Evaluation indicators for assessing the influence of reservoirs on downstream water temperature
摘要
Assessing the influence of reservoirs on downstream water temperature constitutes an important part of environmental impact study for hydropower development.A set of evaluation indicator system is established from the perspective of downstream water temperature fluctuation.The latter is the result of reservoir-induced temperature changes in downstream waters.The evaluation indicators include the baseline deviation,the phase shift and the extreme change.Each indicator is defined and the corresponding formula is provided.An evaluation method using the indictors is proposed for assessing the influence of reservoirs on downstream water temperature.The cascade reservoirs on the upstream of Yellow River are selected for a case study in an effort to test the proposed evaluation indicator system and the evaluation method.A spatial and temporal evaluation of the influence of reservoirs on downstream water temperature is conducted.The result shows that the evaluation indicator system and the evaluation method are able to adequately reveal the seasonal change of water temperature,as well as its time lagging and flattening resulting from reservoir operations.The main characteristics of water temperature variation can also be determined by the system and the method.Furthermore,through analyzing various indicators at different river reaches,the cumulative influence of cascade reservoirs on downstream water temperature can be revealed.The evaluation indicator system and evaluation method provide a general methodology,and can be applied to other river systems to study the influence of reservoirs on downstream water temperature.