In the semi-arid areas of China, where annual precipitation is low and evaporation is high, surface water is relatively poor and groundwater reserves are abundant and easily exploited. With the development of agriculture, industry, and economy, the scarcity of surface water can hardly meet the needs of normal production and living. The abundant local groundwater resources become the main source of water supply for the region (Zhong, Y. et al. 2018). The long-term sustainable utilization of groundwater is fundamental to agricultural and economic development in semi-arid regions, so it is vital to study the groundwater table and develop a sound groundwater management strategy. (Macdonald, D. M. et al. 2014; Zhang, Z. et al. 2021).
Semi-arid irrigation areas are currently facing many water sources problems such as river break and groundwater over-exploitation, which have led to an imbalance in groundwater exploitation and recharge and a rapid decline in groundwater table (Fu, Y. et al. 2016). The continuous decline in groundwater tables has led to a reduction in groundwater recharge, which has exacerbated the imbalance between exploitation and recharge and seriously affected the stability of the regional hydrological cycle. The core issue of groundwater management in semi-arid irrigation areas is to maintain the stability of the hydrological cycle and to ensure the infiltration and recharge of groundwater by precipitation and return flow from irrigation. The depth of the groundwater table is the main factor affecting groundwater infiltration and recharge, therefore it is vital to determine a reasonable groundwater control table.
Current research on groundwater control tables is mainly focused on the depth of critical groundwater (DCD), which has been proposed for different problems faced in the study area. The current research mainly includes the following aspects: (1) research on the depth of critical groundwater to prevent soil salinization (Qi, Z. et al. 2021; Mu, E. L. et al. 2020; Rengasamy, P. 2006). (2) research on the depth of critical groundwater to maintain vegetation growth and ecosystem stability (Wang, Y. et al. 2020; Eamus, D. et al. 2006; Martinetti, S. et al. 2021). (3) research on the depth of critical groundwater to prevent surface subsidence and seawater intrusion (El Kamali, M. et al. 2021; Malik, K. et al. 2019; Chidambaram, S. et al. 2022; Ma, F. et al. 2005).
To maintain the stability of the hydrological cycle in semi-arid irrigation areas so that groundwater resources are not depleted by extraction, the long-time average annual value of groundwater exploitation and recharge should maintain balance. The balance of exploitation and recharge is the basic principle of groundwater control and is an important prerequisite for the long-term sustainable use of groundwater. Based on the relationship between groundwater recharge and discharge in a semi-arid irrigated area, this paper proposes the critical groundwater depth of controlling risk management (CGDC), including the critical groundwater depth of maintaining exploitation and recharge balance (CGDM) and the critical groundwater depth of disrupting exploitation and recharge balance (CGDD), and studies the quantitative calculation method of CGDC.
The measurement of groundwater infiltration recharge is currently based on in situ field experiments, water balance methods, and numerical simulations. In this paper, a combination of in situ field experiments and numerical simulations was chosen to simulate the infiltration recharge of groundwater. The Hydrus-2D model is a finite element computational model for simulating water, solute, and energy transport in saturated-unsaturated porous media. The software can describe complex boundary conditions and is now widely used to simulate soil moisture movement (Shan, G. et al. 2019; Karandish, F. et al. 2019).
The objectives of this paper were (1) to quantify the amount of groundwater infiltration and recharge under the combined effects of precipitation and irrigation for three subsurface conditions: drip irrigation under mulch, border irrigation, and bare ground at different groundwater levels. (2) quantitatively calculate CGDC based on the principle of groundwater exploitation and recharge balance. (3) discuss the risk of imbalance in regional groundwater exploitation and recharge at different groundwater tables and strategies to control groundwater tables.