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Home My WebLink AboutSW 7th Street-Hardie Avenue SW-Lake Avenue S Drainage Investigations SW 7T" STREET/HARD I E AVENUE SW/LAKE AVENUE S DRAINAGE INVESTIGATIONS FINAL LETTER REPORT CITY OF RENTON November 1998 November 23, 1998 ME Mr. Ron Straka,P.E. Supervisor Surface Water Utility City of Renton 200 Mill Avenue South Renton,Washington 98055 Dear Ron: Subject: City of Renton—SW 71h Street/Hardie Avenue SW/Lake Avenue S Drainage Investigations—Final Letter Report We are pleased to submit the final report for the SW 7`' Street, Hardie Avenue SW, and Lake Avenue S Drainage Investigations. We have formatted the report into four main sections, including an introduction, a description of the existing system, system analysis, and the alternative evaluation and selection of preferred alternatives. The results of the study confirm the lack of system conveyance capacities downstream of the known flooding problem areas. Potential alternative solutions to reduce flooding at the problem areas were defined with City input. In evaluating these potential solutions, we have found that, while several of the improvements would substantially increase system capacities, they would not provide significantly more than a 2-year or 10-year level of protection for future land use flows, and in some cases less than a 2-year level of protection. We have therefore concentrated on a phased approach whereby the City would implement initial improvements that would improve the existing system capacities and reduce the frequency of flooding. As resources allow,the City should consider additional improvements. During the interim period prior to the completion of the more extensive improvements, the City should monitor the initial improvements and collect more data on the level of protection provided by these systems. We appreciate the valuable assistance you and other staff members have provided to us. Please call me at (206) 695-4607 if you have any questions. Sincerely, R. W. BECK,INC. Michael S. Giseburt,P. . Project Manager File: 12-00019-10101-0106/3023 X1159121.734 1001 Fourth Avenue,Suite 2500 Seattle,WA 98154-1004 Phone(206)695-4700 Fax(206)695-4701 CERTIFICATE OF ENGINEER SW 7T" STREET/HARDI E AVENUE SW/LAKE AVENUE S DRAINAGE INVESTIGATIONS The technical material and data contained this report were prepared under the supervision and direction of the undersigned, whose seal as a registered professional engineer licensed to practice as such in the State of Washington is affixed below. 5 G .6 24055 1 Mic ael S. Giseburt EXPIRES''. Project Manager X1159121.734 11/19/98 CITY OF RENTON/SW 7TH STREET TABLE OF CONTENTS LETTER OF TRANSMITTAL CERTIFICATE OF ENGINEER TABLE OF CONTENTS SECTION 1 INTRODUCTION..........................................................................1-1 1 . BACKGROUND AND STUDY OBJECTIVES ...........................................1-1 2. AUTHORIZATION .................................................................................1-2 SECTION 2 EXISTING DRAINAGE SYSTEM.....................................................2-1 1 . EXISTING DRAINAGE SYSTEM...............................................................2-1 2. DRAINAGE SYSTEM INVENTORY..........................................................2-1 3. FLOODING PROBLEMS ........................................................................2-2 SECTION 3 SYSTEM ANALYSIS.........................................................................3-1 1. HYDROLOGIC ANALYSIS METHODOLOGY.........................................3-1 A. South Renton Subbasin......................................................................3-1 B. West Hill Basin...................................................................................3-4 2. HYDRAULIC ANALYSIS METHODOLOGY.............................................3-5 3. EXISTING SYSTEM ANALYSIS RESULTS..................................................3-8 4. IDENTIFICATION OF ALTERNATIVE SOLUTIONS .................................3-8 A. General ALTERNATIVE Descriptions...................................................3-9 B. Detailed Alternative Descriptions.....................................................3-10 SW 7`h Street Alternatives.....................................................................3-10 Hardie Alternative SW Alternatives.......................................................3-12 Lake Avenue s Alternatives...................................................................3-13 SECTION 4 ALTERNATIVE EVALUATION AND SELECTION OF PREFERRED ALTERNATIVES.............................................................................4-1 1. GENERAL...................:...........................................................................4-1 2. ALTERNATIVE EVALUATION..................................................................4-1 3. SELECTION OF PREFERRED ALTERNATIVES..........................................4-4 4. IMPLEMENTATION OF PREFERRED ALTERNATIVES..............................4-5 X1159121.734 11/19/98 TABLE OF CONTENTS LIST OF TABLES 1 EXISTING DRAINAGE SYSTEM INVENTORY RESULTS 2 SUMMARY RESULTS OF HYDROLOGIC/HYDRAULIC ANALYSIS - SOUTH RENTON SUBBASINS 3 SUMMARY RESULTS OF HYDROLOGIC/HYDRAULIC ANALYSIS - WEST HILL BASINS 4 SUMMARY RESULTS OF HYDROLOGIC/HYDRAULIC - ALTERNATIVE ANALYSIS 5 ALTERNATIVE EVALUATION TABLE FIGURES 1 SOUTH RENTON BASIN MAP 2 STORM DRAIN INVENTORY FORM 3 WEST HILL BASIN MAP 4 ALTERNATIVE SOLUTIONS REFERENCES APPENDICES (BOUND SEPARATELY) VOLUME 1 A. SOUTH RENTON SUBBASIN - HYDROLOGIC ANALYSIS INFORMATION - HSPF SUBBASIN S-16 FREQUENCY ANALYSIS - BACKUP SPREADSHEETS - BASIN MAP (SHOWING PIPE REACHES, MANHOLE NUMBERS, AND SUBBASINS) B. WEST HILL BASIN - HYDROLOGIC ANALYSIS INFORMATION - TIME OF CONCENTRATION DEVELOPMENT - FUTURE CONDITION RUNOFF CURVE NUMBER . DEVELOPMENT - HYD MODEL SCHEMATIC - HYD MODEL AND RESULTS - BLACK RIVER BOX DIVERSION (LAKE AVENUE S DIVERSION INFORMATION) C. HYDRAULIC ANALYSIS INFORMATION - EXISTING MODEL RUN (ON DISK) D. ALTERNATIVE EVALUATION - HYDROLOGIC/HYDRAULIC BACKUP INFORMATION - ALTERNATIVE BACKWATER MODEL RUNS (ON DISK) E. COST ESTIMATES F. CITY OF RENTON ANALYSIS OF HARDIE AVENUE, LAKE AVENUE SOUTH, AND S. TOBIN STREET DRAINAGE SYSTEM TO ACHIEVE 10-, 25-, AND 1 00 YEAR LEVEL OF PROTECTION G. ANALYSIS OF CURRENT LAND USE CONDITION FLOWS VOLUME 2 A. STORMWATER INVENTORY SUMMARY RESULTS B. INDIVIDUAL STORM DRAIN INVENTORY FORMS C. COPY OF SURVEY FIELD NOTES ii R. W. Beck 11/19/98 X1159121.734 CITY OF RENTON/SW 7TH STREET This report has been prepared for the use of the client for the specific purposes identified in the report. The conclusions, observations, and recommendations contained herein attributed to R. W. Beck, Inc., ("R. W. Beck") constitute the opinions of R. W. Beck. To the extent that statements, information, and opinions provided by the client or others have been used in the preparation of this report, R. W. Beck has relied upon the same to be accurate, and for which no assurances are intended and no representations or warranties are made. R. W. Beck makes no certification and gives no assurances except as explicitly set forth in this report. Copyright 1996, R. W. Beck, Inc. All rights reserved. X1159121.734 11/19/98 R. W. Beck iii i 1 i 1 1 1 1 1 1 1 1 1 1 1 � II14 �E [N 1 SECTION 1 INTRODUCTION 1 . BACKGROUND AND STUDY OBJECTIVES This study included an investigation and analysis of three recurrent flooding problems in the City's South Renton subbasin of the Black River Basin.' One of the problems includes flooding in the vicinity of SW 7" Street and Shattuck Avenues. This area is drained by a pipe system extending west along SW 7t' Street to the Black River Pump Station (BRPS) forebay. The second problem includes flooding of Hardie Avenue SW at the railroad underpass located north of SW 7t' Street. This area is drained by a pipe system that extends southwesterly to connect to the SW 7" Street pipe system. The third problem includes flooding in the vicinity of Lake Avenue S approximately between S 2"1 Street and S Tobin Street and along S Tobin Street just east of Lake Avenue S. The third problem area is drained by a pipe system that extends south along Lake Avenue S, then along Hardie Avenue SW to the intersection of Hardie Avenue SW and the railroad underpass, where it connects to the system that drains the second problem area described above. This problem was partially corrected with a pipe replacement project in 1996. Based upon discussions with City staff, the first and second flooding problems occur during significant flood events, such as the November and January 1990 events, the April 1991 event, and the February 1996 event. The location of these flooding problems and the limits of the South Renton subbasin are illustrated on Figure 1. The study included data gathering and engineering analysis to define the deficiencies in the existing systems that lead to flooding, identification and analysis of potential corrective measures (alternatives), and selecting preferred solutions to each of the three problems. The specific study objectives include: ■ Confirm the pipe system configurations draining the problem areas, including pipe lengths, sizes, material, slopes, elevations, and other factors that substantially affect their hydraulic conveyance capacity ■ Perform backwater analysis to define hydraulic deficiencies in the system ■ Identify potential alternatives to solve problems ' This subbasin is also referred to as subbasin S-16 in the East Side Green River Watershed Plan Hydrologic and Hydraulic Analysis work performed by R. W. Beck, Inc., under separate contract CAG-033-90. X1159121.734 11/19/98 SECTION 1 ■ Analyze the potential alternative solutions with regard to cost, feasibility and constructability, compatibility with the downstream drainage system, environmental considerations, and other advantages and disadvantages ■ Select preferred solutions to the problems ■ Document the study effort for City approval 2. AUTHORIZATION This study was authorized by an engineering agreement with R. W. Beck dated January 27, 1995. 1-2 R. W. Beck 11/19/98 X1159121.734 i 1 1 1 1 1 1 1 1 1 1 i 1 1 1 � Ii6V`�Ffli 1 SECTION 2 EXISTING DRAINAGE SYSTEM 1 . EXISTING DRAINAGE SYSTEM The limits of the South Renton subbasin as well as the problem area locations are illustrated on Figure 1. The subbasin consists of 676 acres that drain to the BRPS forebay. Figure 1 also shows the City's drainage system with several of the main pipe systems highlighted. These highlighted systems were studied as a part of this project and include: ■ SW 7t' Street system from the discharge at the BRPS forebay to Grady Way, and then along Grady Way to Main Avenue S, and then along Main Avenue S to S 3' Street ■ A SW 7" Street tributary system (Hardie Avenue SW system) that begins 1,000 feet west of Hardie Avenue SW and extends northeast along an easement to Hardie Avenue SW, then continues along Hardie Avenue SW to Sunset Boulevard W, and continues along Sunset Boulevard W past Rainier Avenue, where it extends north along Lake Avenue S to S Tobin Street ■ Shattuck Avenue S system from SW 71t' Street to S 4th Street These systems were analyzed because they serve as the main conveyance systems draining the South Renton subbasin and/or they drain one of the study problem areas. 2. DRAINAGE SYSTEM INVENTORY To provide supporting data for evaluating the system capacity, the above described drainage systems were investigated in the field inventory. The information collected for each storm drain structure and connecting pipes included pipe inlet and outlet sizes, material types and depths (as measured down from the grate), and lengths between catch basins/manholes. Any deteriorated condition of storm drain structures or pipes was also noted. A standardized form was used to collect the data, an example of which is included as Figure 2. The inventory results are summarized on Table 1. Copies of the completed inventory forms for each storm drain structure are included in a separately bound appendix (Volume 2). A survey of the structure grates/rims was also conducted so that all elevations could be tied to the City's elevation datum (NAVD 1988). This field survey information is contained in the City's field survey book No. 632. Copies of the field book pages are included in the Volume 2 appendix. It should be noted that the City has changed its elevation datum to NAVD 1988. Many of the past X1159121.734 11/19/98 SECTION 2 drainage design plans and construction drawings were previously designed to NGVD 1929 datum. These datum are related as follows: NGVD 1929 datum + 3.58 feet = NAVD 1988 datum. The City's new datum was used entirely on this project. To obtain depths of the pipeline from the top of the structures, a survey rod was used measuring down from the top of the structure. This method presented some difficulties for some of the larger and deeper storm drains, particularly when the bottom of the pipe was horizontally offset from the access opening. For the larger and deeper pipes, invert elevation accuracy should be considered accurate to approximately 0.2 to 0.3 feet +/-. For most other storm drain structures (where there was good access and depths could be easily measured), the invert elevations should be considered accurate to approximately 0.1 feet +/-. For the purpose of backwater modeling, differences in hydraulic capacity caused by errors of this magnitude are considered negligible. It is important to note that the field inventory was conducted in the Spring of 1995. Since then, pipe replacements were made to the drainage system along Lake Avenue S between approximately S 2"d Street to S Tobin Street. Also, there may be some additional catch basins or manholes constructed along these pipe systems associated with new pipe connections which are not reflected in the inventory. 