PhD student, James Cook University
Sustainable methods to control saltwater intrusion into coastal aquifers in Pacific Island Countries
The availability, quantity and quality of groundwater in coastal aquifers are threatened by saltwater intrusion (SWI). To ensure future sustainability of valuable groundwater resources in coastal areas, development and implementation of groundwater management methodologies are essential. The proposed study aims to develop and implement improved yet sustainable groundwater management strategies to control SWI into coastal aquifers. Specifically, a coupled simulation-optimisation (S/O) framework will be developed for obtaining optimal and sustainable groundwater withdrawal rates from coastal aquifers. New and efficient surrogate modelling tools will be used to approximate the SWI processes in coastal aquifers. Uncertainties in surrogate model prediction will be evaluated using ensemble surrogate model based S/O framework. Finally, a monitoring network will be designed to monitor compliance of the implemented management strategy. The developed methodologies will be applied to a real life coastal aquifer in a tropical Pacific Island country (Kiribati), and will be evaluated for its applicability and practicality. Kiribati is a highly populated island country dependent on groundwater for survival. SWI is reported in Kiribati and the developed methods from my research will enable water resources stakeholders in Kiribati to manage its groundwater resources substantially.
Abstract: The sustainable development and management of groundwater resources in coastal aquifers is complex and, historically, challenging to accomplish. Groundwater models play an essential role in addressing these complexities and providing the basis for planning future sustainable development. For more than 25 years, the authors have applied three-dimensional groundwater models to manage large scale coastal aquifers. The paper will present case studies demonstrating the application of groundwater models to evaluate conditions in complex coastal environments and to develop sustainable groundwater management strategies. These studies include Long Island, a sole source aquifer system in New York serving nearly 3 million people; aquifers in Southern California where injection barriers are used to prevent saltwater intrusion; and Savannah, Georgia in the southeastern US, where concentrated groundwater pumping has contributed to saltwater intrusion at a nearby resort island, and planning is underway to ensure a sustainable groundwater supply to both local industries and municipalities.
Pub.: 25 Aug '15, Pinned: 28 Jul '17
Abstract: Recently, the well-known Princeton Transport Code (PTC), a groundwater flow and contaminant transport simulator, has been coupled with the ALgorithm of Pattern EXtraction (ALOPEX), a real-time stochastic optimization method, to provide a freshwater pumping management tool for coastal aquifers, aiming in preventing saltwater intrusion. In our previous work (Proceedings of INASE/CSCC-WHH 2015, Recent Advances in Environmental and Earth Sciences and Economics, pp 329–334, 2015), the PTC-ALOPEX approach was used in studying the saltwater contamination problem for the coastal aquifer at Hersonissos, Crete. Extending these results, in the present study the PTC-ALOPEX approach is equipped with a nodal safety strategy that effectively controls saltwater front’s advancement inside the aquifer. In cooperation with an appropriate penalty system, the performance of PTC-ALOPEX algorithm is studied considering several pumping and weather condition scenarios. This study also establishes pumping/well scenarios that ensure the needed volume of fresh water to the local community without risking saltwater contamination.
Pub.: 16 Jun '16, Pinned: 28 Jul '17
Abstract: Seawater intrusion (SWI) is a widespread environmental problem, particularly in arid and semi-arid coastal areas. Therefore, appropriate management strategies should be implemented in coastal aquifers to control SWI with acceptable limits of economic and environmental costs. This paper presents the results of an investigation on the efficiencies of different management scenarios for controlling saltwater intrusion using a simulation-optimization approach. A new methodology is proposed to control SWI in coastal aquifers. The proposed method is based on a combination of abstraction of saline water near shoreline, desalination of the abstracted water for domestic consumption and recharge of the aquifer by deep injection of the treated wastewater to ensure the sustainability of the aquifer. The efficiency of the proposed method is investigated in terms of water quality and capital and maintenance costs in comparison with other scenarios of groundwater management. A multi-objective genetic algorithm based evolutionary optimization model is integrated with the numerical simulation model to search for optimal solution of each scenario of SWI control. The main objective is to minimize both the total cost of management process and the total salinity in aquifer. The results indicate that the proposed method is efficient in controlling SWI as it offers the least cost and least salinity in the aquifer.
Pub.: 29 Jan '15, Pinned: 28 Jul '17
Abstract: The literature on the application of simulation-optimization approaches for management and monitoring of coastal aquifers is reviewed. Both sharp- and dispersive-interface modeling approaches have been applied in conjunction with optimization algorithms in the past to develop management solutions for saltwater intrusion. Simulation-optimization models based on sharp-interface approximation are often based on the Ghyben-Herzberg relationship and provide an efficient framework for preliminary designs of saltwater-intrusion management schemes. Models based on dispersive-interface numerical models have wider applicability but are challenged by the computational burden involved when applied in the simulation-optimization framework. The use of surrogate models to substitute the physically based model during optimization has been found to be successful in many cases. Scalability is still a challenge for the surrogate modeling approach as the computational advantage accrued is traded-off with the training time required for the surrogate models as the problem size increases. Few studies have attempted to solve stochastic coastal-aquifer management problems considering model prediction uncertainty. Approaches that have been reported in the wider groundwater management literature need to be extended and adapted to address the challenges posed by the stochastic coastal-aquifer management problem. Similarly, while abundant literature is available on simulation-optimization methods for the optimal design of groundwater monitoring networks, applications targeting coastal aquifer systems are rare. Methods to optimize compliance monitoring strategies for coastal aquifers need to be developed considering the importance of monitoring feedback information in improving the management strategies.
Pub.: 26 Jun '15, Pinned: 28 Jul '17