, the competition causes an indirect effect on population. However, longfin smelt may also serve to buffer predator effects on juvenile sockeye. Longfin smelt have played an important role in the increase in water clarity in the lake (Edmondson and Abella 1988). Daphnia, a small crustacean, eat small particles that make the water cloudy. The major predator on Daphnia was another small crustacean, Neomysis. Neomysis is a major prey species for longfin smelt. When smelt started to increase in abundance, the Daphnia population increased. This caused a corresponding decrease in the particles that caused turbidity in the lake. 14 Approximately 98 percent (Sibley and Brocksmith 1996a) of Cedar River longfin smelt spawn within 0.6 kilometers (km) of the mouth of the Cedar River. This is completely within the proposed project reach. The Sibley study found smelt beginning to spawn as early as January 13 in 1993 and as late as May 18 in 1994. Distribution of smelt in the entire Lake Washington basin indicates that the Cedar River is used as the main spawning area. Surveys for smelt in other Lake Washington tributaries were completed in 1970 (Moulton 1970), 1995 (Sibley and Brocksmith 1996a), and 1996 (Martz et al 1996). Results are shown in Table 4. Table 4. Smelt egg distribution in Lake Washington tributaries. Year of Survey May Creek Coal Creek Juanita Creek Denny Creek Swamp Creek Lyon Creek McAleer Creek Thornton Creek 1970 + + + — — — — — 1995 + + — — — — — — 1996 + + + — — — + — + indicates presence of eggs, - indicates absence Moulton (1974) observed that these fish exhibited a 2-year life cycle with even -numbered year classes being more abundant and showing a lower growth rate than the odd. He also reported that the Cedar River was the major spawning area and that the larger adults of the odd year -class spawn earlier in the year than the smaller adults of the even year -class. Spawning by longfin smelt takes place in freshwater over sandy -gravel substrates, rocks, and aquatic plants. Most longfin smelt die after spawning but a few live to spawn a second year (McGinnis 1984). The accumulated substrate materials of sand and gravel and relatively wide, weedy, shallow areas of the dredged channel in the lower 1.6 miles of the Cedar River have created good spawning habitat for smelt. Nishimoto (1973) reported that small numbers of peamouth chub spawn in Lake Washington tributaries, although he found no direct evidence of peamouth spawning in the lower Cedar River. Spawning likely occurs from late March through June when mature fish begin to migrate inshore during spring. Spawning peamouth show greater preference for sandy or gravelly substrates. This substrate constitutes most of the bottom materials in the project area. In June and July, Tabor (1996 personal communication) caught numerous peamouth in the lower river during studies in 1995. Presumably these fish were spawning at that time. Largescale suckers also feed or spawn within or near the project reach. They have been observed congregating and spawning upstream of the Logan Avenue bridge. These fish usually move upstream from lakes or impoundments into streams where they seek out gravel riffles with a strong current. Sucker fry and fingerlings serve as important forage for many game fishes. On the other hand, the dense populations of suckers characteristic of many impoundments can be detrimental to the production of some salmonids. Largescale suckers have been observed in the project reach by Service and Corps biologists. N focused on the Cedar River and south Lake Washington. This will provide additional information about the turtle population of the lake. Service biologists, working on the predator study, observed turtles on several occasions in the project reach of the river. They captured and photographed one of these turtles and tentatively identified it as a red -eared slider, a non-native species that was probably a discarded pet. However, all of the observed turtles were not identified to species. It is possible that there may have been northwestern pond turtles in the project area. STUDY RESULTS Due to the significant fish and wildlife resources at risk, and the gaps in the information on how these resources utilize the project reach, the Service recommended several studies to determine baseline conditions of fish and wildlife resources, evaluate potential impacts, and identify potential mitigation opportunities. In the following section, we will summarize the results of each study. The concerns that were identified during the early scoping for this project primarily focused on the potential impacts on the fishery resources of the Cedar River. The main concern was the potential impacts of the project on spawning habitat and distribution of both sockeye and longfin smelt. Other concerns included predation on sockeye salmon fry, migration delay due to slower water velocity, and effects on macro invertebrates within the project reach. The results in each of these studies are based on very limited data. The Service believes the studies were not extended over a sufficient time span to yield definitive results. At most, three years of data is available and in most cases only two years of data is available. Because of poor weather conditions, problems with equipment, and problems with methods several of the important studies were not completed as designed. The results and conclusions should therefore be used