Study On Cumulative Effects Assessment Of Hydropower Cascade Development In Tianquan River

Although hydropower project was able to gain huge economic interests, simultaneously, it caused serious damage to the environment. Especially in the development of basin cascade which had cumulative and potential effects of many hydropower projects, besides the environmental impact of a single hydropower project. In order to maintain health of rivers, achieve a harmony between human and nature, it's urgent and necessary to carry out the study on environmental cumulative effects of watershed.In this paper, on the basis of widely read relevant domestic and overseas literature of the environmental impacts of cumulative impact and cascade development to watershed, with Tianquan river watershed which had typical mountain stream characteristics of basin edge in southwestern as research object, analyzed environmental cumulative impact on cascade development in recent years. The studies showed that the cascade development caused changes in the water environment,ecological environment and social environment, and as the level increased, the more significant the cumulative effected of the environment.Cascade development in Tianquan river watershed caused hydrological regime and water environment changes in the river. First of all, it caused the volume of runoff loss which reduced 139 million m3 until 2008. Second, cascade reservoirs reduced the capacity of transporting sediment and concentration of sediment. In 2008, the transport of suspended sediment in Tianquan River reduced 31.4 million tons, and the concentration of sediment decreased by 28.8%.moreover, cascade reservoirs in Tianquan River resulted in deterioration of water quality. In 2008,the water quality has declined, the three water indicators that ammonia nitrogen, total phosphorous and chromium reduced to the national Class II water quality standards. At last, the discharged water from cascade reservoir changed water temperature in the river, and made the water temperature lower in spring and summer and higher in autumn and winter than the natural river.The construction of cascade hydropower project resulted in the destruction of habitat area, reduced the scope of biological activities. While, it caused serious soil erosion, the additional soil erosion caused by the disturbance of cascade hydropower project had up to 10,300 in 2008. Meanwhile, the changes of the watershed environment also had an impact on the biologic population, especially fish, it hindered gene exchange and affected breeding of the population although cascade reservoirs provided a suitable environment to the slow-flow-requiring-fish. Cascade exploitation promoted the economic development of the basin. In 2008, the GDP in Tianquan increased by 83.6% compared with 2000, and the per capita GDP increased by 80.8%. Meanwhile, the proportion of primary industry decreased by 1.6 percentage points, secondary industry declined by 10.6 percentage points, and the tertiary industry increased by 12.2 percentage points. Cascade Station has brought a lot of financial revenue, improved the medical conditions and increased the educational level in Tianquan. In addition, the road network which constructed for the power station improved the local traffic conditions and accelerated economic growth.Through comparison of changes of the watershed environment of before and after the cascade development, predicted the watershed environment cumulative effects in 2025 after the cascade development completed, and advanced the countermeasures at last.According to the study on environmental cumulative effects of cascade development in tianquan river watershed, this paper enriched the concept and research content of cumulative effects, supplied scientific evidence to development and usage of water resource in watershed and sustainable development, simultaneously, had some guiding meanings to programming and scheduling of cascade hydropower project.