Urban Stream Floodplain Restoration and Associated Water Quality Improvements in Yreka, California
Cities are often located in active floodplains. Traditional methods of reducing flood hazards have consisted of structural solutions such as levees, revetments, channelization, and upstream dams and diversions. While these solutions have worked to varying degrees, they have also reduced the ecological health of affected streams. Urbanized streams also tend to become highly incised due to increased hydraulics from loss of floodplain access and increased peak flows due to impermeable surfaces. Ecological approaches to urban stream restoration are limited by the inability to raise or re-route streams to re-access historic floodplains due the extent of adjacent development. An innovative ecological approach has been developed in the City of Yreka, California, that consists of lowering adjacent lands along deeply incised channels to create new accessible floodplains close to existing stream levels. Modeling has shown that this approach can potentially contain up to 100-year or larger flood events completely within the newly-created floodways, thereby substantially reducing flood hazards, and can also satisfy geomorphological requirements for healthy sustainable channels and floodplains. Once floodplain function has been restored, instream and riparian restoration can also be achieved, including side channels for coho salmon. In the City of Yreka, California, this approach has been implemented along a total of 1-1/2 miles of streams to date within the Shasta River Sub-basin of the Klamath Basin, as part of the Yreka Creek Greenway Project, and funding has been obtained for 2 more miles, mostly within designated critical habitat for coho salmon. Changes to adjacent development are being kept to a reasonable level, and spoils from floodplain widening are being used in large part to raise building pads in backwater flood zones as the most cost-effective way to dispose of spoils, with full agency support. The new floodways will double as greenways through the city that will include paved multi-use trails and various interpretive facilities, and the greenways are included in the City’s MS4 Implementation Plan for improving water quality associated with urban stormwater runoff. A greenway master plan update is currently being prepared that will serve as the watershed plan for MS4 implementation, and will include extensive bioswales. Stormwater runoff that is currently intercepted and conveyed to streams via underground stormwater drainage systems will be directed to these bioswales in order to cumulatively reduce peak flows and increase filtration and infiltration. The Yreka Creek Greenway is a community-wide project with many partners, including the Klamath National Forest, U.S. Fish and Wildlife Service, NOAA Fisheries, Shasta Valley RCD, Siskiyou County, the Siskiyou Gardens Parks and Greenways Association, The Nature Conservancy, Ducks Unlimited, and private landowners. Numerous land parcels and easements will be purchased over time to facilitate the project, all on a willing buyer-seller basis. Landowner response has been very positive to date, with a significant number of acquisitions completed or underway.