Sustainable Management of Coastal Aquifers subject to Seawater Intrusion using Reduced-Order Groundwater Flow Models. Presented at EGU General Assembly 2023 Vienna, Austria (23-28 April 2023)

We provide an overview of the challenge of simulating seawater intrusion (SWI) in coastal aquifers with complex hydrogeological conditions using "variable-density" models. These models simulate groundwater flow and the transport of dissolved salt and are valuable in managing groundwater resources in vulnerable coastal systems. However, the application of simulation-optimization (SO) to SWI problems has been hindered by the computational demands of full-scale variable-density models. To address this, the study introduces a surrogate model of SEAWAT, a popular variable-density groundwater flow model, based on the proper orthogonal decomposition (POD) method. The POD method involves mapping coefficient matrices and right-hand side vectors onto a smaller space through finite-difference discretization. Preliminary results indicate that the POD-based surrogate model is significantly faster than the full-scale model while maintaining acceptable accuracy. This makes the surrogate model well-suited for replacing the full-scale variable-density model in the SO framework for managing coastal aquifers.