Abstract:
Groundwater serves as a vital water resource supporting the socio-economic development of the North China Plain. Long-term overexploitation of deep groundwater and a significant decline in groundwater levels have led to a series of ecological and environmental geological problems. Since 2014, new hydrological conditions—such as water source replacement, regular ecological water replenishment, and comprehensive management of overexploitation of groundwater— have influenced deep groundwater dynamics by reducing extraction through alternative water supplies, agricultural water-saving measures, and heavy precipitation-based irrigation. Consequently, the deep groundwater balance has undergone substantial changes. This study used groundwater balance calculation to study the characteristics of key indicators of water balance changes. Using two geological background indicators,
14C age and the distribution characteristics of the middle Pleistocene lithofacies paleogeography, and four hydrologic evaluation indicators, permeability (
K), hydraulic gradient (
I), the difference in groundwater levels between shallow and deep layers (Δ
H), and the interflow coefficient, the renewal capacity of deep groundwater was evaluated. Based on groundwater depression cones and land subsidence, thresholds for groundwater level recovery are identified to scientifically estimate the sustainable yield of deep groundwater. The results show that between 2005 and 2020, under the influence of new hydrological conditions, the seepage velocity of deep groundwater increased by 49.4%, the lateral replenishment increased by 0.29×10
8 m
3/a, and interflow replenishment increased by 0.14×10
8 m
3/a. These are primarily because the deep groundwater level in the middle and eastern part is still declining; The average annual exploitation of groundwater decreased by 0.20×10
8 m
3/a and the rate of groundwater storage decline slowed down from 12.29×10
8 m
3/a to 9.7 ×10
8 m
3/a. Spatial analysis indicates that the renewal capacity in the piedmont plains is better than that in the central and eastern regions because of the larger hydraulic conductivity. Temporal analysis shows that the renewal capacity of deep groundwater in 2020 has generally increased compared to 2005. The composition and quantity of vertical interflow replenishment and horizontal lateral replenishment change with the change of mining yield. The availability of deep groundwater was evaluated to be 8.52×10
8 m
3/a, primarily concentrated in the middle Pleistocene alluvial fan region of the piedmont plains. Based on the conditions of recharge, flow, and discharge of deep groundwater, as well as differences in the degree of development and utilization, the imbalance of deep groundwater has been alleviated since 2015, fundamental reversal has not yet been achieved. This study provides critical insights into deep groundwater circulation dynamics and offers guidance for the sustainable development and management of groundwater resources in the North China Plain.