Planning infrastructural measures for controlling saltwater intrusion in a coastal aquifer by Global Interactive Response Surfaces: The Nauru island case study

Infiltration galleries and scavenger wells are usually constructed to control pumping based saltwater intrusion in coastal aquifers. The optimal allocation of these infrastructures can be decided by solving a multi-objective optimization problem balancing availability of fresh water supply and installation/operation costs, where the effects of different design options on the planning objectives are simulated through a high fidelity model of the flow and transport processes. The incorporation of these simulation models within an optimization-based planning framework is not always straightforward because of the computational requirements of the model itself and the computational limitations of the optimization algorithms. In this paper we explore the potential for the Global Interactive Response Surface (GIRS) methodology to overcome these technical limitations. The GIRS methodology is used to recursively build a non-dynamic emulator of the processbased model that maps the design options into the objectives values and can be used in place of the original model to more quickly explore the design option space. The approach is used to plan infrastructural interventions for controlling saltwater intrusion and ensuring sustainable groundwater supply for Nauru, a Pacific island republic in Micronesia. GIRS is used to emulate a SEAWAT density driven groundwater flow-and-transport simulation model. The evaluation results show the potential applicability of the proposed approach for optimal planning of coastal aquifers.