Abstract
Eutrophication in lakes and reservoirs is a serious environmental problem that has damaged ecosystem health worldwide. Water diversion is one of the most popular methods for improving the water quality in shallow lakes, as it dilutes pollutants in and diverts them out of the lake. However, simple diversion without rational water distribution cannot significantly enhance water exchange in the entire lake because dead water zones always exist. This paper illustrates a case study on water quality improvement in Xihu Lake by diversion and water distribution. Based on theoretical calculation, the diversion water discharge was determined and rationally distributed into four different locations. According to the field observations after the implementation of the diversion and water distribution project, the average velocity over the dead water zones increased approximately 50 times over that of prior to the project. The average water exchange period reduced from 68 days to 22.5 days. The average turbidity was 8.8% and 12.4% lower than before after two and four months of diversion, respectively. The maximum turbidity reduced from the original 27.5 NTU (Nephelometric Turbidity Unit) to 20.1 NTU after two months of diversion, then to 16.1 NTU after four months of diversion. It shows that this diversion and rational water distribution eliminates most of the dead water zones and achieves a favorable flow field, thus reducing the turbidity and increasing water transparency, which is conducive to the improvement of water quality.
Highlights
Eutrophication in lakes and reservoirs is a serious environmental problem that damages ecosystems worldwide [1,2,3]
Turbidity Unit) to 20.1 NTU after two months of diversion, to 16.1 NTU after four months of diversion. It shows that this diversion and rational water distribution eliminates most of the dead water zones and achieves a favorable flow field, reducing the turbidity and increasing water transparency, which is conducive to the improvement of water quality
The results showed that the original Yangtze River diversion had a positive effect on water quality only in parts of the lake, such as Gonghu Bay and the northwest, southwest and central zones, but had no significant effect on Meiliang Bay based on regression analysis of long-term data
Summary
Eutrophication in lakes and reservoirs is a serious environmental problem that damages ecosystems worldwide [1,2,3]. Water diversion diverts clean and low-nutrient water to a eutrophic lake in order to improve the water quality [22]. The theory behind this mechanism is that adding large amounts of low-nutrient water can dilute the pollution in a lake, and accelerate water exchange and eliminate dead water zones in the water body. This case study concerns the water diversion and distribution project that has been successfully implemented in Beili Lake, which is part of Xihu Lake In this case, the clean water was diverted from.
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