NH Coastal Program Announces Results of Resilient Tidal Crossings Project

Portsmouth, NH – The New Hampshire Department of Environmental Services (NHDES) Coastal Program announces the release of new mapping products and data that characterize tidal crossings for community and ecosystem resilience. This information can be used by community officials and road managers to enact strategic repair/replacement of tidal crossing infrastructure and to identify high priority restoration and conservation opportunities at tidal crossings sites.

A tidal stream crossing (tidal crossing) is a bridge or culvert that conveys two-directional tidal flow. Tidal crossings are a unique and challenging class of transportation assets that have different engineering, regulatory and risk management considerations than their freshwater counterparts. For instance, properly designed tidal crossings need to convey enough tidal flow to periodically cover the salt marsh and at the same time be of sufficient size to accommodate freshwater flows from upstream sources. Additionally, tidal crossing infrastructure is especially vulnerable to coastal storm surge, flooding and sea level rise.

The NHDES Coastal Program was awarded a $187,500 grant from the National Oceanic and Atmospheric Administration for the Resilient Tidal Crossings Project in 2017. The grant enabled the NHDES Coastal Program to work with a team of partners, including The Nature Conservancy and the University of New Hampshire to implement the N.H. Tidal Crossing Assessment Protocol at all 118 tidal crossings in N.H. during the summer of 2018. This collaborative project brought together robust technical expertise and state-of-the-art remote sensing mapping products to implement an ambitious field and data analysis project.

Tidal crossing assessment data were then used to score sites based on structure condition, flood risk and effect on adjacent tidal habitats. The project utilized the Statewide Asset Database Exchange System (SADES), N.H.’s primary inventory of transportation assets, which enabled efficient data collection and establishes a digital inventory of tidal crossing infrastructure for reliable long-term asset management.

To access results, mapping products and other Resilient Tidal Crossings Project material, please visit the Resilient Tidal Crossings webpage at https://www.des.nh.gov/organization/divisions/water/wmb/coastal/resilient-tidal.htm

For more information, please contact NHDES Coastal Program Habitat Coordinator Kevin Lucey at kevin.lucey@des.nh.gov or (603) 559-0026.