3. FLOODING PROBLEMS As previously mentioned, this study focuses on three specific flooding problems. Flooding along SW 7"' Street in the vicinity of Shattuck Avenue S has occurred in the recent events of January 9, 1990, November 24, 1990, April 5, 1991, and February 8, 1998. This intersection is generally the lowest elevation between Rainier Avenue S and Burnett Avenue S. As the downstream undersized pipe system in SW 71' Street backs up, water ponds in this low area. City staff reported that during the January 9, 1990, flood, the ponded area extended into the City's Park and Ride lot located south of SW 7`' Street. This flooding also extended north along Shattuck Avenue S to approximately S Sixth Street. Similar flooding was observed during the February 8, 1996 flood. In reviewing the pipe drainage system that drains this area, an obvious concern is a down sizing in the pipe size. Downstream of Hardie Avenue SW, the SW 7`' Street system is downsized from 48-inch-diameter pipe to 24-inch-diameter pipe. The locations of the pipe reaches listed on Table 1 are shown on Figure 1. During the February 8, 1996 flood, it was also observed that drainage from the Renton Village and Grady Way was overflowing into the SW 71'' Street drainage system. A pipe system conveys Rolling Hills Creek through the Renton Village. There is an apparent bottleneck in this pipe system which can lead to flooding of the Renton Village parking area and that this flooding can lead to overflows into the SW 7`'' Street drainage system. Although not studied in this investigation, 2-2 R. W. Beck, Inc. 11/19/98 X1159121.734 EXISTING DRAINAGE SYSTEM overflows from the Renton Village flooding could be a contributing factor to flooding of SW 7" Street. Therefore, part of the solution to the SW 7" Street flooding is to also solve the Renton Village problem. Flooding of Hardie Avenue SW at the railroad underpass north of SW 7" Street is primarily due to the road being constructed very low under the underpass. The road grade through the underpass is at El 19.3. This is 4 feet lower than the elevation of the road grade in the downstream system at SW 71h Street. While flooding here has been observed by the City generally during major events such as those described above, flooding has also occurred to a lesser degree during less severe rainstorms such as the January 15, 1996, storm (1.6 inches in 24 hours, 1 inch of which occurred in a 12-hour period). Prior to the pipe improvements in 1996, flooding of Lake Avenue S and S Tobin Street occurred in several areas; along Lake Avenue S between S 2nd Street and S Tobin Street; along S Tobin Street a few hundred feet east of Lake Avenue S; along the south side of S 2n1 Street at the intersection with Lake Avenue S; and in a car lot located near the northwest corner of S 3r1 Street and Rainier Avenue. Flooding along Lake Avenue S appeared to be the result of an undersized system draining this area. In addition, it was found during the field review of the pipe system in Lake Avenue S, prior to the 1996 pipe replacement project, that the 12-inch-diameter CMP pipe was quite rusted in places due to corrosion, such that the poor condition of the pipe was an additional factor in reducing its conveyance capacity. Prior to the 1996 pipe improvements, flooding occurred along S Tobin Street, approximately once a year. Flooding along S Tobin Street appeared to be the result of a lack of adequate drainage system in S Tobin Street. Much of the Renton High School drains to S Tobin Street and flows west toward Lake Avenue S. The 1996 pipe improvements included a new drainage system along S Tobin Street east of Lake Avenue S. Based upon the field work, there appears to be a general problem with corrosion of CMP pipe as well as some structures without bottoms. For example, Catch Basin 65 is an old brick catch basin with no bottom. As a result, storm water can flow into the underlying soil, washing out fines and the promoting the development of sink holes in the roadway pavement. Much of the Hardie Avenue SW system is CMP and its condition is unknown. If it is susceptible to corrosion, it may need early replacement due to being undersized in addition to its condition. x1159121.734 11/19/98 R. W. Beck, Inc. 2-3 SECTION 3 1SYSTEM !ANALYSIS 1 1 1 1 1 � 1 1 i 1 1 1 i 1 1 1 1 � o �ti IlEni SECTION 3 SYSTEM ANALYSIS 1. HYDROLOGIC ANALYSIS METHODOLOGY This section provides a description of the methodology used for predicting peak flow rates within the South Renton subbasin drainage system. In addition, it includes a separate discussion of a hydrologic analysis done for the City's West Hill Basin. An analysis of the West Hill Basin was done for the purpose of analyzing one of the problem solutions (alternatives) for the Lake Avenue S flooding problem. A. SOUTH RENTON SUBBASIN Development of design flows at different locations throughout the major conveyance system was necessary to determine inadequacies in the existing system and to evaluate potential flood control improvements. Determining peak flow rates for the various design storm events was done utilizing information developed from the East Side Green River Watershed Plan (ESGWP) Hydrologic Analysis, Draft (Northwest Hydraulic Consultants, 1995). Under the ESGRWP Hydrologic Analysis, the continuous simulation program HSPF was used to predict total outflows for the South Renton subbasin (referred to as subbasin S-16) for various storm events, including the 2-, 10-, 25-, and 100-year floods as well as the major flood of January 9, 1990. The ESGRWP modeling effort was done for both current land use conditions as well as future land use conditions. Only the future land use condition flows were used as a part of the South Renton subbasin hydrologic analysis. This was because, when considering system improvements, policy requires designing such improvements to have sufficient capacity to handle future land condition flows, given available resources. While this study focuses on future land use condition flows, Appendix G does contain an abbreviated analysis of current condition flows for comparison only. This analysis was done by City of Renton staff. The HSPF flows were used to develop "runoff factors" that could be multiplied by a tributary area in acres to estimate design flow rates throughout the system. This was done using a step-by-step approach that is described in the following paragraphs. STEP 1 —ADJUSTMENT OF HSPF FLOWS Under the ESGRWP Hydrologic Analysis, two sets of peak flow data were developed for this subbasin. One flow set was based on a frequency analysis of the subbasin peak outflows assuming the existing reach of 60-inch- diameter pipe along SW 7" Street west of Hardie Avenue SW acts as a capacity restriction. For this set of flows, the 60-inch-diameter acts as a X1159121.734 11/19/98 SECTION 3 constriction, causing upstream flows to be attenuated. The second set of flows was based upon a frequency analysis of surface runoff without the 60-inch-diameter pipe restriction. The second set of flows was based on surface runoff (assuming no system storage). The results of both frequency analyses are included in Appendix A (Volume 1). For the purposes of analyzing the conveyance system, average flow rates of the two flow sets were calculated. This is because the first flow set would tend to underestimate flows once the City implements conveyance improvements and removes some of the existing conveyance restrictions. The second set of flows would tend to be conservative because they do not account for any system storage. System storage generally includes stormwater stored in pipes, ditches, roadway gutters, and surface ponding of streets, parking lots, and yards. During significant events, such as the 10-year through 100-year floods, there will be some attenuation due to system storage. Therefore, the average value of the two sets was selected for this analysis. These average flow sets were then factored up to account for a difference in the basin area used in the ESGRWP Hydrologic Analysis and the City's defined subbasin boundary. The HSPF analysis was based on an overall acreage of 538 acres, whereas the City's defined subbasin boundary is 676 acres. The difference in acreage does not mean that the ESGRWP analysis is incorrect, rather the most westerly portion of the South Renton subbasin was included in an adjacent HSPF subbasin (S-17). The supporting calculations for these modifications are given on the Step 1 spreadsheet in Appendix A, Volume 1. It is noted that the methodology was varied for simulation of the January 1990 flood. For this event, flows were based solely upon the set of flows with the existing 60-inch pipe acting as a pipe restriction. This was done to reflect the existing pipe system without conveyance improvement. However, it should be noted that actual flow rates for the January 1990 flood would be higher if these pipe restrictions were removed. STEP 2 — SUBBASIN DELINEATION This step included dividing the entire South Renton subbasin into 41 smaller subbasins to reflect flow patterns and catchment areas at different locations along the main pipe systems. The smaller subbasins were primarily defined based on the City's storm drainage system inventory maps supplemented by some field observations (in the area of the Renton High School) and City input. Appendix A, Volume 1 contains a map showing the individual subbasin boundaries. The subbasins were digitized using AutoCAD to determine subbasin areas in acres. Refer to the Step 2 spreadsheet in Appendix A, Volume 1. The subbasin areas were characterized into two land use groups, non-residential and residential. This was done for the purpose of predicting runoff rates from these areas as discussed below. 3-2 R. W. Beck, Inc. 11/19/98 x1159121.734 SYSTEM ANALYSIS STEP 3 — DEVELOPMENT OF RUNOFF FACTORS This step includes the development of "runoff factors" for estimating the various storm event flow rates along the pipe systems (i.e., distributing the inflows). The ESGRWP Hydrologic Analysis identified a breakdown of the future land uses as follows: Total Area (acres) Percent Commercial 425 79% Multifamily 30.8 6% High Density Residential 58.8 11% Other Land Uses 23.8 417o Total 538.4 100% To simplify the modeling effort, runoff factors were developed for two categories, high density residential and non-residential, which includes multifamily and "other" land uses. Other land uses include forested and undeveloped uses. This is a valid representation because these two land use categories constitute 90 percent of the basin. In addition, the runoff characteristics of multifamily land uses would be similar in characteristic to commercial area (although producing somewhat lower runoff); therefore, 96 percent of the subbasin would be represented. Any errors produced by the 4 percent of "other" land uses would be negligible. Runoff factors for both high density residential and non-residential (primarily commercial) were developed for several flood events including the 2-, 10-, 25-, and 100-year future land use condition floods and the historic January 9, 1990, flood (which is based on current land use conditions). The runoff factors for each category were developed based upon the assumption that high density residential land uses would generate an average of one-third the runoff of non-residential (primarily commercial) uses. This value was selected based on a review of the King County Surface Water Design Manual methodologies. The calculation of runoff factors is included as the Step 3 spreadsheet in Appendix A, Volume 1. STEP 4 —CALCULATION OF DESIGN FLOWS The final step was to perform a calculation of the various design storm flows at key locations along the conveyance system. This was done by determining the tributary area (in both residential and non-residential acreages) at these locations using the subbasin information developed under Step 2 above. The tributary area was then multiplied by the runoff factors developed under Step 3. This step was done using an Excel spreadsheet, identified as Step 4 spreadsheet in Appendix A, Volume 1. x1159121.734 11/19/98 R. W. Beck, Inc. 3-3 SECTION 3 One item to note about the hydrologic analysis relates to the Rainier Avenue pump station. This pump station is located along Rainier Avenue between S 5`h Street and S 61' Street and receives runoff from an approximate 67-acre catchment (see subbasins V and AN on basin map in Appendix A, Volume 1). Flows are pumped to a gravity storm drain that connects to the Hardie Avenue SW drainage system just south of the railroad underpass. The current capacity of the pump station is approximately 14.2 cfs. Based on the modeling results, the future condition peak flows to the pump station exceed the pump station capacity (a summary of peak future condition flows to the pump station is given in Appendix A, Volume 1). For the hydrologic analysis, it was assumed that the pump station would be upgraded to pump the projected future condition flows. The overall hydrologic analysis methodology was selected to make use of prior hydrologic information and avoids what would otherwise be a much more sophisticated and time-consuming hydrologic modeling effort. While simplified, this approach provides very useful information, particularly for identifying system deficiencies and recommending upgrades to the system to improve capacity as done in this report. Should the City consider improvements to a greater extent than recommended in this report (such as replacing the entire 60-inch-diameter system along SW 7`h Street to the BRPS forebay to achieve a 25-year future condition level of protection), the City should consider performing additional hydrologic analyses to validate the design flows developed herein. Additional hydrologic modeling may be warranted given the more extensive construction costs that would be required to provide a greater level of protection. The hydrologic model results for the South Renton subbasin are presented in Table 2. B. WEST HILL BASIN A hydrologic analysis for the West Hill Basin was developed specifically to evaluate a proposed high flow bypass to the Black River box culvert from an area that is currently located in the South Renton subbasin. This high flow diversion is discussed in Section 3.4, Identification of Alternative Solutions. The hydrologic analysis of the West Hill Basin included the development of an "HYD" model in accordance with KCSWDM procedures. The HYD model incorporated information that was previously developed by R. W. Beck for the Lake Washington Pollution Abatement Project (LWPAP) (Herrera Environmental Consultants, 1994). Information taken from the LWPAP included: ■ Subbasin Delineation. The West Hill Basin subbasin delineation is illustrated on Figure 3, excerpted from the LWPAP 3-4 R. W Beck, Inc. 11/19/98 x1159121.734 SYSTEM ANALYSIS ■ Existing Land Use Condition Runoff Curve Numbers. The methodology for curve number development is discussed in the LWPAP Using this information, a King County HYD model was developed for both current land use and future land use conditions. This involved the following additional steps: STEP 1 — DETERMINE A TIME OF CONCENTRATION FOR EACH SUBBASIN Times of concentration were developed using KCSWDM methods. The results are included in Appendix B, Volume 1. STEP 2 — DETERMINE FUTURE LAND USE CONDITION RUNOFF CURVE NUMBERS Future land use runoff curve numbers were developed using the same methodology as under the LWPAP. Future land was estimated based on a review of the City's 1992 aerial photograph of the area, the City's Comprehensive Land Use Plan (1995), and the City's official Zoning Map (1995). It was assumed that areas would be fully built out according to the land use plan. Some exceptions included very steep slope areas and a power line corridor, which were assumed to remain undeveloped. A summary table of the current and future land use by acreage as well as the development of future land use condition runoff curve numbers are provided in Appendix B, Volume 1. STEP 3 — DEVELOP KING COUNTY HYD MODEL DATA FILES These models were developed in accordance with the KCSWDM methodologies. Copies of the data files are included in Appendix B, Volume 1. A sketch of the model schematic is also included. The hydrologic modeling results for the West Hill Basin are presented in Table 3. 