The Connecticut Department of Transportation (CTDOT) included a concrete pool and weir fish ladder as part of a culvert rehabilitation project. The new fish ladder, designed for a tributary to Hubbard Brook, Middletown, Conn., is providing fish passage through the slip-line-repaired culvert.
The Connecticut Department of Energy and Environmental Protection Inland Fisheries Division and the Fishery department found multiple benefits of adding a fish passageway through this culvert since there are suitable instream brook trout spawning and rearing habitats upstream of the culvert. Additionally, the fish passageway would restore connectivity to more than 1.4 miles of stream habitats. The upstream fish passage also benefits the diadromous American eel; whose numbers are diminishing upstream of the culvert.
Commissioned to design, fabricate, ship, and erect the precast concrete pool and weir fish ladder units and precast concrete footings, Oldcastle Precast cast the required units at its Avon, Conn., manufacturing facility. In all, 14, 7-foot, 4-inch-high by 9-foot, 4-inch-wide fish ladder units with monolithically cast weirs, and 15, approximately 3-foot-wide by 11-foot, 4-inch-long by 10-inch-thick footings installed underneath the fish ladder units for structural support were manufactured.
After installing the precast fish ladder units on a firm bedding at the desired elevation and alignment, the precast units were connected by angle locking devices to provide a silt-tight connection.
“This project required precision manufacturing and had to be manufactured within exacting tolerances, within fractions of an inch, to site assemble the precast components and meet the requirements of the fish ladder specifications,” said Victoria Bazzano of Oldcastle Precast. “We were very happy with the project outcome. The precast fish ladder units fit together perfectly and the project went smoothly with no major issues. The Connecticut Department of Transportation plans on having more of these all over Connecticut.”
At the culvert outlet, the concrete pool-and-weir fish ladder units, at the full width of the culvert, transition from the structure back to the streambed, providing fish navigation upstream. Due to the steep grade downstream of the culvert, a 6-inch vertical drop between pools was specified. Baffles were installed throughout the culvert to maintain a maximum elevation change of 6-inch water depth between each pool for fish navigation.
To protect the fishway structure from scour and erosion, a rip rap swale was installed along the sides of the structure and outlet. At the fishway outlet, the rip rap swale blends into channel outlet protection that consists of a boulder weir that will create a pool to transition wildlife from a natural habitat to the fish ladder passageway structure.
Fish ladders enable fish to pass around the barriers by swimming and leaping up a series of relatively low steps (hence the term ladder) into the waters on the other side. The ladder uses a series of small dams and pools of regular length to create a long, sloping channel for fish to travel around the obstruction. The channel acts as a fixed lock to gradually step down the water level; to head upstream, fish must jump over from box to box in the ladder.
The primary purpose of this CTDOT project was to address the safety of the traveling public, ensure the local hydrology is uninterrupted, and eliminate potential negative impacts to the natural environment by ensuring the structural stability and hydraulic capacity of the culverts. At completion of the construction activities, the roadway embankments were re-graded to the original condition and native vegetation planted within the disturbed wetland and upland areas.
Information provided by Oldcastle Precast (oldcastleprecast.com).