Loading...
HomeMy WebLinkAboutPN_Madsen_Project_Narrative_210420_v1Project Narrative Project Name: Madsen Creek Flood Control Improvement Project Project description, size, and location of the site(s): The Madsen Creek Flood Control Improvement Project is a City of Renton Surface Water Capital Improvement Project funded by the King County Flood Control District. The project consists of four (4) sites requiring improvements to restore and increase the lower Madsen Creek network flood protection and capacity, as well as provide routine maintenance measures. The Madsen Creek Flood Control Improvement Project is located in City of Renton and unincorporated King County, Washington in the west half of the southwest quarter of section 23, township 23 north range 05 east, Willamette Meridian, in King County, Washington. Madsen Creek is a tributary of the Cedar River and is within the Hydrological Unit Code (HUC) 17110012 (Lake Washington Watershed)1 and within Water Resources Inventory Area (WRIA) 8 (Cedar/Sammamish)2.The project consists of construction at four (4) noncontiguous sites. Site 1 is within an existing City of Renton easement (recording number 20091007000046) at the New Life Church property located at 15711 152nd Ave SE. Site 1 is along the northeast corner of the Madsen Creek sedimentation basin approximately 47.462786 latitude, -122.142083 longitude. Site 1 work consists of raising the berm surrounding the sediment basin and adding an emergency spillway that discharges to the high flow bypass. This will provide additional flood protection for the Wonderland Estates development in the event the outlet culverts are blocked, there is an extreme event, or any flood waves occur within the sediment basin. Work at this site is adjacent to a high erosion hazard area; within, and adjacent to, a Type F water; within a seismic hazard area; within a zone 2 wellhead protection area; and within a sensitive slope area. Site 1 consists of approximately 7,170 SF of impact area with 1,160 SF of land disturbance from adding new impervious area, 4,140 SF of replaced impervious area, and 1,160 SF of landscape mitigation. A majority of Site 2 is within an existing City of Renton easement (recording number 20091007000046) at the New Life Church property located at 15711 152nd Ave SE. An additional permanent public utility easement is in progress with New Life Church to complete work outside of the existing easement. Site 2 is within, and along the access road and banks of the Madsen Creek high flow bypass channel from the sedimentation basin outlet to the SR 169 culvert. Site 2 work consists of widening the high flow bypass channel and removing accumulated sediments, as well as raising the right (east) bank of the upper high flow bypass channel to eliminate the low spot acting as a weir diverting flows to the low flow channel. These improvements will reduce the risk of flood water overwhelming the downstream flood conditions within the Madsen Creek low flow channel by increasing the capacity of the high flow bypass channel and providing at lease 6-inches of freeboard for the 100-year flood event. The widening of the channel will also provide compensatory storage for the fill from the flood control berms within the floodplain. Work at this Site is within, and adjacent to a floodplain; within, and adjacent to, a City of Renton 1 Environmental Protection Agency. 2013. Surf Your Watershed. http://cfpub.epa.gov/surf/locate/index.cfm. 2 Washington Department of Ecology. 2013. Washington Water Resource Inventory Area (WRIA) Maps. http://www.ecy.wa.gov/services/gis/maps/wria/wria.htm. classified Type F water; within a seismic hazard area; and within a zone 2 wellhead protection area. Site 2 is approximately 27,500 SF of area which includes 12,630 SF of sediment maintenance removal, 16,850 SF of land disturbance area, 16,850 SF of landscape mitigation area. No new impervious or pervious area is being added or replaced at Site 2. Site 3 is along the south, or left bank of Madsen Creek from the single-family residence 14937 Maple Valley HWY through Wonderland Estates development (14645 Maple Valley Hwy) to the SR 169 culvert. Site 3 work will raise the elevation of the left (south) bank from the private property (14937 Maple Valley Hwy) through Wonderland Estates to the low flow culvert under SR 169. The banks will be raised through a shallow floodwall and flood control berm. This will reduce the risk of flooding during the 100- year event and provide additional protection when SR 169 culvert or any downstream reach is impeded. Work at this Site is within, and adjacent to a floodplain; adjacent to a classified Type F water; within a seismic hazard area; and within a zone 2 wellhead protection area. Site 3 consists of approximately 2,270 SF of area including land disturbance and mitigation (1,820 SF each) and is 1-foot