A Simulation-Optimization Model for Seawater Intrusion Management at Pingtung Coastal Area, Taiwan

Po-Syun Huang,Yung-Chia Chiu

doi:10.3390/w10030251

Abstract

The coastal regions of Pingtung Plain in southern Taiwan rely on groundwater as their main source of fresh water for aquaculture, agriculture, domestic, and industrial sectors. The availability of fresh groundwater is threatened by unsustainable groundwater extraction and the over-pumpage leads to the serious problem of seawater intrusion. It is desired to find appropriate management strategies to control groundwater salinity and mitigate seawater intrusion. In this study, a simulation–optimization model has been presented to solve the problem of seawater intrusion along the coastal aquifers in Pingtung Plain and the objective is using injection well barriers and minimizing the total injection rate based on the pre-determined locations of injection barriers. The SEAWAT code is used to simulate the process of seawater intrusion and the surrogate model of artificial neural networks (ANNs) is used to approximate the seawater intrusion (SWI) numerical model to increase the computational efficiency during the optimization process. The heuristic optimization scheme of differential evolution (DE) algorithm is selected to identify the global optimal management solution. Two different management scenarios, one is the injection barriers located along the coast and the other is the injection barrier located at the inland, are considered and the optimized results show that the deployment of injection barriers at the inland is more effective to reduce total dissolved solids (TDS) concentrations and mitigate seawater intrusion than that along the coast. The computational time can be reduced by more than 98% when using ANNs to replace the numerical model and the DE algorithm has been confirmed as a robust optimization scheme to solve groundwater management problems. The proposed framework can identify the most reliable management strategies and provide a reference tool for decision making with regard to seawater intrusion remediation.

Highlights

In the 1970s, aquaculture was rapidly developed in the coastal area of Pingtung, Taiwan
The objective of this study is to develop a simulation–optimization model to identify the optimal strategies for the remediation of seawater intrusion
Different setting of maximum allowable concentration level (MCL) were considered in the management model to provide alternatives for decision making of seawater intrusion remediation

Summary

Introduction

In the 1970s, aquaculture was rapidly developed in the coastal area of Pingtung, Taiwan. To ensure water quality and increase the profit, groundwater was used to supply aquaculture demand in this area. The agricultural, domestic, and industrial sectors used groundwater to compensate the shortage of surface water due to the uneven distributed rainfall in southern Taiwan. Several decades of groundwater mining without any regulation caused the drawdown of water levels and resulted in consequent seawater intrusion along the coast [1]. The pumpage has been monitored and regulated by the government, the total amounts of pumping are still not regulated. The current water levels are similar to the condition in 1999 and recovered insignificantly [2]. Its impact on the shortage of water resources and the distortion of environments has been

Methods

Results

Conclusion