Optimizing river damming and impounding strategies to mitigate seawater intrusion in the coastal aquifer of Dagu River Basin, China

River impoundment is an alternative to artificial groundwater recharge in coastal aquifers, while mitigating seawater intrusion caused by anthropogenic activities. This study implements a new multiobjective optimization framework for management of the existing engineering measures of river multidamming impoundment and strategies for groundwater abstraction in Dagu River Basin, a water-scarce basin in north China. The optimization framework integrates a calibrated numerical model with a conceptualized river package to simulate the interaction between the Dagu River and groundwater due to river impoundment, and it focuses on the tradeoff among minimizing the seawater intrusion extent, minimizing the river seepage, and maximizing the allowable groundwater abstraction. Then the elitist nondominated sorting genetic algorithm (NSGA-II) is used to search for the Pareto-optimal solutions affected by different climate conditions. Results show that the river water level and groundwater abstraction schemes can be regulated to achieve the optimal tradeoffs among different objectives. To mitigate seawater intrusion, the impoundment river water level behind the dam adjacent to the seawater intrusion associated with years of insufficient precipitation should be raised by at least 0.5–1.5 m, while the river level behind the remaining dams should be reduced by at least 1 m. Moreover, under the constraint of restricting groundwater abstraction, the annual groundwater abstraction in the four county-level administrative subdomains should be adjusted by 1.2–1.5 million m³ or more in years with less precipitation compared to that in years with more precipitation. The implications might also be applied to other coastal aquifers with intense human activities.