192nd Culvert

The 192nd Culvert project included options analysis on the type of culvert and alignment and all the associated required permits, including the traffic control. The project had a King County Metro sewer transmission main and a local sewer line, water main, and fiber optic lines that had to be rerouted through the 14-foot wide, 60-foot-long, 7-foot-deep three-sided box culvert. A fish exclusion area was designed for the bypass with a silt screen placed downstream. The road required it be raised one foot per the flood modeling completed in SWMM. The basins were modeled using HSPF for the large upstream contributing basins. As Little Swamp Creek joins Swamp Creek, the backwater analysis was included as the downstream condition.

Rebekah Weston provided all supporting documents and coordinated the work with the Northshore Utility District (NUD). Rebekah oversaw the PS&E for the entire project, including the fishway habitat elements with the coir logs and large woody material added. She also oversaw the mitigation for the areas where the adjacent wetlands were impacted. She worked with an environmental scientist in obtaining all the permits from the Corp, WDFW, Ecology, and the City. The biological assessment (BA) was completed and incorporated into the design to keep the flows below 1 fps for the Coho Salmon. Since this creek has low flows, the stream sediments were designed to provide enough flow for the fish to swim. Consideration for the fish (i.e., having a 4-inch depth through the year) and soft sediments for the riverbed was considered in the PS&E.