from a regulated stream at the nearest area of work. The shallow floodwall will add 60 SF of new impervious area to Site 3. No new pervious area is being added nor is any pervious or impervious surface being replaced at Site 3. Site 4 is along the right or north bank of Madsen Creek within BNSF railway property (King County Parcel ID 2323059028) within the City of Renton and a single-family residence located at 15214 149th Ave SE within unincorporated King County. Site 4 work will remove the existing Eco Block wall along the right (north) bank of the low flow channel between the outlet of the SR 169 culvert to the 149th Ave SE culvert entrance and replace it with a flood control berm. This will reduce the risk of flooding the properties along 149th Ave SE during the Madsen Creek 100-year flows. Work at this Site is within, and adjacent to a floodplain; adjacent to a classified Type F water; within a seismic hazard area; and within a zone 2 wellhead protection area. Site 4 consists of approximately 3,760 SF of area including land disturbance and mitigation area and is 2-feet from a regulated stream at the nearest area of work. See Table 1 for specific site areas. No new impervious or pervious area is being added or replaced at Site 4. In addition to these improvements, the high flow bypass capacity will be increased, and maintenance actions and agreements will be implemented. The high flow bypass channel was historically built to contain an indeterminate peak flow and has shown to convey less than the 25-year. The high flow bypass will geometry was optimized to allow for compensatory requirements for adding flood control berms within the floodplain, provide capacity and flood prevention during a 100-year event, and reduce the impact to the project site. The high flow bypass requires maintenance to remove sediment accumulation and restore the historic capacity of the channel. The project also intends to create a monitoring and maintenance agreement between the various jurisdictions responsible for maintaining the lower Madsen Creek network; these include King County and Washington Department of Transportation. Table 1: Site Areas Site Jurisdiction Site Area (SF) Land Disturbance Area (SF)* Landscape Mitigation Area (SF) Maintenance Area (SF) 1 Renton 7,170 1,160 1,160 0 2 Renton 27,500 16,850 16,850 12,630 3 Renton 2,250 1,820 1,820 0 4 Renton 1,490 380 380 0 4 King County 2,270 1,060 2,270 0 Total 40,680 21,270 22,480 12,630 Notes: Land disturbance area does not include areas where there is no change to the existing surface condition (i.e. landscape mitigation) or maintenance. Existing site use and improvements: Madsen Creek is a tributary of the Cedar River and collects runoff from a large upland glacial plateau and then descends through a steep hillside ravine before flowing into the Cedar River. Rapid development in the 1970's increased the amount of storm water runoff and sediment deposition into the Madsen Creek system, causing flooding. As a result of flooding, King County constructed a sediment basin and high flow bypass channel in 1976 to help mitigate the impacts. Further flood control improvements and changes to Madsen Creek network were made in 1989 through 2010. The improvements required maintenance dredging of the sediment basin and the high flow bypass channel. The sediment removal activities were documented by King County until 2009, when the area was annexed into the City of Renton. The City took over the maintenance for the Madsen Creek sediment basin and the upper portion of the high flow bypass, from the sediment basin to SR 169. The maintenance and improvements have been documented in the 2019 Lower Madsen Creek Existing Conditions Flood and Sediment Assessment by Watershed Science and Engineering (WSE). The Madsen Creek and Cedar River confluence also underwent modification during the 2001 Nisqually Earthquake which caused a landslide, temporarily damming the River. This landslide and damming occurred at approximately River Mile 5.0, just north of the Ron Regis Park. This caused significant ponding, overbank flooding, and erosion to the area, altering the geomorphology and historical alignment of Madsen Creek. The lower Madsen Creek network begins at the Madsen Creek Sedimentation Basin. Flow from the sediment basin is diverted by two culverts; the culvert to the northeast diverts flows to the high flow bypass channel and the other culvert diverts flows east through the main channel or low flow channel. The low flow channel routes east, north, and west around the New Lift Church Soccer fields, following the historic creek alignment, until reaching the culvert crossing underneath the high flow bypass channel. The main channel continues west from the high flow bypass, parallel SR 169, until it crosses SR 169 north in front of the Wonderland Estates development. Once across