Seasonal Groundwater‐Level Responses Inform a Pumping Rule for a Riverbed Infiltration Gallery

ABSTRACT

Operating riverbed infiltration galleries requires balancing water supply against groundwater‐level limits under seasonally varying hydrological conditions. This study develops a reusable monthly pumping rule and examines how seasonal groundwater responses help explain its structure. A calibrated HydroGeoSphere (HGS) model simulated the coupled river–aquifer–gallery system on the Hutuo River, northern China, under sampled inflow, rainfall and pumping conditions. An Extra Trees surrogate was coupled with regularized multi‐start simulated annealing to optimize monthly inflow thresholds, maximizing pumping volume over 30 historical annual sequences subject to a prescribed month‐end control‐well level. Application requires only the calendar month and anticipated monthly mean river inflow. HGS back‐testing over the same sequences met this target in 350 of 360 months, with a mean annual pumping volume of 20.57 × 10 ⁶  m ³ . The optimized rule generally allowed higher pumping rates at lower inflows in summer than in winter. Monthly regression analysis of the HGS records estimated drawdown associated with pumping after adjustment for inflow, rainfall and initial control‐well level. At 1.2 m ³ /s, estimated drawdown ranged from 1.01 m in August to 2.75 m in January. Within‐month interaction analyses associated higher rainfall with smaller pumping‐induced drawdown, although statistical support varied among months. These model‐based findings suggest that seasonal pumping opportunities reflect differences in both water availability and the groundwater response to abstraction. Relating these responses to operating thresholds provides a hydrological basis for interpreting the rule and a framework for deriving site‐specific rules for comparable river‐connected intakes.