with caution. WILDLIFE STUDY The effect of the project on bird species was the main focus for wildlife studies. Bird surveys were discussed above in the general section on Fish and Wildlife Resources. On February 1, 1996, Corps biologists (Brunner 1996) completed a night avian predator study from the fry trap on the lower Cedar River down to mouth and out into the lake just past the delta. The objective was to provide some quantitative estimate of piscivorous birds that may be drawn to the area due to the emigration of sockeye fry. This date was chosen to coincide with an earlier release of hatchery sockeye fry which should have been reaching the delta at about the same time period as the surveys. Mallards, coots, and gulls were roosting on the logs at the delta and grebes were widely scattered around the lake when the survey began at 1915 hours. Grebes abruptly flew to the mouth just after 2000 hours and were all actively feeding by 2005 hours. This was about 1 hour after the peak fry migration past the fry trap which is about ` a mile upstream from the mouth. By about 2030 the grebes began V. lower Cedar River. The abundance of predators was relatively small until after the peak fry emigration period. Predation in the littoral zone of southern Lake Washington was low. Cutthroat once again exhibited the highest predation rate. In addition to the predators in the river, smallmouth bass showed up as predators in the lake. In 1996, the salmonid populations in the lower river were significantly lower than the previous year (Tabor and Chan 1996b). This was thought to be due to the flooding earlier in the year. Lonzarich and Quinn (1995, cited in Tabor and Chan 1996a) found that water depth seemed to be more important than structure in determining the distribution of large age 1+ cutthroat and steelhead trout while structure and depth were important for coho salmon smolt distribution. Since cutthroat trout are the main predators in the river, the increase in depth by dredging would seem to favor an increase m cutthroat. Obviously, other factors besides depth enter into the potential for predation. Channel configuration, for example, might increase or decrease predator populations. Information is not available to make this determination. Predation rates appeared to be related to discharge levels. Low predation rates were observed at > 17m3s. Seiler and Kishimoto (1996, cited in Tabor and Chan 1996b) found that survival rates of hatchery sockeye salmon fry were positively correlated with discharge. Survival rates for a discharge of IOm3s would be predicted at around 23 percent, whereas a 17es discharge would show a survival rate of around 44 percent. This correlation may be tied to the increased turbidity found during higher discharges. Difficulty with weather, equipment availability and performance limited the population estimates somewhat. However, based on the 1995 data, there did not seem to be obvious movement by predators to the mouth of the Cedar River during the sockeye fiy emigration. The number of piscivorous fish did seem to increase after the peak emigration season (May - June). This trend was also seen in the data collected in 1996 (Tabor and Chan 1996b). Therefore any impacts would be concentrated on the late -emerging part of the sockeye population. LONGFIN SMELT STUDY Smelt seem to occupy a "keystone" position in Lake Washington. The population size of the longfin smelt and their interaction with other river and lake species seems to be implicated in water clarity, zooplankton species diversity, competition with sockeye salmon for food resources, and as a prey base for fish predators. Several investigators have looked at the feeding habits and interactions of longfin smelt and sockeye salmon in Lake Washington (Chigbu and Sibley 1992) (Dryfoos 1965) (Edmondson and Abella 1988) (Moulton 1970) (Moulton 1974). Concerns about possible effects to smelt populations include changes in spawning substrate, changes to food sources, and increases or decreases in actual populations. The smelt food base is also a concern as it is related to possible competition with sockeye salmon. An abbreviated study was conducted on Lake Washington for two years that included one high population year and one low population year. Year one of a two year study was completed by Sibley 20 too hard for sockeye spawning. Overhanging vegetation is found on only 25 percent of the banks, with several 15-20 year old cottonwoods and alders on each side above the south Boeing bridge. Low flow water depth is shallow (<6 inches) in much of the reach between Logan Avenue and the south Boeing bridge. This often causes the water to heat up significantly with estimates of water temperature > 21 ° C. Warmer water and shallow depths may delay the upstream migration of sockeye adults until the release of flows from the dam in early September. SOCKEYE SALMON SPAWNING SURVEY Two years of spawning surveys have been completed by Corps biologists. Service personnel assisted in two of the surveys during the 1994 and 1995 spawning seasons. Results are summarized in Table 3 for 1994 and 1995. The high water and associated turbidity prevented complete surveys on several days of both seasons but the remaining surveys were completed from the just above the Wells Avenue bridge to the mouth. Combinations of visual wading surveys and snorkel surveys were used to gather data over this entire reach. The majority of the