A preliminary assessment of environmental flow in the three rivers' source region, Qinghai Tibetan Plateau, China and suggestions

The three rivers' source region (TRSR) located in the Qinghai-Tibetan Plateau is an important ecological region of China for its location and high elevation. However, the ecological condition of the region is critical to water conservation and ecological security in China. Therefore, the present study focused on determining the environmental flow requirements (EFRs) of the Lancang (above Xiangda streamflow gauge), Yangtze (Zhimenda), and Yellow (Tangnaihai) Rivers, which will be helpful in the sustainable development of the region. Because of lacking ecological data, we used four hydrological methods (i.e., flow duration curve shifting, Tennant, flow duration curve analysis, and low flow index method) to assess the EFRs for the minimum and optimum eco-environmental conditions of these rivers. Since there was missing data on most gauges and we had streamflow data of only one gauge (Zhimenda) in the Yangtze headwater region, a hydrological model was applied to complete the missing data and simulate the streamflow data for the Tuotuo, DamChu, Chumar, and Tongtian Rivers for the estimation of the EFRs insides the region. The environmental flows of 118 m3/s (76% of mean annual flow, MAF), 312 m3/s (72% of MAF), 484 m3/s (77% of MAF) were determined for the conservation of the optimum riverine ecosystem and 67 m3/s (43% of MAF), 155 m3/s (36% of MAF), and 290 m3/s (47% of MAF) for the minimum eco-environmental conditions for the Lancang, Yangtze, Yellow Rivers, respectively. It was also noticed that low flow months (November to April) required more proportions of mean monthly flow than high flow months (May to October). These preliminary results will be very supportive of the water resources managers and policymakers in the case of any sustainable socio-economic development in the region.