Lyon Creek Flood Mitigation Project Restores Salmon Habitat in Lake Forest Park

APWA Environmental Project of the Year 2015

The site history and forecast was demonstrated in a 1999 study and suggested an infrastructure improvement to mitigate future floods. In 2007, a storm caused $4m in damage to homes, buildings, and businesses and closed lanes of state route 522 for several hours.  In the 2010 SMP, LCFM was prioritized and in 2011, CLFP was awarded $3m in pre-disaster grant funding by FEMA. Additional funding of $1m from the King County Flood Control District (KCFCD) financed the mitigation aspect of the project and the initial sensitive areas study.

The study included new scientific findings showing culverts as detrimental to fish passage. Salmon population decline has concerned the community and driven a wide range of restoration efforts. In 2013, initial designs were modified to fit new partner WSDOT’s salmon friendly culvert campaign. The new plan included adherence to WDFW, Endangered Species Act, Clean Water Act, and Ecology’s standards. Through property acquisition, an educational comment period, and social media outreach the final permitting was a smooth process. Final funds were distributed from the state legislature midway through 2015.

Construction dealt with several place constraints and sought a plan with minimal traffic disturbance along the busy corridor.  Contractors use hydraulic pumps to divert stream flows around the construction site after fish were removed from the project area. All soil disturbances were required to take place within the dry season to minimize sediment pollution downstream. Also, in-stream construction was restricted to a period between July 1 and September 15 to reduce the occurrence of conflicts with spawning or maturing salmonids. This is known as the construction “fish window” and is considered the in-stream work standard in western Washington. Conducting twenty-four-hour construction to minimize traffic delays, bypass water systems, and construction planning allowed the project to be approved.

Civil engineers with city and state officials partnered to design a project that would address property damage concerns, community aesthetics, and salmon habitat. Early grey infrastructure designs (hydraulic drainage solution) accommodated the flood risk needs under a limited budget, but a green alternative became required. Salmon-friendly bridges were adopted, and this innovation became the focal point to win support from the public.

Limited staging areas and traffic congestion resulted in six build phases during the summer of 2015, each phase lasting one to three weeks. The budget included acquisitions to comply with wetland buffer requirements, and one parcel was converted into a wetland park for seasonal flooding events and habitat.

Details of the project included a pedestrian path with educational signage sharing the importance of salmon habitat rehabilitation and a boardwalk with seating area. Temporary irrigation was installed to improve the planting success rate of young native plants.

This project was conceived from the FEMA pre-disaster mitigation grant, who prioritized this project after the 2007 event. The $7m cost addresses both flood mitigation and salmon habitat improvement. In December of 2015 just weeks after construction, a larger storm than the 2007 event was contained by the new drainage. Modeling suggests current infrastructure will accommodate the one-hundred-year flood event, and CLFP staff believe that to be a conservative assessment.

Over the past 2 decades, salmon monitoring has shown a sharp decrease in population numbers, with the culverts affecting the habitat since initial construction decades ago. However, salmon catchment during phases of construction revealed unexpectedly large numbers of juvenile Coho salmon, and CLFP is optimistic that mature fish will be returning to the watershed over the next years. There are plans in place to conduct annual fish counts through 2018.

Three times during construction, pump capacity failure caused construction site flooding and delays. The drainage is large, and unexpected volumes of water could have come from a water main flush in another municipality. Effective communication within the watershed can prevent delays in construction of this kind, and capacity planning for the unexpected may keep construction underway during flash floods.

The hydraulic method of flood mitigation is phasing out as it will not suffice with mandates of legal decisions and building codes now in practice. Instream flow flood mitigations include a natural riverbed to allow natural fish passage.  This method is the current best practice and promises to be a standard for years to come.

As this marketplace evolves, vetting the right contractors is important for the success of the project and constant monitoring of the construction effort vital in carefully following the plan and timeline.  RFP criteria for selection of a qualified contractor should specifically include a reference to similar past work and include site visit for prospective contractors. As this field develops, it provides an opportunity for specialization, and future developers will find such professionals an asset.

Working in narrow construction windows with around the clock construction, it is paramount to have a briefed site inspector monitoring all work to maintain quality and stay on schedule.

Budgeting for land acquisitions in the planning process should be generous and negotiating the transfer of land to complete the project should include an educational aspect for property owners. Planners noted the final cost of land acquisitions nearly double their original budget.

• City of Lake Forest Park Municipal Code 16.16
• Washington Shoreline Management Act: RCW 90.58.080

• 2014_PaulWagner.pdf
• Project-of-the-Year2F20162FAPWA_POY2016_LyonCreekFloodMitigationProject_CityLakeForestPark.pdf

• Avoiding the Permitting Standstill: A blog on proactive design, by Adam Tycaster, The Watershed Company, April 19, 2016