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City of Yelm to Address Yelm Creek Flood Problems

by Cynthia Carlstad

Following two severe floods along Yelm Creek in 1996 and with the frequency of lower-magnitude floods increasing, the City of Yelm has launched an effort to prepare a Comprehensive Flood Hazard Management Plan to address flood problems along the creek. The plan will identify solutions to Yelm Creek flood problems that harmonize with and restore the natural stream system in addition to providing relief to residents from flood hazards. The City contracted with the consulting firm Tetra Tech/KCM to assist in developing the plan; the CFHMP is partially funded by the Washington State Department of Ecology.

In a coordinated study during the spring of 2000, the National Resources Conservation Service conducted a field survey of conditions along the Yelm Creek corridor. Results of this survey, along with the research and analysis performed by Tetra Tech/KCM to date, have revealed that the Yelm Creek stream system is severely degraded in its middle reach as it flows across the Yelm Prairie.

The primary problems with this reach of the stream are an abundance of invasive vegetation (primarily reed canarygrass and nightshade), accumulation of fine sediment filling the channel, and artificially straightened and bermed channel segments. These conditions are contributing to increased flooding, the creek drying up in the summer, and poor fish and wildlife habitat.

Previous efforts to clear accumulated sediments from the stream channel and rid the stream of reed canarygrass and nightshade have not been very successful. Preliminary results suggest three key steps to restoring the creek and alleviating some of the flooding:

1. Reconfigure the channel to add sinuosity, in-channel storage, and a variety of in-stream features desirable for aquatic life.
2. Plant vegetation well-suited to the highly permeable soils of the Yelm Prairie. The NRCS team identified several kinds of plants that have been successful in the watershed.
3. Keep the invasive vegetation cleared away until the desired plantings are large enough to compete and shade out the undesirable vegetation. #}

   As the City of Yelm and the Yelm Advisory Committee move into the solution development phase of the CFHMP, they will be seeking solutions that address these conditions without detrimental impacts on upstream and downstream neighbors. The group is optimistic about the possibilities for improving the flooding situation, while at the same time providing endangered species habitat and an amenity for the entire community.

   Cynthia Carlstad is an employee of Tetra Tech/KCM.

   
   

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