Installing the Entrance Structure

The pre-cast entrance structure is located on the downstream end of the fishway. It is configured to attract fish with high velocity water flow. A watertight cofferdam was specified to create a dry work environment during installation. However, stream flows were low, so the team and the permitting agencies agreed to omit it to minimize streambed disruption. The entrance structure is supported by a layer of stone beneath it. Fisheries staff from the Department of Energy & Environmental Protection assisted with placing a band of stones in the stream to help direct fish to the entrance in the spring.

Pouring the Footings

The three turning pools rest upon poured concrete footings reinforced with rebar. After the areas are excavated and leveled with gravel, wooden forms are erected to form the shape of the footing. Concrete is delivered in a concrete truck and directed to the pour location by a driver-controlled chute. While being poured, the concrete is agitated with a probe-like internal vibrator, which is submerged into the wet concrete to eliminate air bubbles. Surfaces are smoothed and leveled with a trowel. The largest footing weighs approximately 23 tons.

Pouring the Turning & Resting Pools

The turning and resting pools allow the fish a break as they ascend through the steep passes. They’re constructed using the same methods as the footings, with rebar to add strength and form work to create the shapes. The concrete is tested to verify its strength and uniformity. Because the pools have a void inside for water, the form work has inner and outer walls into which the concrete is poured. To reduce turbulence, gentle curves are specified, which are constructed using custom bent plywood forms faced with Masonite to create a smooth surface. One pool makes a 180-degree turn. Its form is constructed to make an opening for a viewing window.

Installing the Steeppasses

Constructed by Sheepscot Machine Works in Newcastle, Maine, the steeppass is made up of individual 10-foot pre-fabricated aluminum units that can be bolted together. Internal welded baffles in each unit create turbulence slowing the flow so that fish can ascend through the chute. The slope of the fishway and the length of each sloped ascent between the pools is set according to the fishes swimming ability. Alewife, our target fish, are non-jumpers and do best with fishway slopes no greater than 20 percent and with no more than 8 feet of elevation gain between the pools.

Installing the Exit Structure

The exit structure, located on the upstream end of the fishway on the dam spillway, is fitted with a fish counter and an eel pass to allow upstream migration of young American eel. The curved steeppass connected to it incorporates a gate to stop water flow during the non-migratory period. A pre-cast concrete footing is installed after modifications are made to the spillway to accept it. The exit structure is poured in the same manner as the turning pools. A temporary coffer dam constructed of 21 large sandbags creates a dry work area.

The Centerbrook Rubber Duck Race

On December 6, the entire office joined the project team to “christen” the John T. and Jane A. Wiederhold Fishway. Because there was no ship’s bow on which to crack the champagne bottle, we had a little fun. After a few words from The Nature Conservancy’s Sally Harold, Steve Gephard of the Connecticut DEEP opened the knife gate, sending a raft of rubber ducks racing down the passage. Each was tricked out with decoration, and, at the finish line (the entrance structure), the gaggle was gathered before any escaped downstream. There was a three-way tie for first place, though post-race analysis suggested the fix was in.