Description

Thomas/Wright, Inc. was responsible for preparing reports and design documents for improvements to Taylor Creek that will reduce barriers to fish migration and provide in-stream improvements for channel grade control, bank stabilization, and fish habitat. The project's objectives include controlling excessive erosion/sedimentation along the main stem of Taylor Creek, identifying barriers to fish migration, providing fish passage to upper reaches, and improving spawning and rearing habitat for sockeye, coho, and steelhead.

As a first order of work on Phase I of the project, hydrologic and hydraulic analyses, a fisheries evaluation, and an alternatives (including detention) analysis was performed. T/WI developed a computer model of the watershed and creek using SWMM. The model was used to estimate peak flows for the 2-year, 10-year, and 25-year recurrence interval storms and to evaluate the potential benefit of constructing detention basins at two locations in the upper watershed. The model was also used to evaluate hydraulic conditions for fish passage within a system of three culverts located under Rainier Avenue in the lower reach of Taylor Creek. The model results indicate that flow depths and velocities within the culvert system for a wide range of flows are not likely to allow fish passage.

A predesign report was prepared and included concept level designs to mitigate fish passage at culverts under Rainier Avenue, 68th Avenue, and Holyoke Way, and a driveway weir adjacent to 68th Avenue. The predesign report also recommended construction of detention basins at two locations in the upper watershed to mitigate the volatile flow regime that is downcutting the lower reaches of the creek.

T/WI prepared the plans and specifications for improvements between 69th Avenue and Holyoke Way. These improvements included two six-foot by 14-foot aluminum culverts, eight log flow control structures, streambank stabilization and revetment, and erosion control. Approximately 270 feet of 68th Avenue was replaced.

In Phase II of the project, T/WI evaluated alternatives for the conveyance of Taylor Creek beneath Rainier Avenue and the elimination of a vertical drop in Taylor Creek at the Guth residence on 68th Avenue. A flood profile analysis using HEC-RAS was performed from the mouth of Taylor Creek to the upstream end of the Rainier Avenue culverts.

In Phase I, 1,500 feet of creek was mapped and sixty cross-sections for the modeling was surveyed. In Phase II, an additional 1,600 feet of creek was mapped and 69 cross-sections were surveyed.