Essex 19 Fish Passage Project
Green Mountain Power Company
South Burlington, VT
This fishway and rehabilitation project consisted of final design and construction
of a downstream fishway, spillway automation, intake rehabilitation,
and powerhouse repairs at the Green Mountain Power (GMP) Essex 19 hydroelectric
station.
The existing intake configuration presented several challenging fishway design constraints. The downstream fishway needed to provide passage for adult and juvenile salmonids. The fishway facility consists of two steel entrance boxes with top discharge gates located in 3 ft wide openings along the 78 ft wide intake. Steel pipes connect these two entrance boxes to a flow separation chamber at the spillway crest where the entrance box water levels are controlled by a top discharge flow control weir. Because the entrance boxes had to be installed into a very narrow space behind existing trashracks, close control of the entrance box water level was needed to prevent fish from impacting the downstream face of the entrance boxes. The flow separation chamber was added to provide for the possibility of pumping back part of the attraction flow.
A fishway discharge of 50 cfs was needed as the project's minimum flow. An investigation during final design showed that it was economically beneficial to recycle fishway attraction flow that exceeded the minimum flow. Therefore, the flow separation chamber and pump mounting provisions were included in the final design so that if necessary a recirculating pump could easily be installed.
Water discharges over a flow control weir in the flow separation chamber and then passes over a discharge chute attached to the bottom downstream face of the 46 ft high ogee spillway. Polyethylene sheets are attached to the bottom of the chute to minimize fish abrasion and damage. A 5 degree bucket formed at the bottom of the spillway toe projects the fish above the plunge pool decreasing the impact and travel of the fish into the plunge pool. The plunge pool water elevation is controlled by a downstream concrete weir with an upstream tapered face to allow convenient sluicing of debris.
The design, approval, and construction of the fishway was placed on an accelerated schedule to take advantage of available corporate funding, meet agency requested operational deadlines, and to perform the work with the least cost during the summer period of low river flows.
For more information contact Tom Kahl, P.E.