Skip to main content
scroll to top

Stream Crossings

Where the River Meets the Road: Stream crossing assessments, wetlands permitting and design standards.

Photo taken of a stream flowing underneath a bridgeNew Hampshire’s streams are home to fish and other aquatic animals that travel the flowing waters to obtain food, spawn and reach high quality habitat. These waters carry nutrients, sediment and organic materials to reaches downstream and, ultimately, the Atlantic Ocean. Across the state, there are at least 17,000 road-stream crossings (culverts, bridges, arches) that cross a diverse array of water bodies. Many of these structures are old, damaged or undersized and pose unique risk. Undersized and/or improperly designed stream crossings can become plugged, cause flooding, diminish the structural integrity of the road, erode the landscape, and act as a barrier to fish passage and migration.

New Hampshire is undertaking a variety of efforts to address the impacts of inadequate crossings on river systems and public safety:

  • In May 2010, NHDES first adopted rules for the permitting of structures for stream crossings. 
  • Throughout the last decade, the New Hampshire Geological Survey, in collaboration with the Wetlands Bureau and four other state agencies spearheaded the New Hampshire Stream Crossing Initiative, a multiagency effort to assess and inventory the conditions of stream crossings statewide.
  • In 2018, the NHDES Coastal Program and its partners initiated the Resilient Tidal Crossings Project

Stream Crossing Assessments

An extensive stream crossing assessment protocol has been developed to evaluate how a crossing impacts the landscape, fish passage and structural condition. Crossings are assessed with the intent to make data-driven decisions on stream crossing upgrades. The ultimate goal is for the data to be used to replace crossings to maximize improvements to public safety, infrastructure resilience and aquatic habitat restoration. A properly designed stream crossing will safely pass floodwaters while allowing for full passage of fish and other aquatic species to upstream habitats. Follow the links below for guidance on proper stream crossing design.

U.S. Geological Survey StreamStats

Delineate watersheds and determine corresponding basin characteristics.

Aquatic Restoration Mapper

View all culvert assessment data along with fish habitat information and historical flooding records.

Stream Crossing Projects

Repair or replacement of existing stream crossings, or installation of new stream crossings, generally requires review and approval by the NHDES Wetlands Bureau.