The Longitudinal Range-Gorge Region (LRGR) is the gorge located in north-south directed mountains and valley in southwest China. Unique geographical location and atmospheric circulation lead to stereo-effect and “Corridor-barrier” functions in this region. And the Longitudinal mountain-valley area in northwest YunNan is also the river source area of Yangtze, Lancang and Nujiang rivers, In this area, the special topography and geomorphy and the characteristics of the three river’s parallel running and the alternation of high mountains with deep valley bring about a stereo-effect of water resource. As a result of “Corridor-barrier” function, this area has three major characteristics: distinct influence of stereo-crossing effect; obviously cascade location of vegetation, water resources, climate and other characteristics; developed dry valleys and their fragile environments, and diverse ecosystems and their complicated patterns. In view of abundant biological and esthetic cultural diversities, this region is considered as the most important area of biological diversity projection and scientific research, and ecological changes in this region will influence Chinese trans-boundary ecological security and resource security.
In recent years, with the exploitation and operation of the cascade hydropower station, the ecosystem health of the LANCNAG River of the Longitudinal Range-Gorge Region has been seriously affected by the construction and the operation of those dams. And the ecological water requirements, the most important basis to maintain the ecological health of the Longitudinal Range-Gorge Region, have attracted most of our attention. According to our field investigation of the Longitudinal Range-Gorge Region and analysis of the collected data during the investigation, the ecological water requirement of the Longitudinal Range-Gorge Region mainly includes the following several respects: the basic flow which is used to maintain the basic form of river; the environmental (purifying) flow which Keeps water of the river in a good quality to maintain its basic function; the transporting sediment flow which is used to maintain and regulate water sediment balance; the ecological flow which is used to provide enough water in order to guarantee the survive of living beings in the river and their habitat. Considering the supporting information data, the present paper adopts the ecological runoff-grade coefficient of ecological water requirements methods.
Firstly, based on the analysis of the correlation between ecological run-off and the ecological water requirements, this paper brings forward a new method of the calculation of ecological water requirement, that is, ecological runoff—grade coefficient of ecological water requirements methods. Secondly, built on the annual measure runoff, the present paper uses the ecological characteristic comparison and statistical methods including variation analysis and concentration analysis to calculate the grade coefficient of ecological water requirements in the three different regions of the Longitudinal Range-Gorge Region, and uses the frequency method to calculate the ecological runoff based on principle of small runoff with big frequency.
At last, this paper calculates the ecological water requirements in the Longitudinal Range-Gorge Region. During this process, this paper combines the grade coefficients of EWR with ecological runoff to calculate the Longitudinal Range-Gorge Region ecological water requirement, by using the frequency and Coefficient of variation methods. Considering the big difference in coefficient of variation of runoff in flood and in non-flood season, this paper calculates the ecological water requirement respectively.