2. HYDRAULIC ANALYSIS METHODOLOGY The hydraulic analysis included developing three BWPIPE backwater models of the conveyance systems of interest in accordance with KCSWDM methodologies. The BWPIPE model is a direct-step backwater program that can be used to evaluate capacities of pipe systems. The BWPIPE program computes backwater profiles through the system for a range of flows, considering inlet, outlet, and system losses. The BWPIPE program assumes the pipe system is clean and functioning properly. It does not account for hydraulic losses that result from sediment accumulation unless specific adjustments are made. The pipe systems modeled were described in Section 2 and illustrated on Figure 1. The following paragraphs provide additional background on the assumptions and methodology used. The detailed analysis backup is included in x1159121.234 11/19/98 R. W. Beck, Inc. 3-5 SECTION 3 Appendix C, Volume 1. The modeling results are discussed in the following subsection (Section 3.3). The detailed pipe system data for the model input was developed from the pipe system inventory described in Section 2.2. One exception to this is the portion of the pipe system modeled along Main Avenue S between S 5th Street and S 3`d Street. Pipe system data for this reach of system was based upon City construction drawings and adjusted to match the surveyed downstream invert elevation. All three of the backwater models begin at the SW 71h Street pipe system outlet to the old Black River channel (BRPS forebay). The names of the pipe data files and a brief description are as follows: SW7THPIP.DAT Begins at outfall to BRPS forebay, continues south along Naches Avenue SW to SW 71h Street, continues along SW 71h Street to SW Grady Way, continues along SW Grady Way to Main Avenue S, and continues along Main Avenue S to S 3rd Street. SHATPIP.DAT Begins at outfall to BRPS forebay, continues south along Naches Avenue SW to SW 71h Street, continues along SW 7th Street to Shattuck Avenue, and continues along Shattuck Avenue to S 5th Place. (Extending the model further was not done because it was determined through the field investigation that north of S 5th Street the system flows north.) HARDHPIP.DAT Begins at outfall to BRPS forebay, continues south along Naches Avenue SW to SW 7t' Street, continues along SW 7t' Street to approximately 1,000 feet west of Hardie Avenue SW where it extends northeast along an easement to Hardie Avenue SW, then continues north along Hardie Avenue SW, to Sunset Boulevard W, then continues along Sunset Boulevard W past Rainier Avenue S where it extends north along Lake Avenue S to S Tobin Street. Note that this model reflects the pipe system that existed prior to the 1996 pipe replacement project along Lake Avenue S. In addition to the pipe system data input, a range of flows as well as "Qratios" must be input to the model. For all model runs, the flow range was specified at 10-cfs intervals up to the 100-year future condition flow rate as determined under the hydrologic analysis. "Qratios" are used to identify changes, or inflows, along the system. The "Qratios' are taken from the hydrologic summary spreadsheet, Step 4 spreadsheet in Appendix A, Volume 1. The SW 7" Street system outlet to the old Black River channel has an invert elevation of 10.28 and, based upon the results of the ESGRWP Hydraulic Analysis, (R. W. Beck, 1996), this pipe system would not be influenced by downstream backwater conditions. The maximum BRPS forebay elevation 3-6 R. W. Beck, Inc. 11/19/98 x1159121.734 SYSTEM ANALYSIS produced under the ESGRWP study was 8.28 (NAVD 1988) for the 100-year future condition "conveyance" event and 16.48 (NAVD 1988) for the 100-year future condition "storage" event. As described in the ESGRWP Hydrologic Analysis Report, there are two 100-year flow conditions for Springbrook Creek, referred to as "conveyance" and "storage." The conveyance event reflects a severe local rainstorm. The storage event reflects a major flood on the Green River, which in accordance with the Green River Interlocal Agreement (Green River Basin Program 1992) requires the BRPS to reduce pumping rates. The reduced pumping rates cause excess floodwater to be stored in the BRPS forebay and Springbrook Creek system. The tailwater elevation corresponding to 100-year conveyance event is below the SW 71' Street system outlet and would have no effect on the system. The tailwater elevation corresponding to the 100-year storage event was used for a test simulation and found to have little effect on the system capacity. As such, the remainder of modeling effort was done assuming no tailwater conditions. A copy of the existing condition backwater model with 100-year storage event is included in Appendix C, Volume 1. One reach of the SW 7" Street drainage system between approximately Hardie Avenue SW and Shattuck Avenue S consists of parallel pipes. The main pipe ranged in size from 24- to 48-inch-diameter CMP. The parallel pipe was a 24-inch-diameter concrete pipe; however, it was found to be approximately one- half full of sediment. This reach was simulated in the model using an equivalent pipe size based on equal conveyance. The effect of the parallel pipe was discounted by 50 percent because it was found to be full of sediment. The equivalent pipe size ranged in size from 30- to 50-inch-diameter pipe. The results of the BWPIPE model provides the capacity of each reach segment. This capacity is based upon flow overtopping a specified elevation. The specified overflow elevation is selected by the user and is usually taken as the grate (or top) of the upstream catch basin or manhole. Two other elevations that can be selected are the elevation of the upstream catch basin/manhole grate minus 0.5 feet or the elevation of the upstream catch basin manhole grate plus 0.4 feet (which is intended to approximate the crown of the road for a standard road cross section). These elevations can be used when checking to see if a system meets the City's design criteria, which is generally stated as follows: ■ Pipe systems shall be designed to convey and contain at least the peak runoff rate for the 25-year design storm with a minimum 0.5 feet of freeboard between the hydraulic grade line and the top of the structure ■ Pipe systems shall be considered acceptable for conveying the 100-year design storm provided that runoff is contained within the defined conveyance system element without inundating or overtopping the crown of a roadway The existing system conveyance capacity backwater runs were made for all three of these overtopping elevations. For the alternative analysis runs, the top of the structure (grate) was selected as the overflow elevation. This was done for two X1159121.734 11/19/98 R. W. Beck, Inc. 3-7 SECTION 3 reasons. First, the difference between the three criteria in terms of pipe reach capacity was minimal. Second, much of the system was unable to meet the 25-year or 100-year design criteria and, thus, to determine an idea of the actual level of protection provided by the system, the actual grate elevation was used. It is important to note that the model is only determining capacities of pipe segments for flow ranges. It does not route flows. The model results must be reviewed carefully because the actual flows through pipe reaches will be affected by any upstream capacity limitations. This is discussed under the existing system analysis results in the following subsection. 3. EXISTING SYSTEM ANALYSIS RESULTS The results of the combined hydrologic/hydraulic analysis are presented in Table 2. The location of pipe numbers referenced in this table are illustrated on Figure 1. The results provide a flow capacity for each pipe reach along with the estimated peak flow rates for the different design storms. Again, it is important to understand that these design flow rates assume that there are no upstream capacity limitations. The table identifies the approximate levels of protection for each reach (assuming no upstream capacity limitation). Again, the results for the Lake Avenue S system reflect the drainage system that existed prior to the 1996 pipe improvement project. The modeling results coincide well with observed conditions in that the pipe systems shown to be the most undersized are downstream of the three flooding problems. Another general observation is that the results show much of the other systems besides those systems downstream of the problem areas to be undersized, whereas no reported flooding has been observed for these systems. This is explained for the following reasons: ■ The existing system has capacity limitations such as the three problem areas that cause surface ponding and storage. In effect, the existing capacity limitations at the problem areas reduce downstream flows below system capacities. ■ The simulation results are for future land use conditions, which will include not only new development but also likely redevelopment, which will improve the "connectivity" of the drainage system. Note that, based on the ESGRWP Hydrologic Analysis, there will be an increase of approximately 100 acres of commercial land use in the South Renton subbasin, an increase of approximately 30 percent. 4. IDENTIFICATION OF ALTERNATIVE SOLUTIONS This section describes the alternative solutions considered and analyzed to solve the problems. The solutions were identified in a preliminary nature to the City and revised based upon City input. In general, the extent of improvements for 3-8 R. W. Beck, Inc. 11/19/98 X1159121.734 SYSTEM ANALYSIS the alternative solutions were developed as a range from a low extent of improvements to a greater extent of improvements that increase the level of protection provided by the system. In terms of the technical hydrologic and hydraulic analysis of alternative solutions, it is important to note that the solution to one problem can affect the solutions to other problems. As such, the modeling of alternative solutions were combined (e.g., the modeling of the SW 7" Street Alternative 2 includes the assumption that the Hardie Avenue SW Alternative 2 and the Lake Avenue S Alternative 2 are both implemented). In order to keep track of which set of alternative solutions were combined with other alternative solutions, a set of general alternative descriptions was developed as described below. Following the general description of alternatives are the detailed alternative descriptions. The detailed alternative descriptions describe any modeling assumptions as well as results. The alternative solutions are illustrated on Figure 4. A. GENERAL ALTERNATIVE DESCRIPTIONS GENERAL ALTERNATIVE 1 DESCRIPTION— MAJOR PIPE REPLACEMENT This alternative was originally intended to determine how much of the existing system would need to be replaced with larger diameter pipe to provide a level of protection meeting current City design standards for new systems. A trial-and-error approach was used in which pipe reaches downstream of problem areas were upsized in the backwater model; however, it was found that nearly the entire system would need to be replaced. This led to reducing the extent of improvements to a more realistic scale that still resulted in a large benefit (e.g., increased level of protection and increase in capacity). To simplify the modeling effort for this alternative, it was assumed that existing undersized pipes would be replaced with new larger diameter pipe at the same elevations. The extent of pipe replacement for each of the problems is provided in the detailed alternative descriptions. GENERAL ALTERNATIVE 2 DESCRIPTION — LAKE AVENUE S HIGH FLOW DIVERSION AND MISCELLANEOUS MINOR PIPE REPLACEMENTS/IMPROVEMENTS This alternative includes a high flow bypass that would divert high flows from an area currently draining to Lake Avenue S to the Black River box culvert in the West Hill Subbasin. This area consists of approximately 23 acres. A detailed discussion of the diversion is provided under the Lake Avenue S Alternative 2 description. This alternative would also include pipe replacements along SW 7"' Street. In addition, this alternative would include creating a pressure system along the Hardie Avenue SW underpass by providing watertight locking lids near the underpass. This would limit water from backing up out of the system to pond under the underpass. This would also require that the runoff generated in low areas around the underpass be pumped into the system during high flows. This is further discussed under Hardie Avenue SW Alternative 2. X1159121.734 11/19/98 R. W. Beck, Inc. 3-9 SECTION 3 GENERAL ALTERNATIVE 3 DESCRIPTION— SW 7T" STREET DIVERSION TO SPRINGBROOK CREEK, AND MISCELLANEOUS MINOR PIPE REPLACEMENT IMPROVEMENTS This alternative would include a second system outlet for the SW 7" Street system by constructing a storm drain along SW 7" Street between Springbrook Creek and Naches Avenue S to increase system capacity. In addition, it would include miscellaneous pipe system replacements along SW 7" Street and along Lake Avenue S. The alternative would also include creating a pressure pipe system along Hardie Avenue SW under the railroad underpass. GENERAL ALTERNATIVE 4 — LAKE AVENUE HIGH FLOW DIVERSION, SW 7T" DIVERSION TO SPRINGBROOK CREEK, AND MISCELLANEOUS MINOR PIPE REPLACEMENTS/IMPROVEMENTS This alternative essentially combines the improvements of General Alternative 2 and General Alternative 3 above to reduce flooding. GENERAL ALTERNATIVE 5 — REGIONAL DETENTION OR EXTRAORDINARY ON-SITE DETENTION This alternative was discussed early on in the project and subsequently discounted and not considered further. Regional detention would include large storage ponds to attenuate flood flows and reduce downstream runoff rates. Extraordinary detention would include a development restriction for the South Renton subbasin that would require greater volumes of on-site floodwater storage to further restrict on-site runoff rates (thereby acting collectively to reduce system wide runoff rates). This alternative is not considered viable for the South Renton subbasin. This subbasin is substantially developed with no clear opportunities for regional detention. As the City's comprehensive plan promotes intense land uses in this area, the City identified a concern that extraordinary detention could discourage development and/or redevelopment. Also, because the area is substantially developed, extraordinary detention, by itself, would not solve the flooding problems. B. DETAILED ALTERNATIVE DESCRIPTIONS SW 7T" STREET ALTERNATIVES SW 7T" STREET ALTERNATIVE 1 — MAJOR PIPE REPLACEMENT This alternative includes replacing the existing pipe between Seneca Avenue SW and Burnett Avenue S. Pipe replacement sizes as well as the increase in conveyance capacity are shown on Table 4. 