Municipality of Anchorage

Anchorage Stormwater Manual Volume 1 – Management and Design Criteria (Design Criteria Manual Chapter 2 – Drainage)

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Source PDF is labeled DRAFT March 2015 (ASM Volume 1 / DCM Ch. 2). Confirm whether a later adopted edition supersedes this draft before relying on criteria operationally. Software listed are common models in Table 4.8-1, not an exclusive required list.

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Other manuals in Alaska: Alaska

Document Metadata

Jurisdiction level

municipality

“MUNICIPALITY OF ANCHORAGE”
Title Page

State

Alaska

“State of Alaska 18 AAC 70 Water Quality Standards”
Section 1.4.2

Version / edition

Version 1.0, DRAFT March 2015

“Version 1.0 DRAFT March 2015”
Title Page

Adoption / effective date

Not found in document

No evidence cited

Last revised date

2015-03

“DRAFT March 2015”
Title Page

Relationship to state manual

independent

“Local and State Codes Related to Stormwater... Municipal Stormwater Policies”
Sections 1.4–1.5

Design Criteria

Design storm return periods (years)

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

“Table 4.2-1: MOA Design Storm Depths... 10-year, 24-hour... 100-year, 24-hour... Extended Detention 1-year, 24-hour... Peak Flow Control 2-year, 24-hour... 10-year, 24-hour... 100-year, 24-hour”
Table 4.2-1, Page 4-4

Water quality volume method

Treat runoff from the first 0.52 inches of rainfall from a 24-hour event preceded by 48 hours of no precipitation (90th-percentile water quality storm) using Green Infrastructure (retention, infiltration, bioretention, evaporation, rainfall harvesting, and/or combinations). Volume estimated by Direct Determination Method or SWMM. Extended detention (when GI not used for WQ): detain post-development excess over pre-development for the 1-year, 24-hour storm for 6 hours. Oil/grit separator annual goals include 80% reduction of inorganic sediment ≥100 μm when traditional treatment is used.

“Treatment must be provided for runoff generated from the first 0.52 inches of rainfall from a 24-hour rainfall event preceded by 48 hours of no precipitation.”
Section 3.2.2.1, Page 3-4

Peak flow calculation method(s)

Rational Method, NRCS (SCS) Peak Flow Method (Tabular Method) / TR-55, NRCS (SCS) Tabular Hydrograph Method, Direct Determination Method (water quality volume), USGS Regression Equations, Unit Hydrographs, Kinematic-Wave Method, Non-Linear Reservoir Method, SCS Type I, 24-hour rainfall distribution

“4.5.2 Rational Method... 4.5.3 NRCS (SCS) Peak Flow Method (Tabular Method)... 4.5.4 USGS Regression Equations... 4.5.5 NRCS (SCS) Tabular Hydrograph Method”
Table of Contents / Chapter 4

Required hydrologic/hydraulic software

SWMM (EPA), HEC-HMS, HEC-RAS, PondPack, HY-8

“Table 4.8-1: Common Computer Models... SWMM... HEC-HMS... PondPack®... HEC-RAS... HY-8”
Table 4.8-1, Pages 4-28+

Approved BMP categories

Bioretention, Soakaway Pits, Infiltration Basins, Infiltration Trenches, Vegetative Swales, Pervious Pavement, Chamber Systems, Wet Ponds, Dry Ponds (enhanced), Sedimentation Basins, Filter Strips, Constructed Wetlands, Canopy Cover/Vegetation Retention, Landscaped Depressions, Oil and Grit Separators (traditional treatment when GI infeasible)

“Bioretention • Soakaway Pits • Infiltration Basins • Infiltration Trenches • Vegetative Swales • Pervious Pavement • Chamber Systems • Wet Ponds • Dry Ponds (if they are enhanced) • Sedimentation Basins • Filter Strips • Constructed Wetlands • Canopy Cover/Vegetation Retention • Landscaped Depressions”
Section 3.2.2.1, Page 3-4