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Home My WebLink AboutRS_Appendix_D_Existing_Condition_Report_210420_v1 FINAL LOWER MADSEN CREEK EXISTING CONDITIONS FLOOD & SEDIMENT ASSESSMENT Prepared for: City of Renton Public Works Utility Systems -- Surface Water Utility Engineering 1055 South Grady Way Renton, WA 98057 Prepared by: 506 2nd Avenue, Suite 2700 Seattle, WA 98104 206-521-3000 March 20, 2019 March 2019 Madsen Creek Existing Conditions i ACKNOWLEDGEMENTS Watershed Science and Engineering would like to thank the following individuals for their assistance in providing information that was utilized in this investigation: Landowners • Aran Church, King County Housing Authority • Donna Cleveland, Property Manager Wonderland Estates • John Schommer, Landowner City of Renton • Ron Straka, P.E., Utility Systems Director • Joseph Farah, P.E., Surface Water Engineering Manager Technical Consul t ants • Watershed Science & Engineering o Jeff Johnson, P.E., Project Manager and Hydraulic Engineer o Larry Karpack, P.E., Hydrologist o Bob Elliot, P.E., Hydraulic Engineer o Kaleb Madsen, EIT, Jr. Hydraulic Engineer o Hannah Hampson, Hydraulic Engineer Intern • Herrera Environmental Consultants • Pacific Geomatic Services Project Funded B y • City of Renton • King County Flood Control District March 2019 Madsen Creek Existing Conditions ii CONTENTS Acknowledgements .......................................................................................... i Landowners ............................................................................................. i City of Renton .......................................................................................... i Technical Consultants ................................................................................. i Project Funded By ..................................................................................... i Executive Summary ........................................................................................ 1 1. Introduction ............................................................................................. 4 1.1. Special Notes.................................................................................... 4 2. Background ............................................................................................. 5 2.1. Watershed Geology, Development and Stormwater ....................................... 5 2.2. Flood Control Project Construction History ................................................ 7 2.2.1. Flood History ........................................................................ 10 2.2.1. Maintenance History ............................................................... 12 2.3. Existing Conditions Field Observations ..................................................... 14 2.3.1. Channel Characteristics by Sub-Reach .......................................... 14 3. Analysis ................................................................................................ 34 3.1. Hydrology ....................................................................................... 34 3.1.1. Hydrologic Setting ................................................................ 34 3.1.2. Hydrologic Model Development ................................................ 34 3.1.3. Hydrologic Model Calibration .................................................. 39 3.1.4. Hydrologic Model Application ..................................................... 40 3.2. Hydraulic Modeling ............................................................................ 46 3.2.1. Hydraulic Model Development .................................................... 46 3.3. Sediment Transport and Deposition ........................................................ 62 3.3.1. Sediment Deposition Locations ................................................... 62 3.3.2. Sediment Grainsize Characteristics .............................................. 74 3.3.3. Sediment Basin Performance and Basin Sediment Yield ....................... 84 4. Potential Solutions ................................................................................... 89 5. Conclusions ............................................................................................ 91 6. References ............................................................................................ 92 March 2019 Madsen Creek Existing Conditions iii TABLES 1. Construction History Madsen Creek Flood Control Project. 2. Summary of Significant Flood Events 3. Estimate of Sediment Removed from Sediment Basin and High Flow Bypass 4. Madsen Creek Sub-Reaches. 5. Annual Instantaneous Peak Flows Madsen Creek at Entrance to Sediment Basin 6. Sediment Sample Data. 7. Channel and Incipient Velocities for Stream Sediments by Sub-Reach 8. Sediment pond capture efficiency calculation based on known or estimated volumes of sediment deposition between 1991 and 2018. F IGURES 1. Madsen Creek Drainage Basin & Project Location Map 2. Madsen Creek Sub-Reaches 3. Madsen Creek HSPF Sub-Basins 4. Madsen Creek Watershed Land Cover 5. Madsen Creek Watershed Soils 6. Comparison of HSPF Simulated verses Observed Flows for Water Year 2011 7. Comparison of HSPF Simulated verses Observed Flows for Water Year 2015 8. Flood Frequency Curves Generated from Gage and HSPF Model Data for Period 1989 to 2018 9. Flood Frequency Curves Generated from Gage and HSPF Model Data for Period 2001 to 2018 10. Flood Frequency Curves Generated from Gage and HSPF Model Data for Period 2004 to 2018 11. Hydraulic Model Domain & Boundary Conditions 12. Manning’s n Values – Existing Conditions 13. Simulated Maximum Depths 16 February 2017 Flood Event – Existing Conditions 14. Simulated Maximum Depths 2-yr Flood Event -- Existing Conditions 15. Simulated Maximum Depths 25-yr Flood Event -- Existing Conditions 16. Simulated Maximum Depths 100-yr Flood Event -- Existing Conditions 17. Cedar River Flood Depths > 10-year Event 18. Cedar River Flood Depths 50-year Event 19. Sediment Sample Locations & Bed Material Types 20. Profile Comparison 1974 to 2018 High Flow Bypass 21. Sediment Deposition Comparison Locations March 2019 Madsen Creek Existing Conditions iv 22. Upper High Flow Bypass Cross Section Comparison (1974 vs. 2018) 23. Lower High Flow Bypass Cross Section Comparison (1974 vs. 2018) 24. Profile Comparison 1989 to 2018 Madsen Creek Channel within Ron Regis Park 25. Park Channel Cross Section Comparison (1989 vs. 2018) 26. Grainsize Distribution Curves -- Upstream Channel and Sediment Basin 27. Grainsize Distribution Curves -- High Flow Bypass 28. Grainsize Distribution Curves -- Madsen Creek Channel Downstream from Sediment Basin 29. Simulated Maximum Velocity 2-year Flood Event -- Existing Conditions 30. Simulated Maximum Velocity 25-year Flood Event -- Existing Conditions 31. Simulated Maximum Velocity 100-year Flood Event -- Existing Conditions 32. Rate of Sediment Deposition in Sediment Basin for a Given Inflow 33. Fraction of Flow Exiting Sediment Basin Through the High Flow Bypass 34. Approximate Distribution of Sediment Delivered to and Existing the Sediment Basin March 2019 Madsen Creek Existing Conditions 1 EXECUTIVE S UMMARY The portion of Madsen Creek located within the Cedar River valley is commonly referred to as the lower Madsen Creek. Flooding problems within this reach have grown more frequent within the past decade and the City of Renton, in partnership with King County, desires to reduce or eliminate them. The City retained a consultant team led by Watershed Science and Engineering to conduct an investigation to determine what is causing the flooding and to identify feasible solutions. The project is split into two parts -- Phase 1 which is an investigation to identify the factors that are responsible for the flooding, and Phase 2 which will be completed in 2019, will identify and develop solutions. This report documents the results of the Phase 1 investigation. Flooding has been a problem along lower Madsen Creek for decades. In the 1970s and 1980s, rapid development within the watershed increased stormwater runoff to the stream which in turn increased flow rates and flooding along lower Madsen Creek. To reduce flooding, King County constructed a sediment basin to decrease deposition; and a high flow flood bypass channel to convey flood flows directly to the Cedar River. The system, which was designed in 1974, built in 1976, and improved in 1990, has performed well over the past 42 years; however, recent flooding events indicate that further improvements are needed. The Phase 1 existing condition assessment consisted of five technical tasks: 1) topographic survey of the stream channel and flood bypass, 2) wetland identification and mapping, 3) hydrologic HSPF modeling, 4) hydraulic HEC-RAS 2D modeling, and 5) a sediment transport and deposition investigation. Items 3 through 5 are the focus of this report. Item 2 is the subject of a separate companion report prepared by Herrera Environmental. The results of these investigations revealed that sediment deposition is the primary cause of the flooding due to reduced channel capacity along sections of both Madsen Creek and the high flow flood bypass. The sediment basin is performing well, estimated to capture roughly 50% of the sediment that is delivered to the lower Madsen Creek from the upstream watershed. Approximately, fifty-percent passes through the basin with 90% transported by the high flow bypass and 10% by Madsen Creek (under the current sediment basin outlet configuration in which the inlet to the Madsen Creek culvert is partly blocked by a metal plate). On average about 800 yd3 of sediment deposits in the basin annually, which means about 800 yd3 passes through the basin. Of this, approximately 720 yd3 exits via the high flow bypass and 80 yd3 via Madsen Creek. The reach of Madsen Creek most impacted by sediment deposition is located within Ron Regis Park, downstream from 149th Avenue SE. This portion of Madsen Creek was originally constructed in 1989. It was much larger than it is today and therefore, had the ability to convey much larger flows. Today it is only about 25% of its original size due to sediment deposition. Several residents and stakeholders have suggested that this is the primary cause of recent flooding issues along 149th Avenue SE and within a mobile the home community Wonderland Estates. This is partially true, but it must be recognized that the channel, as March 2019 Madsen Creek Existing Conditions 2 constructed in 1989, was not sustainable. The original channel was much too large to be maintained naturally by the flows carried by Madsen Creek and, therefore, it has effectively served as a sediment trap. A sustainable channel would have required either an active sediment management maintenance removal program or much larger flows. The size of the channel that exists today is much more in-line with what would naturally form given the flows that are actually carried by Madsen Creek. As a result, removing sediment from this section of the stream would only serve as a temporary solution and would require a sustained future sediment removal maintenance program. Additionally, sediment removal would require environmental permits, which may not be obtained due to the current habitat value of the reach. The investigation identified the specific locations where water leaves the channel network and floods adjacent developed properties. It also revealed that most of these flooding problems can be reduced or eliminated with maintenance actions or one-time improvement projects. Proposed solutions for each category are listed below in the order of relative importance as viewed by the consultant team: Recurring Maintenance Projects: 1. Restore the capacity of the high flow bypass and the SR169 culvert by removing accumulated sediment and developing an effective sediment removal and annual vegetation maintenance program. 2. Monitor sediment accumulations within the three culverts listed below. Remove the sediment if it starts to limit the capacity of the culvert to the point flooding upstream worsens. This may require removing sediment from the channel downstream of the culvert to prevent the culvert from rapidly refilling with sediment. a. Madsen Creek culvert under high flow bypass b. Madsen Creek SR169 culvert c. Madsen Creek 149th Avenue SE culvert It is recommended that the City, County, and WSDOT work together to develop a memorandum of understanding that specifies the entity responsible for each maintenance activity identified in this study and the frequency and timing of that maintenance. One-Time Improvement Projects: 3. Raise the right bank berm along the upper high flow bypass. 4. Continue to limit the amount of flow that enters Madsen Creek by either retaining the existing plates or installing a slide gate on the entrance to the Madsen Creek culvert at the outlet of the sediment basin. 5. Raise the right bank berm along the section of channel between SR169 and 149th Avenue SE. March 2019 Madsen Creek Existing Conditions 3 6. Raise the height of the ground that separates Madsen Creek from Wonderland Estates. 7. Raise the berm that surrounds the sediment pond and add a rock-lined emergency spillway that discharges to the high flow bypass. 8. Increase culvert capacity at the downstream end of the ditch along 149th Avenue SE either by improving the existing culvert outlet system, or preferably installing a second culvert outlet that drains to the Cedar River and not the high flow bypass. Also, consider enlarging the ditch. 9. Raise the ground height surrounding the entrance to the SR169 high flow bypass culvert to provide freeboard during the 100-year flood if the entrance to the culvert becomes partially blocked by woody debris. 