3-10 R. W. Beck, Inc. 11/19/98 x1159121.734 SYSTEM ANALYSIS SW 7T" STREET ALTERNATIVE 2 — MINOR PIPE REPLACEMENT This alternative includes pipe replacement similar to SW 7`h Street Alternate 1 except that the improvements are to a lesser extent. The pipe system improvements would extend from Lind Avenue SW to Burnett Avenue S. Most of the system would be replaced with larger diameter pipe as shown on Table 4. However, it was assumed that a reach of existing 48-inch-diameter CMP would be improved by slipping a smooth lined 42-inch-diameter pipe (between Hardie Avenue SW and Rainier Avenue S). For this alternative, the invert elevations of the replacement pipe systems were assumed to be deeper than the existing pipe invert elevations. Proposed invert elevations are given in Table 4. For analysis of this alternative, it was assumed that the Lake Avenue S Alternative 2 (high flow diversion to Black River box) and the Hardie Avenue SW Alternative 2 would be implemented. SW 7T" STREET ALTERNATIVE 3 — SW 7TH STREET DIVERSION TO SPRINGBROOK CREEK AND MISCELLANEOUS MINOR PIPE REPLACEMENTS This alternative would include a second system outlet for the SW 7" Street system by constructing a storm drain along SW 7" Street between Springbrook Creek and Naches Avenue SW, allowing both the existing outlet and the second outlet to function. In addition, it would include the minor pipe system replacements along SW 7' Street as discussed in SW 7"' Street Alternative 2. For analysis of this alternative, it was assumed that the Lake Avenue S Alternative 2 (high flow diversion to Black River box) is not implemented. To simulate this alternative with the backwater model, the following modifications were performed on the existing system model; 1) The four most downstream pipe reaches were removed from the existing condition model and a tailwater rating curve was developed for Pipe Reach 5. 2) A separate backwater model was developed to reflect a pipe diversion between Springbrook Creek and the downstream end of Pipe Reach 5. A 5-foot-diameter pipe was assumed for the diversion. 3) A tailwater rating curve was developed by adding the combined capacity of the diversion system to Springbrook Creek with the capacity of the existing system Reaches 1 through 4. SW 7T" STREET ALTERNATIVE 4 — SW 7T"STREET DIVERSION TO SPRINGBROOK CREEK, MISCELLANEOUS MINOR PIPE REPLACEMENTS, AND LAKE AVENUE S DIVERSION This alternative would include the combined improvements of the SW 7" Street Alternatives 2 and 3 as described above. This alternative would X1159121.734 11/19/98 R. W. Beck, Inc. 3-11 SECTION 3 also include the assumption that the Lake Avenue S high flow diversion is implemented. HARDIE ALTERNATIVE SW ALTERNATIVES HARDIE AVENUE SW ALTERNATIVE 1 — PIPE REPLACEMENT This alternative includes replacing the existing pipe system between the connection to the SW 7" Street system and Hardie Avenue SW For this alternative, it is also assumed that the downstream improvements of SW 7`' Street Alternative 1 are included. Pipe replacement sizes are shown on Table 4. HARDIE AVENUE SW ALTERNATIVE 2 — PRESSURE PIPE SYSTEM AND PUMP STATION (FOR LOCAL FLOWS AT THE UNDERPASS) This alternative would include creating a closed pipe pressure system in the Hardie Avenue SW system in the vicinity of the railroad overpass. This would be accomplished by installing watertight locking lids on the manholes in the vicinity of the underpass. This would prevent pipe system flows from escaping the trunk system during high flows (when the hydraulic grade line is higher than the manhole lids); such escaping flows currently form a pond in the underpass. Because local surface runoff in the vicinity of the under- pass would be unable to drain to the system during high flows, a small pump station would need to be installed. No estimates of the pump station size were performed; however, it would probably be on the order of 200 to 400 gpm (1 to 2 cfs). For analysis of this alternative, it was assumed that Lake Avenue S Alternative 2 (high flow diversion to Black River box) would be implemented. In addition, it was also assumed that the SW 7`h Street Alternative 2 is implemented, which includes replacement of one pipe reach downstream of the Hardie Avenue SW/7"' Street system confluence. HARDIE AVENUE SW ALTERNATIVE 3 — PRESSURE PIPE SYSTEM AND PUMP STATION (FOR LOCAL FLOWS AT THE UNDERPASS) This alternative includes the same improvements along Hardie Avenue SW as Hardie Avenue SW Alternate 2. It differs from Hardie Avenue SW Alternative 2 in that it assumes the Lake Avenue Alternative 3 (minor pipe replacement) would be implemented and that the SW 71h Street Alternative 3 is implemented, which includes the diversion to Springbrook Creek and a pipe reach replacement downstream of the Hardie Avenue SW 7th Street system confluence. 3-12 R. W. Beck, Inc. 11/19/98 x1159121.734 SYSTEM ANALYSIS HARDIE AVENUE SW ALTERNATIVE 4 — PRESSURE PIPE SYSTEM AND PUMP STATION (FOR LOCAL FLOWS AT THE UNDER PASS) This alternative includes the same improvements along Hardie Avenue SW as Hardie Avenue SW Alternate 2. In addition, it is assumed that the Lake Avenue Alternative 4 (high flow diversion to Black River box and minor pipe replacement) would be implemented and that SW 7`' Street Alternative 4 is implemented, which includes the diversion to Springbrook Creek and a pipe reach replacement downstream of the Hardie Avenue SW 7`'' Street system confluence. LAKE AVENUE S ALTERNATIVES LAKE AVENUE S ALTERNATIVE 1 — MAJOR PIPE REPLACEMENT This alternative includes replacing the existing downstream pipe system between SW Langston Road and S Tobin Street. This alternative also includes a new pipe system along S Tobin Street from Lake Avenue S to the low point in the road approximately a few hundred feet east of Lake Avenue S. It should be noted that these improvements along S Tobin Street would reflect the minimum needed to reduce the existing flooding problem. There is a general lack of drainage system between Lake Avenue S and Logan Avenue S, and a more extensive system along S Tobin Street may be warranted. For this alternative, it is also assumed that the downstream improvements of SW 7"' Alternative 1 and Hardie Avenue Alternative 1 are included. Pipe replacement sizes are shown on Table 4. Note that grate elevation at the low point along S Tobin Street is substituted for the grate elevation of Reach 38 so that the improvement in the S Tobin Street problem can be evaluated (elevation 27.90). LAKE AVENUE S ALTERNATIVE 2 — LAKE AVENUE S HIGH FLOW DIVERSION This alternative would include constructing a high flow diversion to the existing Black River box culvert to reduce the high flows through the Lake Avenue S drainage system. The area that could be diverted away from this system is approximately 23 acres and is identified as subbasins AJ and AK on the basin map in Appendix A, Volume 1. This area includes approximately one-half of the Renton High School building and paved area. The high flow diversion would likely be set up such that low flows on the order of 0.5 cfs would continue to drain to the Lake Avenue S system and excess flows would be diverted to the Black River box. The Black River box culvert is shown on Figure 3. To evaluate the impact of this alternative on the Black River box culvert system, a separate hydrologic and hydraulic analysis was completed. The hydrologic analysis of the West Hill Basin, which contributes to the Black River box culvert, was discussed under Section 3.1. The West Hill Basin X1159121.734 11/19/98 R. W. Beck, Inc. 3-13 SECTION 3 hydrologic model was modified by adding an additional subbasin (the combined subbasins AK and AJ, see basin map in Appendix A, Volume 1) to reflect the diversion. In addition, a backwater model was developed of the Black River box culvert to evaluate its capacity. The backwater model was developed using the same methodologies as the South Renton subbasin systems. The backwater model included an assumed tailwater evaluation of 16.78 (NAVD, 1988), which corresponds to the normal Lake Washington winter elevation. The Black River box culvert was also field inventoried to determine invert elevations for the model. The results of the hydrologic/hydraulic analysis of the Lake Avenue S diversion and potential impacts on the Black River box culvert are provided on Table 3. This table shows that the diversion to this system would increase projected peak flows by approximately three percent for the future land use condition 25-year design storm at its outlet to Lake Washington. This diversion would have a negligible impact on the level of protection provided by the Black River box culvert. While the culvert currently does not meet the City's 25-year design criteria, it should be noted that it was originally designed to provide a 10-year level of protection (Wilsey and Ham, 1969). The diversion would not reduce the level of protection below the future land use condition 10-year level. An additional component of this alternative is to provide an adequate stormwater collection system in at least the portion of S Tobin Street near Lake Avenue S. Prior to the 1996 pipe improvements along Lake Avenue S and S Tobin Street, there was little to no collection system. This alternative assumes that SW 7`' Street Alternative 2 and Hardie Avenue SW Alternative 2 are also implemented. LAKE AVENUE S ALTERNATIVE 3 — MINOR PIPE REPLACEMENT This alternative includes pipe replacement of the downstream system from approximately Rainier Avenue to the intersection with S Tobin Street. This alternative would also include providing an adequate stormwater collection system in at least the portion of S Tobin Street near Lake Avenue S (similar to Alternatives 1 and 2). For this alternative, the invert elevations of the replacement pipe systems were assumed to be the same as the existing invert elevations. For analysis of this alternative, it was assumed that the Hardie Avenue SW Alternative 3 (Pressure Pipe System and Pump Station) and SW 7" Street Alternative 3 (SW 7" Street Diversion to Springbrook Creek, and Miscellaneous Minor Pipe Replacements) would be implemented. LAKE AVENUE S ALTERNATIVE 4 — LAKE AVENUE S HIGH FLOW DIVERSION/MINOR PIPE REPLACEMENT This alternative includes the combined improvements of both Lake Avenue S Alternatives 2 and 3 to further increase the level of protection. 