Culverts & Dams
Dealing with Dams and Culverts
To many people, “fish passage” means salmon migrating upstream to their spawning grounds and downstream out to sea. There’s more to the story. American shad and river herring (both alewife and bluebacks) once came up and down the Farmington by the tens of thousands too, and some still make the attempt. American eels and sea lampreys still make the journey every year also. Even local fish like trout and dace need to travel freely within the river to find good habitat. Many more animals—reptiles, amphibians, and mammals—need free passage along the edges of rivers and streams to in order survive and maintain healthy populations. There are hundreds of barriers in their way, either old dams or culverts where streams pass under roads.
At FRWA, we work with many partners to remove these barriers.
Dam Removals and Retrofits
The upper reaches of the Farmington offer abundant spawning habitat to migratory fish, but the habitat is under-used because of dams that block upstream passage. Not every dam can be removed– but FRWA is actively engaged in dam-related projects that would provide real benefits to fish and people. FRWA is a member of the River Restoration Network.
In 2009, FRWA received funding from the State of CT (from polluter restitution payments) to coordinate an engineering study of the old
Spoonville Dam in Bloomfield/East Granby. The dam, breached in 1955, pinches the river’s flow to a narrow, fast current that blocks upstream passage for migratory fish such as shad, alewife, and blueback herring as they return from the ocean and swim upstream to spawn. The engineering study concluded that the best way to restore fish passage would be complete removal of the dam, and it provided the design for removal. (Engineering study is available upon request).
Benefits of Removal
River flow rates that once again allow American shad, alewife, and blueback herring to swim up through Tariffville Gorge and access more than 20 additional miles of river. Improved safety for boaters and swimmers. A restored scenic waterfall in place of a derelict dam at a popular fishing site.
The towns of East Granby and Bloomfield endorsed removal. The whitewater paddling community benefits from Tariffville Gorge (just upstream of the dam) as the venue for world-class whitewater paddling events. The engineering study demonstrates no adverse impact of dam removal on the whitewater paddling run, except of course losing the chute through the dam breach. The gain in boater and swimmer safety was seen as offsetting the loss of this whitewater play feature. The dam owner, CT Light and Power (a subsidiary of Northeast Utilities) supported removal.
All forms of wildlife require routes of passage within their habitat in order to find food and shelter. Many forms of aquatic wildlife such as fish, mollusks, crustaceans, and insect nymphs also require the ability to move up and down the length of their stream habitat. However, human transportation needs require building infrastructure that allows us to safely pass over these streams. Structures such as bridges allow us to drive over streams on an elevated platform, and culverts divert streamflow to pass underneath roads.
By their nature, rivers and streams are very responsive to changes in hydrology, or the movement of water throughout the landscape. This means that rivers change their course naturally over time, and that water can (and does) transport debris and sediments downstream. These facts can be problematic when part of the river channel is confined to a specific path, such as a tube or tunnel. Unfortunately these structures can interrupt aquatic wildlife corridors if they are not installed or maintained properly. Moreover, failure of a damaged or undersized crossing during flood conditions can pose risks to public safety.
FRWA performs stream crossing assessments through the North Atlantic Aquatic Connectivity Collaborative (NAACC) to prioritize crossings for repair or replacement within the watershed. Learn more at streamcontinuity.org