10. Raise the right bank berm of Madsen Creek where it overtops near the downstream end of the park channel. March 2019 Madsen Creek Existing Conditions 4 1. I NTRODUCTION Flood and sediment deposition problems along Madsen Creek are typical of those found on small streams in reaches of transitioning channel slope. Madsen Creek collects runoff from a large upland glacial moraine plateau then descends 400 feet through a steep hillside ravine before flowing onto and across the floodplain of the Cedar River. The creek slope begins to flatten as it emerges from the ravine and flows across a small alluvial fan, and flattens further as it flows across the Cedar River floodplain before its confluence with the river. The rapid decrease in channel slope reduces the stream’s ability to convey sediment, which causes sediment to deposit in and beside the channel. This reduces channel capacity and in turn increases flooding. To reduce sediment deposition and flooding, King County constructed a sediment basin at the outlet of the ravine and a high flow flood bypass channel from the sediment basin to the Cedar River. The system, which was built in 1976 and improved in 1990, has performed well over the past 42 years; however, within the past decade significant flood problems have developed which are impacting residential and commercial properties adjacent to or near the stream. The City, in partnership with King County, has initiated this project to determine the causes behind the flooding problems and to identify feasible near- and long-term actions to reduce or eliminate them. Watershed Science and Engineering, along with subconsultants Herrera Environmental and PGS Surveying, were retained by the City to complete the investigation. The project is divided into two phases -- Phase 1 is an existing condition assessment to determine what is causing the flood problems, and Phase 2 is the identification and preliminary design of solutions. This report documents the findings of the Phase 1 Existing Condition Assessment. 1.1. Special Notes • The terms right and left are used in this report to identify the right and left sides of the stream channel, assuming the reader is looking downstream. • Elevations reported in this document are referenced to vertical datum NAVD’88. March 2019 Madsen Creek Existing Conditions 5 2. B ACKGROUND 2.1. Watershed Geology, Development and Stormwater Madsen Creek collects runoff from a large upland glacial moraine plateau and then descends through a steep hillside ravine before flowing across the historical floodplain of the Cedar River (Figure 1). In the 1970s, the upper plateau saw rapid residential development (Fairwood) with stormwater runoff collected and discharged directly to Madsen Creek and its tributaries. The larger volume of stormwater increased the frequency and magnitude of peak flows in Madsen Creek which increased sediment recruitment and transport to the project area, necessitating the installation of the sediment basin and high flow flood bypass channel. Over past 40 years, actions have been taken within the upper watershed to reduce stormwater impacts including the construction of multiple stormwater detention facilities. These improvements have reduced sediment transport to the project area, but sediment deposition continues to be a problem. MadsenCreekUnn a m e d Summ erfieldCr eekUn n a m e d Madsen CreekUnnamed MadsenCreekM adsenCreek MadsenCreek UnnamedMolassesCreek MadsenCreekUnnamed MadsenCreek S u m m erfield Creek M adsen Creek M a d s e n Creek Cedar River King CountyRentonRentonKing CountyRentonKing CountyRenton Esri., Inc., City of Renton, WA, City of Renton 0 1,000 2,000500 Feet ´City of Renton Legend Renton City Limits Potential Annexation Area Stormwater System Renton Private Print Date: 05/05/2017 Madsen CreekSediment Basin 149th Avenue SE Ron Regis Park Madsen CreekChannel Madsen Creek High Flow Bypass Channel Madsen CreekLow FlowChannel Madsen Creek Drainage Basin & Project Location Map Total Basin Area = 2.09 sq miBasin Area in King County = 1.88 sq miBasin Area in Renton = 0.21 sq mi Madsen Creek Drainage Basin: Lower Madsen Creek Project Reach Figure 1Figure created by Renton Public Works March 2019 Madsen Creek Existing Conditions 7 2.2. Flood Control Project Construction History Table 1 provides a historical account of the construction of the Madsen Creek flood control system, compiled from existing documents and discussions with landowners and property managers. Each key event is identified in the table and described in greater detail following the table. Table 1. Construction History Madsen Creek Flood Control Project. Year Event 1976 King County built the original flood control system which included: • sediment basin. • high flow bypass channel. 1989 King County relocated Madsen Creek downstream from 149th Avenue SE to flow through land owned by City of Renton Parks, now Ron Regis Park. The project included: • new culvert under 149th Avenue SE. • small “sediment trap” just downstream from 149th Avenue SE. • improvements to the ditch along the east side of 149th Avenue SE. • filling of the abandoned portion of Madsen Creek downstream from 149th Avenue SE. • log weirs at the mouth of Madsen Creek to allow fish to enter the stream from the Cedar River. 1993 to 1995 (est.) WSDOT widened SR169. Project included: • new box culvert under SR169 and the Cedar River Trail for high flow bypass channel. • extension of Madsen Creek box culvert under SR169 and the Cedar River Trail. • new Madsen Creek box culvert under high flow bypass channel. • modifying Madsen Creek channel along south side of SR169 in front of Wonderland Estates. March 2019 Madsen Creek Existing Conditions 8 1996 King County modified the primary sediment basin to make sure that during low flow periods the water entering the sediment basin exited to Madsen Creek and not to the high flow bypass. Project included: • lowering the floor of the sediment basin one foot. • lowering the 36” CMP culvert that discharges to Madsen Creek one foot. • installing a weir just upstream from the high flow bypass outlet culvert to divert low flows directly into the Madsen Creek low flow channel. • elevating the floor of the high flow bypass outlet culvert 0.8 feet. • installing an additional log weir at the inlet to the sediment basin. 1997/1998 City of Renton installed a bridge over Madsen Creek as part of building the entrance road to Ron Regis Park. 1998 King County replaced the log weirs at entrance to sediment basin. 2002 King County constructed a concrete side weir just upstream from the 149th Avenue SE culvert on the right bank at entrance to road-side ditch. 2009/2010 New Life Church detention pond was expanded and a new outlet pipe system discharging directly to Madsen Creek was installed. The discharge point from the outlet is 20 feet upstream from the Madsen Creek culvert that passes under the high flow bypass. Additional detail describing the events in Table 1 • 1976 (King County, 1974) – Original flood control system was constructed. System elements included: o Sediment basin outlet: ▪ The entrance to the high flow bypass was an open trapezoidal channel. ▪ The connection to Madsen Creek was through two 36” by 22” CMP culverts. o High flow bypass channel: ▪ Three 58” by 36” CMP culverts carried the high flow bypass under SR169 and a wooden trestle carried it under the railroad. o Two 36” by 22” CMP culverts carried Madsen Creek under the high flow bypass just upstream from the SR169. • 1989 (King County, 1989) – Madsen Creek downstream from 149th Avenue SE was relocated to flow through land owned by City of Renton Parks. Project included: o New 9’2” by 3’3” structural arch culvert under 149th Avenue SE near intersection with SR169. March 2019 Madsen Creek Existing Conditions 9 o Channel was diverted from the roadside ditch along the east side of 149th Avenue SE into a newly constructed channel through park land. The roadside ditch remained. o Downstream portion of the roadside ditch along 149th Avenue SE was extended to the high flow bypass channel just upstream from the two 72” CMP culverts that connect the high flow bypass to the Cedar River. The ditch extension included an open ditch segment and two 18” culvert pipe segments in series, one that included an inline 48” type 2 catch basin which houses a backflow check value. o Two 36-inch existing culverts originally carried the roadside ditch portion of Madsen Creek under 149th Avenue SE at a site approximately 700 feet north of SR169. One culvert has been plugged with concrete and at the other a 48” type 2 catch basin was installed at its outlet. The basin does not have an outlet other than a grate on top. • 1993 to 1995 (est.) (WSDOT 1993) – SR169 was widened and three new box culverts installed. Project included: o New 8’ by 6’ concrete box culvert was installed to carry the high flow bypass under SR169. This new culvert was extended north to pass under the Cedar River Trail (formally the railroad grade). o The existing Madsen Creek culvert under SR169 was extended north to accommodate the highway widening and to pass under the trail. The existing culvert was a 6’ by 3’ concrete box. It was extended by adding a 6’ by 4’ box to the north end and filling the floor of the extension with 12 inches of stream bed gravel. o New 6’ by 4’ concrete box culvert was installed to carry Madsen Creek under the high flow bypass. It replaced two 36’ by 22’CMP culverts. • 1996 (King County, 1996) – sediment basin inlet and outlet were modified. Project included: o One log weir was added at sediment basin inlet 10 feet downstream from existing log weirs. o One log weir was installed at sediment basin outlet approximately 10 feet upstream from the 36” CMP culvert that connects to Madsen Creek. o A concrete weir was installed approximately five feet upstream from concrete box culvert that connects to the high flow bypass. o The 36” CMP outlet pipe to Madsen Creek was lowered one foot. o The fill along the downstream side of the sediment basin was raised to elevation 120.5 feet (datum not specified). • 1997/1998 (City of Renton, 1997) – New bridge installed over Madsen Creek along the park entrance road. Project included: o An 18-foot wide reinforced cast-in-place single span bridge. March 2019 Madsen Creek Existing Conditions 10 • 1998 (King County, 1997) – The log weirs at the entrance to the sediment basin were replaced • 2002 (King County, 2002) – A concrete weir was constructed at entrance to the road- side ditch along east side of 149th Avenue SE. o This was installed to reduce flooding along 149th Avenue SE by limiting the amount of flow entering the road-side ditch. • 2009/2010 (Barghausen, 2009) – New Life Church detention pond was expanded and a new outlet pipe system installed that discharges to Madsen Creek just upstream from high flow bypass undercrossing. o The pipe is a 24” Corrugated Poly Ethylene Pipe (CPEP). 2.2.1. Floo d Hi story Madsen Creek has experienced a number of notable floods since the early 1970s. Significant events are identified in Table 2 below, followed by a description of many of these events by persons that live and work in the area. Table 2. Summary of Significant Flood Events. Year Event 1960 to 1972 No noteworthy floods occurred February 28, 1972 First major flood in 1972 March 2, 1972 Second major flood in 1972 September 21 to 23, 1972 Third major flood in 1972. This event produced major landslides in Madsen Creek ravine 1970 to 1990 Other instances of flooding between 1972 and 1990 have likely occurred but were not reported or documented. January 9, 1990 Flood of record December 2005 and January 2006 Floods inundated portions of Wonderland Estates 1990 to 2016 Other instances of flooding between 1990 and 2016 have likely occurred but were not reported or documented. March 2019 Madsen Creek Existing Conditions 11 October and November 2016 Flooding along 149th Avenue SE February 9 and 15- 16, 2017 Significant flooding along 149th Avenue SE which resulted in a claim against King County and the City of Renton by a landowner January 11 and 15, and April 16 2018 Flooding within Wonderland Estates Mr. Kolcsey, owner and developer of the Wonderland Estates Mobile Home Park, provided the following written historical account of flooding problems along lower Madsen Creek (Kolcsey, 1990). • Mr. Kolcsey stated that prior to 1972 there were no flood problems. • First significant flood occurred February 28, 1972 and another one a few days later on March 2, 1972. In Mr. Kolcsey’s opinion the cause was “overloaded Madsen Creek by the Fairwood development, and lack of proper maintenance by King County.” • A third significant flood occurred between September 21 and 23, 1972. • The largest and most damaging flood occurred on January 9, 1990 flood. According to Mr. Kolcsey, the amount of water overwhelmed the stream, clogged culverts with debris and sediment, forcing flood over the sediment basin berm causing water to flow into and through Wonderland Estates. The property manager at Wonderland Estates met with project team members on June 28, 2018. She noted that flooding within the parking area at the front of Wonderland Estates has been relatively frequent, although the stormwater system improvements installed in 2012 have helped reduce flooding. She noted that in December 2005 and January 2006 floods inundated the Wonderland Estates office and that floods in 2018 on January 11 and 15 and April 16 flooded the parking area. The owner of the private residence immediately east of Wonderland Estates met with project team members on August 27, 2018. It was his opinion that recent flooding on his property and within Wonderland Estates is due to lack of capacity within Madsen Creek downstream from 149th Avenue SE. March 2019 Madsen Creek Existing Conditions 12 The property owner at 15205 149th Avenue SE also met with project team members on August 27, 2018 and provided the following observations and opinions: • The ditch along 149th Avenue SE has filled up with flood water 10 to 15 times in the past two years. • Water stops moving at the north end of 149th Avenue SE because the 18-inch CMP culvert(s) that connect the ditch to the high flow bypass channel is too small. • The property owner showed where two 36-inch concrete culverts used to carry Madsen Creek under 149th Avenue SE prior to the stream diversion into