3-14 R. W. Beck, Inc. 11/19/98 x1159121.731 SYSTEM ANALYSIS For analysis of this alternative, it was assumed that Hardie Avenue SW Alternative 4 (Pressure Pipe System and Pump Station) and SW 7`h Street Alternative 4 (SW 71h Street Diversion to Springbrook Creek, and Miscellaneous Minor Pipe Replacements) would be implemented. It is interesting to note that, as shown on Table 4, the level of protection provided by this alternative exceeds Alternative 2 while the capacity of the improved drainage system is less than the existing system capacity. This is counterintuitive and is a function of the change in the backwater model "Qratios" resulting from the diversion. It occurs because, for a given flow within a pipe reach of the improved system, the percentage of the downstream tributary flow is greater, which results in a higher tailwater condition and lower capacity. LAKE AVENUE ALTERNATIVE 5 — LAKE AVENUE DIVERSION TO CEDAR RIVER As shown in Figure 1, the Cedar River is located near the northeast portion of the South Renton subbasin (more specifically subbasins AK and AJ, see basin map in Appendix A). Some thought was given early on to diverting a portion of the South Renton subbasin around the Renton High School to the Cedar River to reduce flows in the Lake Avenue S system. To be effective in collecting runoff from the high school, the system would need to begin along S Tobin Street approximately midway between Lake Avenue S and Logan Avenue S. The system could then extend east to Logan Avenue S and the north to discharge to the Cedar River. No detailed hydrologic/hydraulic modeling was done to evaluate this alternative. However, a comparison of the Cedar River floodplain levels and approximate road grade elevations along S Tobin Street were reviewed. The Cedar River floodplain elevations are based on a floodplain study (NHC, 1992). Cedar River 2-year flood elevation at 26.6(NAVD 1988) Logan Avenue S Cedar River 100-year flood elevation at 30.6 (NAVD 1988) Logan Avenue S Approximate road grade elevation of 31.6(NAVD 1988) S Tobin Street(31.6 elevation is midway between Lake and Logan; elevation based on City's 1962 aerial topography (USC &GS data) Note: The low point on S Tobin Street is 27.90. A comparison of the above elevations indicates that it may be possible to divert drainage from the Renton High School to the Cedar River. Based on a review of these elevations, a system could be designed to function during a 2-year Cedar River flood; however, during 100-year floods +/- on the Cedar River, a backflow prevention device would be needed to prevent the Cedar X1159121.734 11/19/98 R. W. Beck, Inc. 3-15 SECTION 3 River from backing up into such a system during high Cedar River flows. It is important to note that comparison of the above elevations is considered approximate. During our review of the City's 1962 aerial topographic maps, we noted spot elevation discrepancies of up to 2 feet. If the City were interested in pursuing this alternative further, some quick elevation checks would be suggested before any extensive analysis is performed. This alternative, while having some merit, was not considered further because of the disadvantage of not being able to function during a major flood (100-year event) on the Cedar River and because less area could be diverted than with the diversion alternative to the Black River box. Some thought was also given to diverting flows to the Cedar River with a new system that includes an overflow outlet to an improved Lake Avenue S system (to provide an outlet when the Cedar River is high). A detailed analysis of such an alternative was not performed because it was beyond the scope of this study. Also, it would not provide as much benefit as a diversion to the Black River box with an overflow to the Lake Avenue S system. Based upon measurements of water levels made by the City on February 8, 1996 and on data from the Cedar Gage at Bronson Avenue, water levels in the Black River box at Airport Way were lower than the Cedar River. Therefore, based on this observed flood, diversion to the Black River box would have resulted in a greater benefit. City staff estimate that at 10:00 am on February 8, the elevation in the Cedar River was 27.85 feet, while the water level measured at 10:20 am north of Airport Way was 23.78 feet. SHATTUCK AVENUES ALTERNATIVE 1 — PIPE REPLACEMENT Only one alternative was considered to reduce flooding along Shattuck Avenue S. This alternative includes replacing the existing pipe system between the intersection with SW 7tn Street to the railroad right-of-way (just south of S 5th Street.) For this alternative, it is also assumed that the downstream improvements of SW 7t' Street Alternative 1 are included. Pipe replacement sizes are shown on Table 4. 3-16 R. W. Beck, Inc. 11/19/98 x1159121.7334 SECTION 4 ALTERNATIVE EVALUATION AND SELECTION OF PREFERRED ALTERNATIVES SECTION 4 ALTERNATIVE EVALUATION AND SELECTION OF PREFERRED ALTERNATIVES 1 . GENERAL This section includes an alternative evaluation of the study alternatives including the no-action alternative. Alternatives were evaluated in terms of the following criteria: ■ Effectiveness in solving flooding ■ Feasibility and constructability ■ Compatibility with downstream drainage system ■ Cost ■ Environmental considerations ■ Other advantages and disadvantages A summary of the alternative ratings for these criteria is shown on Table 5. Construction cost estimates were developed for each alternative and are included in Appendix E, Volume 1. Construction cost estimates include allowances of 40 percent for administrative cost (design, construction engineering, survey, administration, and sales tax, although sales tax may not be required if the improvement is conducted concurrently with a roadway improvement project), and a 30 percent construction contingency. Cost estimates are generally for pipe replacements or improvements of the main pipe system and do not include replacement of the existing roadside collection systems. 2. ALTERNATIVE EVALUATION The alternative evaluation is summarized in Table 5. The hydrologic and hydraulic analysis results that provide a predicted level of protection for future land use conditions were presented in Table 4 (Black River box diversion is in Table 3). As discussed previously, the capacity of the main trunk system in SW 71h Street is limited. Without major improvements that include replacement of most of this system, the City could not provide a level of protection for future land use condition flows that meets current City standards. Preliminary indications from City staff indicated that the possibility of implementing such a major project is unlikely at this time. As a consequence, the alternative solutions were generally reduced in scale, but in some cases are still very significant projects. The following paragraphs provide a discussion of the various alternatives that supplement Table 5. X1159121.734 11/19/98 SECTION 4 SW 7" STREET ALTERNATIVES The selection of the preferred alternative for the SW 7" Street problem is highly dependent on the preferred alternative for the SW Hardie Avenue problem. The analysis shows that the only way to provide a significant increase in the Hardie I Avenue SW level of protection is to implement the Hardie Avenue SW Alternative 1, which includes the assumption that the downstream system along SW 7" Street is improved as defined in SW 7"' Street Alternative 1. Therefore, if the Hardie Avenue SW Alternative 1 is selected, the SW 7" Street Alternative 1 should also be the preferred alternative. If one of the other Hardie Avenue SW alternatives is selected, then the SW 7"' Street Alternatives could be evaluated on their own merit. The SW 71' Alternatives provide approximately the same level of protection. Alternative 4 provides a somewhat greater level of protection then the other alternatives, particularly in the downstream reaches of the SW 71' Street system. This is because this alternative assumes that the Lake Avenue S diversion to the Black River box culvert (Lake Avenue S Alternative 4) is implemented and because the diversion to Springbrook Creek increases the capacity of the downstream portion of the system. Any of the alternatives could be phased. HARDIE AVENUE SW The analysis shows that a significant downstream improvement would be necessary to completely solve the problem. The major pipe replacement alternative (Alternative 1) provides the greatest level of protection; however, the improved level of protection is just shy of the future condition 2-year event. At the same time, Alternative 1 would result in a 64 percent increase in capacity downstream of the problem area. Alternative 1 provides the greatest level of protection. Alternatives 2 through 4 would reflect a lower construction cost. One item to note about the cost estimate for alternatives 2 through 4 is that their cost would be highly dependent on the type of pump station that the City would desire. The pump station cost could range from $100,000 to $400,000 depending on pump station features as well as dewatering needs. A disadvantage of the pump station is the long-term operation and maintenance required as well as emergency provisions should a power outage occur during a flood event. Alternatives 2 through 4 include an additional disadvantage by the creation of a pressurized system. Raising the hydraulic grade line through the underpass would reduce the capacity of the upstream system. If the upstream system were to become surcharged (causing flows along the street), there would be a concern that additional surface flows along Hardie Avenue SW would be directed to the low area and possibly exceed the capacity of the pump station. The other alternative for the Hardie Avenue SW is the no-action alternative. This alternative may be worth some consideration given the lower traffic volume through the area and the cost of improvements necessary to reduce flooding. 4-2 R. W. Beck, Inc. 11/19/98 x1159121.734 i ALTERNATIVE EVALUATION AND SELECTION OF PREFERRED ALTERNATIVES However, one item to note is that, as the City implements other improvements such as along SW 7" Street, flows to the downstream system will increase. Such system improvements combined with continued development in the watershed would result in more frequent and more severe flooding at Hardie Avenue SW. LAKE AVENUE S ALTERNATIVES One item to note about the Lake Avenue S hydrologic analysis is that it is assumed that the Renton High School playfield, located east of Lake Avenue S is developed in the future conditions to the level of commercial uses. Should this grassy field remain permanent, the future predicted flows as shown in Table 4 likely over predict the flows that would be directed to this system. Following the completion of the draft report, the City performed additional inspection of the corrosion problem along Lake Avenue S. The pipe was found to be completely worn in some areas. In fact, the pipe video camera fell through a hole in the pipe and had to be dug out by cutting into the pavement. Because of its poor condition and because the City had committed to reducing the flooding problem as quickly as possible, the City moved forward with designing a replacement system for the section of pipe between S 2nd Street and S Tobin Street as well as an improvement to the S Tobin Street system. The sizing of the pipe improvements did not exactly follow the alternatives presented in this report based on additional hydraulic modeling performed by the City staff. One of the objectives of the City's modeling effort was to minimize the pipe size for replacement but at the same time checking to make sure that the City will be able to provide at least a 25-year level of protection for future land use conditions if other downstream improvements are made in the future as resources allow. This analysis was done by the City and included in Appendix F. The analysis was done two ways, assuming downstream improvements as in Alternative 1 as well as diverting a portion of the basin to the Black River box as in Alternatives 2 and 4. In this way, the City has selected a phased approach for correcting the Lake Avenue S drainage problem. Additional improvements beyond the 1996 pipe replacement project will be necessary to completely solve the problem. As resources allow, the City should consider additional improvements. During the interim period, prior to the completion of the more extensive improvements, the City should monitor the initial improvements and collect more data on the level of protection provided by these systems. In comparing the Black River box system and the South Renton subbasin system, the Black River box has a substantially greater level of protection. Diverting high flows from the Lake Avenue S system (as in Alternative 4) would result in a negligible impact to the Black River box. It should be noted again that until such time as the high school ball field is developed, the flows to Lake Avenue S would be lower than predicted in Table 4. Following the pipe replacement program completed in 1996, the City should monitor the system for continued flooding. Alternative 4, or diversion to the x1159121.734 11/19/98 R. W. Beck, Inc. 4-3 SECTION 4 Black River box in addition to the City's 1996 pipe replacement program is recommended to completely solve the problem. The diversion to the Black River box should be implemented as resources become available. While the Lake Avenue S Alternative 4 appears to be the most favorable solution, one general disadvantage to the alternative is diverting flows from one basin to another. Flow diversions such as this must be considered carefully as a result of the potential liability of claims should flooding along the diversion route occur. It is suggested that City legal staff be consulted. 3. SELECTION OF PREFERRED ALTERNATIVES The recommended solutions contained in this report were developed after review and consultation with the City. The comparison of the alternative solutions to arrive at a recommended solution was described above. The recommended solutions include: SW 7T" STREET, ALTERNATIVE 2 The City should initiate a phased approach for reducing flooding along SW 71'Street. Initially, the City should complete the Alternative 2 (minor pipe replacement) improvements. In addition, the City should coordinate the improvements to the Renton Village conveyance system to prevent overflows into the SW 7"' Street drainage system. During design of the minor pipe replacement improvements, the design should include additional analysis to ensure that the replacement pipe sizes are large enough so as not to preclude further downstream improvements to achieve the City's design criteria of 25-year storm for future land use conditions. This analysis is similar to what the City performed on the Lake Avenue S 1996 system improvements. The City should also monitor flooding and consider additional downstream improvements as resources allow. One additional item to note is that the King County Department of Natural Resources is planning a large sewer interceptor along SW 7" Street. The City of Renton should consider pipe improvements along SW 71' Street to coincide with the sewer improvements to reduce restoration costs and construction impacts. HARDIE AVENUE SW - ALTERNATIVE 2 Alternative 2 is preferred primarily due to lower initial capital cost. Early on in design, the City should confirm what design requirements would be placed on the pump station. As noted in the previous section, the cost of the pump station could vary significantly. If the cost of the pump station becomes such that the overall cost of this alternative approaches the cost of Alternative 1, the City should reconsider the preferred solution. Alternative 2 will help reduce the frequency of flooding, however, some flooding during significant storms should be expected. As with the SW 7`h Street preferred alternative, the City should 4-4 R. W. Beck, Inc. 11/19/98 x1159121.734 ALTERNATIVE EVALUATION AND SELECTION OF PREFERRED ALTERNATIVES monitor flooding and consider additional downstream improvements as resources allow. LAKE AVENUE S - ALTERNATIVE 4 As described in the previous section, the City has already completed some pipe replacement work along Lake Avenue S and S Tobin Street in 1996. This has helped reduce the frequency of flooding, but is not a complete solution. The City should pursue the diversion to the Black River box as resources allow. In the interim, the City should monitor the system for continued flooding and collect more data on the level of protection provided by the system. One additional consideration relates to the Renton High School playfield. If this area is developed to a more impervious use, consideration should be given to requiring the diversion at that time to mitigate for an increase in runoff volume to an already undersized system. SHATTUCK AVENUE S It is also recommended that the City implement a pipe replacement system along Shattuck Avenue S from SW 7`' Street to S 6"' Street to improve the capacity of this system. The pipe replacement shown on Table 4 would provide a 2-year level of protection for future land use conditions. This pipe replacement scenario was based upon the assumption that SW 7t'' Street Alternative 2 would be implemented. 