City of Seattle

Stormwater Manual

CityWashingtonhighNo

Open source PDF ↗Official agency page ↗

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Other manuals in Washington: City of Lacey, City of Seattle, Washington

Document Metadata

Jurisdiction level

municipality

“City of Seattle”
Title Page

State

Washington

“Washington State Department of Ecology”
1.1

Version / edition

Joint Directors' Rule Public Utilities DWW-200 (rev. 3) / Department of Construction & Inspections 03-2026

“JOINT DIRECTORS’ RULE Public Utilities DWW-200 (rev. 3) Department of Construction & Inspections 03-2026”
Title Page

Adoption / effective date

2026-07-01

“Effective: July 1, 2026”
Title Page

Last revised date

Not found in document

No evidence cited

Relationship to state manual

deemed equivalent to state manual

“which Ecology has determined meets the requirements contained in the Phase I NPDES Municipal Stormwater Permit, with reference to the Stormwater Management Manual for Western Washington (SWMMWW)”
1.1

Design Criteria

Design storm return periods (years)

2-year, 5-year, 10-year, 25-year, 50-year, 100-year

“2-year, 5-year, 10-year, 25-year, 50-year, and 100-year recurrence intervals”
3.8, 5.3, 5.3.5, 4.3.6

Water quality volume method

The daily runoff volume at or below which 91 percent of the total runoff volume for the simulation period occurs, determined by ranking daily runoff volumes and sequentially summing them until the total equals 9 percent of the total volume.

“The daily runoff volume at or below which 91 percent of the total runoff volume for the simulation period occurs, as determined using an approved continuous model.”
5.4.1.1

Peak flow calculation method(s)

Single Event Hydrograph Method, Continuous Simulation Method, Rational Method

“Single Event Hydrograph Method, Continuous Simulation Method, Rational Method”
4.3.6

Required hydrologic/hydraulic software

Western Washington Hydraulic Model (WWHM), MGSFlood

“the Western Washington Hydraulic Model (WWHM) can be used to size flow control... The same design steps can generally be used for MGSFlood”
4.4.1

Approved BMP categories

Soil Amendment, Tree Planting and Retention, Dispersion BMPs, Infiltration BMPs, Rainwater Harvesting BMPs, Alternative Surface BMPs, Detention BMPs, Non-infiltrating BMPs

“Soil Amendment, Tree Planting and Retention, Dispersion BMPs, Infiltration BMPs, Rainwater Harvesting BMPs, Alternative Surface BMPs, Detention BMPs, Non-infiltrating BMPs”
Volume 3 Table of Contents