Analysis of water environment during construction of Xiaolangdi Hydro Project for the reservoir region and lower reaches

A series of water quality monitoring was performed from March 1993 for the reservoir region and impacted downstream regions of the Xiaolangdi Hydro Project. Five years' monitoring showed that the water in the regions was mainly polluted by aerobic organisms, the pollution in the mainstream of the Yellow River was more serious than that in the tributaries, and the pollution was more serious during the non flood period than that during the flood period. Monitoring also indicated that the water quality was mainly affected by the water from upstream regions, the pollution sources in the reservoir region, project construction, and the variation of water volume. After the completion of the project and with the development of the reservoir region, the quality of water from upstream regions and the development activities may gradually become the main factors affecting the water quality of the reservoir region and its downstream regions