Initial CSI basin planning, 1999-2003

Northwest Lake Washington planning area

The Northwest Lake Washington planning area includes the Thornton Creek and Matthews Park drainage basin in the area of the north and west Lake City Trunks. The issues in this basin include capacity limitations in portions of the Thornton Creek Interceptor (immediately upstream of the Matthews Park Pump Station). According to the Norhwest Lake Washington Report (below), there is limited capacity for approximately two-thirds of the Interceptor to convey the current peak 20-year flow, however, the North and West Lake City Trunk Sewers have sufficient capacity to convey the peak 20 year flow through 2050. The next stages of project development include:

• Verifying the capacity analysis using hydraulic modeling software that computes the surcharged water surface profile during large storm events.
• Comparing the challenges of routing the parallel sewer along the current right-of-way across private property versus building a potentially longer route with deeper sewers entirely within the public street right-of-way.
• Evaluating the working alternative routes for congested utilities.

Northwest Lake Washington Report, October 2003 (5.7 MB)

• Appendix A. Capacity Assessment Tables
• Appendix B. Flow Allocation Tables and Figures
• Appendix C. Planning-Level Construction Cost Estimates, Details from Tabula