redds were above reference point 15 (1,500 meters) and concentrated along the bank edges. With exception of the December 12, 1995 survey, there were never more than 4 redds downstream of the south Boeing bridge during any survey. Assuming that all redds observed were distinct (with no double -counting between surveys) and had been spawned in, a maximum of 1 percent of the overall sockeye run spawns in the project reach. FISH UTILIZATION STUDIES Daytime and night time snorkeling surveys were conducted to assess fish use of the project reach and related side channels. Corps biologists completed several snorkel surveys from July to September 1995. In the lower mile of the river the only fish observed were rainbow and cutthroat trout, large- scale suckers, mountain whitefish, sculpins, and yellow perch. By the last survey in September, adult sockeye and chinook salmon were appearing in the river. Sculpin and mountain whitefish were the most common. Yellow perch were only observed in the lake backwater and only in small numbers (<10). Crayfish were also observed during the snorkee surveys. An assessment of the impacts of the proposed project on downstream juvenile migration was recommended by the Service. This assessment has not been initiated due to difficulty correlating flows from upstream dams with the City of Seattle. This type of information is still needed to compare the pre- and post -project migration rate for sockeye salmon. Impacts due to increased migration times can not adequately be assessed without this type of information. This should be considered in the mitigation planning for this project. AQUATIC INVERTEBRATE STUDY This study (Sibley and Brocksmith 1996b) was completed in 1996 from field work done in 1995. For the most part, the aquatic invertebrate populations were found in the expected velocity and substrate 22 POTENTIAL PROJECT IMPACTS TO FISH AND WILDLIFE RESOURCES Under the proposed alternatives, direct project effects on fish and wildlife species and their habitats may be both short-term and long-term. Short term impacts may be on the order of one or two seasons and primarily the result of construction activities. An increase in turbidity and sediment will occur during the actual dredging work. The actual dredging will be limited to between June 15 and August 15. This will minimize the impact on sockeye salmon and other anadromous fish. Depending on the severity of the sediment increase, fish and other aquatic dependent species could be displaced from the project area. Disturbances to the spawning gravels above Logan Avenue could cause scouring of redds during the first winter storms. It could also cause deposition of sediment on top of these redds. Any impacts on the fish populations in the project reach could cause a ripple effect within the food chain by decreasing the food source or by increased predation on other species within the basin. The sloping of the gradient above Logan Avenue should minimize this effect. But, there may be a significant adjustment of the stream channel during the first winter high flows. These changes may also cause impacts over an extended period. Effects to fish and wildlife resources would vary in magnitude, primarily according to the sensitivity of the species impacted and how important a role it serves in the function of the lake and lower river ecology. Shifts in species distribution and use patterns may be expected from direct habitat modifications, which could cause immediate or long-term ecological changes in the lower river. Long term impacts may result due to permanent habitat losses or degradation. Depending on which alternative is chosen these effects will vary in significance. Each of the "dredge" alternatives and the "no -dredge" alternative have levees associated with them. Short term impacts will be related to sediment from surface erosion on the newly constructed levees and berms. Intensive revegetation should restrict this impact to one season. Long-term aquatic effects from the levees should be minimal as long as best management practices are followed to prevent sedimentation and other disturbances of the stream course. IMPACTS TO WILDLIFE Direct impacts to terrestrial wildlife species and habitats will be largely related to the loss of riparian zone; habitat and associated shallow water habitats along both shorelines. Loss of shallow water habitats would directly affect foraging for wading birds such as great blue herons, and feeding dabbling ducks such as mallards. Various gulls may also be displaced as well as fish -eating birds like belted kingfishers, which generally forage in water that is less than 24 inches deep. The loss of existing vegetation could also preclude duck nesting and rearing of duck broods, particularly for mallards and common mergansers, which currently utilize herbaceous and overhanging 24 Alternative 2 - Shallow Dredging (s 4) The Service's preferred alternative. We believe that this alternative best protects fish and wildlife resources while still providing flood protection for the lower Cedar River corridor. The known impacts have been avoided or mitigated as much as possible. Detailed mitigation plans have yet to be finalized but the Corps seems willing to work cooperatively with the resource agencies to reach final resolution. The dredging will slope the bottom gradient to meet the present gradient about 400 yards above Logan Avenue. In this alternative, the potential