and through the park in 1989. The upstream culvert has been plugged with concrete. The downstream culvert is open and ties into a catch basin on the west side of the road. The catch basin is a tall standpipe with the top extending approximately one foot above the ground. The standpipe has an open grate on the top. During the 1990 flood, the property owner said someone broke a foot wide by six-inch tall hole in the side of the standpipe which allowed water to flow out and enter a neighboring constructed fish habitat channel. This helped drain water and lower flood levels on 149th Avenue SE. The hole has been filled. • He stated that the plate installed over the entrance to the culvert that exits the sediment basin has helped reduce the frequency of flooding along 149th Avenue SE. The plate was installed by the City in 2018. • His property flooded twice in February 2017. The first time was on the 9th and the second was on the 16th. During both events, water overtopped the right bank of Madsen Creek upstream from 149th Avenue SE. This water flowed to his house through a swale in the backyard of his neighbor. During the February 16 flood water rose to within one inch of the top step at his front door (about 14 inches deep), he had about 12 inches of water in his garage, and water rose to the first row of siding along the south side of his house. • He stated that King County mows the high flow bypass downstream from SR169 once or twice a year. He agreed that this is good, but he is concerned that the County also needs to improve conveyance by removing other obstructions in the floor the channel (e.g. sediment, old stumps and rocks, etc.). • He said that following the 2017 floods, King County concluded that the 149th Avenue SE ditch was not the cause of the flooding, but rather the ditch was receiving too much flow due to lack of capacity within Madsen Creek downstream from 149th Avenue SE. 2.2.1. Maintenance History Maintenance records provided by the City reveal that the sediment basin has been cleaned almost annually since 1981 and that portions of the high flow bypass channel have also been cleaned several times (Table 3). March 2019 Madsen Creek Existing Conditions 13 Table 3. Estimate of Sediment Removed from Sediment Basin and High Flow Bypass. Year1 Volume Removed from Sediment Basin and High Flow Bypass Channel (yd3) Notes 1981 912 Approx. 680 yd3 from basin, 232 yd3 from channel 1984 1428 Unknown if material removed from high flow bypass 1985 624 20% additional volume removed from high flow bypass 1986 1630 Same as above 1987 1424 Same as above 1988 948 Same as above 1989 720 Same as above 1990 6386 Same as above 1991 1860 Unknown if material removed from high flow bypass 1992 552 Same as above 1993 280 Same as above 1994 890 Same as above 1995 830 Same as above 1996 3430 Same as above 1997 1100 Same as above 1998 460 No sediment removed from the high flow bypass 1999 500 Same as above 2000 260 Same as above 2001 270 Same as above 2002 1117 Same as above 2003 70 Same as above 2004 850 Same as above 2005 390 370 yd3 from basin 20 yd3 from high flow bypass 2006 500 No sediment removed from the high flow bypass 2009 unknown2 Same as above 2010 unknown2 Same as above 2011 unknown2 Same as above 2013 unknown2 Same as above 2014 unknown2 Same as above 2015 unknown2 Same as above 2016 unknown2 Same as above 2017 unknown2 Sediment removed from upper high flow bypass. Quantity unknown. 2018 unknown2 No sediment removed from the high flow bypass 1King County cleaned the sediment basin 1981 through 2006. The City of Renton took over maintenance in 2009. 2The volume removed from the sediment basin was not recorded. March 2019 Madsen Creek Existing Conditions 14 2.3. Existing Conditions Field Observations 2.3.1. Channel Characteristics by Sub -Reach The channel network includes a number of geomorphically unique sub-reaches. These sub- reaches are identified in Table 4 and shown in Figure 2. A description and photographs of each sub-reach are provided after the figure. Table 4. Madsen Creek Sub-Reaches. Sub-Reach Location A Madsen Creek upstream from sediment basin B Sediment basin C Madsen Creek from sediment basin to culvert under high flow bypass D Madsen Creek from culvert under high flow bypass to 149th Avenue SE E Madsen Creek from 149th Avenue SE through Ron Regis Park F Madsen Creek open water wetland downstream from Ron Regis Park to Cedar River G High flow bypass channel upstream from SR169 H High flow bypass channel downstream from SR169 I Ditch along east side of 149th Avenue SE !(B !(A !(D !(F !(I !(H !(G !(E !(C Figure 2 Madsen Creek Sub-Reaches 27 Jan 2019 0 270 540 Feet Scale: 1:4,555NAD 1983 HARNStatePlane WashingtonNorth FIPS 4601 Feet U March 2019 Madsen Creek Existing Conditions 16 Sub-Reach A: Madsen Creek Upstream of Sediment Basin Channel Type: Pool Riffle Bed Material Characteristics: Gravel / Cobble, d50 = 50mm, d90= 250mm Large Wood: Typical characteristics of small natural streams found in the pacific northwest-- logs visible in stream bed, downed trees spanning channel from bank to bank. Vegetation Characteristics: Naturally vegetated stream banks and floodplain – alder and maple trees, salmon berry, black berry, etc. Comments: Channel appears to be stable and in equilibrium. Photo 1. Typical channel upstream from sediment basin (Photo taken June 7, 2018). March 2019 Madsen Creek Existing Conditions 17 Sub-Reach B: Sediment Basin Channel Type: Constructed Basin Bed Material Characteristics: Gravel with a few small cobbles, d50 = 10mm at head of basin grading to fine sand and silt at the outlet. Vegetation Characteristics: Alder trees line the banks except along the right (east) side which is intentionally open to allow machinery access to clean sediment from the basin annually. Structures: Inlet weirs and outlet weirs and culverts. Photo 2. Viewing south (upstream) across sediment basin to weirs at entrance (January 19, 2018). March 2019 Madsen Creek Existing Conditions 18 Photo 3. Viewing northeast (downstream) toward the outlet of the sediment basin (January 19, 2018). Photo 4. Viewing upstream (south) to log weirs at the entrance to the sediment basin (June 7, 2018). March 2019 Madsen Creek Existing Conditions 19 Photo 5. The inlet to flow bypass pipe located within weir reach at upstream end of the sediment basin. Plate that covers inlet is missing. Photo 6. The culvert at the basin outlet that carries water from the sediment basin to Madsen Creek. Two metal plates have been installed to reduce the amount of flow that is conveyed to Madsen Creek. They cover approximately three-quarters of the inlet (June 7, 2018). March 2019 Madsen Creek Existing Conditions 20 Photo 7. Viewing downstream (north) to the box culvert and weir at the outlet of the sediment basin which discharges to the high flow bypass. The floor of the culvert is partially undermined (June 2018). Photos 8 and 9. Concrete weir at sediment basin outlet (flow is from right to left). The outlet pipe to Madsen Creek is visible in background. Photo 9 is viewing upstream to the outlet of the culvert that discharges to the high flow bypass (June 7 and January 19, 2018). March 2019 Madsen Creek Existing Conditions 21 Sub-Reach C: Madsen Creek natural channel between sediment basin and culvert under high flow bypass Channel Type: Pool-Riffle Bed Material Characteristics: Gravel upstream grading to fine sand at high flow bypass undercrossing. Vegetation Characteristics: Thick buffer of alder trees and blackberry. Large Wood: Reach does not contain large pieces of wood, but it does contain numerous small trees on the banks and across the stream. Structures: A small wooden foot bridge in the upper portion of the reach provides the church access to the track and play field. Photos 10 and 11. Typical example of Madsen Creek within sub-reach C (June 7, 2018). March 2019 Madsen Creek Existing Conditions 22 Photo 12. Stormwater pipe outlet. Pipe carries stormwater to Madsen Creek from the church property and development east of church (June 7, 2018). Photo 13. Inlet to Madsen Creek culvert under high flow bypass (June 7, 2018). March 2019 Madsen Creek Existing Conditions 23 Sub-Reach D: Madsen Creek channel from culvert under high flow bypass to 149th Avenue SE Channel Type: Constructed ditch upstream from SR169. Channel downstream from SR169 has a natural appearance, but likely has been modified over the past 40 years. Bed Material Characteristics: Fine gravel to sand and silt Vegetation Characteristics: Grass along ditch upstream from SR169 and blackberries and small alder trees downstream. Large Wood: Ditch segment has no wood. Small maple and alder trees line banks downstream from SR169. Structures: Culverts under High Flow Bypass and SR169 Photo 14. Viewing east (upstream) along excavated ditch along the south side of SR169. Photo 15. Typical channel between SR169 and 149th Avenue SE. March 2019 Madsen Creek Existing Conditions 24 Photos 16 and 17. Entrance to Madsen Creek culvert under SR169 viewing upstream (east) and downstream (west) respectively (June 7, 2018). Photos 18 and 19. Entrance to Madsen Creek 149th Ave SE Culvert (June 7 & January 19, 2018). March 2019 Madsen Creek Existing Conditions 25 Sub-Reaches E and F: Madsen Creek channel from 149th Avenue SE through Ron Regis Park to Cedar River Channel Type: Plain Bed Bed Material Characteristics: Fine sand with silt at channel margins and on inset benches Vegetation Characteristics: Small alder and thick blackberries. Large Wood: Small diameter pieces are present on the channel bed. Large wood was installed in the channel bed when the channel was constructed in 1989, but it has been completely covered with silt and sand. Numerous small live maple tree trunks crisscross the channel. Structures: 149th Avenue SE culvert, Sediment Trap (oversized channel segment) in channel just downstream from 149th Avenue SE, Park entrance road bridge. Photo 20. Viewing upstream (east) along Madsen Creek through sediment trap to 149th Avenue SE culvert (January 19, 2018). Photo 21. Typical channel segment between the sediment trap and the bridge on the park entrance road (June 7, 2018). March 2019 Madsen Creek Existing Conditions 26 Photo 22. Typical Madsen Creek channel within Park. Photo 23. Abandoned channel that once carried the stream to the Cedar River before it was diverted into the pond in Photo 24 below. It is now filled with Reed Canary grass. (Both photos taken June 7, 2018). Photo 24. Viewing into pond at location where Madsen Creek enters pond (June 7, 2018). March 2019 Madsen Creek Existing Conditions 27 Photo 25. Viewing downstream to the park entrance road bridge over Madsen Creek (June 7, 2018). Photo 26. Upstream side of park entrance road bridge over Madsen Creek. Photo 27. Flood protection berm/ecology block wall along west side of Madsen Creek along the Ron Regis Park cricket field (January 19, 2018). March 2019 Madsen Creek Existing Conditions 28 Sub-Reach G: High flow bypass channel upstream from SR169 Channel Type: Constructed trapezoidal earth channel Bed Material Characteristics: Riprap is visible in the floor of the upstream portion of the channel; but no riprap was visible in the downstream portion above the Madsen Creek culvert undercrossing. Riprap is present between the undercrossing and the SR169 culvert. Vegetation Characteristics: Grass Large Wood: None Structures: Madsen Creek natural channel culvert undercrossing and SR169 culvert. Photo 28. Viewing upstream (south) along high flow bypass upstream from SR169. Photo 29. Viewing downstream (north) to SR169 (Both photos taken January 19, 2018). March 2019 Madsen Creek Existing Conditions 29 Photo 30. Viewing upstream (south) to exposed top of culvert that carries Madsen Creek under the high flow bypass (June 7, 2018). Photo 31. Viewing downstream (north) to SR169. Person is standing on top of the Madsen Creek culvert that passes under high flow bypass channel (June 7, 2018). March 2019 Madsen Creek Existing Conditions 30 Photo 32. Viewing downstream (north) to entrance of culvert that carries the high flow bypass under SR169 (June 7, 2018). Photo 33. Viewing upstream (south) to the outlet of the high flow bypass culvert under SR169 (June 7, 2018). March 2019 Madsen Creek Existing Conditions 31 Sub-Reach H: High Flow Bypass channel downstream from SR169 Channel Type: Constructed trapezoidal earth channel Bed Material Characteristics: Silt and sand Vegetation Characteristics: Grass, blackberries, and brush. Large Wood: None Structures: Two 72-inch CMP pipes at outlet to Cedar River. Photos 34 and 35. Viewing downstream (north) along High flow bypass downstream from SR 169. Photo 34 taken on January 19, 2018 shortly after the channel was mowed. Photo 35 was taken June 7, 2018; vegetation in channel is eight feet tall and dense. March 2019 Madsen Creek Existing Conditions 32 Photo 36. Viewing downstream (north) to the inlet of the twin 6-foot CMP pipes at the end of the high flow bypass (January 19, 2018). Photo 37. Viewing downstream (northwest) along Cedar River at outlet of high flow bypass culverts (January 19, 2018). March 2019 Madsen Creek Existing Conditions 33 Sub-Reach I: Ditch along east side of 149th Avenue SE Channel Type: Constructed ditch Bed Material Characteristics: Silty sand Vegetation Characteristics: Grass and black berries Large Wood: None Structures: Concrete side weir into ditch, Multiple driveway bridges, 18-inch CMP culvert connecting ditch to high flow bypass, and 36-inch concrete culvert under 149th Avenue SE near north end of road that connects to a vertical catch basin. Photo 38. Viewing downstream (north) along ditch along the east side of 149th Avenue SE (January 19, 2018). Photo 39. One of the 18-inch culverts at end of ditch (June 28, 2018). March 2019 Madsen Creek Existing Conditions 34 3. A NALYSIS Three technical disciplines were examined as part of the existing condition assessment – hydrology, hydraulics, and sediment transport and deposition. Methods and results for each are presented below. 