SR 169, the low flow channel flows through the southwest corner of a residential property (15214 149th Ave SE), through a culvert under 149th Ave SE and into Ron Regis Park. The low flow routes west and north through Ron Regis Park until it reaches a designated wetland area where the historical alignment has been re-routed and undefined; alignment for this reach based on best available data. The high flow bypass channel, built in 1976, routes north from the sediment basin within a City of Renton easement on the New Life Church property until crossing over the low flow channel and underneath SR 169. When the bypass channel was build, the main channel was converted to a culvert where the high flow bypass crossed over. The bypass channel continues north from SR 169, where in outfalls into the Cedar River. The high flow bypass channel requires maintenance to remove sediment. Sediment removal maintenance has occurred, and vaguely documented since 1976, but over time the channel has lost the capacity to adequately convey flood waters. Flooding has occurred more frequently as increased development flows enter the Creek from upstream the basin (Fariwood). The lower Madsen Creek network is maintained by the City of Renton, Washington State Department of Transportation (WSDOT), and King County. WSDOT maintains two box culverts within SR 169; the culvert directing the high flow bypass north across SR 169 and the main channel culvert routed north to 149th Ave SE and Ron Regis Park. King County maintains the lower high flow bypass channel after it passes through the SR 169 channel. A small portion of the main channel is also within unincorporated King County as it enters the 15214 149th Ave SE property. The City maintains all other features of Madsen Creek; including the sediment basin, upper high flow bypass, the low flow culvert underneath the high flow bypass, and the 149th Ave SE culvert. The Madsen Creek sediment basin has an ongoing Hydraulic Project Approval (HPA) to remove sediment, which is typically done on an annual basis. The last recorded sediment removal from the upper high flow bypass channel was in 2017; removal amount was not documented. The last removal from the lower high flow bypass (below SR 169) was recorded in 2019 by King County. Further information on the sites existing conditions can be found in the 2018 WSE Existing Conditions Report. The lower Madsen Creek network is within, and adjacent to, multiple critical areas; zone 2 of the aquifer protection area, floodplain and floodway, wetlands, Cedar River regulated shoreline, seismic hazard area, regulated slopes (<=40%, mostly <=25%), and high erosion hazard. The Madsen Creek low flow channel is a perennial tributary to the Cedar River, and is mapped by the Washington Department of Natural Resources (WDNR) as a Type F (fish bearing) water. The high flow bypass channel of Madsen Creek is mapped by WDNR as a Type N (non-fish bearing) water. The City manages this channel as a storm water facility (Facility ID# 146244) in relation to its purpose to route flood flows directly to the river. Flows within the high flow bypass channel are intermittent, occurring when the sediment basin engages the outlet weir, usually during moderate to large storm events in the drainage basin. The channel is mapped by the City as a Type F water for the purposes of protecting the riparian corridor according to the City’s Critical Areas regulations. The high flow bypass channel north of SR 169, within King County jurisdiction, is considered a Type N water. The WDNR and Washington Division of Fish and Wildlife (WDFW) do not consider any portion of the high flow bypass channel as a Type F or fish bearing water. Further documentation can be found in an Environmental Assessment Report: Madsen Creek Improvement Project developed in 2018 by Herrera Environmental Consultants included as an Appendix to the included Mitigation Plan. Anticipated Dates of Work: September 2021 through October 2021 Basis for Exemption: The City of Renton is requesting a Critical Areas Exemption for the project as removal of sediment and widening of the high flow bypass is considered exempt under maintenance and construction for an existing use facility activity. Widening the high flow bypass channel classifies as a remodel of an existing public use facility, and sediment removal is considered normal or routine maintenance and repair of an existing use facility. The flood control berms and shallow flood wall are exempt under the surface water alteration activity for flood hazard reduction. Other Permits Required: The City is also coordinating with the following regulatory agencies to obtain other environmental permits: Washington Department of Fish and Wildlife for Hydraulic Project Approval; King County shoreline exemption, critical areas review, grading permit, and flood hazard certificate; and