Screening and dynamic analysis of water body characteristic indexes in the middle route of South-to-North Water Transfer Project
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Abstract:
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 (2H), oxygen (18O), strontium (87Sr), sulfur(34S) 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 (2H), oxygen (18O), strontium (87Sr) 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(2H), and oxygen (18O) 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.