Numerical Simulation of Flow in A Pool and Weir Fishway for Environmental Considerations

Pool and weir is a type of fishways that make possible migration of fish to upstream of the dam. Velocity, water depth and turbulence are the effective parameters in swimming of fish. In order to construct this structure in interaction with the environment on the rubber dams, numerical models have been presented to evaluate the results of measuring the flow velocity in the instruments constructed in Karkhe-Hamidieh dam of Khouzestan and comparing the results with a field method. In this paper, the three-dimensional equations governing shallow water in weir and orifice fishway are solved with suitable models of turbulence that flow pattern and turbulence can be calculated. The results of simulation of flow were compared with results of field study by Micromollineh. The results show velocity lines in the pool (4) of fishway at nonsubmerged mode with constant velocity about 0.4 to 0.6 meters per second that is close to amount of measurement by Micromollineh about 0.469 meters per second. The results show velocity lines in the pools of fishway at submerged mode with constant velocity about 0.4 to 0.6 meters per second that is close to amount of measurement by Micromollineh about 0.54 meters per second. The results show velocity lines in the pools of fishway at submerged mode with explosive velocity about 1.59 meters per second that is close to amount of measurement by Micromollineh about 1.6 meters per second. In the submerged area of Karkheh-Hamidiyeh dam, the weakest fish have the maximum power of 1.513 watt of energy and can not overcome 4.2 watt of energy and able to climb a submerged fishway with an height of 80 cm will not be. In the nonsubmerged state, as it is seen, the fish have the maximum power of 2.41 watt of energy and do not have the ability to overcome 3.653 watt of energy and can not climb a non submerged state with a water height of 24 centimeters. This condition is dominant for the weakest fish in the Karkheh River. Cyprinidae fishes in Mazandaran rivers have the maximum power of 0.176 watt of energy and have the ability to overcome 0.132 watt of energy and will be capable of climbing a submerged fish with a water heights of 80 centimeters. In fact, there is no need to reduce the flow rate in a submerged state with devices such as the use of baffles inside the pools. Small Cyprinidae fishes are also able to cross the fishway due to the slow flow in non-submerged state. the Vimba persa fishes will not be able to climb a non-submerged with a water height of 24 centimeters. In fact, there is a need to reduce the flow rate in a non-volatile state with measures such as the use of baffles within the pools, or the use of other fish structures should be investigated. Keywords - Pool and weir Fishway; Fish migration; Energy depreciation; Turbulence models.