City of Renton for State Environmental Policy Act (SEPA) approval, and other local construction permits. Project Impacts and Mitigation: The wetlands within the project area located at Site 3 and Site 4 and identified as Category II riverine Palustrine Emergent/Scrub-Shrub wetland and Category II riverine Palustrine Forested wetland. These wetlands are associated with the Madsen Creek low flow channel and neither are considered to be a wetland of high conservation value as they do not intersect with a rare plant species, rare high-quality wetland, or riparian vegetation community. There are several wetlands near the project area on the New Life Church property that are associated with the forested Madsen Creek low flow channel riparian corridor and are defined as a habitat area relatively important to various native fish and wildlife species. No direct wetland impacts are associated with the project. Site 4 is regulated by King County and City of Renton. Site 2, 3, and 4 are located within the Cedar River 100-year floodplain. Work at Site 1 and Site 2 require work below the OHWM within the high flow bypass channel. The majority of the proposed spillway construction at Site 1 will overlay an existing gravel-surfaced maintenance access road. The assessment of buffer alterations at Site 1 is limited to only that portion of the work that extends beyond the existing roadway. In-water work is restricted to approximately 10 cubic yards of rock placement within an area of 100 square feet where the downstream end of the spillway will extend to the bottom of the high flow bypass channel at Site 1. Site 2 work proposes removing sediment accumulation below the OHWM in the high flow bypass channel of Madsen Creek, along with minor widening of the channel beyond its originally constructed dimensions to increase flood storage. The in-stream work at Site 2 is considered to be a temporary alteration because the channel will require periodic maintenance in the future when the extent of sediment accumulation reaches a level that affects 100-year flood conveyance capacity. It is anticipated that new sediment and vegetation within the channel will regenerate naturally with time. Table 2 summarizes the environmental impacts and mitigation associated with the project actions. Further information on project impacts on the riparian habitat are addressed in the project Mitigation Plan. Vegetation removal will be limited to those areas necessary for placement and compaction of soil for new berm and wall construction, to access construction work areas, and to remove all nonnative and invasive vegetation from the disturbed riparian areas within the project sites. No clearing of the forested riparian buffer along the Madsen Creek low flow channel on the New Life Church property will occur in association with the project. Site 1 fill will include approximately 145 CY of rock ballast, Class A rock for erosion and scour protection, smaller crushed rock for spillway bedding, and earthen fill to raise the existing access driveway. Berms for Site 2, 3, and 4 consist of compacted earthen fill with low permeability for flood control covered with at least 6-inches of native topsoil for plantings. An erosion control grass seed mix will be used where soils are exposed during construction. The Madsen Creek Project will impact regulated critical areas and associated buffers within the City of Renton and King County unincorporated area but will be mitigated with no net loss of function. Alterations to buffer areas within the project limits will be mitigated through a sequence of actions intended to maintain or improve existing ecological functions upon project completion. Disturbed project areas will be restored by removing invasive vegetation, removing nonnative vegetation, and planting native vegetation. Compensatory mitigation for project associated buffer alterations will be achieved in accordance with RMC 4-3-050.L and KCC 21A.24.340 and KCC 21A.24.380. Enhancement of riparian buffers, through invasive plant species removal and native revegetation, will increase existing buffer areas in the Madsen Creek corridor and will encourage use by a diversity of wildlife. All planting zones will be monitored for a minimum of 5 years to document the success of the site against established performance standards. All temporarily disturbed wetland, stream, and buffer areas will be restored, and high visibility fencing and TESC materials will be removed from the site once construction is completed. All disturbed vegetated areas and ground surfaces (e.g., stream banks and access areas) will be restored to similar or improved conditions through a combination of seeding, mulching, and planting. Mitigation to compensate for project-associated alterations to the floodplain and stream buffers will be provided to achieve no net loss of habitat