Hydraulic and biological aspects of fish passes for dams
The primary purpose of the dissertation is to quantify the efficiency and operation of various types of fish passes for dams. This is achieved through a novel experiment of testing juvenile salmon in a scale model fish-passes with a range of small structures including vertical slots, orifices, weirs and combinations of all three. Direct comparisons of the efficiency of each type of fish pass in terms of upstream migration. Two identical physical models were constructed, one at the Fisheries Research Services Freshwater Laboratory at Almondbank, Perth, Scotland where observations were made of fish behaviour. The other model at the University of Glasgow, Glasgow tested only hydraulic conditions. The physical models were simplified representations of a reach of a river downstream of a dam, weir or any other obstruction to fish migration. A removable cross wall incorporating one of the types of pass tested divided the flume into two pools. A significantly higher proportion of fish moved through submerged orifices or vertical slots than through weirs for a given flow rate and velocity. The orifice and vertical slot passing efficiencies are directly correlated to the velocities existing in their vicinity. To reach the weir/slot/orifice devices, salmon parr tended also to stay near the bottom of the flume and followed a path along the sides of the arena, which provided them with low velocities and cover. In the vicinity of the weir/orifice/slot devices, the movements of salmon parr were consistent with energy-conserving strategies. Clearly, the extrapolations of results from the behaviour of small to large salmon remains cautious, the intention of this research being to characterise the behaviour of small salmon and to develop clear testable hypotheses about how large salmon may respond to water flow. Preliminary field tests were then conducted at Tongland Dam fish pass to test the main recommendation extrapolated from the parr behavioural study. The particular situation of this fish pass, which contains both weirs and orifices, allows a comparison between the two. Passive Integrated Transponder (PIT) tags together with antennae installed at a weir and an orifice were used to individually monitor the movement of wild spawning salmon passing through the fish pass. The results of the field test are as yet, inconclusive.