The Evolution Of Flow And Sediment Regime In The Yangtze River And Its Fish Response Mechanism

With the continuous development of social economy,climate change and uncontrolled development of rivers by human beings have led to the change of natural flow and sediment situation of rivers,causing serious ecological degradation and loss of biodiversity.Therefore,understanding the relationship between river water resources development and river ecosystem,especially the contradiction between river water and sediment process and river ecological environment,is of important theoretical and practical significance to realize the sustainable development of water resources in the Yangtze river basin and maintain the healthy development of river system.This paper mainly takes the Yangtze river as the research object,selects the measured water and sediment data of Pingshan,Cuntan,Yichang,Hankou and Datong stations,and discusses the river water and sediment situation theory and its ecological impact.This paper analyzes the spatial and temporal variation characteristics of water and sediment in the main stream of the Yangtze river in recent decades and evaluates the change degree of water and sediment situation in the Yangtze river.The effects of water and sediment changes in the Yangtze river on fish species were evaluated with the Chinese sturgeon and tetrapod as the target species.The main contents and results of the research are as follows:(1)Based on the theory of river ecosystem,discussed the theory of river flow and sediment situation and ecological effect,expounded the theory of natural hydrological situation,summarized the response relationship between the change of river hydrological characteristic variable and sediment variable and river ecosystem,and the influence of river flow and sediment situation change on important fish in river system.(2)The annual runoff of the Yangtze river has no obvious change,and the sediment transport in the middle and lower reaches has a significant downward trend.The abrupt change point mainly appeared in the water storage node of the water conservancy project,especially the three gorges reservoir.The annual runoff of each hydrologic station mainly has the main cycle change of 14-18 years,and the sediment transport mainly has the main cycle change of 20-24 years.The change of annual runoff is mainly affected by precipitation,while the significant decrease of sediment transport is mainly affected by human activities such as reservoir water storage,river drainage and soil and water conservation.(3)Through the quantitative evaluation of RVA method,DHRAM method and RI method,it can be concluded that Ertan hydropower station caused moderate change in the flow rate of Pingshan station,and the water and soil conservation work caused a low change in the flow rate of Cuntan station.Ertan hydropower station caused moderate change in the sediment transport capacity of Pingshan station,medium height change in the sediment transport capacity of Cuntan station,Yichang station,Hankou station and Datong station caused by soil and water conservation work in the upper reaches of the Yangtze river.(4)Stepwise regression method was used to identify the water and sediment indexes that affect the runoff of the fry of the four groups.The water and sediment indexes affecting the breeding population of Chinese sturgeons were the mean value of flow in January,the average annual 3-day minimum value,the occurrence time and reversal times of the annual maximum value,the high pulse times of sediment transport,the average annual 90-day minimum value and the base flow index.