Snohomish County Master Drainage Plan Analysis

WSE was tasked under an On-call contract with Snohomish County to assist the County with Master Drainage Planning in the Lake Serene (Norma Creek) and Waxen Road (North Creek) drainage basins. WSE updated hydrologic and hydraulic models of these drainages and used them to investigate current flood issues and develop solution alternatives.

Role / Services: Previous WSE work for the Lake Serene Project area included hydrologic and hydraulic modeling (HSPF, steady state HEC-RAS, and SWMM), identification of flooding problems, evaluation and cost estimating of alternative solutions, and reporting. For Waxen Road an HSPF model and an unsteady HEC-RAS model were developed and applied to investigate flooding problems. WSE also provided geomorphic and habitat evaluations for Norma Creek downstream of the Lake Serene outfall to facilitate the design of potential mitigation for drainage improvements.

Outcome: WSE coordinated extensively with the County's project manager to address significant changes over the course of this project. Specifically a flood emergency at Lake Serene prompted the County to request additional work by WSE to evaluate potential interim and comprehensive solutions to flooding. The flood emergency elevated the visibility of this project and required analyses to be conducted with great urgency. WSE responded to all County requests and provided timely information to allow the County to keep the public well informed.