3.1. Hydrology 3.1.1. Hydrologic Setting Madsen Creek collects runoff from a 1,400-acre upland glacial moraine plateau to the south side of the Cedar River valley, in the community of Fairwood east of Renton. The Madsen Creek drainage basin saw rapid development, primarily in residential construction, in the 1970s and 1980s. This development led to higher discharges, and subsequently, the current flooding and sedimentation problems in Madsen Creek, as described previously. The Madsen Creek drainage basin includes approximately 1,245 acres upstream of the sediment basin. Land-use upstream of the sediment basin consists primarily of medium density residential, golf course development, and steep forested hillslopes. Downstream of the sediment basin the Madsen Creek drainage basin covers approximately 155 acres. Land uses in this area include a mobile home park, a large Church, high density residential development, portions of SR-169, and less developed park and pasture areas in the Cedar River floodplain. King County operates a stream gaging station (KC Gage 31d) on Madsen Creek upstream of the sediment basin. This gage has been in operation since October 1987 and provides 15-minute flow and stage data for Madsen Creek. 3.1.2. Hydrologic Model Development A Hydrologic Simulation Program – FORTRAN (HSPF) model was developed and calibrated for the Madsen Creek drainage basin. The HSPF model includes 21 sub-basins as shown in Figure 3. Previous hydrologic modeling for the Madsen Creek basin was completed in the early 1990s by King County as part of the Cedar River Current and Future Conditions Report (King County, 1993). That model was obtained from King County (Jeff Burkey, personal communication, 2018) for this study and used as the basis for the current model development. Updates to the model were made to reflect current data, changed land-use conditions, additional or modified stormwater management facilities, and the requirements of the current project. The HSPF model developed for this project was calibrated to data from the Madsen Creek stream gage. Sediment Basin 39 42 6057 36 18 9 1 27 33 12 3 13 24 21 30 54 6 45 48 51 CedarRiver Madsen Creek Watershed §¨¦5 §¨¦90 28 Jan 2019 0 1,100 2,200 Feet Scale: 1:19,487NAD 1983 HARNStatePlane WashingtonSouth FIPS 4602 Feet U Figure 3 Sub-Basins March 2019 Madsen Creek Existing Conditions 36 Input data for the HSPF model were derived from the following sources: • Topographic data - 2016 LiDAR dataset available on WADNR LiDAR Portal • Land cover data – based on GIS processing of USGS 2012 NAIP imagery • Soils Data: NRCS Soil Survey Geographic (SSURGO) database Drainage subbasins in the Madsen Creek drainage basin were delineated at key hydraulic controls and points of interest. Subbasins were delineated using the 2016 LiDAR topographic data and these delineations were checked against the earlier King County model. Differences or discrepancies between these delineations were field verified to confirm the new model basin boundaries were appropriate. Stage storage discharge relationships (FTABLEs in HSPF) for each subbasin were adapted from the earlier King County model or developed based on review of the conveyance system characteristics in each subbasin. Land cover inputs for the HSPF model were developed by image processing of the multispectral NAIP aerial photos. This process utilizes the four bands available in the NAIP imagery (red, green, blue, and near infrared) and performs a textural analysis to delineate areas with similar land cover. The following six categories of land cover were delineated: impervious, bare ground, pasture grass, lawn or turf, forest, and open water. Land cover in several “test areas” was first hand delineated and used to train the classification process. Land cover for the entire drainage basin was then delineated using the automated process, and spot checks were made to verify the final delineation. The final land cover classification is shown in Figure 4. Soils data for the Madsen Creek basin were obtained from the NRCS SSURGO database. Data were downloaded from the Web Soil Survey at https://websoilsurvey.sc.egov.usda.gov/App/WebSoilSurvey.aspx. Soils data were grouped into three categories as follows: till, outwash, and wetland/water based on hydrologic properties of the soil units. All but a small portion of the basin is underlain by Till as shown in Figure 5. The subbasins, land cover, and soils data were then overlain with each other in GIS and polygons created for each combination of these (e.g. Sub basin 1/Forest/Till). The output of the GIS processing was then imported into Excel and post processed to generate HSPF inputs. HSPF requires the acreage of each combination of soil and land cover for each subbasin. For most land cover classes this simply involved summing the polygons by soil and cover. For impervious areas, however, an additional step was required. The spectral image processing delineates total impervious area (TIA) but hydrologic modeling is typically based on effective impervious area (EIA). The difference is that EIA assumes that some portion of the TIA is not well connected to the conveyance system (for example older residential roof top drainage spilling out onto lawns) and as such responds hydrologically more like grass than impervious. There is no single value of the ratio between TIA and EIA that is appropriate for all areas but WSE’s experience is that in a basin with mostly older residential development like the Madsen Creek basin this ratio should be approximately 50%. Therefore, for the current work, a value of 50% was initially selected and then tested as part of the model calibration process. CedarRiver Watershed Land Cover §¨¦5 §¨¦90 13 Dec 2018 0 1,100 2,200Feet Scale: 1:19,357NAD 1983 HARNStatePlane WashingtonSouth FIPS 4602 Feet U Madsen Creek Figure 4 Bare Ground Forest Impervious Pasture Turf/Lawn Open Water CedarRiver Watershed Soil Classifications §¨¦5 §¨¦90 13 Dec 2018 0 1,100 2,200 Feet Scale: 1:19,357NAD 1983 HARNStatePlane WashingtonSouth FIPS 4602 Feet U Madsen Creek Figure 5 Outwash Till Wetland March 2019 Madsen Creek Existing Conditions 39 HSPF defines runoff response using 16 parameters for each pervious hydrologic unit (PERLND) and four parameters for each impervious unit (IMPLND). PERLNDs corresponding to the following classes were defined in HSPF: Till forest all slopes, Till pasture all slopes, Till grass all slopes, Outwash forest all slopes, Outwash pasture all slopes, Outwash grass all slopes, and saturated soils all covers and slopes. PERLND and IMPND parameters for the initial model setup were obtained from the King County model. These parameters were subsequently calibrated as described below. The HSPF model was configured using the sub-basin, soils and cover data described above. The other major input required for the HSPF model is meteorological data. Meteorological data for the current study was obtained from the following sources: • Precipitation data – 15-minute data from King County gage 31Y2 Fairwood (2009-2018), King County gage 31Y Fairwood (1995-2009), and King County gage 31W Layton (1987- 1995). Missing data in the precipitation data time series were infilled using data from King County gage 31Z Hobart times a multiplier of 0.75. • Evaporation Data – daily data from Puyallup Experimental Station for 1948 – 2012 provided by King County (Jeff Burkey, personal communication, 2018) extended using long term monthly averages 3.1.3. Hydrologic Model Calibrat ion The HSPF model was configured using the data described above and run for the period October 1, 1987 through May 14, 2018. Discharges at key locations in the model were saved to WDM database and reviewed as part of the model calibration. Simulated data for Madsen Creek upstream of the sediment basin was saved as Data Set (DSN) 130. These data were compared to the observed King County Madsen Creek gage data and the following parameters were evaluated: mean annual flow, mean winter (November – March) flow, and annual peak flows. Although the King County gage data extends back to 1987 the comparisons were only made for data from 2001 to present. Review of the King County data and discussions with King County staff (Dan Smith, personal communication, 2018) led WSE to conclude that data prior to 2001 was suspect. Initial calibration runs showed a fair match to the observed data. However, some of the HSPF PERLND parameters used in the earlier King County model seemed unusual relative to more recent model calibration studies (Dinicola, 2001). Therefore, WSE changed the model PERLND parameters to match values determined by the USGS in a regional study of Puget Sound (Dinicola, 1990) and then made final calibration adjustments to that parameter data set. The calibrated HSPF model matched observed annual runoff volumes within 4% and observed seasonal runoff volumes within 2%. Calibration of peak flows was evaluated by comparing simulated and observed runoff over the period of record. Figures 6 and 7 show plots of average daily flows for two years in the record, water year 2011 which had one of the highest flows in recent years and water year 2015 which had more moderate flows. As shown in Figures 6 and 7 the simulated results generally match the observed data quite well including March 2019 Madsen Creek Existing Conditions 40 the rise, peak, and recession of significant storm events as well as base flows. Flood flow frequency curves generated from the simulated and observed data were also compared. Figures 8 to 10 show this comparison for three different periods of record as follows: • 1989 – 2018 covering the full period of record for both the simulation and the Madsen Creek gage (Figure 8) • 2001 – 2018 covering the period for which the flow data are considered reasonably accurate and used for volume comparisons (Figure 9) • 2004 – 2018 covering the period with the most accurate gage data, based on review of the peak discharge observations and discussions with KC staff (Figure 10) As seen in these figures, the HSPF simulated peak flows do a reasonably good job at matching flow frequency quantiles across each of the reporting periods (2- through 100-year flows matched within 15% or better for all comparison periods). In particular, the match for the period 2004 to 2018 is exceptionally good. This is the period with the most reliable gage data. However, it should be noted that because the period of record for this last comparison is quite short from a frequency analysis perspective caution must be used when making judgements based on these curves. Fortuitously for the current study, the frequency analyses for all three periods result in very similar flow quantiles meaning that the flow frequency data for any of these periods can be used for this and other locations without biasing the results. Table 5. Annual Instantaneous Peak Flows Madsen Creek at Entrance to Sediment Basin. Flow Quantile (cfs) Period of Comparison 2-year 10-year 100-year 1989 - 2018 100 173 286 2001 - 2018 102 176 284 2004 - 2018 109 184 294 3.1.4. Hydr ologic Model Application The calibrated HSPF model was used to generate inflows to the hydraulic model. A version of the HSPF model was set up without any streamflow routing downstream of the sediment basin (except in the few locations where the conveyance system was not included in the hydraulic model). This HSPF model was run for the period of record and unrouted outflows for each hydraulic model inflow point were saved to the WDM. These were then exported from the WDM and imported to a HEC-DSS database for use in the hydraulic modeling described in Section 3.2. Figure 6. Comparison of HSPF Simulated verses Observed Flows for Water Year 2011. Data from Water Year 2011 Madsen Creek upstream of Sediment Basin Simulated versus Observed Flows Data Set:summed over 24 hours Summed over a 24 hour fixed window Madsen Creek Above Sed Pond (KC Gage 31D) Madsen Creek SB 30 Flow (KC Gage) WSE Parm KC-WLRD 15-MIN PRECIP GAGE 31Y2 [Aux Axis] OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEPVolume (acft)0. 30. 60. 90. 120. 0.0 5.0Precip(in/d)? Figure 7. Comparison of HSPF Simulated verses Observed Flows for Water Year 2015. Data from Water Year 2015 Madsen Creek upstream of Sediment Basin Simulated versus Observed Flows Data Set:summed over 24 hours Summed over a 24 hour fixed window Madsen Creek Above Sed Pond (KC Gage 31D) Madsen Creek SB 30 Flow (KC Gage) WSE Parm KC-WLRD 15-MIN PRECIP GAGE 31Y2 [Aux Axis] OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEPVolume (acft)0. 30. 60. 90. 120. 0.0 5.0Precip(in/d)? Figure 7. Flood Frequency Curves Generated from Gage and HSPF Model Data for Period 1989 to 2018. Percent Chance Exceedance Madsen Creek Above Sed Pond (KC Gage 31D) Madsen Creek SB 30 Flow (KC Gage) WSE Parm Fit Type:Log Pearson III distribution using the method of Bulletin 17B, Hosking Plotting Position Annual Peak Frequency Analysis Observed versus Simulated Peak Flows at Sediment Basin Madsen Creek Flood Flow Frequency Analysis Discharge (cfs)0. 40. 80. 120. 160. 200. 240. 280. 320. Ret Period(years)-->100251052 19649010802050 Figure 8. Flood Frequency Curves Generated from Gage and HSPF Model Data for Period 2001 to 2018. Percent Chance Exceedance Madsen Creek Above Sed Pond (KC Gage 31D) Madsen Creek SB 30 Flow (KC Gage) WSE Parm Fit Type:Log Pearson III distribution using the method of Bulletin 17B, Hosking Plotting Position Annual Peak Frequency Analysis Observed versus Simulated Peak Flows at Sediment Basin Madsen Creek Flood Flow Frequency Analysis Discharge (cfs)0. 40. 80. 120. 160. 200. 240. 280. 320. Ret Period(years)-->100251052 19649010802050 Figure 9. Flood Frequency Curves Generated from Gage and HSPF Model Data for Period 2004 to 2018. Percent Chance Exceedance Madsen Creek Above Sed Pond (KC Gage 31D) Madsen Creek SB 30 Flow (KC Gage) WSE Parm Fit Type:Log Pearson III distribution using the method of Bulletin 17B, Hosking Plotting Position Annual Peak Frequency Analysis Observed versus Simulated Peak Flows at Sediment Basin Madsen Creek Flood Flow Frequency Analysis Discharge (cfs)0. 40. 80. 120. 