Nashua, NH Environmental Rules: Stormwater Management (2026)
Key Facts
- Governing law
- Land Use Code Art. XXXI
- Peak discharge standard
- 10-yr post ≤ pre-development rate
- Water quality volume
- 0.5 in. (1.0 in. in Conservation Zone)
- TSS removal target
- 80% of annual pollutant load
- Applies to
- All subdivision & site plans
Summary
Nashua requires stormwater management and erosion control plans for subdivision and site plan applications, with numeric peak-discharge and water-quality treatment standards.
No new stormwater conveyances may discharge untreated stormwater directly to or cause erosion into wetlands or water bodies.
(2) Rooftop runoff is considered uncontaminated for the purposes of these standards and therefore does not require treatment.
B. Postdevelopment peak discharge rates.
(1) Stormwater management systems must be designed so that the ten-year, twenty-four-hour postdevelopment peak discharge rate does not exceed the ten-year, twenty-four-hour predevelopment peak discharge rates.
(2) In order to meet this standard, controls must be developed for the two-year, ten-year and fifty-year, twenty-four-hour storm events. The hundred-year, twenty-four-hour storm event must be evaluated to demonstrate that there will not be increased flooding impacts off site. [Amended 6-26-2018 by Ord. No. O-18-015]
(3) Measurement of peak discharge rates shall be calculated using point of discharge or the downgradient property boundary. The topography of the site may require evaluation at more than one location if flow leaves the property in more than one direction. An applicant may demonstrate that a feature beyond the property boundary is more appropriate as a design point.
C.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: rev 4805762; v29 updated 2026-02-10; through 02-10-2026).
Full Breakdown
Under Land Use Code Article XXXI, every subdivision or site plan in Nashua must include a stormwater management plan unless the Planning Board waives it for a site too small or naturally suited to need one. New systems can't discharge untreated stormwater directly into wetlands or water bodies, and post-development peak discharge rates for the 10-year, 24-hour storm can't exceed pre-development rates. Water-quality treatment volume is set at 0.5 inch of runoff over the site's impervious area citywide, rising to 1.0 inch in the Water Supply Protection District's Conservation Zone, and systems must remove 80% of the average annual load of total suspended solids, floatables, greases and oils.
Violations & Fines
The Planning Board can withhold subdivision or site plan approval until a compliant stormwater plan is submitted; redevelopment projects must certify compliance via a registered professional engineer.
Frequently Asked Questions
Does every new development in Nashua need a stormwater plan?
Can Nashua developments infiltrate stormwater without treating it first?
Sources & Official References
Other rules in Nashua
Compare Nashua to another location·View the New Hampshire environmental rules overview
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Stormwater Management in Nearby Cities
How other cities in this county handle stormwater management.