Numerical Simulation And Optimization Modeling Of Seawater Intrusion In Zhoushuizi District Of Dalian City

Seawater intrusion in coastal aquifers is one of the most common groundwater contaminations.Since 1980s,seawater intrusion in coastal aquifers caused by groundwater over-abstraction has resulted in extensive deterioration in groundwater quality and quantity,fazing local residents in Zhoushuizi district of Dalian City in China.With population growth and economic development,the need of fresh water resources is increasing continuously and the seawater intrusion caused by groundwater over-abstraction would be more severe than the current situation,so the rational groundwater abstraction is becoming more and more urgent.A groundwater simulation-optimization code,namely MOSWTGA,is developed by coupling a genetic algorithm with a density-dependent groundwater flow and solute transport simulator,SEAWAT,to solve multiple-objective groundwater resources optimization.A simulation-optimization model is developed in Zhoushuizi district of Dalian city by running MOSWTGA,the study is based on the real hydrogeology parameters and groundwater abstraction conditions,providing the theoretical basis of implementing a reasonable allocation of groundwater resource.Also,an efficient and reliable simulation-optimization tool for the groundwater management of multi-objective optimization is created,being of significant environmental and economic benefits.The main conclusions are as follows:(1)The carbonate fracture-karst aquifer in Zhoushuizi district of Dalian City was simplified as an equivalent porous medium(EPM).A three-dimensional density-dependent groundwater numerical model considering tidal effect was constructed to simulate the seawater intrusion process in heterogeneous and anisotropic coastal aquifers.The results of calibration and validation indicated that the 3D density-dependent flow and solute transport model was with highly precise based on the real hydrogeological and abstraction conditions.(2)The calibrated and validated model was then applied to predict the dynamics and trend of seawater intrusion in the future in different rainfall scenarios.The overall extent of seawater intrusion in the future would be even more severe,especially in the dry years with less rainfall considering tidal effect.Also,in order to control the extent of seawater intrusion in coastal aquifers,the further work should focus on achieving better strategies for reasonable groundwater abstraction in the aquifers by using the simulation-optimization management model.(3)Based on the single-objective simulation-optimization groundwater code SWTGA,a multi-objective simulation-optimization groundwater code,namely MOSWTGA,was developed by coupling a improved genetic algorithm(adding probabilistic niched technique and the Pareto solution set filter)with a density-dependent groundwater flow and solute transport simulator,SEAWAT,to obtain the optimal strategies for utilization of groundwater resources.A general multi-objective groundwater optimization management model under variable-density is constructed.(4)Simulation-optimization models were developed in Zhoushuizi district of Dalian city by running a single-objective simulation-optimization code SWTGA and a multi-objective simulation-optimization groundwater code MOSWTGA.After the optimization,the optimal pumping scheme,the largest amount of total pumping water and a set of Pareto near-optimal solutions of tradeoffs between maximization of total pumping rate and minimization of the extent of seawater intrusion were obtained with the precondition that seawater intrusion was controlled to a certain degree,providing the theoretical basis for controlling the further deterioration of groundwater quality and implementing a reasonable allocation of groundwater resource in coastal aquifers.