160. 200. 240. 280. 320. Ret Period(years)-->100251052 99 19649010802050 March 2019 Madsen Creek Existing Conditions 46 3.2. H ydrau lic Modeling 3.2.1. Hydraulic Model Development Hydraulic conditions within the project area are complex; therefore, WSE elected to create a two-dimensional HEC-RAS numerical model of the entire stream network. The model domain, which is illustrated in Figure 11, begins upstream of the sediment basin, and includes the basin, the stream channel, high flow bypass, ditch along 149th Avenue SE and all surrounding floodplain areas that may be impacted by flooding. The colored lines and dots in Figure 11 are boundary condition locations which are discussed below. Topographic Surface The topographic surface used in the HEC-RAS 2D model was developed from existing LiDAR and ground survey data collected as part of this investigation. The LiDAR was collected in 2016 and was obtained from the Washington Department of Natural Resources LiDAR portal (WADNR, 2018). The ground survey included cross section and profile surveys of all channel segments including the sediment basin, stream channel, high flow bypass, and 149th Avenue SE ditch. It also included surveys of all culverts and bridges. The survey was performed by Pacific Geomatic Services (PGS) in June and July 2018 (PGS, 2018). Hydraulic Structures Bridges, culverts, and weirs are present throughout the model domain. Each structure was represented in the model geometry using the HEC-RAS 2D flow connection and structure editor. Structure dimensions were based on field survey data collected by PGS and supplemented with field measurements collected by WSE. The latest version of HEC-RAS 2D at the time of this analysis (version 5.0.5, USACE, 2016) does not have the capability to represent bridges. Therefore, bridges are represented as culverts in the model, which given the small size of the bridges is a reasonable assumption. Hydraulic Roughness Surface roughness, in the form of Manning’s n values, is based on engineering judgement and was refined during model validation. Final n values used in the existing condition model are shown in Figure 12. Noteworthy comments regarding the values are: 1) The portion of the high flow bypass downstream from SR169 was assigned an elevated roughness because the channel was choked with dense and tall vegetation during field inspections in October 2018, just prior to flood season. King County is responsible for maintaining this reach and they mowed the channel in January 2018, and again in November 2018 following a letter sent by the City of Renton. However, for the purpose of existing conditions modeling, a conservative approach has been taken and the higher roughness reflecting the dense vegetation was assigned to this reach. 2) Instead of modifying the terrain to include the numerous mobile homes, carports, and sheds within Wonderland Estates and the housing development just to the west, the entire March 2019 Madsen Creek Existing Conditions 47 area was assigned a high n-value designed to account for the blockage effect of the structures. !( !( !( !( !( !(!( !( !( !( !( !( Basin 27 Basin 6 Basin 24 Basin 13 Basin 21 Basin 9 Basin 1 Basin 33 Basin 18 Madsen -Upstream Basin 3 Basin 12 Hydraulic Model Domain & Boundary ConditionsUV169 UV169 CedarRiver 11 Dec 2018 0 300 600Feet Scale: 1:5,357NAD 1983 HARNStatePlane WashingtonSouth FIPS 4602 Feet U Madsen Creek Model Domain Figure 11 !(Internal Point-Inflow Boundary Normal Depth Boundary Stage Boundary Basin # corresponds to sub-basin output of HSPF model 0.06 0.04 0.04 0.04 0.045 0.15 0.045 0.04 0.045 0.03 0.15 0.045 0.045 0.05 0.02 0.2 0.15 0.045 0.1 0.1 0.2 0.035 0.06 0.05 0.03 Existing Conditions Manning's n ValuesUV169 UV169 CedarRiver 11 Dec 2018 0 290 580 Feet Scale: 1:5,115NAD 1983 HARNStatePlane WashingtonSouth FIPS 4602 Feet U Madsen Creek Figure 12 March 2019 Madsen Creek Existing Conditions 50 Boundary Conditions Three external and twelve internal boundary condition nodes were coded into the model domain. These are identified by the colored lines and dots in Figure 11. External boundaries (double yellow and red dashed lines) are locations where water surface elevations within the Cedar River had to be estimated for each event modeled on Madsen Creek. Water surface elevations at the downstream end of the model domain were estimated automatically by the model using normal depth methods. Water levels at the outlet of the high flow bypass and at the outlet of the constructed King County habitat channel were estimated from stage discharge curves generated from an existing hydraulic model of the Cedar River (explained below). Internal boundaries (red dots) are locations where inflows are specified to the model domain as predicted by the HSPF hydrologic model. For each Madsen Creek model simulation, water surface elevations within the Cedar River had to be input at the outlet of the high flow bypass and King County habitat channel. Stage hydrographs were developed for both sites using an existing hydraulic model of the Cedar River developed by WSE for King County’s Cedar River Interactive Mapping Project (CRIMP) (WSE, 2013). For the February 16, 2017 validation model run, the stage hydrographs at these locations represent the actual flow that occurred on the Cedar River on that day as estimated from data collected at the two USGS Cedar River stations -- Landsburg (12117500) and Renton (12119000). Similarly, the 2-year event that was modeled is based on a flood that occurred on January 30, 2006; therefore, boundary conditions for the Cedar River are the actual hydrographs that occurred on that day. The 25-year and 100-yr event hydrographs on Madsen Creek are both scaled versions of the January 9, 1990 flood. Therefore, boundary conditions on the Cedar River are represented by the actual January 9, 1990 Cedar River hydrograph. The same set of hydrographs was used for both events. Model Validation Although limited data availability precluded full model calibration, WSE validated the model with sensitivity testing, interviews with residents who observed flooding, flood photograph and historical records, and other anecdotal information. The primary flood event used for model validation occurred on February 16, 2017 and had a peak discharge measured at the Madsen Creek stream gage of approximately 150 cfs, which corresponds to about an 8-year event. During this event, significant flooding occurred along 149th Avenue SE and on private parcels adjacent to the road (Photos 40 and 41). Flood water overtopped the right bank berm of the high flow bypass channel upstream from SR169, and flowed onto the church field and entered Madsen Creek. Photo 42 shows grass and leaf debris left by the overtopping flow along the bottom of a chain link fence that sits on top of the berm. The stream did not flood Wonderland Estates (Photo 43). March 2019 Madsen Creek Existing Conditions 51 Photo 40. Viewing south along 149th Avenue SE at the residence located at 15205 (February 16, 2017, City photograph). Photo 41. Viewing east across the 149th Avenue SE ditch at the residence located at 15205 (February 16, 2017, City photograph). March 2019 Madsen Creek Existing Conditions 52 Photo 42. Viewing northeast across the upper high flow bypass. The right bank berm overtopped at the peak of the storm, leaving debris along the bottom of the fence (February 16, 2017, City photograph). Photo 43. Viewing west along Madsen Creek at Wonderland Estates. Flow overtopped the sandbags on the left bank, but significant flooding in Wonderland Estates was not reported (February 16, 2017, City photograph). March 2019 Madsen Creek Existing Conditions 53 The initial validation model run did not replicate the February 16, 2017 flood well. Computed water levels were too low to overtop the right bank berm of the upper high flow bypass. This resulted in flowrates along 149th Avenue SE which were too low to produce the flooding that was observed. Further investigation revealed that the City removed sediment from the floor of the bypass channel after the flood, which was prior to the survey that was completed for this investigation; therefore, the capacity of the high flow bypass in the HEC-RAS model is greater than it was at the time of the flood. To compensate for this added channel capacity, WSE estimated the discharge that overtopped the berm based upon the height of the debris left on the chain link fence and added this flow to Madsen Creek at the lower end of the church field. After accounting for the overtopping of the high flow bypass berm, the existing condition model successfully reproduced the pattern of observed downstream flooding along and in the vicinity of 149th Avenue SE. The results are presented in Figure 13 which shows maximum flow depth at the peak of the event. Model Results Existing Condition The validated model was used to estimate hydraulic conditions within the project area for existing conditions for three flood events -- the 2-, 25-, and 100-year annual instantaneous peak floods. The results, presented in the form of maximum flow depth, are illustrated in Figures 14, 15, 16. General insights and observations revealed from the inundation maps are: 1. The sediment basin is able to pass the 100-year flood without overtopping the berm that surrounds the basin assuming debris does not block any portion of the outlet. There is, however, no freeboard on the berm during the 100-year flood. 2. The right bank berm of the high flow bypass channel upstream of SR169 currently does not overtop during the 2-year event, but it does during the 25- and 100-year floods. The overtopping flow enters the church field where it ponds and eventually drains to Madsen Creek, passing through the culvert beneath the high flow bypass. Currently the berm begins to overtop at an 8- to 10-year event, but overtopping will occur more frequently over time if sediment is allowed to accumulate within the bypass. During the 25- and 100-year events approximately 50 and 100 cfs overtop the berm respectively, which causes flow rates in Madsen Creek to increase significantly. This added flow is one of the principal causes of the flooding within Wonderland Estates and along 149th Avenue SE. 3. Water overtops the banks at the entrance to the SR169 high flow bypass culvert and the left bank immediately downstream during the 25-year and 100-year floods. This is because the capacity of the high flow bypass has been reduced due to sediment deposition in the SR169 culvert along with sediment deposition and vegetation in the high flow bypass downstream from the culvert. Flows that overtop the left bank upstream of the SR169 culvert increase flooding within Wonderland Estates, and those March 2019 Madsen Creek Existing Conditions 54 that overtop the left bank downstream of the culvert, increase flooding within the residential properties east of 149th Avenue SE. 4. The 25-year and 100-year floods overtop the left bank of Madsen Creek along Wonderland Estates, flooding the north end of the mobile home park. 5. The 100-year flood overtops the left bank of the high flow bypass at the entrance to the Madsen Creek SR169 culvert. This water flows through the front yard of the private residential property east of Wonderland Estates, then through Wonderland Estates, and into the housing development west of Wonderland. 6. The existing right bank berm along the section of Madsen Creek between SR169 and 149th Avenue SE overtops during the 25-year and 100-year events. It also overtopped during the February 16, 2007 event (about an 8-year event). The overtopping water flows north to flood several residential properties. In addition, water that leaves the channel at this location is the first contributor to flooding along the 149th Ave SE properties, as shown by the inundation map of the 2-year event. Water overtopping the 149th Ave SE ditch seems to occur following the overtopping of the Creek and only during events larger than the 2-year flood. 7. The culvert that carries Madsen Creek under 149th Avenue SE was generally free of sediment and therefore, does not restrict flow. However, as will be described in the next section, the channel in the park has filled with sediment which has reduced its capacity. 8. Water ponds up along 149th Avenue SE because the existing culvert drain at the north end of the ditch does not have sufficient capacity. In addition, because the culvert empties into the high flow bypass just above its outlet to the Cedar River, the capacity of the culvert will be reduced when water levels within the high flow bypass are high. 9. Flooding along Madsen Creek through the park is generally contained in the stream corridor by existing berms and concrete eco-block walls. The only significant exception is near the downstream end of the cricket fields where water leaves the channel both to the west and east. The flow to the west enters a large undeveloped natural wetland area while to the east it enters the backyard of a private residence. Simulated Maximum Depths- 16 Feb 2017 Flood Event - UV169 UV169 CedarRiver 14 Dec 2018 0 150 300 Feet Scale: 1:2,000NAD 1983 HARN StatePlaneWashington South FIPS 4602Feet U Depths (ft) 0 - 0.5 0.5 - 1 1 - 2 2 - 3 >3 Madsen Creek Existing Conditions Figure 13 Simulated Maximum Depths- 2yr Flood Event - UV169 UV169 CedarRiver 14 Dec 2018 0 150 300 Feet Scale: 1:2,000NAD 1983 HARN StatePlaneWashington South FIPS 4602Feet U Depths (ft) 0 - 0.5 0.5 - 1 1 - 2 2 - 3 >3 Madsen Creek Existing Conditions Figure 14 Simulated Maximum Depths- 25yr Flood Event - UV169 UV169 CedarRiver 14 Dec 2018 0 150 300 Feet Scale: 1:2,000NAD 1983 HARN StatePlaneWashington South FIPS 4602Feet U Depths (ft) 0 - 0.5 0.5 - 1 1 - 2 2 - 3 >3 Madsen Creek Existing Conditions Figure 15 Simulated Maximum Depths- 100yr Flood Event - UV169 UV169 CedarRiver 14 Dec 2018 0 150 300 Feet Scale: 1:2,000NAD 1983 HARN StatePlaneWashington South FIPS 4602Feet U Depths (ft) 0 - 0.5 0.5 - 1 1 - 2 2 - 3 >3 Madsen Creek Existing Conditions Figure 16 March 2019 Madsen Creek Existing Conditions 59 Cedar River Flooding Although Madsen Creek is the focus of this investigation, it is important to recognize that even if Madsen Creek flooding is reduced, properties along 149th Ave SE will remain at risk because they are in the Cedar River floodplain. Figures 17 and 18 show Cedar River flood depth and inundation limit estimates for approximately the 10-year and 50-year annual instantaneous peak floods, revealing that Cedar River flooding continues to pose a serious threat to these properties. The data used to create these figures were obtained from a hydraulic modeling project known as the CRIMP (Cedar River Interactive Mapping Project) which was completed by WSE for King County in 2013 (WSE, 2013). > 10-year Cedar RiverInnundation DepthsUV169 UV169 CedarRiver 12 Mar 2019 Figure 17 0 280 560 Feet Scale: 1:5,000NAD 1983 HARNStatePlane WashingtonSouth FIPS 4602 Feet U Depth (ft) 0 - 0.5 0.5 - 1 1 - 2 2 - 3 >3 Note: This figure represents flooding that would occur during a King County Phase 4 flood alert. The discharge is slightly higher than a 10-year flood. 