spawning area for at least 90 pairs of sockeye salmon will be disturbed (see Table 3). Most of this spawning habitat should be available after the dredging but may be affected due to the adjustment of the stream channel during the first winter high flows.. With less depth to the dredging the gravel deposition in the lower reach should begin providing some minimal sockeye spawning after the first major winter storm. Other concerns within the dredged area include the potential for increased predation on sockeye fry as they migrate downstream to the lake. The slower velocities resulting from this shallow dredging will increase the time needed for the fry to move through the project area and will make them more vulnerable to.predation. Tabor and Chan (1996) documented several fish species that preyed on sockeye fry during the outmigration period. Assuming that longfin smelt actually have a preference for lower velocity as implied in the smelt studies, then this alternative should increase available smelt spawning habitat. The first year after dredging the habitat may have reduced value for smelt spawning due to channel readjustment. The actual impact of this is unknown. Also it is expected that finer sediment may settle out below Logan Avenue and create a sand and mud substrate. Winter flows should flush this finer material out but with the increased depth of the channel, velocity will be slower. This may prevent this flushing action and reduce the success of smelt spawning. Aquatic invertebrates make up one of the major food sources for fish within the project reach. This shallow dredge option will change the velocity and substrate that largely determine the invertebrate populations. The dredging process will displace or kill most of the resident invertebrates and will cause a zone depauperate of aquatic invertebrates for several weeks to months depending on the species and the specific rate of recolonization. Species which prefer faster, more turbulent water such as mayflies, stoneflies and caddisflies will be eliminated or greatly reduced. Recolonization by these species may be delayed until velocity and substrate within the project reach return to pre -disturbance level. In order to maintain flood control under this alternative, dredging will be more frequent and it is unlikely that habitat for these macro invertebrates will be replaced to the same extent as present. On the other hand, species that prefer slow velocity and fine substrate material, such as oligochaets and most chironomids, should increase due to the increase in available habitat. Initially this group of invertebrates will also be eliminated or reduced because of the dredging operation. Recolonization should occur, assuming that these species exist upstream of the project area. 26 Washington tributaries. It is also possible that smelt may increase beach spawning to a greater degree than now exists. Nevertheless, the smelt population is considered a key, and perhaps the most important, fish species in the Lake Washington ecosystem. Should this population decline or expand dramatically, the cascading effects on the dynamics of the Lake Washington fish community and lake ecology could be highly disruptive. RECOMMENDATIONS During coordination with other resource agencies, there have been concerns raised about constructing this project at this time, given the current sensitivity of the Lake Washington/Cedar River system. Significant efforts are underway to understand why the changes in the ecosystem are occurring. Serious declines in sockeye salmon and steelhead are being observed in the Lake Washington ecosystem. This project, which may have significant effects on the fish community, could be untimely and damaging. The newest alternatives being considered have much less impact on fish and wildlife resources than the historic deep dredging projects. In discussions with the Corps, we have been encouraged by their willingness to protect and mitigate for potential fishery habitat loss with this project. We welcome the opportunity to work with the Corps and the local sponsor to plan the mitigation and any enhancement projects connected with the lower Cedar River flood control project. The mitigation measures recommended by the Service for wildlife have been accepted and incorporated into the latest alternatives. Mitigation will be required for natural resource losses resulting from project implementation. Opportunities to enhance the values of the existing habitat beyond those that currently exist should also be identified pursuant to the Fish and Wildlife Coordination Act. Mitigation involves a series of actions (National Environmental Policy Act, as amended, 42 U.S.C., 4321 et. seq.). These include the following: 1. Avoiding the effect all together; 2. Minimizing the effect; 3. Rectifying the effect; 4. Reducing or eliminating the effect over time; and, 5. Compensating for the effect. The availability, extent, location, and uniqueness of a habitat dictates its value to its constituent fish and wildlife populations. The goal of mitigation ranges from no loss of in -kind habitat values to minimal loss of habitat value. 28 the newly created shallow water habitat should be explored. Care should be taken to avoid the invasion of Eurasian watermilfoH, particularly during construction. It is vital to identify new colonies early in order to eradicate it. We recommend an extended monitoring program in the area following construction to ensure watermilfoil is controlled. 