Stormwater Atlas

City of Seattle

Stormwater Manual

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Document Metadata

Jurisdiction level
City

“City of Seattle”

Page 2 of 1086

State
Washington

“Washington State Department of Ecology”

Volume 1, Chapter 1, Page 1-1

Version / edition
Not found in document

No evidence cited

Adoption / effective date
Not found in document

No evidence cited

Last revised date
Not found in document

No evidence cited

Relationship to state manual
deemed equivalent to state manual

“Ecology has determined to meet the requirements contained in the Phase I NPDES Municipal Stormwater Permit, with reference to the Stormwater Management Manual for Western Washington (Ecology 2019).”

Volume 1, Chapter 1, Page 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, 100-year”

Volume 1 & Volume 3

Water quality volume method
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.

“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.”

Volume 1, Chapter 5, Page 5-14

Peak flow calculation method(s)
Continuous Simulation Method, Single Event Hydrograph Method, Rational Method

“Single Event Hydrograph Method... Continuous Simulation Method... Rational Method”

Volume 3, Chapter 4, Page 4-46 & Page 4-65

Hydrologic/hydraulic software
Not found in document

No evidence cited

Approved BMP categories
On-site stormwater management, Flow control, Water quality treatment, Conveyance, Soil amendment, Tree planting and retention, Dispersion, Infiltration, Rainwater harvesting, Alternative surface, Detention, Non-infiltrating

“This volume covers four primary functional categories of stormwater BMPs: On-site stormwater management, Flow control BMPs, Water quality treatment BMPs, Conveyance BMPs”

Volume 3, Chapter 2, Page 2-1