level of the uppermost notch lower than the adjoining weir or spillway
crest; the discharge and head calculations may be achieved by using appro-
priate weir–notch or orifice formulae.
The entrance to the fish pass (ladder) must be located in the down-
stream white water parallel to the main flow, whereas the exit (at the
upstream end) should be well within the reservoir away from the spillway
structure. The pools are usually 1–2 m deep, 2–5 m long and 2–10 m wide,
depending on the number of fish migrating. Cross-walls may be provided
with staggered notches–orifices, with the velocities in the ladder being
around 0.5 m s^1. Guiny et al. (2005) investigated the efficiency of different
passages through the baffles in a fish pass (orifice, slot, weir) and found –
with limited data – a strong preference of the migrating juvenile Atlantic
salmon for the orifice type.
The maximum swimming speed U(m s^1 ) of a fish is a function of the
fish length L(m) and the water temperature T(°C) and is predicted (Zhou,
1982) by
U0.7L/2t (9.30)
wheretis the muscle twitch contraction time (related to tail beat fre-
quency) given by
t0.17L0.43(0.0028 0.0425L0.43)lnT 0.0077. (9.31)
Equations (9.30) and (9.31) are recommended for the ranges of
L0.05 m–0.80 m and T2 °C–18 °C. The fish may be able to swim at this
412 DIVERSION WORKS
Fig. 9.33 Fish ladder