4. IMPLEMENTATION OF PREFERRED ALTERNATIVES This section describes some of the issues that will need to be considered as the City moves forward to implement the preferred solutions. 1) Data Needs. The following data needs should be considered. a) Additional investigation into potential utility conflicts. A brief investigation was performed as a part of this study. This investigation included a review of the City's comprehensive sewer and water system maps and the sewer system data. Conflicts between a pipe replacement alternative and existing water lines were noted and an average cost of $800 was included in the alternative estimate assuming that a short section of waterline would need to be relocated. In terms of the sewer system data, no obvious conflicts were identified. However, we could not investigate the SW 71h System alternatives east of Lind Avenue because the data in the sewer system inventory was missing. Also, the data for the system along S 3`d Street (crossing Lake Avenue S Alternative 1) appeared to be incorrect. The Lake Avenue S alternatives also cross over and under existing sewers with little apparent clearance. As a part of design work, the City should confirm sewer invert elevations early on in the design. No x1159121.734 11/19/98 R. W. Beck, Inc. 4-5 SECTION 4 research was conducted of other utilities such as gas, telephone, or electrical. b) The City should TV the Hardie Avenue S system to evaluate its condition. c) Field surveys will be required for design. d) The original field inventory and technical analysis for this study was completed in 1995. Since that time, additional catch basins/pipe connections may have been construction on the pipe systems analysis for this study. Prior to additional analysis such new catch basins should be added to the computer analysis. 2) Phasing Project Improvements. As discussed above, the preferred alternatives follow a phased approach whereby the City would implement initial improvements that would improve the existing system capacities and reduce the frequency of flooding. As resources allow, the City should consider additional improvements. During the interim period prior to the completion of the more extensive improvements, the City should monitor the initial improvements and collect more data on the level of protection provided by these systems. In addition, improvements should be coordinated with planned street or utility improvement projects or with large development proposals that affect the drainage system. If the SW 7`h Street Alternative were phased, the initial phase should be between the confluence with the Hardie Avenue SW system and Shattuck Avenue S. Additional analysis could be done using the backwater model to maximize capacity improvements. 3) Optimizing Pipe Replacements. The backwater models developed during this project will serve as an excellent design tool during the design phase to optimize replacement pipe size and pipe slopes. Some trial-and- error iterations were performed through the alternative development; however, there are an extreme number of possibilities for how the pipe replacements are configured. The backwater models should be taken one step further during design to optimize performance at the least cost. An option to the BW pipe program is an Excel spreadsheet that generally uses the same direct step backwater methodology. An example of this approach is included in Appendix F, done for the Lake Avenue S design. 4) Design Considerations. During design of improvements to the system, additional, more detailed, considerations should be taken into account that were not investigated as a part of this study. Some of these items include checking available cover for replacement systems, using an actual profile rather than a profile of manhole rim to manhole rim, separation from other utilities, traffic considerations, premarking utilities, installing a parallel pipe system instead of replacing a system with larger diameter pipe, using box culvert or an arch pipe instead of a round pipe, roadway 4-6 R. W Beck, Inc. 11/19/98 x1159121.734 i ALTERNATIVE EVALUATION AND SELECTION OF PREFERRED ALTERNATIVES restoration requirements, as well as other specifics that affect final design of improvements. As previously discussed, during the final sizing of the pipe replacements, the City should confirm that the replacements will be able to provide at least a 25-year level of protection for future land use conditions if other downstream improvements are made in the future as resources allow. The scenario to be avoided is performing a pipe system replacement project only to discover later that a 25-year level of protection cannot be achieved even with additional downstream improvements. Regarding the diversion to the Black River box for the Lake Avenue S Alternative 4, the City should attempt to collect additional field measurements during storm events of the hydraulic grade line in the first two Black River box pipe sections north of S 2nd Street. This data would provide hydraulic grade line information and could be used to confirm that the diversion would function properly. If there is concern that during a major event, the flows in the Black River box could back up into the diversion pipe, consideration could be given to a flap gate at the diversion pipe connection to the box. X1159121.734 11/19/98 R. W. Beck, Inc. 4-7 � ■ 1 1 i 1 1 1 1 1 1 1 � �� iv �IFai 1 TABLE 1 SW 7th Street,Hardie Avenue,Lake Avenue Drainage Investigation EXISTING DRAINAGE SYSTEM INVENTORY RESULTS SYSTEM:SW7TH,GRADY,MAIN RWB DWN BW Struc. RWB CITY GRATE INLET OUTLET GRATE 0= PIPE PIPE SLOPE STREAM Pipe# TYPE Ref. INDEX # TYPE CB ? Elev IE IE TYPE SEP. DIAM. TYPE LENGTH (%) STRUCT ft ft ft ft MH_ 1 15.G8-2 2-144 N 20.38 10.13_ 10.28_ C_ N 95x67" CMP 35 -0.43% Black River __1 MH 5 _ 2-120 N 20.95 11 10.13 C N 60" C 215 0.40% 1 _ 2 MH _10 15.G8-1 2-120 N 21.27 11.57 11 C N 60" C 92 0.62% 5 3 _ MH 15_ 20.G2-6_ 2-120 N 20.67 12.08 11.57 C N 60" C 318 0.16% 10(1) 4 MH_ 20 20.G2-1 4-60(2) N 21.22 12.72_ 12.08 C N 60" C 396 0.16% 15 5 MH 25 4-60(2) N 21.24 12.82 12.72 C N 60" C 344 0.03% 20 6 MH_ 30 20.H2-2 4-60(2) N 21.88 12.63 12.82 C N 60" C 128 -0.15% 25 7 MH _ 35 _ 20.1-12-1 2-120(2) N 22.46 12.81 12.63 C N 60" C 472 0.04% 30 8 _MH 40 16.B8-5 2-120(2) N 22.52 13.07 12.81 C N 60" C 607 0.04% 35 _ 9 MH 45 16.C8-7 2-120(2) N 22.61 13.11 13.07 C N 60" C 56 0.07% 40 10 MH 50 16.C8-8 2-120(2) N 22.87 13.37 13.11 C N 60" C 654 0.04% 45 11 MH 55 _16.D8-5__ 2-96(2) N 23.87 13.77 13.37 C N 1 54" C 312 0.13% 50 12_ _MH_ 60 16.138-4 2-72(2) N 24.52 14.02 13.97- C N 36" C 223 0.02% 55 _ 13_ MH 65 16.DS-3 2-60 N(2) 24.62 15.72 15.02 C N 24" C 14 5.00% 60 14 MH__ 70 16.D8-2__ 2-48 N(2) 25.72 16.42 15.52 C N 24"_ C 311 0.29%, 65 _ 15 MH_ 75 16.E8-14_ 2-48 N(2) 26.03_ 16.71 16.47 C N 24" C 315 0.08% 70-_ 16 MH 80 16.E8-4 2-48 Y 2 25.43 16.73 16.93 C N 24" C 167_ -0.12% 75 17_ _ MH 85 16.E8-18 2-72 Y 2 25.29 16.69 16.78 C N 24" CMP 18 -0.50% 80 18 _MH 90 16.EB-17 2-72_ Y 2 25.2 15.45 14.59 C N 48" CMP 123 0.70% 85 MH 105 _ - _ 2-72 Y 2 25.03 16.03 15.4 C N 48" CMP 215 0.29% 90 20_ _MH 110 16.EB-15 2-72 Y 2 25.02 11.27 17.28 C N 30" CMP 14 -0.07% 105 21 _MH 115 2-60 Y 2 25.65 17.9 17.32 C N 30" CMP 300 0.19% 110 22 MH SHt 16.F8-1 2-48 Y 2 24.49 19.19 18.45 C N 24" CMP 481 0.15% 116 23 MH 250 2-48 Y 2 25.46 20.36 19.34 C N 24" CMP 243 0.42% SH1 24 MH 245 2-48 Y 2 25.18 20.76 20.26 C N 24" CMP 317 0.16% 250 25 MH 240 16.H8-7__ 2-48 Y 2 27.33 21.33_ 20.78 C N 24" CMP 506 0.11% 245 26 _ MH 235 16.1-18-4 2-48(2) Y 2 29.86 22.36 21.33 C N 24" CMP 82 1.26% 240 27 _ _CB _ 230 16.1-18-6_ 4'x4'sq. Y 2 28.51 23.37 23.06 C N 24" CMP 42 0.74% 235 28 225 _ 16.HB-8 - N 28.75 25.05 23.96 C N 24" C 44 2.48% 230 _ 29 CB 220 16.HB-9 4'x4'sq. N(2) 30.31 25.46 25.05 C N 24" C 161 0.25% 225 30 _ - 215E - 30.76 26 25.51 S N 24" C - - - 31 _ - 215 17.B9-1_ - N 29.91 26.61 26 S N 24" C 40 1.53% 215B 32 - 210 17.BB-3 Y(2) 30.3 27.7 26.91 S N 18" C 169 0.47% 215_ 33 - -_ 205 - - _ Y(2) 32.12 27.92 27.75 C N 12" C 69 0.25% 210 34 MH _200 _ 17.B8-2 2-48 Y_ 32.52 29.47 27.92 C N 12" C 260 0.60% 205 35 MH 195 17.C8-5__ 2-48 rN(2) Y 35.78 31.78 29.42 C N 12" C 284 0.83% 200 36_ MH 190 _17.CB-4__ 2-36N 38.2 33.55 31.78 C N 12" C 167 1.06% 195MH 185 17.C8-3 2-48N 40.02 34.82 33.7 C N 18" C 30 3.73% 190 38 _MH 175 17C8 2 2 48 (2) 41 AS 34.5 35.02 C _ N 12" C 62 -0.84% 185MH 170 17_C7_5 2-48 41.9 36.5 34.8 C N 15" C -408 0.42% 175 _ 40 Notes: (1) Elevation Datum NAVD 88 TABLE 1 (cont.) SW 7th Street, Hardie Avenue, Lake Avenue Drainage Investigation EXISTING DRAINAGE SYSTEM INVENTORY RESULTS SYSTEM:SW7TH PARALLEL SYSTEM RWB DWN Struc. RWB CITY GRATE INLET OUTLET GRATE O/W PIPE PIPE SLOPE STREAM TYPE Ref. INDEX # TYPE CB ? Elev IE IE TYPE SEP. DIAM. TYPE LENGTH (%) STRUCT ft ft ft ft MH 300 16.E8-12 2-48 N 24.89 17.29 17.45 C N 24" CMP 13 -1.23% 90 MH 3 55 16.E8-11 2-48 N 24.82 17.62 17.39 C N 24" C 48 0.48% 300 16.E8-13 2-54 Y 24.69 17.24 17.32 C N 30" CMP 12 -0.67%° 110 MH 310(1)_ 16.E8-13 2-54 Y _ 24.69 17.29 17.62 C N 24" C 180 -0.18% 305 MH 315 - 2-48 Y 26.04 17.54 17.29 C N 24" C 85 0.29% 310 4X4 SQ Y 25.44 18.04 17.74 C N 24" C 115 0.26% 315 MH _ SH5 16.F8-19AB 2-48 Y 24.1 18.9 18.29 C N 24" C 578 0.11% 320 -1AB 1895 9.19 C N PVC SH1M 9 2 MH 345 - 2-36 N 25.18 21.18 19.7 C N 21" CLAY 580 0.26% SH5 Notes: (1) Elevation Datum NAVD 88. TABLE 1 (cont.) SW 7th Street,Hardie Avenue,Lake Avenue Drainage Investigation EXISTING DRAINAGE SYSTEM INVENTORY RESULTS SYSTEM:HA"IE/LAKE AVENUES RWB DWN BW Struc. RWB CITY GRATE INLET OUTLET GRATE O/W PIPE PIPE SLOPE STREAM Pipe# TYPE Ref. INDEX # TYPE CB ? Elev IE IE TYPE SEP. DIAM. TYPE LENGTH (%) STRUCT ft ft ft ft MH_ 55 16.D8-5_ 2-96 N 23.87 13.77 13.37 C N 54" C 312 0.13% 50 MH 56A 16.D8-12_ 2-72 Y 25.79 14.69 13.82 C N_ 48" CMP 229 0.38% 55 13_ MH 57A 16.D8-11 2-72 Y 25.82 14.72 14.69 C N 48" CMP 133 0.02% 56A 14 MH 58A 16.D8-10 2-60 Y 27.33 15.33 14.72 C N 48" CMP 315 0.19% 57A 15 MH 59B 16.E8-19 2-72 N 21.38 15.58 15.33 C N 36"X60" CMP 328 0.08% 58A 16 _MH 59A 16.E8-6 2-72 N 22.75 15.65 15.33 C N 36"X60" CMP. 187 0.17% 59B 17 MH 60A 16.D7-10 2-72 N 23.65 15.96 15.85 C N 36"X60" CMP 272 0.04% 59A _ 18 MH 60B - 3-96 N 24.2 16 15.96 C 36"X60" CMP 100 0.04% 60A 19 MH_ 65A 16.D7-7 2-72 N 24.4 16.25 16.2 C N 36"X60" CMP 199 0.03% 60B _ 20 _MH 67A_ 16.D7-6 2-72 N 25.54 16.49 16.25 C N 36"X60" CMP 353 0.07% 65A MH 70A 16.D6-13 2-96 N 27.35 16.75 16.54 C N 36"X60" CMP 252 0.08% 67A 22 MH 73A 16.D6-12 2-96 N 30.37 16.87_ 16.75 C N 36"X60" CMP 125_ 0.10%__ 70A 23 MH 75A 16.E-19 2-60 N 31.14 17.14 16.77 C N 24"X48" CMP 210 0.18% 73A_ 24 MH 78A 16.E6-23 2-60_ N 30.07 17.37 17.39 C N 24"X48" CMP 172_ -0.01% 75A 25 MH 79A 16.F6-22 2-54 N 30.17 17.47 17.26 C N 24"X48" CMP 154 0.14% 78A 26_ MH 80A 16.E6-21 2-60 N 30.22 17.09 17.37 C N 24"X48" CMP 38 -0.74% 79A 27 CB_ 95A 16.E6-20 VAULT N 30.25 18.25 17.22 C N 24"X48" CMP 241 0.43% 80A 28 MH 100A - 2-48 N 30.09 18.64 18.25 C N 24" C 46 0.85% 95A 29 MH 105A 16.F5-16 2-48_ N 30.8 19 18.64 C N 24" C 220 0.16% 100A 30_ MH 110A 16.F5-2_ 2-48 N 30.34 18.79_ 19 S N 24" C 309 -0.07% 105A 31 MH 115A 16.F5-9 2-48 N 30.4 20.85 18.99 C N 24" C 62 3.00% 110A 32 MH 120Ar16.F5-3 2-48 N 29.31 20.86 20.85 C N 18" C 81 0.01% 115A 33 MH 125A 2-48 Y 29.24 21.14 20.66 C N 15" CMP 28 1.71% 120A 34 MH 130A 2-48 Y 28.56 21.56 21.24 C N 15" CMP 112 0.29% 125A 35 MH 135A 2-36 Y 27.91 22 21.56 C N 15" CMP 180 0.24% 130A 36 MH 140A 2-48 Y 28.16 21.96 21.86 C N_ 15" CMP 289 0.03% 135A 37 CB 145A 16.F4-12 1 _ Y 28.73 22.98 21.96 C N 1 12" C 145 0.70% 140A 38 MH 150A 16.F4-1 2-36 Y 29.9 23.4 23.03 C N 12" C 123 - 0.30% 145A 39 NOTES (1)Sediment observed in pipes. (2)Elevation Datum NAVD 88. TABLE I (cont.) SW 7th Street, Hardie Avenue, Lake Avenue Drainage Investigation EXISTING DRAINAGE SYSTEM INVENTORY RESULTS SYSTEM: SHATTUCK AVENUE RWB DWN BW Struc. RWB CITY GRATE INLET OUTLET GRATE CAN PIPE PIPE SLOPE STREAM Pipe# TYPE Ref. INDEX # TYPE CB ? Elev IE IE TYPE SEP. DIAM. TYPE LENGTH (%) STRUCT (ft) (ft) (ft) (ft) MH SH1 16.F8-1 2-48 Y 24.49 118.9 9.19 18.4,5 C N 24" CMP 481 0.15% 115 MH SH5 16.F8-19AB 2-48 Y 24.1 8.95 19.19 C N 12" PVC 11 -2.18% SH1 MH SH5(1 16.F8-19AB 2-48_ Y 24.1 18.29 C N 24" CLAY 578 0.11% 32_0_ MH SH10 16.F8-5 2-36 Y 25.12 19.79 18.95 C N 12" C 224 0.38% SH5 24 MH SH15 _ 16.F8-8 2-48 Y _25.92 19.72 19.82 C N 12" C 217 -0.05% SH10 25 MH SH2O_ 16.F8-7 2-48 Y 25.63 20.08 19.82 C N 12" C 22 1.18% SH15 26 MH SH25_ 16.F8-3 2-48 Y 25.61 20.11 20.08 C N 12" C 13 0.23% SH2O 27 MH SH30 - 2-48 N 25.88. 