Strategies for Fixing Puget Sound’s Stormwater Problem

Abstract

Stormwater is one of the biggest threats to Puget Sound. King County was awarded a Puget Sound Watershed Management Assistance Program FY 2009 grant of $999,981 by Region 10 of the U.S. Environmental Protection Agency, to conduct estimate the numbers of different types of stormwater facilities, and their costs, needed to restore stream flows in a Puget Sound watershed. Partners included the University of Washington, the Cities of Auburn, Covington, and SeaTac, and the Washington State Department of Ecology. The study area covers 278 square miles of the Green/Duwamish watershed and portions of the Central Puget Sound watershed that comprise Water Resources Inventory Area 9, excluding the areas upstream of the Howard Hanson Dam and the city of Seattle. The project estimated the number of different types of facilities needed to restore streams throughout the project area. This project coupled the watershed hydrology model, with a relatively new stormwater BMP modeling and planning tool developed by the U.S. EPA, to estimate stormwater facility needs and costs. The number of existing facilities was found to be small relative to the estimated need. The fraction of facilities to be built as mitigation associated with new or redevelopment by 2040 was estimated. Uncertainties from climate change impacts on precipitation patters were assessed. Public and private capital and operating costs were estimated under different mitigation strategies. Critical policy considerations for defining a strategy for reducing stormwater impacts include • The trade-off between the environmental benefit of stormwater mitigation associated with new and redevelopment and the private cost of building these facilities, • The trade-off between the environmental benefits of a robust public retrofit program to address stormwater issues that might be otherwise privately mitigated during redevelopment in the distant future, • The apparent need for public investment in stormwater treatment for roads and highways, • The large increase in operation and maintenance programs for public facilities, • The large increase in the public program required to inspect private facilities, and take enforcement actions as necessary, • The need for substantial expansion of public funding for stormwater facilities, including the possible creation of new funding mechanisms