area and functions within the City of Renton’s regulated critical areas. Reduction of public flood hazard areas is considered an exempt activity if buffer restoration and enhancement is provided at a 1:1 ratio. Mitigation for impacts to the City of Renton’s protective buffer areas will be compensated by the removal of invasive vegetation and the installation of native plants in direct proportion to the disturbed area. Temporary impacts resulting from construction access and equipment operation will be mitigated for by restoring in-kind; thus, no additional mitigation is necessary in those areas. Table 2: Alterations to Regulated Shoreline and Critical Areas and Mitigation for the Madsen Creek Flooding Improvement Project. Type of Alteration 100-Year Floodplain In-Stream (below OHWM) Mitigation Site ID Area (square feet) Volume (cubic yards) Area (square feet) Volume (cubic yards) Buffer (square feet)Ratio Type Area (square feet) 1 N/A 100 square feet Fill: 10 Proposed Spillway: 1,160a 1:1 Buffer Enhancement 1,160 Channel Maintenance: 3,485 Channel Maintenance: 54 (cut) Berm Construction: 0 Channel Widening for Flood Storage: 71 (cut) 2 Total: 3,485 Total: 125 (cut) Channel Maintenance: 4,276; 500 linear feet Cut: 110 Fill: 0 Net: -110 Channel Maintenance: 12,625 Berm Construction Right Bank: 4,225 Total: 16,850b,c 1:1 Buffer Restoration/ Enhancement 16,850 3 Berm: 1,120 Wall: 60 Total: 1,180 Fill: 33 Not Applicable Fill: 1,180 Temporary Access: 640 Total: 1,820 1:1 Buffer Restoration/ Enhancement 1,981 Renton: Berm: 380 1:1 380 King County: Berm: 755 2,270d Temporary Access: 300e 0e 4 972 Fill: 38 Not Applicable Total: 1,435 3:1 Buffer Restoration/ Enhancement TOTAL:5,637 Net: -54 4,376 Net: -100 21,265 22,480 N/A – Not Applicable a Excludes overlay of gravel on existing maintenance access road, which is not assessed as a buffer impact. b Excludes minor overlay of gravel on existing maintenance access roadway along left (west) bank at completion of construction to fill ruts (up to 4,500 square feet). c Grass seed will be broadcast as an erosion control measure along the edges of the elevated roadway. d Includes restoration of the temporary access routes. e Temporary access areas are currently private lawn – grass to be restored in kind. Access: Site 1 access is through an existing maintenance access road off SR-169 on an existing City of Renton Public Utilities easement (recording number 20091007000046). Site 2 is accessed through the same easement as Site 1 and will also require an amendment to the existing public utilities easement to complete the work after widening the high flow bypass channel and adding flood control berms. This amendment is currently being negotiated with New Life Church. Site 3 work will be accessed through a new public utility easement being negotiated with Wonderland Estates and will also be within City of Renton right-of-way. Site 4 will be accessed through a private access road on 15214 149th Ave SE. This will be done through a new public utility easement currently under negotiation within the private property owner at 15214 149th Ave SE. Work within BNSF property will be completed within an existing easement for developing, constructing, and maintaining a stream enhancement area (Recording #9306182810). Total Estimated Construction Cost: The estimated project cost opinion put together by Herrera Environmental Consultants, Inc. at the 75 percent design was $277,000. The cost opinion covered berm construction, sediment removal, spillway construction, SWPPP, planting and mitigation assuming a 20% contingency. Tree Removal: The project work will require the removal of six of a total of seven existing multi-stemmed deciduous trees present at the site on the east side of the high flow bypass channel. The results of an arborist survey of trees potentially impacted by the project work at Site 2 are documented in the Mitigation Report of this submittal. The six trees proposed for removal include one native red alder (Alnus rubra), reported in poor health, two nonnative Norway maples (Acer platanoides) in good and fair condition, one common hawthorn (Crataegus monogyna) that is in excellent condition, one cherry (Prunus sp.) that is in poor to fair condition, and one Oregon ash (Fraxinus latifolia) reported in good condition. A bigleaf maple (Acer macrophyllum), reported to be in excellent condition near the southern end of the Site 2 work area, will be retained and protected from construction activities. With the exception of the Oregon ash, measured as 5.8 inches in caliper, he trees at Site 2 meet the City of Renton’s following tree size definitions: greater than 8-inch caliper (equivalent to diameter at breast height [dbh]), individual measurements of stem diameter at 4.5 feet above ground level for alder and cottonwood, and greater than 6-inch caliper for other species.