Oldcastle Precast Supplies Concrete Fish Ladder to Conn. DOT

Oldcastle Precast prefabricated a precast concrete pool and weir fish ladder, designed for a tributary to Hubbard Brook, Middletown, as part of the Connecticut Department of Transportation’s State Route 410 (Aircraft Road) culvert rehabilitation project.

The Connecticut Department of Transportation included a concrete pool and weir fish ladder to the culvert rehabilitation project under State Route 410 after learning about the benefits of a fish ladder, on this site, by the CT DEEP Inland Fisheries Division and the fishery department. The new fish ladder is providing fish passage through the slip line repaired culvert. Slip lining entails installation of a small culvert to line and to stabilize the existing, deteriorating culvert barrel.

The Connecticut DEEP and the fishery department found multiple benefits of adding a fish passageway through this culvert since there are suitable in-stream brook trout spawning and rearing habitats upstream of the culvert. Additionally, the fish passageway would restore connectivity to over 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 ,weir fish ladder units and precast concrete footings, Oldcastle Precast cast the required precast units at its Avon, Conn. manufacturing facility.

In all, 14 7-ft-4-in tall by 9-ft-4-in wide fish ladder units, with monolithically cast weirs, and 15 approximately 3-ft wide by 11-ft-4-in long by 10-in thick footings, which are 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 fish ladder units were connected by angle locking devices to provide 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, which provides fish navigation upstream. Due to the steep grade downstream of the culvert, a 6-in vertical drop between pools was specified. Baffles were installed throughout the culvert to maintain a maximum elevation change of 6-in water depth between each pool for fish navigation.

To protect the fishway structure from scour and erosion, a rip rap swale (rock used to armor the streambed) 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 to 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 Connecticut Department of Transportation 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.

Source: Oldcastle Precast