峡谷型水源水库蓄水过程水质变化特征及其影响要素

Characteristics and Influencing Factors of Water Quality Change in the Process of Filling Gorge Source Reservoir

水源水库是城镇居民最主要的饮用水水源,新建水库选取引水水质一般较好,然而由于水库蓄水过程中水质受到降雨径流入库、水动力条件和分层结构变化的共同影响,库区水体水质仍可能呈恶化趋势.本研究重点探索水库蓄水过程中水质演变规律,解析水源水库污染特征.以固定频率取样检测的方法,跟踪监测陕西省汉中市三河口水库蓄水过程上游河道及库区水质,分析上游来水水质、库区水体分层结构及水动力条件等要素的改变对水库水质的影响.结果表明:①2021年6−7月三河口首次较大流量蓄水过程受来水温度影响,来流水体以底部潜流的形式进入库区,并在底部形成新的温度分层;双温跃层结构的形成导致在水体中部和底部各自形成厚度达15和10 m的厌氧水层.②9月初第二次特大流量径流入库彻底破坏水体热分层结构,水体在径流和气温的共同作用下实现完全混合.③水源水库蓄水过程水质受入库径流与水体分层结构共同影响:6−8月水库入库径流量小且污染负荷低,库区氮磷及有机物浓度有较小波动,而热分层结构阻碍了污染物的垂向传递,温跃层水体总氮浓度和高锰酸盐指数在垂向上呈较大值,分别为1.78和6.0 mg/L;8月至9月初入库径流量大且污染负荷较高,全库区氮磷及有机污染物浓度升高明显,总氮浓度由1.07 mg/L升至1.56 mg/L,总磷浓度由0.021 mg/L升至0.029 mg/L,高锰酸盐指数平均值由5.18 mg/L升至6.18 mg/L.水库蓄水过程中,上游径流入库是影响主库区水质的重要因素之一.

Water source reservoirs are the most important drinking water source for urban residents.Although the water quality of newly built reservoir is generally good,the water quality of the reservoir is constantly changing due to the common influence of rainfall flowing into storage,and changes in hydrodynamic conditions and stratified structure during reservoir impoundment.This study focuses on exploring the water quality changes in the process of reservoir storage and analyzing the pollution characteristics of water source reservoir.The water quality of the upstream channel and reservoir area of Sanhekou Reservoir in Hanzhong City,Shaanxi Province was tracked and monitored using the fixed-frequency sampling method.The effects of the upstream water quality,the stratification structure of the reservoir water and the change of hydrodynamic conditions on the water quality of the reservoir were analyzed.The results show that:(1)The first large-scale discharge water storage process in Sanhekou from June to July 2021 was affected by the incoming water temperature.The incoming water entered the reservoir in the form of undercurrent,forming a new temperature stratification at the bottom.The formation of the double thermocline structure led to the formation of anaerobic water layers with thicknesses of 15 and 10 m in the middle and bottom of the water body,respectively.(2)In early September,the second large runoff entered into the reservoir,completely destroyed the thermal stratification structure of the water body,and the water body reached complete mixing under the combined action of runoff and air temperature.(3)The water quality of the water source reservoir during the storage process was affected by the inflow runoff and the stratified structure of the water body.From June to August,the runoff of the reservoir was small and the pollution load was low.The concentration of nitrogen,phosphorus and organic matter in the reservoir area fluctuated slightly.The thermal stratification structure hindered the vertical transfer of pollutants,so that the total nitrogen concentration and permanganate index of the thermocline water showed large vertical values,1.78 mg/L and 6.0 mg/L,respectively.From August to early September,the runoff of the reservoir was large and the pollution load was high.The concentration of nitrogen,phosphorus and organic pollutants in the whole reservoir increased significantly.The total nitrogen concentration increased from 1.07 mg/L to 1.56 mg/L,and the total phosphorus concentration increased from 0.021 mg/L to 0.029 mg/L.The average permanganate index increased from 5.18 mg/L to 6.18 mg/L.In the process of reservoir storage,upstream runoff into the reservoir is one of the important factors affecting water quality of the reservoir.