Research On Ecological Water Requirement In The Upstream Of Lijiang River Basin

Ecological water demand of rivers is an important research focus of scholars in the ecological hydrology field both at home and abroad. This paper conducts a comprehensive analysis of the hydrological and water quality conditions, basic elements of river ecosystem and ecological water demand function and type of the Lijiang River; and systematically calculates the upstream ecological water demand of the Lijiang River, which can provide the theoretical basis for the upstream water resource management of the Lijiang River. Since the spatial and temporal distribution of upstream resources of the Lijiang River is uneven and inadequate attention has been paid to the ecological water demand in the water resource allocation, the ecological water has been squeezed by the industrial and life water. Concerning the upstream ecological environment problems of the Lijiang River, this paper studies the ecological water demand of rivers. This paper analyzes the natural geographical environment of the upstream of the Lijiang River and the major problems facing its ecological environment,studies various methods to calculate the ecological water demand and analyzes their feasibility, merits and demerits; and chooses the feasible ecological water demand calculation method for the upstream of the Lijiang River. The main research issues and findings of this paper are listed below.(1)The monthly assurance rate method is adopted to calculate the ecological water demand. Since the seasonal distribution of precipitation in the upstream of the Lijiang River is uneven and the runoff volume features large annual and interannual variations, the monthly assurance rate method is improved. It is found that the monthly assurance rate should reach 50% so as to ensure feasible ecological water demand, which is 58.50m3/s(1.845 billion m3); and the minimum ecological water demand is 17.25m3/s(544 million m3). At last, the Tennant method is employed to test the finding and analyze the cause of the error.(2)The TN, TP, COD and NH3-N content in the upstream of the Lijiang River is analyzed. It is found that the TP, COD and NH3-N content in the upstream of the Lijiang River is in line with the III type water quality required by Guilin Municipal Water Function Zoning. However, the TN discharge is quite serious, which exceeds the required standard. The TN content near the downtown area of Guilin is of the V type. According to requirements of Guilin Municipal Water Function Zoning, the ecological water demand for TN, TP, COD and NH3-N is 60.72m3/s(19.15m3), 39.98m3/s(12.61m3), 28.30m3/s(8.92m3) and 37.95m3/s(11.97m3), respectively. The ecological water demand fully meeting the water quality requirement for the sake of safety should be 60.72m3/s(19.15m3).while the basic ecological water demand to prevent pollution is 30.23m3/s(953 million m3).(3) Requirement of the comprehensive water quality and water volume,This paper confirms that the feasible ecological water demand of the upstream of the Lijiang River is 60.72m3/s(19.15m3) and the minimum ecological water demand is 17.25 m3/s(544 million m3).In order to meet the requirement of the feasible ecological water demand of the upstream of the Lijiang River, this paper conducts a statistical calculation of the average annual water supply on a daily, monthly and annual basis. According to the positioning of ecological functions and the calculation results of the ecological water demand of the upstream of the Lijiang River, an ecological water demand guarantee plan is put forward for the upstream of the Lijiang River.