50-year Cedar RiverInnundation DepthsUV169 UV169 CedarRiver 12 Mar 2019 Figure 18 0 280 560 Feet Scale: 1:5,000NAD 1983 HARNStatePlane WashingtonSouth FIPS 4602 Feet U Depth (ft) 0 - 0.5 0.5 - 1 1 - 2 2 - 3 >3 March 2019 Madsen Creek Existing Conditions 62 3.3. Sediment Transport and Deposition Sediment deposition has reduced the capacity of portions of Madsen Creek and the high flow bypass. To determine how sediment is moving through the system, where it has accumulated and what type of sediment it is, WSE conducted: 1) a detailed field inspection that included collecting sediment samples throughout the system; 2) estimating sediment deposition volumes within the high flow bypass and portions of Madsen Creek by comparing channel cross sections and profiles surveyed for this study to the original channel design drawings; and 3) evaluating the trap efficiency of the sediment basin. These investigations provided an understanding of sediment transport and deposition processes that are active within the system, an understanding that is required to develop effective solutions. The results of the sediment investigation are summarized below. 3.3.1. Sedim ent Deposition Locatio ns WSE identified where sediment has accumulated within the channel system, both through field observations and data analyses. Figure 19 uses different colors to identify the typical type of sediment that is found on the bed of Madsen Creek and the high flow bypass. In general, the reaches highlighted in yellow have experienced significant sediment deposition. These sediment deposits are discussed below. The figure also shows where sediment samples were collected. Collected data is presented and discussed later in this report. D D D D D D D D D D D D D DD D D A1 B2 B3 B4 C1 C2 C3 F1 F2 F3 G1 G2 E1 E3 E2 E7 D1 Sediment Sample Locations& Bed Material Types 14 Dec 2018 0 190 380 Feet Scale: 1:3,279NAD 1983 HARNStatePlane WashingtonNorth FIPS 4601 Feet U D SedimentSampleLocations Bed Material Type Silt Fine Sand Medium Sand (Fine Sand to Coarse Gravel) Medium to Coarse Gravel Coarse Gravel to Cobbles Riprap Figure 19 March 2019 Madsen Creek Existing Conditions 64 High Flow Bypass Upper High Flow Bypass (upstream from SR169) Figure 20 compares the longitudinal profile from the 1974 high flow bypass design plan set (blue line) to the profile surveyed for this investigation (orange line). The comparison reveals that there has been significant deposition from approximately station 1000 to station 2100, while the remainder of the high flow bypass experienced minor levels of degradation. Within the upper high flow bypass, deposition begins at approximately station 1000, which is about 100 ft upstream of the change in slope. The 1974 profile shows that the channel along the upstream 600 feet of the bypass was constructed at a slope of 0.025 (2.5%) while the next 400 feet of channel was built at a slope of 0.0028 (0.28%), nearly a ten-fold decrease. The maximum deposition, equaling 20 inches, occurs near the point of the slope change (station 1125). Hence, the significant extent of deposition is primarily attributed to the flatter slopes in the downstream reaches of the watershed. In 2017 the City removed an unknown amount of sediment from the upper high flow bypass (upstream of SR169); however, we do not know the exact location or the amount of material that was removed. Visible excavation signs on the channel banks suggest that the pre- excavation profile may have been something in the vicinity of the black dashed line in Figure 20. Sediment was also removed from the upper high flow bypass multiple times in the 1980s and 1990s. Notes in Table 3 indicate that sediment was removed routinely between 1981 and 1990 and may have been removed between 1991 and 1997 and again in 2005. There is no information about the exact location and quantity of sediment removal. The table does show that 232 yd3 was removed from the bypass in 1981 and 20 yd3 in 2005. It also shows that about 20% of the amount removed from the Sediment Basin was removed from the high flow bypass each year from 1985 through 1990, but removal locations are not provided. The table suggests that no sediment was removed from the bypass from 1998 through 2006 with the exception of the 20 yd3 removed in 2005. The City took over maintenance of the sediment basin and the upper high flow bypass in 2009, and according to City staff no sediment was removed between 2009 and 2016. In summary, this information suggests that sediment was not removed from the high flow bypass from 1998 through 2018, except in 2005 and 2017. Figure 21 identifies locations along the upper high flow bypass and lower Madsen Creek where the design cross section is compared to the 2018 surveyed cross section. The cross sections in the upper high flow bypass are shown in Figure 22. The comparisons reveal that the steeper upstream reach has not seen significant deposition, but rather channel incision within the downstream one-half. The deepest incision, approximately 18 inches, is at cross section 963. Within the flatter downstream reach, the changes caused by sediment deposition since 1974 are clearly visible in both the profile (Figure 20) and the cross-section comparisons. The channel is narrower and shallower due to deposition on both the banks and bed. Sediment was removed from the channel in 2017 prior to the 2018 survey, so these comparisons do not capture the considerable sediment deposition that existed at that time. Figure 20. Profile Comparison 1974 to 2018 high flow bypass. Culvert Outlet to Cedar SR169 Culvert Inlet Top of Low Flow Culvert Sediment Basin Outlet 90 95 100 105 110 115 120 500 750 1000 1250 1500 1750 2000 2250 2500 2750Elevation (ft, NAVD88)Distance Along Channel (ft) High Flow Bypass Profile 1974 Design 2018 Survey Estimated Channel Prior to Recent Excavation Slope = 0.025 Slope = 0.0028 Slope = 0.0036 1753 1928 248472189 2360 1391 963 1048 459 687 785 Sediment Deposition Comparison Locations 05 Dec 2018 0 175 350 Feet Scale: 1:25,000NAD 1983 HARNStatePlane WashingtonSouth FIPS 4602 Feet U TextText Figure 21 Full Cross Section ComparisonsThalweg Comparison Points 110 109 111 112 113 Elevation (ft, NAVD88)10 20 30 40 50 Station (ft) Cross-Section 785 104 103 105 106 107 Elevation (ft, NAVD88)10 20 30 40 50 Station (ft) Cross-Section 1048 101 100 102 103 104 Elevation (ft, NAVD88)10 20 30 40 50 Station (ft) Cross-Section 1391 105 104 106 107 108 Elevation (ft, NAVD88)10 20 30 40 50 Station (ft) Cross-Section 963 1974 Design Cross-Section 2018 Surveyed Cross-Section Fill Cut Upper High Flow Bypass Cross Section Comparison (1974 vs. 2018) Figure 22 March 2019 Madsen Creek Existing Conditions 68 SR169 Culvert The floor of the SR169 high flow bypass culvert has filled with fine to medium sand. The deposit is approximately 18 inches deep at the culvert entrance and 24 inches at the outlet. Lower High Flow Bypass (downstream of SR169) Within the lower high flow bypass, the channel has been impacted by sediment deposition both on the channel bed and banks. As shown by the profile and cross section comparisons in Figures 20 and 23, the most significant deposits are within the first 300 feet downstream of the SR169 culvert. The floor of the channel has risen up to 20 inches near the culvert outlet tapering to zero approximately 300 feet downstream. This deposit is an extension of the sediment that has filled the SR169 culvert. As shown by the cross-section comparisons, the channel has also narrowed significantly within the reach downstream of SR169 due to deposition on the banks. In the downstream half of the lower high flow bypass, however, there has been little to no deposition and up to six inches of incision at cross section 2360. The pattern of sediment deposition within the channel suggests that vegetation has been present within the channel during the most recent floods, because vegetation increases roughness which increases sediment deposition. Vegetation management is critical within this reach because sediment deposition therein, would also contribute to sediment depositing within the SR169 culvert. 98 97 99 100 101 Elevation (ft, NAVD88)10 20 30 40 50 Station (ft) Cross-Section 1753 96 95 97 98 99 Elevation (ft, NAVD88)10 20 30 40 50 Station (ft) Cross-Section 2189 95 94 96 97 98 Elevation (ft, NAVD88)10 20 30 40 50 Station (ft) Cross-Section 2360 97 96 98 99 100 Elevation (ft, NAVD88)10 20 30 40 50 Station (ft) Cross-Section 1928 1974 Design Cross-Section 2018 Surveyed Cross-Section Fill Cut Lower High Flow Bypass Cross Section Comparison (1974 vs. 2018) Figure 23 March 2019 Madsen Creek Existing Conditions 70 Madsen Creek Channel through Ron Regis Park Figure 24 compares the 1989 longitudinal profile of Madsen Creek downstream of 149th Avenue SE from the original design plan set (blue line) to the profile surveyed for this investigation in 2018 (orange line). The comparison reveals significant deposition along the entire length of the constructed channel, with the stream bed profile rising an average of approximately 1.5 feet. Changes in cross section area along this reach are shown in Figure 25, and cross section locations are shown in Figure 21. Deposition has been substantial throughout the reach, and the channel is now only about 25% of the size that it was when it was constructed in 1989. This equates to approximately 1600 yd3 of deposited sediment in the Ron Regis Park reach of the creek. To our knowledge, no sediment has been removed from the channel here since it was constructed, with the exception of occasional removals from a short section of channel immediately downstream from 149th Avenue SE, an area that is referred to as a “sediment trap” on the 1989 plan set. The reduction in channel cross section area is not surprising, because the channel was constructed too large to self-maintain. According to commonly used regime principles (ASCE, 1996), channels flowing through unconsolidated alluvium will typically size themselves to carry a dominate channel forming discharge. In the Pacific Northwest, the channel forming discharge for alluvial streams like Madsen Creek is typically a 1.5- to 2-year annual instantaneous peak flood. Based upon the hydrologic investigation conducted for this investigation, a two-year event on Madsen Creek at the entrance to the sediment basin is approximately 100 cfs; however, most of this flow never reaches the park channel because it is diverted into the high flow bypass and transported directly to the Cedar River. During a 2- year event, the hydrologic and hydraulic models predict that approximately 20 cfs will pass through the 149th Avenue SE culvert and enter the park channel. Regime formulas predict that a channel with a dominate discharge of 20 cfs and a channel slope of 0.0028 (0.28%) (the design slope) will have a depth of approximately two feet and a top width of approximately eight feet. Assuming near vertical banks, the cross-section area will be approximately 16 sq ft. Based upon the 2018 survey, the channel currently has a cross section area of approximately 15 sq ft, which is in line with what should be expected. To maintain the channel cross section that was constructed in 1989 would require a dominate channel forming discharge of approximately 200 cfs, about 10 times the size of the flow that actually reaches the park channel. Figure 24. Profile Comparison 1989 to 2018 Madsen Creek Channel within Ron Regis Park. ~ 50 ft downstream of 149th Ave SE culvert Upstream face of park entrance road bridge End of constructed channel 93 94 95 96 97 98 0 100 200 300 400 500 600 700 800 900 1000Elevation (ft, NAVD88)Distance Along Channel (ft) Madsen Creek Profile through Park 2018 Survey 1989 Design Channel 97 96 98 99 100 Elevation (ft, NAVD88)10 20 30 40 50 Station (ft) Cross-Section 47 96 95 97 98 99 Elevation (ft, NAVD88)10 20 30 40 50 Station (ft) Cross-Section 459 95 94 96 97 98 Elevation (ft, NAVD88)10 20 30 40 50 Station (ft) Cross-Section 687 97 96 98 99 100 Elevation (ft, NAVD88)10 20 30 40 50 Station (ft) Cross-Section 248 1989 Design Cross-Section 2018 Surveyed Cross-Section Fill Cut Constructed Channel ·Top Width 30 ft ·Depth 4 ft Natural Channel ·Top Width 8 ft ·Depth 2 ft Park Channel Cross Section Comparison (1989 vs. 2018) Figure 25 March 2019 Madsen Creek Existing Conditions 73 Other Reaches and Features Madsen Creek from Sediment Basin to High Flow Bypass Undercrossing Significant sediment deposition was not observed along the reach of Madsen Creek that extends from the sediment basin to where the stream turns west at SR169 (upstream of the high flow bypass undercrossing). However, significant deposits of fine sand are present within the reach of the stream that parallels SR169. This reach has a much flatter slope than the upstream portion, which is the primary reason sediment has deposited. Madsen Creek Culvert under High Flow Bypass Fine sand has deposited on the floor of this 4’ X 6’ concrete box culvert. The sand is 15 inches and 20 inches deep at the entrance and exit respectively. Madsen Creek Channel between Culvert under High Flow Bypass and SR169 No significant deposition was observed within this reach. Madsen Creek SR169 Culvert Fine sand has deposited on the floor of this 3’ X 6’ concrete box culvert. The sand is 0 inches and 15 inches deep at the entrance and exit respectively. Madsen Creek between SR 169 Culvert to 149th Avenue SE The channel bed is covered with fine sand and silt. 149th Avenue SE Culvert Fine sand has deposited on the floor of this 2’ X 8’ aluminum arch-type culvert (due to unique shape of the culvert the dimensions are approximate). The sand is 4 inches and 8 inches deep at the entrance and exit respectively. 