Ecological flow in lower Hanjiang River based on habitat simulation of four major Chinese carps

The operation of cascade reservoirs has significantly changed the natural hydrological regime of rivers, leading to adverse impacts on the river water ecosystem.The four major Chinese carps were selected as the indicator species in the lower reaches of the Hanjiang River, and considering the preferences of the four major Chinese carps for the flow velocity and water depth in the habitat, a suitability index curve for spawning and growth periods was constructed.The River 2D hydrodynamic model was used to simulate the changes of the suitable habitat of the four major Chinese carps under different flow conditions.Combined with habitat simulation and hydrological regime in the natural period, the ecological flow and high flow pulse to maintain the demand of the four major Chinese carps during spawning and growth periods were proposed.The results show that the minimum and suitable ecological flow of the four major Chinese carps in the lower reaches of the Hanjiang River is 1310 m3/s and 3520 m3/s, respectively.High flow pulse with a duration of no less than 3 days and flow no less than 1310 m3/s at least twice a year should be provided to stimulate the natural spawning and increase the spawning scale of the four major Chinese carps.The minimum and suitable ecological flows during the growth period are 441 m3/s and 1520 m3/s, respectively.Compared with the Tennant method and the actual ecological monitoring, the calculation results in this study are more reasonable and reliable, but compared with the historical measured flow process, the satisfaction rate of ecological flow during the spawning period of the four major Chinese carps are not high enough.Therefore, it is necessary to choose an opportunity to implement the joint ecological dispatch of cascade water conservancy projects in the middle and lower reaches of the Hanjiang River to improve the satisfaction degree of ecological flow.