NEW TOOLS AND APPROACHES FOR SIMULATING THE EFFECTS OF SEA LEVEL RISE ON COASTAL AQUIFERS (Invited Presentation)

Sea level rise can have dramatic effects on coastal aquifers. Numerical models offer one way to study and predict these effects. A common approach is to develop and calibrate coastal aquifer models to current conditions, and then use these models to predict conditions under a variety of alternative sea level rise scenarios. Results from these scenarios can then be used to evaluate changes in groundwater flow patterns and salinity distributions in response to rising sea levels. A variety of numerical modeling programs can be used to perform these types of simulations. This presentation describes several new capabilities that are being developed for the MODFLOW suite of programs. Coastal aquifers can now be discretized using flexible meshes so that grid resolution can be focused in areas where the impacts of sea level rise are the largest. For example, the accuracy of groundwater salinization predictions can be substantially improved by increasing resolution around and beneath groundwater extraction wells. A new strategy based on the use of hydraulic head as the dependent variable, instead of freshwater head, is combined with the Newton-Raphson formulation for groundwater flow to efficiently simulate coastal aquifer water table fluctuations in response to changing sea level. These new advancements and the capability to script development and analysis of sophisticated variable-density flow and transport models with the Python programming language offer a powerful new environment for studying and predicting the effects of sea level rise on coastal aquifers.