Hydrologic-Economic Optimization of a Brackish Coastal Pumping Well

Saltwater intrusion and upconing phenomena affect coastal aquifers worldwide. Over-exploitation leads to high salinity levels which threaten sustainable use of these freshwater resources. There is an increasing need to accurately, and practically, model the physics of these coastal pumping systems while also incorporating the relevant economics. We formalize a decision model able to define the optimal pumping trajectories for a coastal, brackish water well that minimizes overall costs, including desalinization and pumping costs, while keeping track of aquifer head and salinity levels near the well. A binary decision variable is defined to determine when the well is turned off or on, and a state equation defined to relate pumping level and pumping duration to the salinity of pumped water. Unlike most published models on coastal well optimization, pumping is related to salinity empirically. Real pumping and rebound curves are derived from on-site pump tests at Kuki'o, Hawaii. Further hypothetical cases are developed based on these field-derived salinity curves.