基于水电梯级开发的河流生态健康研究

RESEARCH ON RIVER ECO-HEALTH BASED ON HYDROPOWER CASCADE DEVELOPMENT

为进一步了解水电开发对河流健康的影响,本文以雅砻江下游水电梯级开发为例,构建河流健康评价指标体系,选择无人为干扰和干扰较小的河流为参照,以指标变化率衡量水电梯级开发前后河流受扰动程度,分别采用综合评价法和赋值评分法进行了定量评价。综合评价结果显示,雅砻江下游河段的综合健康指数为0.71,该研究区域在丰水期、平水期和枯水期的综合健康指数分别为0.74、0.70和0.69,均处于亚健康状态;赋值评分法结果显示建库前的河流健康指数(River health index,RHI)为19.1,等级为健康,建库后为14.3,等级为亚健康,两种方法评价结果基本一致。本文以期完善河流健康评价体系,并为生态修复提供依据。

The development of hydropower has destroyed the integrity of the basin ecological system. In order to evaluate the effects aroused by cascade development of hydropower stations to the health of watershed eco-system through quantitative analysis, this paper constructs a comprehensive watershed health evaluation index system within 6 aspects,which separately is based on the integrity of hydrology, the integrity of physical structure, the integrity of chemicals, the integrity of terrestrial organism, the integrity of aquatic organism as well as the integrity of ecological service function.Relying on this system, the structural entropy method is used to calculate the weight of the index and the weighted average method is used to calculate the overall health index of river basin. In order to know the variation relationship among the indexes after cascade reservoir construction, the property of the indexes are analyzed and used to demonstrate the variance ratio. Then this paper sets a case study taken an example of the downstream of Ya-long basin and compares all indexes＇ variation in high flow period, normal level period and rainless period before and after the construction of cascade hydropower station. At last, the paper is aimed at evaluating the health condition of the eco-system health in the downstream of Ya-long basin after the standardizing treatment of the data. The data shows that the overall health index of the Ya-long river in the downstream is 0.69. While the health index in different stages are different as follows： in high flow period the health index is 0.72; in normal level period is 0.69; in rainless period is 0.68; all of them are in the state of subhealth. That is to say, the study demonstrates that the physical structure integrity and biological integrity in this region are seriously damaged while chemical integrity and hydrological integrity vary relatively small to some degree. However, the integrity of ecological service is improved largely. Seeding from different period, we can conclude that the comprehensive index in high flow period is relative high, so the ecological flow that aquatic organism needed is insured, the biological integrity maintain in a high degree, the ecological benefit improve a lot and the ability of basin water purification is strengthened; while in normal level period and in rainless period, the chemical index changes a lot compared with high flow period, so the integrity of chemical decreases relatively. Moreover, the flow in normal level period is close to nature condition, the index like water temperature and dryness degree variance ratio is low, so the hydrological integrity is relative high. In rainless period, these index vary within wide limit, so the comprehensive health index in normal level is a litter more higher than rainless period. In brief, this paper furthers the study of elements that influenced watershed eco-system by cascade hydropower stations. And some suggestions are provided to serve as reference in evaluation of watershed and reason in restoration.