Abstract
Abstract. In order to solve the problem of lack of unified evaluation criteria for water quality evaluation in the Three Gorges Reservoir under different hydrologic condition, hydraulic retention time and flow rate were calculated wih the hydrological data of 6 intact hydrological years after the 175 m impoundment in the Three Gorges Reservoir using the concept of segment capacity. Results indicate that the hydrological conditions of the Three Gorges Reservoir have obvious spatial and temporal differences. The whole river should be evaluated according to the river standard during the wet season. In the dry season, the upstream of Wanxian should be evaluated according to the river standards and the downstream of Wanxian should be evaluated according to lake standard. The tributary bay should be evaluated according to the lake standard. The conclusion obtained by this evaluation method is consistent with actual situation of the reservoir, providing a theoretical basis and technical support for the targeted protection of water environment in river-type reservoirs.
Highlights
The operation of the reservoir changes the reservoir area periodically
Considering the principle of “the most unfavorable” and the actual conditions of the Three Gorges Reservoir area, this paper proposes a rough classification of the speed of the water body type: the lake flow rate is < 0.01 m s−1, the transitional flow rate is 0.01– 0.05 m s−1, suitable for Lake evaluation standard; river type flow rate is > 0.05 m s−1, suitable for river evaluation standard
Based on the storage capacity curve of storage capacity-water levelflow, this paper derives the storage capacity of the reservoir under the dam water level and estimates the total hydraulic retention time based on the inflow or outflow
Summary
In the “Environmental Quality Standards for Surface Water (GB3838-2002)”, different quality assessment standards are given for lakes and rivers (Table 1). The lake is directly applied to the reservoir and no distinction is made between different types of reservoirs. This has caused many confusions and difficulties in the actual water quality assessment of the reservoir area. Taking the Three Gorges Project as an example, the total storage capacity of the reservoir reached 393 billion m3 after 175 m of water storage in the reservoir. When assessing the water quality of the reservoir area, the water conservancy system shall evaluate the rivers according to the requirements of the “River reservoirs evaluated by rivers and lake-type reservoirs by lakes” in the Technical Regulations for Surface Water Resources Quality Evaluation (SL395-2007).
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