speed for a specified length of time (endurance time, tm) which is also a
function of fish length and water temperature and is given by
tmE/(|Pc Pr|) (9.32)whereE (energy store)19 400L^3 , Pc(chemical power) 0.97e^ 0.0052T
U2.8L^ 1.15andPr(power supplied) 48 L^3. It is suggested that the swim-
ming speed and endurance times as proposed by equations (9.30) and
(9.32) should not be exceeded in the design of a fish pass. Some other
examples of fish ladder passes in use are the weir-type fish entrance at
Priest Rapides, and the slotted fish entrances at Wanapum dam (Columbia
River) in the United States.
Flow control structures such as flood relief channels should be so
designed that the fish are not stranded; the minimum sluice opening
should be around 0.3 m0.3 m and the water velocity not more than
3ms^1 (a head difference of about 450 mm and a discharge rate of
0.27 m^3 s^1 ).
(b) Denil fish pass
The Denil fish pass (Denil 1936; see Beach (1984)) consists of closely
spaced baffles (for energy dissipation) and set at an angle to the axis of the
channel to form secondary channels for the passage of the fish. A typical
Denil fish pass with a channel width (b) (of say 0.9 m) may consist of
simple single-plane baffles with rectangular opening over a V-shape
opening (similar to a compound notch) set at a spacing of about 2/3b
(0.6 m) sloping upstream at an angle of 45° to the channel bed whose slope
itself should not exceed 1:4; the width of the opening is approximately
0.58b, whereas the height of the sill of the V-shape opening above the
channel bed is around 0.24bwith its top level (from bed) at about 0.47b.
Large rest pools (3 m long2 m wide1.2 m deep) are provided at verti-
cal intervals of 2 m. An example of the Denil fish pass complex is at
Ennistyman on the river Inagh in the Republic of Ireland.
(c) Fish lift (Borland type)
The fish lifts are primarily intended for high impounding structures and
the arrangements of the Borland fish lift are shown in Fig. 9.34. Its opera-
tion is very similar to navigation locks; however, in the fish lock through-
flow is maintained (bypass pipes) to induce the fish into and out of the
chamber. The fish are attracted into the lower pool (chamber) by the
downstream flow through the pool. The chamber is then closed at its
downstream end, and the fish are induced to swim out into the reservoir by
the flow through the exit from the lift. The operation of a fish lock is cyclic,