Assessment of Road Crossings for Improving Migratory Fish Passage in the Winnicut River Watershed

This report summarizes the results of a river continuity assessment focused on roadstream crossings. The Winnicut River is the site of a restoration project that removed a head-of-tide dam and resulted in the only free-flowing major tributary to the Great Bay Estuary. The river system currently supports a small annual run of river herring, and with the removal of the dam and ladder system, migratory fish will now have access to a total of 37 miles of potential upstream habitat. In anticipation of improved access, The Nature Conservancy conducted a fish passage assessment for all stream crossings above the head-of-tide dam. We used an assessment methodology based on the Massachusetts Riverways Program, with adjustments following a similar crossing study in the Ashuelot River system (NH). We assessed a total of 42 road crossings in the Winnicut watershed, and classified them as severe, moderate, minor, or passable for fish passage. One crossing was identified as severe, thirty-five were moderate, six were minor, and no crossings were determined to be fully passable for all fish. To develop a priority list of crossings for improvements, we focused on culverts with moderate or severe barrier rankings and screened out crossings associated with major highway infrastructure. We then used GIS analysis to determine the habitat potential upstream of each crossing, and prioritized crossings with greater than 0.5 miles of upstream habitat. We ordered priority crossings from nearest to furthest from the dam site at the river mouth. Our analysis produced a final list of 11 crossings that, if all were improved, would reestablish 19.5 miles of unfragmented habitat for migratory fish. We are sharing results of this study with local and state officials in hopes of securing funds and making structural enhancements to priority road crossings. Going forward, we hope that this information will lead to increases in migratory fish populations in the Winnicut River and throughout the entire Great Bay Estuary