As cascade power stations are constructed and operated,more concerns are attracted to their negative impact on fish from supersaturated total dissolved gas (TDG) generated by high dam spilling.The supersaturated TDG dissipates very slowly in natural rivers,even more slowly in reservoirs.Generally the spilling flow with high TDG saturation level exists from the upstream cascade's stilling basin to the downstream cascade's forebay.The fishway,which is an important facility to recover the non-continuity of the river,is a region of fish gathering.The TDG supersaturation flow in the fishway,which uses the water in reservoir as replenishment,is harmful for fishes.To explore the transportation and dissipation of TDG in the fishway,the experimental studies of different flow rates were conducted in a T shape fishway channel.The numerical simulations were performed according to the experimental conditions to obtained dissipation rate of different cases.The results revealed that water depth affected the disspation rate significantly.The dissipation rate of TDG decreased with the increase of water depth in fishway.No clear relations were found between TDG dissipation rate and mean velocity,turbulence and turbulent dissipation rate.Furthermore,it showed that the TDG dissipation rate in fishway was obviously higher than that in channel without clapboards,because the clapboards rose the residence time for flow and TDG in the flow dissipated adequately.The research provides scientific basis of the exploration of negative impact to fish in TDG supersaturation flow in fishway,and provides new ideas and reference for the research of the mitigation measures for the problem.