21.08 20.11 C N _ 12" C 19 5.11% SH25 28 MH SH35 - 2-48 N 26.92 24.12 (3) C N 12" C - - - MH SH40_ 16.F7-17 2-42 N 27.41 20.72 20.86 C N 12" C 167 _ -0.08% SH45 MH SH45 16.F7-2 2-42 N 27.61 20.76 16.8 C N 12" C 117 3.38% SH50 MH SH50 16.F7-3AB 248 N 28.3 16.8 (4) C N 24" - C - - Rainier Ave._ MH SH55 1617-1 2-48 N 29.56 21.56 20.2 C N 12" C 445 0.31% SH50 MH SH60 16.F6-6 2-48 N 29.61 21.61 21.56 C N 12" C 10 0.50% SH55 NOTES (1) 2nd outlet to west, 7th Avenue parallel system (2) Elevation Datum NAVD 88. (3) Does not appear to be connected to the main drainage system. (4) Connected to Rainier Avenue drainage system. L TABLE 2 Summary Results of HydrologiclHydraulic Analysis South Renton Sub-basins SYSTEM: SW7TH,GRADY,MAIN BW BW BW BW Capacity Capacity Capacity y Future Land Use Peak Flows(cfs) Pipe# GRATE INLET OUTLET PIPE PIPE SLOPE Rim Elev Rim Elev+0.4 Rim Elev-0.5 /V; 2-yr 10-yr 25-yr 100-yr (1) ELEV IE IE DIAM. TYPE LENGTH (%) (2) (2) (2) (4) (ft) (ft) (ft) (ft) (cfs) (cfs) (cfs) (cfs) 1 20.38 10.13 10.28 95x67' CMP 35 -0.43% >300 375 346 i 02 122 165 186 213 2 20.95 11 10.13 60' C 215 0.40% 255 263 248.2 93 111 150 169 194 3 21.27 11.57 11 60' C 92 0.62% 228 234 222.7 93 111 150 169 194 4 20.67 12.08 11.57 60' C 318 0.16% 171 176 165 93 111 150 169 194 5 21.22 12.72 12.08 60' C 396 0.16% 150 151 142 86 103 138 155 179 6 21.24 12.82 12.72 60' C 344 0.03% 135 139 130 86 103 138 155 179 7 21.88 12.63 12.82 60' C 128 -0.15% 135 139 131 86 103 138 155 179 8 22.46 12.81 12.63 60' C 472 0.04% 127 131 124 86 103 138 155 179 9 22.52 13.07 12.81 60' C 607 0.04% 115 119.5 112.5 86 103 138 155 179 10 22.61 13.11 13.07 60' C 56 0.07% 108 110 103.5 80 96 130 146 167 11 22.87 13.37 13.11 60' C 654 0.04% 102 106 99 80 96 130 146 167 12 23.87 13.77 13.37 54' C 312 0.13% 99 101 95.5 80 96 130 146 167 - 13 24.52 14.02 13.97 36' C 223 0.02% 30 30.5 29 25 30 40 45 52 14 24.62 15.72 15.02 24' C 14 5.00% 27 27.5 26 25 30 40 45 52 15 25.72 16.42 15.52 24' C 311 0.29% 21 21.3 20.5 21 26 35 39 45 16 26.03 16.71 16.47 24' C 315 0.08% 18 19.3 18.5 21 26 35 39 45 fu 17 25.43 16.73 16.93 24' C 167 -0.12% 17 17.6 16.5 21 26 35 39 45 Gnp� 18 25.29 16.69 16.78 24' CMP 18 -0.50% 15 15.5 14.8 20 24 32 37 42 19 25.2 15.45 14.59 48' CMP 123 0.70% 15 15.4 14.6 20 24 32 37 42 20' 25.03 16.03 15.4 48' CMP 215 0.29% 15 15.2 14.4 20 24 32 37 42 21' 25.02 17.27 17.28 30' CMP 14 -0.07% 15 15.2 14.4 20 24 32 37 42 22' 25.65 17.9 17.32 30' CMP 300 0.19% 14 14.2 13.7 19 22 30 34 39 23' 24.49 19.19 18.45 24' CMP 481 0.15% 10 10.6 10 16 19 26 29 34 24 25.46 20.36 19.34 24' CMP 243 0.42% 8 7.7 7.3 12 14 19 21 24 25 25.18 20.76 20.26 24' CMP 317 0.16% 6.5 7 6.7 12 14 19 21 24 26 27.33 21.33 20.78 24' CMP 506 0.11% 7.5 7.5 7.4 9 11 15 17 20 27 29.86 22.36 21.33 24' CMP 82 1.26% 15.5 15.5 15.5 9 11 15 17 20 28 28.51 23.37 23.06 24' CMP 42 0.74% 4.8 4.7 4.7 4 5 7 8 9 29 28.75 25.05 23.96 24' C 44 2.48% 6.6 6.1 6.2 4 5 7 8 9 30 30.31 25.46 25.05 24' C 161 0.25% >10 16.5 16.5 4 5 7 8 9 31 30.76 26 25.51 24' C 180 0.27% >10 14.7 14.4 4 5 7 8 9 32 29.91 26.61 26 24' C 40 1.53% 9.5 10.4 9.2 4 5 7 8 9 33 30.3 27.7 26.91 18' C 169 0.47% >4.5 5.1 1 4.9 2 2 3 1 4 4 34 32.12 27.92 27.75 12' C 69 0.25% >4.5 5.4 6.4 2 2 3 4 4 35 32.52 29.47 27.92 12' C 260 0.60% 3.4 3.3 3.3 2 2 3 4 4 36 35.78 31.78 29.42 12' C 284 0,83% 4 3.9 3.9 2 2 3 4 4 37 38.2 33.55 31.78 12' C 167 1.06% 4 4 4 2 2 3 4 4 38 40.02 34.82 33.7 18 C 30 3.73% >2 7 6 0.58 0.69 0.93 1.05 1.21 39 41.05 34.5 35.02 12' C 62 -0.84% >2 7 6 0.58 0.69 0.93 1.05 1.21 40 41.9 36.5 34.8 15' C 408 0.42% >2 5 4.5 0.58 0.69 0.93 1.05 1.21 Notes:(1) See Basin Map in Appendix A,Volume 1 Red-Leval of Protection(LOP)<January, 1990 (2) Backwater capacity Is based on various overtopping elevations,see text. Light Red=January, 1990<LOP<2-year =Parallel pipe system along this reach,. For pipe equivalent size diameter, Cyan-2-year<LOP<10-year refer to model output In Appendix C,Volume 1. Green- 10-year<LOP<25-year (3) Elevation datum NAVD 88. Magenta=25-year<LOP<100-year (4) January 1990 simulation reflects pipe restrictions that reduce peak flows. Blue-LOP>100-year If these restrictions are removed,flows would be higher. See Section 3 of Text. X1159121.734 11/19/98 R.W.Beck,Inc. TABLE 2(CONT.) Summary Results of Hydrologic/Hydraulic Analysis South Renton Sub-basins SYSTEMMARDIE/LAKE BW BW BW BW Capacit Capacity Capacity January, Future Land Use Peak Flov(cfs) Pipe# GRATE INLET OUTLET PIPE PIPE SLOPE Rim Elev Rim Elev+0.4 Rim Elev-0.5 991, 10-y' 100-yr (1) ELEV IE IE DAM. TYPE LENGTH (%) (2) (2) (2) (5) (ft) (ft) (ft) (ft) (cfs) (cfs) (cfs) 23.87 13.77 12.37 54" C 312 0.45% 13 25.79 14.69 13.82 48" CMP 229 0.38% 65 65 62.5 51 61 82 92 106 14 25.82 14.72 14.69 48" CMP 133 0.02% 59.5 61 58.5 51 61 82 92 106 15 27.33 15.33 14.72 48" CMP 315 0.19% 59.5 57.5 51 61 82 92 106 16 21.38 15.58 15.33 36"X60" CMP 328 0.08% 36 34.5 °>1 61 1 82 92 106 17 22.75 15.65 15.33 36"X60" CMP 187 0.17% 35 4 s3 40 53 60 69 18 23.65 15.96 15.85 36"X60" CMP 272 0.04% 33.5 31 s0 27 33 44 49 57 19 24.2 16 15.96 36"X60" CMP 100 0.04% 36.5 32.5 2.5 27 33 44 49 57 20 24.4 16.25 16.2 36"X60" CMP 199 0.03% 30 ')7 r, t7 24 28 38 43 49 21 25.54 16.49 16.25 36"X60" CMP 353 0.07% 30 24 28 38 43 49 22 27.35 16.75 16.54 36"X60" CMP 252 0.08% 42 41.5 41 24 28 38 43 49 23 30.37 16.87 16.75 36"X60" CMP 125 0.10% >56 63.5 63 24 28 38 43 49 24 31.14 17.14 16.77 24"X48" CMP 210 0.18% )0 36 35.5 22 27 36 40 47 25 30.07 17.37 17.39 24"X48" CMP 172 -0.01% 19.5 19.5 19.5 14 17 23 25 29 26 30.17 17.47 17.26 24"X48" CMP 154 0.14% 18.5 18.5 18.5 14 17 23 25 29 27 30.22 17.09 17.37 24"X48" CMP 38 -0.74% 19 18 18 14 17 23 25 29 28 30.25 18.25 17.22 24"X48" CMP 241 0.43% 16 15.5 16 13 15 20 23 26 29 30.09 18.64 18.25 24" C 46 0.85% 14 14 14 11 13 18 20 23 30 30.8 19 18.64 24" C 220 0.16% 14 14 13.5 13 18 20 23 31 30.34 18.79 19 24" C 309 -0.07% 12.5 12.5 12.5 13 18 2r 23 32 30.4 20.85 18.99 24" C 62 3.001% 11.5 11 11 12 16 20 33 29.31 20.86 20.85 18" C 81 0.01% 7.3 7 7 10 14 10 18 34 29.24 21.14 20.66 15" CMP 28 1.71% 6.7 6.5 6.5 9 10 14 16 18 35 28.56 21.56 21.24 15" CMP 112 0.29% 5.5 5.5 5 9 10 14 16 18 36 27.91 22 21.56 15" CMP 180 0.24% 4.3 4.5 4 9 10 14 16 18 37 28.16 21.96 21.86 15" CMP 289 0.03% 3 3 3 7 9 12 13 15 38 28.73 22.98 21.96 12" C 145 0.70% 2.2 2 2 4 5 7 8 9 39 29.9(4) 23.4 23.03 12" C 123 0.30% 1.6 1.7 1.5 4 5 7 8 9 Notes: (1) See Basin Map in Appendix A. Red= Level of Protection(LOP)<January, 1990 (2) Backwater capacity is based on various overtopping elevations,see text. uglrt Red= January, 1990<LOP<2-year (3) Elev Datum NAVD 88. Cyan=2-year<LOP<10-year (4) Rim of 27.9 was used to reflect low point along Tobin. Green= 10-year<LOP<25-year (5) January 1990 simulation reflects pipe restrictions that reduce peak flows. Magenta= 25-year<LOP< 100-year If these restrictions are removed,flows would be higher. See Section 3 of Text. Blue= LOP> 100-year X1159121.734 11/19/98 R.W. Beck,Inc. TABLE 2 (cont.) Summary Results of Hydrologic/Hydraulic Analysis South Renton Sub-basins SYSTEM: SHATTUCK BW BW BW BW Capacity Capacity Capacity Future Land Use Peak Flows(cfs) Pipe# GRATE INLET OUTLET PIPE PIPE SLOPE Rim Elev Rim Elev+0.4 Rim Elev-0.5 January 2-yr 10-yr 25-yr 100-yr (1) IE IE IE DIAM. TYPE LENGTH (%) (2) (2) (2) 1990 (cfs) (cfs) (cfs) (4) 24 25.12 19.79 18.95 12' C 224 0.38% 2.7 2.7 2.6 4 5 7 8 9 25 25.92 19.72 19.82 12' C 217 -0.050/0 2.7 2.7 2.5 4 5 7 8 9 26 25.63 20.08 19.82 12' C 22 1.18% 2.3 2.3 2.2 4 5 6 7 8 27 25.61 20.11 20.08 12' C 13 0.23% 2.2 2.3 2.2 4 5 6 7 8 28 25.88 21.08 20.11 12' C 19 5.11% 2.2 2.3 2.2 4 5 6 7 8 Notes: (1) See Basin Map in Appendix A. Red= Level of Protection (LOP)<January, 1990 (2) Backwater capacity is based on various overtopping elevations,see text. Light Red= January, 1990 <LOP<2-year (3) Elev Datum NAVD 88. Cyan= 2-year<LOP< 10-year (4) January 1990 simulation reflects pipe restrictions that reduce peak flows. Green= 10-year<LOP<25-year If these restrictions are removed,flows would be higher. See Section 3 of Magenta= 25-year<LOP< 100-year Blue= LOP> 100-year X 1159121,734 11/19/98 R.W. Beck,Inc. TABLE 3 Summary Results of Hydrologic/Hydraulic Analysis WEST HILL BASINS SYSTEM: BLACK RIVER BOX Equiva- Exist. Existin System Alt. Including Diversion From Lake Ave lent Orig. BW BW Existingand Use Peak Flows(cfs Future Land Use Peak Flows(cfs) BW Future Land Use Peak Flows(cfs) Grate PIPE PIPE Pipe# Capacity 10-yr 100-yr 10-yr 100-yr Capacity 2-yr 10-yr 100-yr Elev. DIAM. TYPE (2) (1) (ft) (cfs) (cfs) 21.78 82' C 1 300 104 187 237 288 115 201 252 304 300 118 207 259 312 23.48 82' C 2 320 104 187 237 288 115 201 252 304 320 118 207 259 312 32.08 82" C 3 400 104 187 237 288 115 201 252 304 400 118 207 259 312 23.08 82' C 4 260 104 187 237 288 115 201 252 304 260 118 207 259 312 26.18 77' C 5 215 93 167 210 255 101 177 222 267 215 105 183 229 275 29.48 60' C 6 145 68 126 160 196 75 135 170 206 145 78 140 176 213 32.08 60' C 7 155 63 118 150 183 ,^ 126 159 192 149 75 133 168 203 30.4 24" C 8 - - - - - - - - - i.v 6 9 11 12 27.9 24" C 9 - I - I - I - I - - - - - 6.5 z 9 '' 12 Notes: (1) Existing capacity based on existing land use flows and grate elevation Red= Level of Protection (LOP) <2-year as overtopping elevation. Cyan= 2-year<LOP< 10-year (2) BW Pipe#8&9 are for Lake Ave. S. Alternatives 2 and 4. Green= 10-year<LOP<25-year (3) Elevation Datum NAVD 88. Magenta= 25-year< LOP< 100-year Blue= LOP> 100-year XI159121.734 11/19/98 R. W. Beck, Inc. TABLE 4 Summary Results of HydrologictHydraulic Analysis ALTERNATIVE ANALYSIS SYSTEM: SW7TH,GRADY,MAIN Aft. 1 Alt.2(4) Alt.3(5) Alt.4(6) AR.2 3 8r4(2) Exist. Alt. 1 Alt.3 Alternative 1 and 3 Alt.2 Alt 4 Alternative 2 and 4 Pipe Pipe Pipe Pipe Frop. Prop. Orig. Orig. BW BW BW BW Future Land Use Peak Rows((cfs) BW BW Future Land Use Peak Flows(cfs) Replac. Replan Replac. Replac. Inlet Outlet Grate PIPE PIPE Pipe# Capacity Capacity Capacity -yr 10-yr 25-yr 100-yr Capacity Capacity lU-yl - 100-yr DIAM.(1) DIAM.(1) DIAM.(1) DIAM.(1) IE IE ELEV DIAM. TYPE (2) Exlst.lE's Prop.IE's Prop.IE's Prop.IE's (ff (ff) ff cfs (cfs) (cfs) (cfs) cfs 10.13 10.28 20.38 95x67' CMP 1 >300 >300 22 I ot, 186 213 >300 117 158 204 11.00 10.13 20.95 60' C 2 255 255 111 150 169 194 255 106 143 160 184 11.57 11.00 21.27 60' C 3 228 228 111 150 169 194 228 106 143 160 184 12.08 11.57 20.67 60' C 4 171 171 111 150 169 194 171 106 143 160 184 12.72 12.08 21.22 60' C 5 150 150 260 103 138 155 179 148 250 97 131 147 169 12.82 12.72 21.24 60' C 6 135 135 196 103 138 155 179 136 186 97 131 147 169 12.63 12.82 21.88 1 60' C 7 135 135 175 103 138 155 179 140 176 97 131 147 169 12.81 1 12.63 22.46 1 60' f C 8 127 127 155 103 138 155 179 129 155 97 131 147 169 13.07 12.81 22.52 60' C 9 115 115 131 103 138 155 179 116 131 97 131 147 169 Parallel 60' 13.11 13.07 22.61 60' C 10 108 110 1 121 96 130 146 167 108 121 91 122 137 158 Parallel 60' 13.37 13.11 22.87 60' C 11 102 I10 107 96 1 130 146 1 167 100 107 1 91 122 137 158 Parallel 60' 72' 72' 72' 13.77 13.37 23.87 54' C 12 99 118 117 96 130 146 167 108 117 91 122 137 158 60' 60- 60' 60' 13.99 13.77 24.52 36' C 13 30 39 40 30 40 45 52 38.5 43 30 41 46 52 60' 60' 60' W. 14.01 13.99 24.62 24' C 14 27 39 41 30 40 45 52 38.5 43 30 41 46 52 64' 60' 60' 60' 14.32 14.01 1 25.72 24' C 15 21 48 50 26 35 39 45 48 53 26 35 39 45 64' 60' 60' 60' 14.63 14.32 26.03 24' C 16 18 50 52.5 26 35 39 45 50 65.5 26 35 39 45 64' 60' 60' 60' 14.80 14.63 25.43 24' C 17 17 38 42.5 26 35 39 45 39.5 42.5 26 35 39 45 64' 60' 60' 60' 14.82 14.80 25.29 24- CMP 18 1 15 33 37 24 32 37 42 36.5 38 24 33 37 42 54' 42' 42' 42' 16.68 14.82 25.2 48' CMP 19 15 31.6 35 24 32 37 42 32.5 35 24 33 37 42 48' 42' 42' 42' 16.32 15." 25.03 48' CMP 20 15 31.5 32.5 24 32 37 42 30.5 33 24 33 37 42 48' 42' 42' 42' 16.42 16.32 25.02 30' CMP 21 15 31.5 32.5 24 1 32 37 1 42 30.5 32.5 24 33 37 42 48' 42' 42' 42' 17.62 16.42 25.65 30' CMP 22 14 35 32.5 22 30 34 39 31 33.6 23 30 34 39 48' 42' 42' 42' 18.68 17.62 24.49 24' CMP 23. 10 23.5 22.5 19 26 29 34 21.5 23 19 26 29 34 j 10 36' 42' 1 42- 42' 19.07 18.58 25.46 24' CMP 24 8 23 26 14 19 21 24 25 26 14 19 21 25 ?S 36' 42' 42' 42' 19.70 19.07 25.18 24' CMP 25 6.5 18 20.5 14 19 21 24 19 20.5 14 19 21 25 yro 36' 36' 36' 36' 21.73 19.70 27.33 24' CMP 26 1 7.5 >28 32 11 15 17 20 >29 32 11 15 17 20 .27 U. U. M. 22.30 21.73 29.86 24' CMP 27 15.6 22 >34 11 15 17 20 >29 >36 11 15 17 20 a 36' 36' 36' 22.47 22.30 28.51 24' CMP 28 4.8 8 16 5 7 8 9 >14 16 5 7 8 9 ? + 26.05 23.96 28.75 24' C 29 6.6 9 15.5 5 7 1 8 9 >14 15.6 5 7 8 9 3• 25.46 25.05 30.31 24' C 30 >10 >13 >16 5 7 8 9 >14 >17 5 7 8 9 3 1 26.00 25.51 30.76 24' C 31 >10 >13 >16 5 7 8 9 >14 16 5 7 8 9 26.61 1 26.00 29.91 1 24' C 32 9.5 10 13.6 5 7 - 8 9 >14 13.5 5 1 7 8 9 27.70 26.91 30.3 18' C 33 >4.5 5 6.3 2 3 4 4 6.3 6.3 3 3 4 4 27.92 27.75 32.12 12' 1 C 34 >4.5 5.5 6 2 3 4 4 6.1 6.1 3 3 4 4 29.47 27.92 32.52 12' C 35 3.4 3.5 3.8 2 34 4 3.8 3.8 3 3 4 4 31.78 29.42 35.78 12' C 36 4 4 4 2 3 4 4 4 14 3 3 4 4 33.55 31.78 38.2 17 C 37 4 4 4 2 3 4 4 4 4 3 3 4 4 34.82 33.70 40.02 18 C 38 >2 >2 >2 0.69 0.93 1.05 1.21 >2 >2 0.72 0.97 1.09 1.25 34.50 35.(Q 41.05 IT C 39 >2 >2 >2 0.69 0.93 1.05 1.21 >2 >2 0.72 0.97 1.09 1.25 36.50 34.80 41,9 15' C 40 >2 >2 >2 094 1.21 >2 >2 O32 1 0.97 1.09 1,25 Notes:(1) All Pipe replacements are assumed to be'N12'pipe type(conc.for modeling purposes) Level of Protection(LOP)<January,1990 (2) Assumed Invert elevations for Alternatives 2,3,&4. Alternative 1 assume existing Invert elevations. Junuury, I99u<LOP<2-year (3) Existing capacity based on grate elevation as overtopping elevation. 2-year<LOP<10-year (4)Includes Lake Street Diversion to Airport(Black River)Box Culvert. 10-year<LOP<>25-year (5)Includes Diversion to Springbrook Creek 25-year<LOP<100-year (6)Includes Both Diversions of Aft.2&Alt.3 Blue= LOP> 100-year (7)Elevation Datum NAVD 88. X1159121.734 11/19/98 R.W.Beck,Inc. TABLE 4(cont.) Summary Results of Hydrologic/Hydraulic Analysis ALTERNATIVE ANALYSIS SYSTEM: HARDIE/LAKE AVENUE Exist. Alt.1 AB.3 Alternative 1 and 3 Alt.2 AR.4 Alternative 2 and 4 All.1 Alt.2(3) Alt.3(4) Alf.4(5) GRATE Orig. Orig. BW BW BW BW Future Land Use Peak Flows(cfs) BW BW Future Land Use Peak Flows(cfs) Pipe Replac. Pipe Replan ripe Replac. Pope Replan ELEV PIPE PIPE Pipe# Capacity Capacity Capacity 10-yr 25-yr 100-yr Capacity Capacity 10 yr 100-yr DIAM.(1) DIAM.(1) DIAM.(1) DIAM.