Abstract
Storm runoff events in the flooding season affect the water quality of reservoirs and increase risks to the water supply, but coping strategies have seldom been reported. The phenomenon of turbid current intrusion resulting in water turbidity and anoxic conditions reappearing after storm runoff, resulting in the deterioration of water quality, was observed in the flooding season in the deep canyon-shaped Heihe Reservoir. The objective of this work was to elucidate the effects of storm runoff on the Heihe Reservoir water quality and find a coping strategy. In this study, an intensive sampling campaign measuring water temperature, dissolved oxygen, turbidity, nutrients, and metals were conducted in the reservoir over a period of two years, and the water-lifting aerators were improved to achieve single aeration and a full layer of mixing and oxygenation functions using different volumes of gas. The operation of the improved water-lifting aerators mixed the reservoir three months ahead of the natural mixing time, and good water quality was maintained during the induced mixing period, thereby extending the good water quality period. The results can provide an effective coping strategy to improve the water quality of a source water reservoir and ensure the safety of drinking water.
Highlights
A source water reservoir is different from a general lake reservoir in that its requirements for water quality are higher; it is critical to improve the water quality and control the pollution of source water reservoirs [1,2].It is predicted that the frequency of extreme rainfall events will occur more frequently than the mean precipitation rate in the near future [3,4], while the amount of total precipitation is predicted to change only slowly [5]
Significant turbid currents coupled with a large amount of dissolved oxygen (DO) entering the bottom of the reservoir can effectively inhibit the release of contaminants from the sediments [11]
Anoxic conditions reappeared after the storm runoff ended, caused by the increase of the oxygen consumption rate that could accelerate the release of pollutants from the bottom sediment
Summary
A source water reservoir is different from a general lake reservoir in that its requirements for water quality are higher; it is critical to improve the water quality and control the pollution of source water reservoirs [1,2].It is predicted that the frequency of extreme rainfall events will occur more frequently than the mean precipitation rate in the near future [3,4], while the amount of total precipitation is predicted to change only slowly [5]. A source water reservoir is different from a general lake reservoir in that its requirements for water quality are higher; it is critical to improve the water quality and control the pollution of source water reservoirs [1,2]. A significant density of turbid flow follows high rainfall events in many lakes and reservoirs [8]. The inflowing water will enter the reservoir as a plunging underflow if the density of the inflow water is significantly higher than that of the reservoir, and it may flow into the bottom and fill up the reservoir from the bottom if the inflow density is large enough [9,10]. Significant turbid currents coupled with a large amount of dissolved oxygen (DO) entering the bottom of the reservoir can effectively inhibit the release of contaminants from the sediments [11]
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