City of Portland

Stormwater Management Manual

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Open source PDF ↗Official agency page ↗

Document Metadata

Jurisdiction level

municipality

“City of Portland”
Cover

State

Oregon

“Portland, Oregon”
Cover

Version / edition

December 2020

“December 2020”
Cover

Adoption / effective date

2020-12

“December 2020”
Cover

Last revised date

2020-12

“December 2020”
Cover

Relationship to state manual

independent

“The SWMM is a BES Administrative Rule and is authorized by Portland City Code Chapter 17.38.”
Page 1-5, Section 1.1

Design Criteria

Design storm return periods (years)

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

“2 2.4 ... 5 2.9 ... 10 3.4 ... 25 3.8 ... 100 4.7”
Appendix A, Table A-9

Water quality volume method

Achieve 70% TSS removal from runoff resulting from 90% of the average annual rainfall (1.61 inches over 24 hours, or 0.19 in/hr for a 5-minute time of concentration); the water quality design storm is sized for 90% of the average annual rainfall.

“70% removal of total suspended solids (TSS) is required from the runoff from 90% of the average annual rainfall (1.61 inches over 24 hours, or 0.19 in/hr for a time of concentration of 5-minutes).”
Page 1-19, Section 1.3.4

Peak flow calculation method(s)

Rational Method, Santa Barbara Urban Hydrograph (SBUH) Method, NRCS TR-55, HEC-HMS, HEC-1, EPA-SWMM, Continuous Simulation

“use either the Santa Barbara Urban Hydrograph (SBUH) Method, NRCS's TR-55, the Army Corps of Engineers' Hydrologic Modeling System (HEC-HMS) or HEC-1, or the Environmental Protection Agency's Storm Water Management Model (EPA-SWMM)”
Page 2-41, Section 2.5.3

Required hydrologic/hydraulic software

Presumptive Approach Calculator (PAC)

“The Presumptive Approach can be used by design professionals to size green streets, planters, and basins using the Presumptive Approach Calculator (PAC), an online calculator maintained by BES.”
Page 2-36, Section 2.5.2

Approved BMP categories

Ecoroof, Permeable Pavement, Filter Strip, Driveway Center Strip, Green Street, Rain Garden, Basin, Planter, Surface Sand Filter, Grassy Swale, Wet Pond, Extended Wet Pond, Dry Pond, Sump, Drywell, Soakage Trench, Subsurface Sand Filter, Manufactured Stormwater Treatment Technologies (MSTT), Structured Detention

“Ecoroof ... Permeable Pavement ... Filter Strip ... Green Street ... Rain Garden ... Basin ... Planter ... Drywell ... Soakage Trench ... MSTT ... Structured Detention”
Page 2-34, Table 2-9