Publication Summary

The objective of this manual is to provide guidance in stormwater design and management for eastern Washington.

The objective of this manual is to provide guidance in stormwater design and management for eastern Washington. The Stormwater Management Manual for Eastern Washington aims to provide a commonly accepted set of technical standards in addition to presenting new design information and new approaches to stormwater management. These stormwater management practices, if properly applied at a project site, should protect water quality in the receiving waters (both surface and ground waters). Improperly managed stormwater runoff is one of the principal sources of water quality and habitat degradation in urban areas. A number of existing laws and regulations require that project proponents properly manage stormwater runoff to avoid adverse impacts to water quality and aquatic resources. This manual is intended to provide technically sound and realistic guidance on how to properly manage stormwater runoff from individual project sites.

This manual identifies eight core elements for managing stormwater runoff from new development and redevelopment projects of all sizes. This manual also provides guidance for preparation and implementation of stormwater site plans. The requirements of the core elements are generally satisfied by the application of best management practices (BMPs) selected from Chapters 5 through 8 of this manual. Projects that follow this approach will apply reasonable, technology-based BMPs and water quality-based BMPs to reduce the adverse impacts of stormwater.

This manual is applicable to all types of land development. BMPs for residential, commercial and industrial development and road projects are included. A manual with a more specific focus, such as the Highway Runoff Manual or a stormwater manual adopted by a local jurisdiction, may provide more appropriate guidance to the project proponent.

The Stormwater Management Manual for Eastern Washington is limited in scope for addressing environmental problems caused by urbanization. This manual does not include site development standards or limit where development should be allowed. Project by project management of stormwater runoff from new development and redevelopment alone will not correct existing water quality and instream habitat problems. The engineered runoff treatment and flow control facilities recommended in this manual can reduce the adverse impacts of development, but such facilities cannot remove sufficient pollutants to replicate the pre-development water quality, nor can they replicate the natural functions of the watershed that existed before development.

This manual is applicable to all of eastern Washington, including the area bounded on the west by the Cascade Mountains crest; on the north by the Canadian border; on the east by the Idaho border; and on the south by the Oregon border. At the southern end of Washington′s Cascade Mountain