4. Due to the sighting of turtles in the project reach, we recommend that turtle surveys be conducted to determine species. Species identification is important because one of the two native turtle species that may occur in this location, the northwestern pond turtle, is a species of concern to the Service. PROPOSED MITIGATION FOR AQUATIC RESOURCE rYIPACTS I. If a dredging alternative is chosen, a monitoring program should be developed to test the assumptions concerning habitat. Smelt could be monitored by looking at the resulting substrate composition during the spawning run, looking at actual use in the dredged area for spawning and by checking egg viability. Sockeye could be monitored by marking a representative number of redds above the test site and looking at depositional rates, or scour depth at each redd site. Potential head -cutting and channel configuration changes should also be monitored after several significant storm events. 2. If this monitoring produces unacceptable results, we recommend that the Corps reconsider the proposed three year dredging cycle. The Service believes that the precarious situation of salmon and steelhead resources in the Lake Washington/Cedar River basin and the potential of the proposed project to adversely affect these resources warrants a cautious approach. Close monitoring as described above could provide early detection of potential fish resource problems and possibly avoid catastrophic results to the fish community in this system. 3. Before dredging, sediments should be tested for contaminants and a determination of whether disturbance of any contaminants found could be toxic to fish and wildlife resources. We are concerned about the possible presence of contaminants due to the close proximity of two major industrial sites, and the heavy use of fuel, oil, solvents, and other chemicals. Contaminated sediments should be isolated and. stored away from water, particularly rivers, creeks, and lakes. All new concrete structures should be sealed during construction to contain runoff from the construction site until the concrete is fully cured. Runoff should be collected and pumped to a settling basin or other treatment area to remove contaminants before discharge into the Cedar River or other surface water course. Fuels, oils, solvents, and other potentially toxic chemicals should be properly stored and protected from accidental release into the river or lake. 4. Construction activities should take place between mid -June and mid -August. This timing is necessary to miss most of the major fish migrations and minimize project impacts on this part of the life cycle. 30 that a new location for a fry trap be found in cooperation with WDFW. This trap will need to be installed at least two years in advance of the implementation of this project. This will allow both traps to be fished for two years and a calibration curve to be established. The Service will remain involved in this project and will be available for advice and support as needed. We intend to assist the Corps in the development of the mitigation and monitoring plans for this project and expect that other appropriate resource agencies and the Muckleshoot Tribe will also be involved. 32 Lonzarich, D.G. and T.P. Quinn. 1995. Experimental Evidence for the Effect gf.Depth andStructure on the Distribution, Growth, and Survival of Stream Fishes. Canadian Journal of Zoology 73 :2223 -223 0. Martz, M. Jeff Dillon. and Paulinus Chigbu. 1996. 1996 Longfin smelt (Spirinchus thaleichthys) Spawning Survey in the Cedar River and Four Lake Washington Tributaries. U.S. Corps of Engineers, Seattle District. Department of the Army. October, 1996. 21 pp. Martz, M. 1996. Memorandum For the Record. Seattle District Corps of Engineer. Department of the Army. July 15, 1996. 11 pp. McGinnis, S. 1984. Freshwater Fishes of California. Univ. California Press, Berkeley, California. 316pp. Morton, E.S. and R. Greenberg. 1989. The Outlook for Migratory Songbirds; "Future Shock" for Birders. American Birds. Spring. Moulton, L.L 1970. The Longfin Smelt Spawning Run in Lake Washington with Notes on Egg Development and Changes in the Population since 1964. M.S. Thesis, University of Washington. 84 PP' Moulton, L. 1974. Abundance, Growth, and Spawning of the LongEm Smelt in Lake Washington. Trans. Amer. Fish. Soc. 103(1) 46-52. Nishimoto, M.L. 1973. Life history of the peamouth (Mylocheilus caurinus) in Lake Washington. M.S. Thesis. University of Washington. Seattle, Washington. Pfeifer, B. 1993. Comment Letter on Draft Outline for Lake Washington Basin,$alrponid Restoration Plan. State of Washington. Department of Wildlife. Mill Creek. 4pp. Rees, W.H. 1959. Effects of Stream Dredging on Young Silver Salmon and Bottom Fauna. Washington Department of Fisheries. Annual Report. 2:52-65. Reiser, D.W., and T.C. Bjornn. 1979, Habitat Requirements of Anadromous Salrnonids. in: Meehan, W.R., ed. Influences of Forest and Rangeland Management on Salmonid Fishes and Their Habitats. General Technical Report PNW-96. U.S.D.A. Forest Service. 54 pp. Seattle Water Department. 1991. Final Report, Cedar River instream flow and salmonid habitat utilization study. Prepared by Cascades Environmental Services, Inc. Seiler, D. and L.E. Kishimoto. 1996. 1995 Cedar River sockeye salmon fry production program. Annual Report, Washington Department of Fish and Wildlife, Olympia 34