Calculation and evaluation on ecological water demand under the influence of Hydropower Development in Southwest Mountain—As an example of the main upper reaches of Minjiang River

Hydropower Development in Southwest Mountain brings to some influence on ecological environment. The ecological water demand of the important segments of hydropower development must be ensured is a very important factor to guarantee the eco-environmental system and the sustainable development of the social economy. The measuring method of the minimum water demand for maintaining the ecobalance of the watershed is carried out by means of analysis on the main impact that the hydropower cascade development of the main upper reaches of Minjiang River brings to the eco-environment. After calculation, the water demand of the Minjiang River upper stream is 6.5–40 m 3 /s. The closer to the lower reaches, the more eco-water demand is. The water demand of the Minjiang River upper stream takes up 6.1%–33.4% of the average flow rate for years. The closer to the headstream, the more proportion eco-water demand takes up. The evaluations show that the reaches which have been developed shall ensure the ecological water demand of the watershed and the undeveloped river reaches shall keep the regional ecological water demand satisfaction as the prerequisite, from planning to designing, from construction to operation.