New Hampshire

Model Stormwater Standards, 2025 update

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Statewide model municipal standards template (placeholder towns). Stored as NH state guidance; municipalities fill in local name when adopting.

Fields not found in document: design_criteria.required_hydrologic_hydraulic_software

Document Metadata

Jurisdiction level

state

“as specified in the latest New Hampshire Stormwater Manual”
ELEMENT C, Section 2.a, page 2

State

New Hampshire

“latest New Hampshire Stormwater Manual”
ELEMENT C, Section 2.a, page 2

Version / edition

Draft: May, 2025

“Draft: May, 2025”
Title page, page 1

Adoption / effective date

Not found in document

No evidence cited

Last revised date

2025-05

“Last Edited: May 2025 1”
Title page, page 1

Relationship to state manual

adopts state manual directly

“The site shall be designed to meet the Watershed Protection Standard (WPS) to the Maximum Extent Practicable (MEP) as specified in the latest New Hampshire Stormwater Manual”
ELEMENT C, Section 2.a, page 2

Design Criteria

Design storm return periods (years)

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

“the 1-inch rainstorm and the 2-year, 10-year, 25-year, and 50-year 24-hour storm events”
ELEMENT C, Section 2.c, page 3

Water quality volume method

WQV = (P)(Rv)(A) where P = 1 inch of rainfall, Rv = 0.05 + 0.9(I) where I = percent impervious cover draining to the structure converted to decimal form, and A = total site area draining to the structure

“WQV = (P)(Rv)(A)”
Table 1, page 9

Peak flow calculation method(s)

TR-55

“qu = unit peak discharge from TR-55 exhibits 4-II and 4-III”
Table 1, page 9

Required hydrologic/hydraulic software

Not found in document

No evidence cited

Approved BMP categories

raingardens, bioretention systems, tree box filters, subsurface gravel wetlands, filtration practices, infiltration practices, swales, detention areas

“SCMs (such as raingardens, bioretention systems, tree box filters, and similar stormwater management landscaping techniques)”
ELEMENT C, Section 1.b, page 2