Abstract:

The authors proposed the ecohydraulics in calculating the lowest ecological flow in river channels to resolve ecological water demand of Jinping Waterpower Station Stage II (Jinping II) reducing reach. The lowest ecological flow in river channels was determined by satisfying hydraulic habitat of objective aquatic biology. The change in hydraulic habitat parameters in whole reducing reach was considered and the conception of the percentage of cumulated river length to the reducing reach length in fulfilling the hydraulic habitat parameters was put forward. The gained results avoid the misjudgment conduced by using lower parameter value when the percentage of the length of reducing reach to the total is very small. Referring to the characterization of hydraulic habitat parameters in related literature, using specific situation of fish habitat in Jinping II reducing reach of Yalong River, the authors confirmed the fish habitat requirements to various hydraulic parameters, such as velocity, water depth, water surface width etc. It is indicated that the lowest ecological discharge in the reducing reach in dry seasons is 45 m3/s in order to meet the subsistence of fishes. 95 percentage of river channels can satisfy the hydraulic factors for the subsistence of fishes, including water depth, velocity, water surface width, wetted perimeter ratio, cross section area, and water surface area. The change of water temperature will not affect fish spawning in 45 m3/s. The places of hydraulic forms including torrent, subcritical flow, riffle and deep pool will change, yet their amount will remain the same as in 45 m3/s. When the river discharge reduces, the biomass will reduce. However, the amount of animal community will remain as long as the river discharge exceeds 45 m3/s. This method provides feasible means to determine the flow for ecological requirement of fishes in river channels.

Key words: ecological basing flow, method of ecohydraulics, hydraulic factors for subsistence, Yalong River