The Study On The Threshold Of Ecological Impact Assessment For Cadcade Hydropower Development

Cascade hydropower development means steg water conservation projects on the river of the model of water resource development, it main objective is to make full use of rivers drop, cement barriers and water resource, this model is the main form of water resource exploitation. Hydropower cascade development promotes socio-economic development, the ecological problems caused showing up little by little, such as a river hydrodynamic conditions change, the traditional process of food delivery change, food chain destruction, habitat degradation, disappearance of signature species and so on, so it damages the natural ecosystem integrity of original watershed.How to alleviate the contradiction between socio-economic benefits and ecological protection, coordinate the relationships between cascade hydropower development and river ecosystems, attain the harmony between between man and nature, is a major problem that must be considered.Because river river basin is a complete ecosystem, compared with a single power station development, the effects wirh inlay and disturb to river ecosystems are more more significant, with groupment, systematicness, consecutiveness, cumulativeness in the river ecosystem modification, lack of effective distinguish and proclamation of ecological factors and impact feature, also is impossible to assess the ecological impact for cadcade hydropower development scientific. In this study: utilize the cascade hydropower development as the background to reveal the ecosystem change characteristic which cased by cascade hydropower development,build a frame of indicators of ecological impact assessment and the threshold of ecological impact assessment. On this basis, the Yalong River hydropower cascade development is assessed, and we can see that this basin is sub-health. Study mainly includes the following content:(1) And based on the essence of ecosystem impact which drived by cascade hydropower development, analyze the impact features of ecological factors from non-biological and biological effects.(2)Based on the impact characteristics and laws of ecological factors that caused by cascade hydropower development, clear and definite the response properties, response level and logical relationship between each other, build the network of ecological factors, establish the framework of assessment indicators which based on ecological integrity.(3) Demarcate the weight of indexes of ecological impact assessment with Deliphi, define the threshold of ecological impact assessment as very poor, poor, medium, good, excellent based on the relative change rate of indicators, and according to demand for ecological impact assessment, set the lower threshold level "good" as the trigger poing of the cascade hydropower development, as the indicator of ecological integrity A is 0.739.(4)Take the cascsde hydropower development in the lower-reach of Yalong River as an example, according to the river basin planning, evaluate the ecological impact with the understanding that 50% inflowing water frequency, reveal that the ecological integrity in lower-reach of Yalong River is under relatively poor.