Reasons of water salinization and its prevention measures in Beitang Reservoir, Tianjin City

Abstract

为确定天津市北塘水库作为南水北调供水调节和事故备用水库的水质安全性, 于2005年7-12月, 监测分析水体、底泥和库周土壤中全盐量和Cl^-浓度的变化, 研究水源补给、底泥释放、降雨蒸发和地下水水位变动等因素对水库水质的影响。结果表明在目前蓄潮白新河水的条件下。北塘水库水中的Cl^-浓度变化幅度为302-409mg/L, 超过饮用水水源地的水质标准(GB3838-2002)。库区0-100cm底泥全盐量平均值为0.253％, Cl^-含量为0.048%, 分别是库周土壤的1/8和1/18.3。因此, 蓄水造成水库底泥盐分的大量释放。经计算, Cl^-的平均释放强度为1.3 g/(m²·d)。南水北词通水后, 若水库保持在5.60 m以上的运行水位, 底泥释放虽造成Cl^-浓度上升, 但水质能达到供水水源地的标准。水库周边地下水的矿化度为59.63 g/L, Cl^-浓度为26.17 g/L, 远高于水库水体的含盐量, 但只要在5.60m以上水位运行, 水库就不会受到高矿化度地下水的补给影响。因此, 在合理调度的基础上, 北塘水库作为天津市南水北调供水调节和事故备用水库是安全的。;Beitang Reservoir is planed as a regulating and accident standby reservoir in Tianjin city in the project of the South-to-North Water Diversion Engineering. To determine the security of water quality, total ion amount and Cl^- in reservoir water and sediment and in soil around reservoir were detected from July to December of 2005. Effects of water supply, sediment release, rainfall, evaporation and groundwater level on water quality of reservoir were analyzed too. In this period, Cl^- concentration varied from 302 mg/L to 409 mg/L, which exceeded the maximum of drinking water source standard. The mean content of total ion amount in reservoir sediment from 0-100cm was 0.253% , and chloride content was 0.048% , which account for only 1/8 of total ion amount and 1/18. 3 of chloride content in soil around Beitang Reservoir. Therefore, water storage in reservoir led to release of salt from sediment. According to the 1.3 g/m² release intensity of chloride every day, water quality of Beitang Reservoir can satisfy to the standard of drinking water source when water level keeps above 5.6m. Total ion amount and Cl^- concentration in groundwater around reservoir were 59.63g/L and 26.17g/L respectively, which were much higher than that in reservoir water. As long as the running water level of reservoir keeps above 5.6m, the reservoir would be not affected by groundwater. By the reasonable control, Beitang Reservoir is feasible to work as a regulating and accident standby reservoir in Tianjin city in the near future.