149th Avenue SE Ditch The ditch along 149th Avenue SE appeared to be relatively clean and free of sediment. The only exception is that fine sand and silt have partially filled the two 18” culverts that connect the ditch in series to the High Flow Bypass Channel. March 2019 Madsen Creek Existing Conditions 74 3.3.2. Sediment Gr ainsize Cha racteristics To identify the characteristics of the sediments that are depositing, WSE collected sediment samples at 16 locations throughout the system (Figure 19). A Wolman Pebble Count was also performed to determine the grainsize distribution for sample A1 which is located in the natural channel upstream from the sediment basin. Grainsize distributions were determined by laboratory sieve analyses of bulk samples collected at the other 15 locations. At three of these sites an additional hydrometer test was performed because the samples contained a large amount of silt. The grainsize distribution curves for all 16 samples are presented in Figures 26, 27, and 28. Figure 26 shows the curves within the sediment basin and the natural channel upstream. Figure 27 shows curves for the high flow bypass and Figure 28 includes those for Madsen Creek downstream from the sediment basin. The D50 size of each sample and the material classification based upon the Unified Soil Classification System (USCS) are presented in Table 6. Conclusions about the sediment characteristics within each reach, drawn from the grainsize distributions, are revealed on the following pages. Table 6. Sediment Sample Data. Sediment Sample No. D50 (mm) Classification1 Location of Sample A1 50 coarse gravel Channel Bed B2 10 fine gravel Upstream end of basin B3 0.4 fine to medium sand Middle of basin B4 0.1 fine sand and silt Downstream end of basin F1 0.12 fine sand and silt Channel Bank F2 0.085 fine sand and silt Channel Bank F3 0.25 fine to medium sand Floor SR169 Culvert G2 0.055 Silt Channel Bed C1 17 fine to coarse gravel Channel Bed C2 13 fine gravel Channel Bed C3 0.35 fine sand Channel Bed D1 0.25 fine sand Channel Bed E1 0.35 fine sand Channel Bed E2 0.045 Silt Floodplain Bench E3 0.35 fine sand Channel Bed E7 0.35 fine sand Channel Bed 1 Unified Soil Classification System (USCS) 0 10 20 30 40 50 60 70 80 90 100 0.0001 0.001 0.01 0.1 1 10 100 1000Percent Finer, %Grain Size (mm) Madsen Creek Grainsize Distribution Curves Upstream Channel and Sediment Basin A1 Channel Bed Upstream from Sediment Basin Wollman Pebble Count B2 Sed Basin Delta B3 Mid Sed Basin B4 Sed Basin Lower Figure 26 0 10 20 30 40 50 60 70 80 90 100 0.000 0.001 0.010 0.100 1.000 10.000 100.000Percent Finer, %Grain Size (mm) F1 Upper High Flow Bypass Bank F2 Upper High Flow Bypass Bank F3 Inside SR-169 High Flow Bypass Culvert G2 Lower High Flow Bypass Bed Madsen Creek Grainsize Distribution Curves High Flow Bypass 1000.000 Figure 27 0 10 20 30 40 50 60 70 80 90 100 0.000 0.001 0.010 0.100 1.000 10.000 100.000 1000.000Percent Finer, %Grain Size (mm) Madsen Creek Grainsize Distribution Curves Madsen Creek Channel Downstream from Sediment Basin C1 Madsen Creek Bed C2 Madsen Creek Bed C3 Madsen Creek Bed D1 Madsen Creek Bed E1 Madsen Creek Sediment Trap E2 Madsen Creek Bank E3 Madsen Creek Bed E7 Madsen Creek Bed Figure 25 March 2019 Madsen Creek Existing Conditions 78 Sediment Basin and Channel Upstream As documented by the grainsize distribution curves shown in Figure 26, the bed of the natural channel upstream from the sediment basin is comprised of sand, gravel, and cobble. Within the sediment basin grainsize decreases from upstream to downstream. Near the inlet, the material is a mixture of sand, gravel, and small cobbles. The grain size decreases to fine to medium sand near the middle of the basin, and fine sand and silt near the outlet. The basin is performing well, capturing nearly all coarse bedload material and a significant percentage of fine sand and even some silt. That said, the sediment deposition documented in both the high flow bypass and Madsen Creek reveal that some sand and silt pass through the basin. The performance of the sediment basin is discussed in the next section. High Flow Bypass Figure 27 shows four grainsize distribution curves for deposit samples collected within the high flow bypass. Samples F1 and F2, which were taken from the banks of the channel, are located in the upper high flow bypass (Figure 19), F3 is from the floor of the SR169 Culvert and G2 is from the bed of the high flow bypass near the Cedar River. Curves F1 and F2 reveal that fine sand and silt have deposited on the banks of the high flow bypass. Sample F3 reveals that the sediment that has filled the bottom of the SR169 culvert is fine to medium sand. This is the same material that has deposited on the bed within the first 300 feet of the high flow bypass channel immediately downstream from SR169. It is likely that these deposits are in-part due to slow velocities caused by tall and dense vegetation in the channel. It is our understanding that the County usually mows the vegetation each year in January, which means that thick vegetation is present in the channel in November and December, the first two months of the flood season. As previously stated, it is important to mow the lower high flow bypass before the flood season to decrease both the probability of flooding and the potential for sediment deposition. Relatively little sediment has deposited within the downstream half of the lower high flow bypass. The material present in the latter reach is silt. Madsen Creek Channel Figure 28 shows eight grainsize distribution curves for deposit samples collected within Madsen Creek downstream of the sediment basin. Samples C1, C2, and C3 are in the channel upstream of the high flow bypass; sample D1 is in the short section of channel between SR169 and 149th Avenue SE; and, samples E1, E2, E3, and E7 are within the channel in the park. Within the reach that passes through the church property, the bed material decreases in size from gravel in the upper reach, to medium/coarse sand in the middle, to fine sand at the culvert under the high flow bypass. This decrease in size is directly related to a decrease in the channel slope which occurs along the reach. Within the reach downstream of SR169, the bed and bank materials are fine sand and slit respectively. March 2019 Madsen Creek Existing Conditions 79 Channel Velocities and Sediment Deposition The type of sediment that deposits within each sub-reach is directly correlated to flow velocity. Figures 29, 30, and 31 show maximum simulated velocities under existing conditions for the 2-, 25-, and 100-year events. Table 7 lists these velocities and compares them to the velocity that is required to move the average particle size found on the bed of the different sub-reaches (commonly referred to as incipient motion velocity). Table 7. Channel and Incipient Velocities for Stream Sediments by Sub-Reach. Sub-Reach Dominate Bed Material Type Average Channel Velocity During 2- to 100-year Flood (fps) Incipient Motion Velocity (fps)1 Upstream Sediment Basin Coarse Gravel (D50 = 50mm) 5 to 8 7 Sediment Basin Full Range Cobble to Silt (D50 = 0.1 to 10mm) 1 to 3 2 to 4 Upper High Flow Bypass Riprap (upper half) Sand (Lower Half) (no sediment sample from bed) 6 to 8 4 to 5 N/A (Sediment size on bed unknown) Lower High Flow Bypass (just downstream from SR169)2 Fine Sand (same material in SR169 culvert) (D50 = 0.25 mm) 2 to 3 2 North-South portion of Madsen Creek along Church Property Coarse Gravel to Medium Sand (D50 = 13 to 17mm) 3 to 5 4 to 5 Madsen Creek Parallel to SR169 Fine Sand (D50 = 0.35mm) 0.5 to 2 2.5 Madsen Creek within Park Fine Sand (D50 = 0.35mm) 1 to 2 2.5 1Incipient motion velocity for each material type obtained from USACE, 1994 assuming flow depth < 5 ft. 2Assumes channel vegetation has not been mowed/maintained. Simulated Maximum Velocities- 2yr Flood Event - UV169 UV169 CedarRiver 06 Dec 2018 0 150 300 Feet Scale: 1:2,000NAD 1983 HARN StatePlaneWashington South FIPS 4602Feet U Velocities (ft/s) 0 - 0.5 0.5 - 2 2 - 3 3 - 5 5 - 10 > 10 Madsen CreekExisting Conditions Figure 29 Simulated Maximum Velocities- 25yr Flood Event - UV169 UV169 CedarRiver 06 Dec 2018 0 150 300 Feet Scale: 1:2,000NAD 1983 HARN StatePlaneWashington South FIPS 4602Feet U Velocities (ft/s) 0 - 0.5 0.5 - 2 2 - 3 3 - 5 5 - 10 > 10 Madsen CreekExisting Conditions Figure 30 Simulated Maximum Velocities- 100yr Flood Event - UV169 UV169 CedarRiver 06 Dec 2018 0 150 300 Feet Scale: 1:2,000NAD 1983 HARN StatePlaneWashington South FIPS 4602Feet U Velocities (ft/s) 0 - 0.5 0.5 - 2 2 - 3 3 - 5 5 - 10 > 10 Madsen CreekExisting Conditions Figure 31 March 2019 Madsen Creek Existing Conditions 83 Noteworthy take-aways from the table are: 1. Velocities within the sediment basin are low enough to capture the full range of sediments transported by Madsen Creek. However, as will be described in the next section, approximately 50% of the suspended sediment load that enters the basin passes through the basin. 2. Once Madsen Creek turns left (west) to parallel SR169, average velocities for all three events fall to less than 2 fps. This continues downstream through the park. This is lower than the incipient motion velocity required to move fine sand which is why these reaches have experienced significant deposition. 3. Velocities within the upper high flow bypass slow downstream at mid-reach where the slope flattens, however, velocities tend to remain relatively high. A bed material sample was not be collected within the lower half of this reach because most of the material had been removed in 2017 when the City cleaned the channel. 4. Velocities within the lower high flow bypass slow significantly if vegetation is not mowed or maintained. This is likely the reason fine sand has deposited within the SR169 culvert and the first 300 feet of the channel. March 2019 Madsen Creek Existing Conditions 84 3.3.3 . Sedimen t Basin Performance and Basin Sediment Yield It would be useful to know how much sediment is delivered to the sediment basin and project reach each year. The most reliable estimates are those generated from actual sediment data of which we have two data sets from within the project reach: 1) the volume of sediment that has been removed from the sediment basin annually and 2) the amount of sediment that has deposited within the reach of Madsen Creek that was constructed within Ron Regis Park. The volume of deposited sediment that is removed from the basin can be used to create a rating curve which relates stream discharge to volume of sediment deposited within the basin, assuming the original basin topography was restored with each cleaning. The relationship between flow and sediment deposition can be described as: , where is the rate of sediment deposition, is the discharge entering the basin, and a and b are fitting coefficients. Through a series of statistical analyses which compared 15 minute flow data to the total volume of sediment removed from the basin each water year, WSE found that the discharge to sediment deposition relationship is best described when a = 0.00004 and b = 2.66, where is cubic yards of sediment deposited over a 15-minute period and is the average flow rate into the basin in cubic feet per second as observed at 15-minute intervals at the King County stream gage located at the entrance to the basin. The rating curve represented by this formula is illustrated in Figure 32. Figure 32. Rate of Sediment Deposition in Sediment Basin for a Given Inflow. March 2019 Madsen Creek Existing Conditions 85 While the above relationship provides an estimate of the rate of sediment deposition in the basin for a given flow rate, it does not provide an estimate of the volume of sediment that passes through the basin. Sediment leaving the basin will either enter the high flow bypass where most of it will be conveyed to the Cedar River, or to Madsen Creek where nearly all of it will deposit along the flatter slopes of the channel because velocities slow and the stream has been diverted into a series of ponds and no longer connects directly to the Cedar River. If we assume that the volume of sediment leaving the basin via the high flow bypass and Madsen Creek is directly proportional to the discharge that each route carries, then Figure 33 can be used to compute these volumes. The figure shows the percentage of the total flow leaving the sediment basin through the high flow bypass, as calculated by the project HEC-RAS model. The figure includes two curves, one that assumes the entrance to the culvert that discharges to Madsen Creek is completely open (bottom curve), and another that represents the current condition in which the entrance is partially covered by metal plates. This pair of curves suggest that during the large events (greater than about a 2-year (100 cfs)) the high flow bypass has carried 60% to 90% of the total flow leaving the basin. Figure 33. Fraction of Flow Exiting Sediment Basin through the High Flow Bypass. (Two conditions presented – one with the Madsen Creek culvert entrance partially blocked by metal plates and the other with it fully open.) March 2019 Madsen Creek Existing Conditions 86 To estimate the trap efficiency of the current sediment basin, we need to make an estimate of the quantity of sediment that has passed through the basin since it was built in 1991. Although sediment data is limited, we know that