2.2. Denil fishways
The Denil fishway consists of a channel containing symmetrical closely spaced baffles (or fins, or vanes) on the sidewall and the floor (Fig. 4). The vanes cause part of the flow to turn and oppose the main stream in the central part of the flume. The baffles conduct a part of the energy of the main flow to the walls and to the bottom of the channel. This arrangement provides considerable energy dissipation and establishes low velocity flow in the central zone of the fishway. Fish ascend in Denil fishways by swimming in the middle of the flume in the depth they prefer. While there are no resting areas in the fishway flume, Denil fishways must be equipped with special resting pools at certain intervals. The resting pools also function as energy dissipating pools.
The flow in a Denil fishway consists of two interacting parts, namely, of the main stream in the central portion of the channel and of a series of systematic lateral streams, each one corresponding to a side pocket created by baffles. The interaction between the main stream and the lateral ones provides the main mechanism for transferring mass and momentum, and produces considerable turbulence and energy loss. The water mass on the surface in this fishway type is fast moving and reasonably smooth (Katopodis & Rajaratnam 1983).
The highest velocities in the cross section of Denil fishways are not located in the centerline, but on the sides. The velocities on the sides are distributed unsymmetrically to the mid-axis (Kamula & Bärthel 2000).
Figure 4. A schematic representation of a plain Denil fishway with definitions for dimensions. For standard design, B = 0.56 m, b = 0.36 m, a = 0.25 m, k = k’ = 0.13 m and ψ = 45°.
The hydraulics of Denil fishways have been studied at the University of Alberta, Canada since the early 1980’s (App. 3). In these studies, Katopodis & Rajaratnam (1984) used equation (5) to scale the results of the studies:
where So is the bottom slope and bo is the free opening. They proposed that dimensionless discharge of Denil fishways could be expressed by equation
where α and β are constants dependent on the structure geometry, yo is water depth in the flume and bo is the width of the free opening. For standard Denil fishway the equation is defined as
