Effects Of Hydraulics On Fish Fauna

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1. Effect of obstructing hydraulic structures on the fish fauna:
Dams, barrages, weirs or navigation locks built on a river for various purposes act as obstruction to the migration of the fishes. Various effects of such hydraulic structures are as follows:
a) Barrier to the movement of fish to their spawning grounds.
Several fish species require special regions to spawn. These hydraulic structures obstruct the movement of such species to their upstream spawning grounds where they reproduce. As the movement of such species get blocked or delayed their population is declining.
b) Destruction of spawning grounds
Fishes prefer the sites with sandy or gravel bed with shallow depth having low or no stream currents for spawning purposes. Generally
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The orientation of entrance should be such that maximum attraction current should be generated. Adult fishes generally migrate against the stream current, the phenomenon known as positive rheotaxis. When the main current is blocked due to any hydraulic obstruction, then the fishes try to escape through the side of the obstruction. While trying to guide themselves towards the current i.e. reacting to the positive rheotaxis they are guided towards the entrance of the fish pass. The attraction current at the entrance of the fish pass must be in the range of 0.8 m/s to 2.0 m/s. Some fishes tend to move in daylight, hence it is advised not to cover the fishways and if some part of the fishway is covered and lacks sunlight then it must be light artificially so that it may have same light intensity as that of the sunlight during the …show more content…
The fish pass must always have the minimum water depth required to operate the fish pass in order to facilitate the safe passage of the fish species. The slope of the fishway must not generally exceed the 1:15 value in order to avoid the stress induced on the species while moving upstream through the fish pass.
f) Design of the bottom of the fish pass
The bottom of the fishway should be covered with 200mm thick coarse substrate along its entire length in order to mimic the river bed conditions. Naturally available river bed material should be used while doing so. The small gaps in the coarse substrate provide refuge to the small fishes and other aquatic fauna during their

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