approximately 1600 yd3 of sediment has deposited within the 1000-ft long section of Madsen Creek that was constructed through Ron Regis Park since 1989. This alone does not tell us how much sediment passed through the Madsen Creek culvert at the outlet of the sediment basin, but if we make several, albeit broad assumptions, we can estimate the amount. Reports from residents and historical photographs indicate that a significant amount of sediment was delivered to and deposited within the constructed park channel during the 1990 flood when the sediment basin berm was breached and failed. The basin was rebuilt following that event, so the current basin configuration has existed since 1991, therefore, we need to reduce the 1600 cubic yard estimate by the amount that was deposited by the 1990 flood. We don’t know how much sediment deposited in the park channel during the event, but we do know it was large enough that King County considered removing it (based upon King County maintenance notes reviewed for this investigation). We know that it did not fill the channel and we also know, based upon eye witness accounts, that most of the sediment from the event deposited within Wonderland Estates and other properties upstream from SR169. Therefore, based upon the anecdotal information, it may be reasonable to assume that no more than a third of the 1600 yd3 of sediment was delivered during the 1990 flood. If true, then roughly 1100 yd3 has deposited since 1991. This estimate is only a portion of the total load that has moved through and deposited in Madsen Creek downstream from the sediment basin; and we need to know the total load in-order to estimate trap efficiency. Unfortunately, due to a lack of data we can only make broad assumptions to arrive at this estimate. Based upon field observations, we know that a significant amount of sediment has deposited on the floodplain adjacent to the Madsen Creek within Ron Regis Park, within the channel and on the floodplain in the large wetland downstream from the park, along the relatively flat section of Madsen Creek between the park and the point that the stream first encounters SR169 upstream from the high flow bypass, and on the floodplain between SR169 and the sediment basin; however, due to the steeper channel slope in this reach, the quantities are less than along the flatter reaches downstream. In addition, in the early 1990s the channel maintained a direct connection to the Cedar River so some sediment passed through Madsen Creek to the river. The channel no longer connects directly to the Cedar River, but instead has been diverted into a relatively large pond adjacent to the river. The total length of these reaches is approximately four times that of the constructed channel. If, we use this channel length ratio to assume that the total amount of sediment delivered to and deposited within Madsen Creek downstream from the sediment basin is 3 to 5 times the 1100 yd3 that we have assumed has accumulated in the park channel between 1991 to 2017, then the total sediment delivered to Madsen Creek would be in the range of 3,000 to 6,000 yd3 (see Table 8). If, based upon Figure 33 above, we assume that during this time an average of 80% of the flow exited the sediment basin through the high flow bypass, then one also can assume that 80% of the sediment exited through it too. This suggests that four times as much sediment has been transported through the high flow bypass as compared to Madsen Creek. Multiplying the Madsen Creek sediment deposition volume estimate by four, suggests that the amount of sediment transported by the high flow bypass since 1991 may be in the range of 12,000 to March 2019 Madsen Creek Existing Conditions 87 24,000 yd3. This combined with the Madsen Creek volume, provides a very rough range suggesting that 15,000 to 30,000 yd3 of sediment may have passed through the basin since 1991, most of it finding its way to the Cedar River via the high flow bypass. To estimate trap efficiency, we need to compare the estimate above to the quantity of sediment that actually deposited in the sediment basin between 1991 and 2017. Sediment basin cleaning removal records in Table 8 indicate that approximately 12,500 yd3 of material was removed from the basin between 1991 and 2006. Removal records are not available for the period 2007 to 2017 except for 2009, but they can be estimated using 15-minute flow data from the King County gage and the sediment basin deposition rating curve in Figure 32. This method suggests that approximately 9000 yd3 deposited between 2007 and 2017 for a total deposition within the basin of 21,500 yd3 between 1991 and 2017. Comparing this value to the 15,000 to 30,000 yd3 that we have estimated passed through the basin, suggests that the basin is capturing 40% to 60% of the total volume of sediment that is transported to the project reach. The sediment basin removal records indicate that on average approximately 800 yd3 of sediment accumulates within the basin each year. If the basin captures 50% of the sediment load, then approximately 800 yd3 passes through. Under the current sediment basin outlet configuration which in which metal plates block 75% of the entrance to the Madsen Creek culvert, approximately 90% (720 yd3) currently leaves the basin through the high flow bypass and 10% (80 yd3) through Madsen Creek. Table 8. – Sediment Basin Capture Efficiency Calculations Based on Known or Estimated Sediment Volumes Deposition between 1991 and 2017. Location of Sediment Volume of Sediment (yd3) Assumption/Calculation Madsen Creek Channel downstream from Sediment Basin 3,000-6,000 (years 1991 to 2017) Very rough estimate based on known deposition in Ron Regis Park combined with field observations along stream Sediment Passing through the sediment basin 15,000-30,000 Based upon assumption that 80% of sediment passes through High Flow Bypass and 20% through Madsen Creek Deposition in Basin (1991-2006) 12,500 Recorded by King County (Table 3) Deposition in Basin (2007-2017) 9,000 Estimate based on flow record and sediment rating curve (Figure 32) Total Sediment Captured by Basin 21,500 Period 1991 to 2017 Sediment Basin Capture Efficiency 40% - 60% Total Captured Sediment / (Total Captured Sediment + Total Passing Sediment) March 2019 Madsen Creek Existing Conditions 88 Figure 34 shows a conceptual layout of sediment distribution within and leaving the basin. Based upon the rational described above, of the sediment that enters the basin, approximately 50% is captured and 50% passes through. Of the 50% portion passing through, currently about 45% leaves via the high flow bypass and 5% through Madsen Creek. Based upon the sediment samples collected for this investigation, the basin captures nearly all particles larger than medium sand, and a significant portion of the fine sand and silt. The material that leaves the basin is primarily fine sand and silt transported as suspended load. Trap efficiency in the range of 50% is relatively good for sediment basins of this type, therefore, it is our opinion that it was well designed and is serving its intended purpose. Figure 34. Approximate Distribution of Sediment Delivered to and Existing the Sediment Basin. March 2019 Madsen Creek Existing Conditions 89 4. P OTENTIAL S OLUTI ONS Based upon our understanding of the hydrologic, hydraulic, and sediment transport characteristics of Madsen Creek gained through this existing condition assessment, the following solutions are suggested. The proposed solutions are grouped into two categories: 1) recurring maintenance activities, and 2) one-time capital improvement projects. Within each category the solutions are listed in the order of relative importance as viewed by the consultant team: Recurring Maintenance Projects: 3. Restore the capacity of the high flow bypass and the SR169 culvert by removing accumulated sediment and developing an effective sediment removal and annual vegetation maintenance program. 4. Monitor sediment accumulations within the three culverts listed below. Remove the sediment if it starts to limit the capacity of the culvert to the point flooding upstream worsens. This may require removing sediment from the channel downstream from the culvert to prevent the culvert from rapidly refilling with sediment. a. Madsen Creek culvert under high flow bypass b. Madsen Creek SR169 culvert c. Madsen Creek 149th Avenue SE culvert It is recommended that the City, County, and WSDOT work together to develop a memorandum of understanding that specifies the entity responsible for each maintenance activity identified in this study and the frequency and timing of that maintenance. One-Time Improvement Projects: 11. Raise the right bank berm along the upper high flow bypass. 12. Continue to limit the amount of flow that enters Madsen Creek by either retaining the existing plates or installing a slide gate on the entrance to the Madsen Creek culvert at the outlet of the sediment basin. 13. Raise the right bank berm along the section of channel between SR169 and 149th Avenue SE. 14. Raise the height of the ground that separates Madsen Creek from Wonderland Estates. 15. Raise the berm that surrounds the sediment pond and add a rock-lined emergency spillway that discharges to the high flow bypass. 16. Increase culvert capacity at the downstream end of the ditch along 149th Avenue SE either by improving the existing culvert outlet system, or preferably installing a second culvert outlet that drains to the Cedar River and not the high flow bypass. March 2019 Madsen Creek Existing Conditions 90 Also, consider enlarging the ditch. 17. Raise the ground height surrounding the entrance to the SR169 high flow bypass culvert to provide freeboard during the 100-year flood if the entrance to the culvert becomes partially blocked by woody debris. 18. Raise the right bank berm of Madsen Creek where it overtops near the downstream end of the park channel. March 2019 Madsen Creek Existing Conditions 91 5. C ONCLUSION S The existing condition assessment described here in has identified the significant factors that are responsible for the flood and sediment problems that are currently impacting lower Madsen Creek. It has also revealed that there appear to be feasible solutions that can be implemented with relative ease, solutions that consist of a series of one-time construction activities and a renewed commitment to a multi-jurisdictional updated and improved maintenance program. March 2019 Madsen Creek Existing Conditions 92 6. R EFERENCES ASCE, 1996. “Channel Stability Assessment for Flood Control Projects.” Technical Engineering and Design Guides as adapted from the US Army Corps of Engineers, No. 20. Published by ASCE Press 345 East 47th Street New York, New York. Barghausen, 2009. “New Life Church”. Proposed site development plan set showing modified stormwater drainage plan and detention pond. Barghausen Consulting Engineers, Inc. Kent, WA. Sheets R-348301 to R-348316. Plans are NOT identified as “As-Built”. Plan set contains multiple dates all between 2008 to 2009. City of Renton, 1997. “Plan Set Cedar River Regional Park, Madsen Creek Bridge.” City of Renton Department of Parks and Recreation. Sheets 81 to 84. Plans are NOT identified as “As-Built”. Plan set is dated September 16, 1997. Dinicola, R.S. 1990. Characterization and Simulation of Rainfall-Runoff Relations for Headwater Basins in Western King and Snohomish Counties, Washington. Water-Resources Investigation Report 89-4052. U.S. Geological Survey, Tacoma, WA. Dinicola, R.S. 2001. Validation of a Numerical Modeling Method for Simulating Rainfall-Runoff Relations for Headwater Basins in Western King and Snohomish Counties, Washington. U.S. Geological Survey, USGS Water Supply Paper No. 2495. Prepared in Cooperation with the King County Department of Public Works, and Department of Planning and Community Development. USGS, Tacoma, WA. King County, 1974. “Plan Set Madsen Creek Settling Basin and Channel Relocation”. King County Dept. Of Public Works, Division of Hydraulics. Three sheets numbered consecutively from F-67-1 to F-67-3. Plans are NOT identified as “As-built”. King County, 1989. “As-Built Plan Set, October 2, 1989. Madsen Creek Channel Improvements Near 149th. Ave S.E. & Maple Valley Highway – (SR169)”. King County Dept. Of Public Works, Paul Tanaka Deputy Director, Surface Water Management Division. Seven sheets numbered consecutively from 2000-60 to 2000-60F. King County, 1995. “Plan Sheet Madsen Creek Sediment Pond” improvements. King County Dept. of Public Works, Survey & Mapping. Single plan sheet identified as 1 of 14. Dated February 1995. King County, 1998. “Madsen Creek Sediment Pond Fish Ladder” plan set. King County Surface Water Management. Plan Set dated March 31, 1998. Three sheets numbered 1 to 3, plus a fourth unnumbered log notched detail sketch. King County, 2002. “149 Avenue SE Concrete Cutoff Wall”. Design plan for concrete weir structure to limit flow into ditch along east side of 149th Avenue SE. King County Water and Land Resources Division, Stormwater Service Section. Dated August 20, 2002. March 2019 Madsen Creek Existing Conditions 93 Kolcsey, Stephen, J., 1990. “Catastrophic Flood January 9, 1990 to Mobile Home Wonderland & The Kolcsey Residence from the 16-year Old King County Madsen Creek Drainage System. U.S. Army Corps of Engineers (USACE), 2016, “HEC-RAS River Analysis System 2D Modeling User’s Manual”. U.S. Army Corps of Engineers (USACE), 1994, “Stability of Flood Control Channels. EM1110-2- 1418”. WADNR (2018), Washington Department of Natural Resources online LiDAR portal, https://www.dnr.wa.gov/lidar, accessed July 2018. WSDOT, 1993. “SR169 196th Avenue S.E. / Jones Road to Maplewood” SR 169 highway widening project. Plan sheets 91,103, 247 of 333. Plans stamped “for “As Constructed Plans” Only. Multiple dates appear on the plan set all between July and August 1993. WSE (2013), “Cedar River Interactive Mapping Project Model and Mapping Development”, Watershed Science and Engineering, technical memorandum to King County, 21 August 2013.