Development of land changes both the quality and amount of stormwater that runs off into downstream streams, lakes and ponds.
Stormwater runoff from a forest, meadow or other natural environment is filtered by natural processes as it flows along the ground and over native vegetation, and filtered further when it passes through the soil before reaching groundwater. Stormwater pollution from developed land (and from construction activities) is one of the leading causes of water pollution nationally, and the largest source of water pollution in New Hampshire. Stormwater can become polluted when it runs off of streets, lawns, farms and construction and industrial sites if there are fertilizers, sediment (small soil particles), pesticides, oil and grease, or other pollutants in its path. When stormwater is left untreated, it enters our surface and coastal waters and can introduce pollutants that can impact drinking water supplies, stream health, and aquatic and land-based wildlife. In addition to introducing pollutants into surface and groundwater, development can increase the amount and rate of stormwater runoff which, if unchecked, can contribute to flooding in other areas.
The Alteration of Terrain (AoT) permitting program requires the control and treatment of stormwater from large developments. The program applies to earth moving operations, such as gravel pits, as well as industrial, commercial and residential developments. Treatment usually occurs through biological or physical means, and can take the form of rain gardens, infiltration ponds, gravel wetlands or other best management practices. Controls implemented to satisfy the requirement of no increase in runoff from the developed property include detention ponds and underground storage facilities. The same structures that provide treatment can also be used to store and control the rate of stormwater runoff.
To help protect surface water and groundwater, the Alteration of Terrain (AoT) regulations require a permit whenever a project proposes to disturb more than 100,000 square feet of contiguous terrain (50,000 square feet, if any portion of the project is within the protected shoreland). In addition to these larger disturbances, disturbances of greater than 2,500 square feet over terrain having grades of greater than 25%, may also require an AoT permit. In addition, an AoT General Permit by Rule applies to smaller sites and does not require an application or notification to the department.
If you think you need a permit, check out our Alteration of Terrain Permit Forms and Applications page in our NH Online Forms portal. AoT amendment request forms, start and stop construction forms, and more, can be found there.
The AoT Bureau provides Best Management Practice Worksheets for permit applicants.
Publications and guidance
- Northeast Regional Climate Center Precipitation Data
- Atlas 14 (NOAA, National Weather Service)
- Sea-level Rise, Storm Surges, and Extreme Precipitation in Coastal New Hampshire: Analysis of Past and Project Future Trends
- UNH Stormwater Center (UNHSC) Subsurface Gravel Wetland Design Specifications
- UNHSC Porous Asphalt Pavement and Infiltration Beds Specifications
- UNHSC Bioretention System with Internal Storage Reservoir Specification
- UNHSC BMP Maintenance Checklists
- NRCS Web Soil Survey
- Site Specific Soil Mapping Standards for New Hampshire and Vermont
- Ksat Values for New Hampshire Soils
Archived agendas and recordings of public input sessions and the April 8th, 2021 public hearing for Alteration of Terrain administrative rules relating to threatened and endangered species can be found here:
- Updated guidance on wildlife biologist qualifications under NHDES Env-Wq 1503.19(h)
- Template for threatened and endangered wildlife and habitat assessment
- September 2020 Update! Revised Best Management Practices (BMP) Worksheets