Lihong Yang

Rising water demand for agricultural, industrial, and domestic sectors continue to stress water resources worldwide. In southeastern China, coastal cities and megacities typically rely on thousands of reservoirs, incurring high construction and maintenance costs. However, rural areas in this region, underlain by shallow, low‐permeability bedrock due to regional metamorphism, host exploitable groundwater resources along major tectonic fault lines. To understand groundwater dynamics in these fractured aquifers, this study investigates a local site in Longquan (Zhejiang Province, China). Field investigations informed a three‐dimensional geological model, which provided the basis for numerical flow modeling analysis using the USGS‐MODFLOW code. Results indicate that permeable damage zones along the tectonic fault lines are recharged by a weathered bedrock blanket layer and are laterally bounded by low‐permeability bedrock, limiting the spatial extension of the aquifer. The sub‐tropical climate and hydrostratigraphic conditions make groundwater exploitation feasible, despite the modest groundwater yield of the damage zones (2.2 × 10⁵ m³ per km of damage zone). Intensified fracturing also produces recognizable morphological changes, transitioning from steep, incised valleys to rounded hills with flatter streambeds. This distinctive morphological feature was identified in 140 basins across southeastern China, suggesting the presence of strategic groundwater resources throughout this region. Harnessing these fracture‐controlled groundwater resources may bolster economic growth in rural communities and help narrow the development gap with more urbanized coastal areas.

A modified Water-Table Fluctuation (WTF) method is developed to quantitatively characterize the regional groundwater discharge patterns in stressed aquifers caused by intensive agricultural pumping. Two new parameters are defined to express the secondary information in the observed data. One is infiltration efficiency and the other is discharge modulus (recurring head loss due to aquifer discharge). An optimization procedure is involved to estimate these parameters, based on continuous groundwater head measurements and precipitation records. Using the defined parameters and precipitation time series, water level changes are calculated for individual wells with fidelity. The estimated parameters are then used to further address the characterization of infiltration and to better quantify the discharge at the regional scale. The advantage of this method is that it considers recharge and discharge simultaneously, whereas the general WTF methods mostly focus on recharge. In the case study, the infiltration efficiency reveals that the infiltration is regionally controlled by the intrinsic characteristics of the aquifer, and locally distorted by engineered hydraulic structures that alter surface water-groundwater interactions. The seasonality of groundwater discharge is characterized by the monthly discharge modulus. These results from individual wells are clustered into groups that are consistent with the local land use pattern and cropping structures.