Abstract
The large number of users and the small scale of wells greatly complicate monitoring of groundwater abstraction in areas of intensive pumping by numerous smallholders such as in the North China Plain. This paper presents a study in a typical county in the North China Plain. It discusses the application and challenges of an indirect, energy-based approach to groundwater abstraction monitoring. Intensive field experiments at individual wells were carried out to provide a basis for the conversion from electric energy consumption to groundwater abstraction and to explore the feasibility of direct and indirect abstraction monitoring methods in the study area. The results show that the main challenge of electricity-to-water conversion lies in the large spread of conversion factors between wells. The conversion error at an individual well is found to be less than 20%. The same accuracy is achieved on spatially aggregated levels by testing only a small number of wells. Trade-offs can be made to obtain groundwater abstraction estimates at the required accuracy and with reasonable efforts regarding data collection. The analysis shows that energy-based groundwater abstraction monitoring outperforms direct water metering with respect to cost and robustness. It provides satisfactory data accuracy and equitability in regions where irrigation wells are powered by electricity.
Highlights
Compared to surface water, groundwater offers the beneficial features of high reliability, year-round availability and easy access at the place of use
The cost of indirect monitoring strategies is substantially lower, compared to the direct metering method, because energy consumption of each well is metered by the monitoring system of EPSC for electricity fee collection and only minor costs for pumping tests to determine the electricity-to-water conversion factors arise
Failures of smart water meter systems show that direct water metering is difficult to implement in areas of intensive pumping by numerous smallholders such as the North China Plain
Summary
Groundwater offers the beneficial features of high reliability, year-round availability and easy access at the place of use. Due to the “invisible” nature of groundwater and difficulties in monitoring and control, trade-offs have to be made between measurement accuracy, monitoring cost and ease of implementation This aspect has not been covered sufficiently by previous research. Constant yearly conversion factors over a region (e.g., at village, country and basin levels) have been commonly used to relate energy consumption and groundwater abstraction in previous studies [25,26,27,28]. Such a conversion can be based on the theoretical relation between lift, energy use and pumping rate.
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