(1) (ft) DIAM. TYPE (2) ExlAlli's ExIst.IE's ExId.lE's 6dsHE's (cfs) (cfs) (cfs) 72" 72" 72" 23.87 54' C 12 Parallel 72' 25.79 48' CMP 13 65 104.5 71 61 82 92 106 66 71 55 75 84 97 Parallel 72" 25.82 48' CMP 14 69.6 99.5 65 61 82 92 106 60 65 55 75 84 97 Parallel 72" 27.33 15 59.6 124.6 63 61 82 92 106 60 61 55 75 84 97 Parallel 72" 21.38 36'X60' CMP 16 36 59 44 61 82 92 106 43 44 55 75 84 97 22.75 36"X60" CMP 17 35 45 30.6 43 57 64 74 28 29.6 37 50 57 65 23.65 36"X60' CMP 18 33.5 37.5 24.5 36 48 54 62 23 24 30 41 46 53 24.2 36"X60' CMP 19 36.5 38 31 36 48 54 62 28 28 30 41 46 63 24.4 36'X60' CMP 20 30 32 25.5 31 42 47 65 22 24 26 36 39 45 25.54 36'X60' CMP 21 32 34 30 31 42 47 65 28 29.6 26 35 39 45 27.35 36'X60' CMP 22 42 43.6 42 31 42 47 55 _ 41 42 26 36 39 46 30.37 36'X60' CMP 23 >66 64 63.6 31 42 47 SS 64 64 26 35 39 45 48" 31.14 24"X48' CMP 24 36 62.6 36.6 30 40 45 52 36 36 24 33 37 43 48" 30.07 24'X48' CMP 25 19.6 _ 34 19.6 20 27 30 34 17.6 17.5 14 20 22 26 48' 30.17 24'X48" CMP 26 18.6 33.5 18.6 20 27 30 34 17 17 14 20 22 25 48" 30.22 24'X48" CMP 27 19 33.6 19 20 27 30 34 _ 17 17 14 20 22 25 48" 30.25 24"X48" CMP 28 16 30 16 18 24 27 31 14 14 13 17 19 22 48' 48' 48" 30.09 24' C 29 14 26 14 16 22 25 29 _ 11.5 12 11 15 17 19 48" 48" 48' 30.8 24' C 30 14 33.6 24 16 22 25 1 29 12 21.5 11 15 17 19 48" 48' 48" 30.34 24" C 31 12.5 26.5 16 16 22 25 29 11 13.6 11 15 17 19 48' 48' 48" 30.4 24' C 32 11.6 24 15.5 14 20 22 25 9 12.6 9 12 14 16 36' M. 36" 29.31 18" C 33 7.3 14 8.4 10 14 16 18 _ 4.5 5.1 5 7 8 9 36' 36' 36' 29.24 15' CMP 34 6.7 14 8.9 10 14 16 18 _ 4.5 S.2 5 7 8 9 36' 36' 36" 28.56 15' CMP 35 5.5 13 7.8 10 14 16 18 3.7 4.8 5 7 8 9 24' 24' 24" 27.91 15' CMP 36 4.3 11 7.1 10 14 16 18 3.3 4.5 5 7 8 9 24" 24' 24' 28.16 �15' CCMP 37 3 9 6.4 9 12 13 15 2.2 4.3 3 5 S 6 24" 24' 24' 28.73 38 2.2 8.5 7.4 5 7 8 9is" 18" 18' 29.9(6) 39 1 1.6 5 3.5 5 7 8 9 Notes:(1)AN Pipe replacements are assumed to be'N12'pipe type(cons.for modeling purposes) Red=Level of Protection(LOP)<2-year (2) Existing capacity based on grate elevation as overtopping elevation. Cyan=2-year<LOP<10-year (3)Includes Lake Street Diversion to Airport(Black River)Box Culvert.Also,create a pressure system on Hardie at the RR X-ing. Green=10-year<LOP<25-year (4)Includes Diversion of downstream SW 7th system to Springbrook Creek. Also,create a pressure system on Hardie at the RR X-ing. Magenta=25-year<LOP<100-year (5)Includes Both Diversions of Alt.2&Alt.3. Also,create a pressure system on Hardie at the RR X-ing. Blue-LOP>100-year (6)The grate elevation of the low point along Tobin(27.90)was substituted for the grate elevation of the Reach 39 catch basin to reflect the controling elevation. (7)Elev Datum NAVD 88. X 1159121.734 11/19/98 R.W.Beck,Inc. TABLE 4 (cont.) Summary Results of Hydrologic/Hydraulic Analysis ALTERNATIVE PIPE REPLACEMENT ANALYSIS SYSTEM: SHATTUCK Exist. Alt. 1 Alt. 1 (3) Orig. Orig. BW BW BW Alternative 1 Pipe Replac. GRATE PIPE PIPE Pipe# Capacity Capacity Future Land Use Peak Flows(cfs) DIAM.(1) ELEV DIAM. TYPE (2) 11lUt11 y 2-yr 10-yr 25-yr 100-yr EXIsLIE's (ft) (cfs) (cfs) 1990 18" 25.12 12" C 24 2.7 5.7 4 5 7 8 9 18" 25.92 12" C 25 2.7 6 4 5 7 8 9 18" 25.63 12" C 26 2.3 5 4 5 6 7 8 18" 25.61 12" C 27 2.2 5 4 5 6 7( : 8 18" 25.88 12" C 28 2.2 5.3 4 5 6 7 8 Notes; (1) All Pipe replacements are assumed to be"N12"pipe type(conc.for modeling I Red= Level of Protection(LOP)<January, 1990 (2) Existing capacity based on grate elevation as overtopping elevation. Light Red= January, 1990<LOP<2-year (3)Downstream parameters are the some as Alternative 2 of SW 7th. Cyan= 2-year<LOP< 10-year (4) Elev Datum NAVD 88. Green= 10-year<LOP<25-year Magenta= 25-year<LOP< 100-year Blue= LOP> 100-year X1159121.734 11/19/98 R.W. Beck,Inc. ALTERNATIVE EVALUATION AND SELECTION OF PREFERRED ALTERNATIVES TABLE 5 ALTERNATIVE EVALUATION— SW 7T" STREET ALTERNATIVES Criteria No Action Alternative 1 Alternative 2 Alternative 3 Alternative 4 Effectiveness in Flooding problems will worsen Approximate Level of Same as Alternative 1 Same as Alternative 1 Approximate LOP is given in Solving Flooding if no action is taken Protection(LOP)is given in Table 4;somewhat greater Table 4;capacity downstream LOP than other alternatives of flooding problem would be doubled. However,portions of system would have between 2-yr.and 10-year LOP(future land use condition) Feasibility and Not Applicable Difficulty with busy streets, Makes use of existing 48-in. Makes use of existing 48-in. Makes use of existing 48-in. Cons tructabili ty particularly between Hardie pipe between Hardie Avenue pipe between Hardie Avenue pipe between Hardie Avenue Avenue SW and Rainier SW and Rainier Avenue S: SW and Rainier Avenue S: SW and Rainier Avenue S: Avenue S;could be phased could be phased could be phased could be phased Compatibility with Increased flows to BRPS Same As Alternative 1 Same As Alternative 1 Same As Alternative 1 Downstream Drainage forebay would be insignificant. System Increased downstream flows could negatively impact Hardie Avenue SW problem if no Hardie Avenue SW improvements are implemented Cost $1,9000,000 $1,6000,000 $2,000,000 $2,000,000 Environmental Current flooding is a water Environmental impacts are Same as Alternative 1 Same as Alternative 1;Impacts Same as Alternative 3 Considerations quality concern short-term related to to Springbrook Creek from construction and considered second outfall considered minor minor Advantages No construction cost Greatest level of protection particularly in downstream section of SW 7°i Street Disadvantages Flooding will worsen as area Greatest transportation continues to develop impact X1159121.734 11/19/98 R. W Beck, Inc. TABLE 5 (CONTINUED) ALTERNATIVE EVALUATION— HARDIE AVENUE SW ALTERNATIVES Criteria No Action Alternative 1 Alternative 2 Alternative 3 Alternative 4 Effectiveness in Flooding problems will Approximate LOP is given in Approximate LOP is given in Same as Alternative 2 Same as Alternative 2. Solving Flooding worsen if no action is taken. Table 4;capacity Table 4;minor increase in downstream of flooding capacity just at problem area problem would be but less LOP upstream of significantly increased to just problem area shy of the 2-yr LOP(future land use condition) Feasibility and Not Applicable Largest construction scope: Least extensive Same As Alternative 2 Same As Alternative 2 Constructability update of easements on improvements;however, private property probably requires pump station and required associated long-term opera tion/maintenance Compatibility with Based on loss of current Same As Alternative 1 Same As Alternative 1 Same As Alternative I Downstream flood storage;increase in Drainage System flows to BRPS forebay would be insignificant Cost $450,000 $280,000 $280,000 $280,000 Environmental Current flooding is a water Environmental impacts are Same as Alternative 1 Same as Alternative 1; Same as Alternative 3 Considerations quality concern short term related to impacts to Springbrook construction and considered Creek from second outfall minor considered minor Advantages No construction cost Does not require pump station;provides greatest level of protection;if Lake Avenue S Alternative 2 or 4 is implemented,level of protection would be even higher than shown on Table 4 Disadvantages Flooding will worsen as area Requires private property Long-term operation and Same as Alternative 2;also Same as Alternative 2 continues to develop approvals;greatest cost maintenance associated with lowest level of protection pump station;requires emergency power outage provisions;decreases upstream capacity X1159121.734 11/19/98 R. W. Beck, Inc. TABLE 5 (CONTINUED) ALTERNATIVE EVALUATION— LAKE AVENUE S ALTERNATIVES Criteria No Action Alternative 1 Alternative 2 Alternative 3 Alternative 4 Effectiveness in Flooding would continue and Approximate LOP is given in Approximate LOP is given in Approximate LOP is given in Approximate LOP is given in Solving Flooding become worse as area Table 4;would provide 2-yr Table 4;would provide 2-yr Table 4;would double capacity Table 4;would provide 2-yr continues to develop LOP(future land use LOP for S Tobin Sheet;would at problem area,but would be LOP condition) provide just shy of 2-yr LOP less than 2-yr LOP for Lake Avenue S Feasibility and Not Applicable Extensive improvements; Least extensive improvements Requires some construction Requires some construction Constructability requires new crossing of along private property north along private property north Rainier Avenue;also requires of S Third Street of S Third Street some construction along private property north of S Third Street Compatibility with Not Applicable Would increase downstream Would increase flows to Black Would increase downstream Same as Alternative 2 Downstream Drainage flows to Hardie Avenue SW River box;however,10-year, flows to Hardie Avenue SW System problem LOP would be maintained in problem Black River box;would decrease flows to Hardie Avenue SW Cost No Cost $1,000,000 $320,000 $734,000 $1,100,000 Environmental Current flooding is a water Environmental impacts are Same as Alternative 1 Same as Alternative 1 Same as Alternative I Considerations quality concern short term related to r construction and considered minor Advantages Greatest LOP for Lake Avenue Lowest cost while large Does not require diversion to Large increase in LOP; S;does not require diversion improvement in capacity: another basin;includes reduction in flows to Hardie to another basin;includes reduces downstream flows to replacement of system in poor Avenue SW system replacement of system in poor Hardie Avenue SW condition condition Disadvantages Flooding Continues Requires crossing of Rainier Does not address poor Does not provide a 2-yr LOP High cost Avenue;high cost condition of Lake Avenue S system X1159121.734 11/19/98 R. W. Beck, Inc. i � � �i' IlFcr t City of Renton Catch Basin/Manhole Inventory Form Date: Personnel: Weather: _dry;_wet;_very wet Reference Number: Type:_Type-1 CB; _Type -2 (48")CB; _Type-2 (48'� MH;_Type-2 (54'D CB; Type-2(54'�MH; Type-2 (give size/type "/_CB_MH);_Inlet; _other (describe) _cannot determine Grate Type: standard grate;_vein grate; _through curb inlet; _solid rectangular; _solid round;_solid round locking; _other(describe) Downstream CB/MH Reference No.: ; Pipe length to downstream CB/MH: ft CB/MH Location: feet from feet from CB/MH Condition:_good;_fair;_poor (describe defects) Infiltration Observed: yes; no: Measure down to top of seepage; feet Pipe No. 1: (generally outlet pipe) Size: (in); Material Type:_CP;_CMP;_other : Measure Down: invert;(if can't get invert, get the following: standing water; pipe crown): Other comments; Pipe No. 2:_inflow:_outflow: Size: (in); Material Type:_CP;_CMP;_other : Measure Down: invert;(if can't get invert, get the following: standing water; pipe crown): Other comments; Pipe No. 3:_inflow:_outflow: Size: (in); Material Type:_CP;_CMP;_other : Measure Down: invert;(if can't get invert, get the following: standing water; pipe crown): Other comments; Pipe No. 4:_inflow:_outflow: Size: (in); Material Type:_CP;_CMP;_other : Measure Down: invert;(if can't get invert, get the following: standing water; pipe crown): Other comments; Pipe No. 5:_inflow:_outflow: Size: (in); Material Type:_CP;_CMP;_other : Measure Down: invert;(if can't get invert, get the following: standing water; pipe crown): Other comments; Pipe No. 6: _inflow:_outflow: Size: (in); Material Type:_CP;_CMF-_other : Measure Down: invert;(if can't get invert, get the following: } standing water; pipe crown): Other comments; o F- z Other comments/ Sketch structure and label pipes: j _z W C7 Q Z Q N 0 W M O O H L F•' 41"� •' ..r.. IN Z TrJ Ala io � .-• .. \ ! ate' `�- txs ��.. 35 .... --- 1. 1754 34 a�sax sas,cam sea, F� ." ..• 105A \i? 29 toot. ._) [i E 26 `.i \.!: f\: :/'• < Sea f' \;. �� •�' 7% 26 27 43 +'y j}•, ��: 'J ._ 1.t '? 1 . 3 42 22 y�5 g� .. r 5e a AY 2120 \ Cat 19 Q \iI i• SKIS .— 0 � .-....._..._.... \ { .M iLF3 m�Q" LaPdt�W'�� ".:�y. 75 17 16 SOB Qffi.9)�25a' .. t05 10 57 15 5nt i 4 t..� •�... +y t3 v7( { 3 O 35 \.Z'•i r r k �\a 305 tea` p j•; ` 71a 3 6 9 40 t0 4. tt eo 12 a5 13 a0 70 t 71i a00 >t t i ro A 911 °° M56 7 ' 14 a 273 32 >is taro aam altm 23 Q 26 m •'t( 63 e18 19� L21 22 f�88 29 30 t1 .mx¢o'Fa»us. sxce r&¢s mtt aum (;i ( 600 0 600 1200 w> ��.. — LEGEND 1" — 600' BW PIPE NO. 1 (D SW 7TH ST SYS A > , FIGURE 1 a CITY OF RENTON >' BW PIPE 1SYS :;'s•v; r a 13 c�,: ; a �,:• . SW 7th ST. / HARDIE AVE. SW / — ¢' ,Y ::jam LAKE AVE. S DRAINAGE BW PIPE N0. 24 ^I . ' i' :(;I :'; a INVESTIGATION SHATTUCK AVE SYS SOUTH RENTON BASIN MAP % + RWB MH N0. 1 BASIN BOUNDARY .............. .......... .................. ....... LAKE �: is :� .. _....__...._._..__ .. ............. ------.......... L........ t .................. :7-1 .......... r -J .................. r 4 .......... .. ........ :w J b, F- 41Y L 400 0 400 FL- ................ 800 A L e C7 E t-,l L A C-W, X-1 0 15a:'Y' Co SUe>-'&AC,1 -J 13904A10.3-1 4WD WS .............. '3LkF> NJ N Wi .444 AREA THAT CAN BE DIVERTED TO BLACK RIVER BOX UNDER LAKE AVE.ALTERNATIVES 2 AND 4 61 'Fe ... ........-................ .......... ........... .......... ...... ... ------. .. ...... ......\'.I Fill FIGURE 3 U CITY OF RENTON SW 7th ST HARDIE AVE SW .......... LAKE AVE S DRAINAGE ................ ----------- INVESTIGATION L U WEST HILL BASIN MAP Source of Basin Boundary is Lake Waslihig-ton Pollution ZZ., Abatement Project(Herrera Environmental Consultants,1994) tips .............. 6 L ...... A r por L 0 nd at (,' T�D L it LAKE AVE S LT 2 AND 4 1 f _.. _AREA TO BE J / DIVERTED t > �0 125A q�, L Jo/./ -f f4j Lj, 27 2a • 7110h f 29 30 rJ 4 Dj S\ 25 7�, 'Z 7z 4 7- __1 _ti 2� p F 3 A ' 11 I __ j ALTERNATIVE E, LEGEND it I L FOREBA ALTERNATIVE, 1'\ L I Y a — ALTERNATIVE\1, 15A !!j tl Ji ' p�p !: /^ t I ? f X.j - ALTERNATIVE 3 tp-,. ALTERNATIVE 4 < 20 HARDIE AVE S _41 CREATE PRESSURE\ ALT 2, 3, AND 4 (SEE TEXT FOR ALTERNATIVE 'S k 4 lot , la SYSTEM AND 40 CONSTRUCT PUMP" f Q STATION -————-————- �l i' ' i 3 (r` j if � t t! I �f I � ae - 17 505 r lo 15 WIA VV 41, 14 131 215 33 46 70 76.) 210 L 32 2=225 o, 1z; w f !I .11"4io v �� r { i j � i— ) i r � , uz : 7 /� -/' \ 600 0 600 1200 LEGEND 600' CID BW PIPE NO. 1 c" (D L FIGURE 4 SW 7TH ST SYS CITY OF RENTON BW PIPE NO. 13 H SW 7th ST. / HARDIE AVE. SW T HARDIE/LAKE SYS LAKE AVE. S DRAINAGE BW PIPE NO. 24 INVESTIGATION SHATTUCK AVE SYS ALTERNATIVE SOLUTIONS RWB MH NO. 1 BASIN BOUNDARY ti 1 1 1 1 1 � inn liFi ii 1 REFERENCES REFERENCES 1. Green River Basin Program. 1992. Green River Interlocal Agreement. Sponsors: King County; Cities of Auburn, Kent, Renton, and Tukwila. 2. Herrera Environmental Consultants. 1994. Lake Washington Pollution Abate- ment Project. City of Renton. 3. Northwest Hydraulic Consultants. 1995. East Side Green River Watershed Plan-Hydrologic Analysis, Draft. City of Renton. 4. R. W. Beck. 1996. East Side Green River Watershed Plan—Hydraulic Analysis. City of Renton. 5. Wilsey and Ham, Inc. 1969. Renton Municipal Airport, Storm Drainage, Black River Channel. City of Renton. X1159121.734 11/19/98