Hydraulics and Rating Curves for a 36-Inch Wide Denil Fishway: Final Report
adult, Alosa sapidissima, American shad, anadromous fish, baffles, blueback herring, channel, denil, engineering, flow velocities, herring, hydraulics, prototype, rating curves, shad, slope, survey, turbulent, upstream
A prototype Denil fishway was designed, constructed, and tested at the Conte Anadromous Fish Research Center (CAFRC) (of the U.S. Geological Survey in Turners Falls, Massachusetts). The hydraulic characteristics of the 36-inch wide by 25-foot long fishway were evaluated at various bottom slopes and headpond elevations. Fishway discharge versus upstream headpond elevation rating curves were established. Numerical equations were derived to predict fishway flow discharge as a function of the headpond elevation at various slopes. The 36-inch wide fishway, with 48-inch high walls, passed a maximum of 20.3, 21.9, 23.0, and 23.3 f3/s at floor slopes of 1:10, 1:8, 1:6, and 1:4, respectively (1 being in the vertical direction). These flows corresponded to a headpond elevation of 42-inches (measured from the fishway bottom to the water surface just upstream of the fishway). Higher headpond elevations caused water to spill over the sides of the fishway. Flow discharge can be determined from the derived equation; by substituting for the headpond elevation above the fishway floor, measured just upstream of the fishway or in the exit channel, and knowing the slope of the fishway bottom. Flow velocities at various cross sections along the fishway were documented. These remained relatively unchanged within the fishway downstream of the vena contracta region (the vena contracta region was within the top two to three upstream baffles). The main flow velocities, downstream of the vena contracta and throughout the fishway, ranged between 2.2 and 5.0 ft/s, depending on the fishway slope and headpond elevation. Velocities were highest within the vena contracta region, ranging between 4.8 and 7.4 ft/s, depending on slope and headpond elevation. Limited measurements of the air concentration were taken at a few locations along the fishway (these corresponded with velocity traverse locations). Air concentration increased with increasing slope, headpond, and in the downstream direction as the flow became more turbulent. In a separate biological evaluation study, the Denil fishway was found to be capable of passing adult American shad Alosa sapidissima and blueback herring A. aestivalis.
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