南水北调中线干线水体特征指标筛查与动态分析

Screening and dynamic analysis of water body characteristic indexes in the middle route of South-to-North Water Transfer Project

为掌握南水北调总干渠的水体特征指标情况,对中线干渠12个断面的99项水化学指标和5项同位素指标在2020—2021年度的变化情况进行系统分析,按照可以在干渠沿线普遍检出并能广泛使用(普适性)、干渠本身指标稳定(稳定性)、与周围水体有明显差异(差异性)的原则,建立干线水体特征指标体系,尝试识别出总干渠的特征指标,进而评估特征指标的正常动态范围,以期为快速研判南水北调干渠边坡渗水、漏水等问题提供技术支撑。研究结果表明:对于“普适性”,中线干渠水体有10项水化学指标可以满足;对于“稳定性”,中线干渠水体中锶、钠、钾、钙、镁和氯等8项水化学指标总体稳定,受季节变化影响具有一定的波动性,氘(^(2)H)、氧(^(18)O)、锶(^(87)Sr)和硫(^(34)S)同位素具有较好的稳定性,受季节影响较小;对于“差异性”,氯和钠两项单项指标及氯/镁离子比、钠/镁离子比与周围水体差异最为显著。结合多项原则和影响因素进行综合考虑,最终选定氯、钠、锶、氯/镁离子比、钠/镁离子比以及氘(^(2)H)、氧(^(18)O)、锶(^(87)Sr)共8项指标作为具有普适性、稳定性和差异性的特征指标。发现边坡渗水的第一时间,可以采用氯、钠、氯/镁离子比、钠/镁离子比以及氘(^(2)H)、氧(^(18)O)等6项特征指标为快速分析研判提供支撑。

The topographic features and rivers along the middle route of the South-to-North Water Transfer Project are complex and diverse, and the groundwater burial conditions are different. Once the canal water is mixed or exchanged with groundwater, it would constitute a potential hazard of canal water pollution. Therefore, the traceability of side slope seepage outside the embankment of the main canal is of great significance to the safety of the main canal project and water quality. It is important to select representative "characteristic indexes" as few as possible for real-time and fast monitoring in emergencies.To master the hydrochemistry characteristic index system of the main canal, the changes of 99 hydrochemistry indexes and 5 isotope indexes in 12 sections of the main canal of the middle route of the South-to-North Water Transfer from 2020 to 2022 were systematically analyzed. Along the main canal for more than 1 000 km and according to three principles that can be widely used along the main canal(universality), the stability detection of the main canal itself(stability), and obvious difference with the surrounding water body(difference), identified the specific indexes of the main canal, and then evaluated the normal dynamic range of the characteristic indexes,provided technical support for rapid study and judgment of side slope seepage and engineering safety of the main canal of South-to-North Water Transfer.The results showed that there were 10 hydrochemistry indexes in the main canal water, which could meet the "universality". For stability, the eight hydrochemistry indexes of strontium, sodium, potassium, calcium,magnesium, and chlorine in the water body of the main canal were generally stable and had a certain volatility due to seasonal changes, deuterium(^(2)H), oxygen(^(18)O), strontium(^(87)Sr), sulfur(^(34)S) isotopes were the most stable, and were less affected by seasons. For the difference, it was finally determined that the four indexes of chlorine, sodium,chlorine/magnesium ratio, and sodium/magnesium ratio were the most different from the peripheral groundwater.Based on summarizing the hydrochemistry and isotopic characteristic values of the main canal in the middle route of the South-to-North Water Transfer Project, the most representative chemical and isotopic indexes of the main canal are briefed according to three principles for universality, stability, and difference. After comprehensive consideration of several principles and influencing factors, there were 8 indicators of chlorine, sodium, strontium,chlorine/magnesium ratio, sodium/magnesium ratio, deuterium(^(2)H), oxygen(^(18)O), strontium(^(87)Sr) as characteristic indicators with universality, stability, and difference. When water seepage was found in the slope, the chlorine,sodium, chlorine/magnesium ratio, sodium/magnesium ratio, deuterium(^(2)H), and oxygen(^(18)O) could help analyze and judge problems such as side slope seepage quickly. The selection of characteristic indicators could play a good supporting role in the early warning of the main canal project safety and water quality safety.