by The Nature Conservancy
November 29, 2016

Reduced aquatic connectivity, the fragmentation of river habitats by dams, road-stream crossings (e.g. culverts) and other aquatic barriers, is one of the primary threats to aquatic species in the United States. These barriers limit the ability of sea-run fish to reach freshwater spawning habitats and prevent resident fish populations from moving between other critical habitats.

Many of these in-stream barriers are also aging infrastructure, reaching the end of their useful lifespan. Many dams no longer serve their intended purpose and some pose a risk of catastrophic failure, beyond the risk of accidental drownings posed by all dams.

Old and poorly functioning culverts increase the risk of road failure in storm events. Removing dams and upgrading culverts can restore functioning ecosystems, reduce liability and increase property values, and stimulate recreational opportunities and economic activity.

The Nature Conservancy (TNC), working with the North Atlantic Aquatic Connectivity Collaborative (NAACC), has recently completed an updated version of the Northeast Aquatic Connectivity project, originally dating from 2011. This new assessment includes culverts as well as dams, and is designed to support planners and managers in their efforts to target dam removals, fish passage improvements, and other aquatic connectivity projects where they can have the most benefit for migratory fish or other species of interest.

This work has been carried out in conjunction with partners including the North Atlantic Landscape Conservation Cooperative of the US Fish & Wildlife Service, and the University of Massachusetts.

Products from this work include:

  • The most comprehensive database of dams in the region and NAACC culvert data that leverages a regional network of field surveyors

  • A suite of ecologically relevant metrics calculated for each barrier to help assess its relative priority for restoration efforts

  • A consensus-based prioritization that ranks barriers based on their ability to benefit migratory fish if removed / bypassed

  • A tool that enables users to create customized prioritizations based on user-defined objectives (within a given state or watershed, for the benefit of a specific fish species, or modeling the removal of one or more barriers)

These products can be used in multiple phases of a barrier removal project. Early on, planners can use the consensus priorities or custom analysis tool to identify barriers that match their objectives for fish passage projects. After a potential barrier removal project has been identified, the prioritized results can be used to demonstrate the ecological value of the proposed project to funders with similar objectives. Likewise, they can be used by funders to help inform funding allocation decisions.

Later, while a barrier removal project is underway, the web map can be used in outreach efforts to help dam owners, transportation agencies, and the general public better understand the importance of the passage project in a regional context. Finally, after a project is complete, the results can provide measures to help managers understand and track the ecological impact of the project.