NUMERICAL ANALYSIS OF ICE HARVOR TYPE FISHWAY AND MODIFICATION OF ITS FUNCTION UNDER LOW DISCHARGE AND BED DEGRADATION CONDITION

Ice harvor type fishway has commonly installed in Japan because it is a hybrid type fish ladder which is comprised of weir and orifice. But under severe low discharge and bed degradation condition, only the orifice flow state exists. In this case, fish cannot migrate through the fishways. To operate fishway in such severe flow condition, we proposed to close part of the orifices and put triangular shape blocks on the weir. Function of fishway was investigated by using 3D flow simulation. Numerically obtained flow state in the fishway with ten series of ice harbor type fishway shows in good agreement with the experimental results. And the proposed method can maintain favorable fishway function under low discharge and bed degradation condition.