Development of a Practical Modeling Platform for Assessing Saltwater Intrusion Impacts Under Future Sea-level Change Scenarios
Christopher Patterson | NAVFAC EXWC
The primary objective of this project is to develop a practical, flexible, and robust mathematical modeling tool to quickly assess future impacts of saltwater intrusion due to sea-level rise at Department of Defense (DoD) installations worldwide. The approach used for this project uses a rigorous, physics-based reduced order numerical model that incorporates sea-level change scenarios, confined and unconfined groundwater flow with vertically averaged density effects in each aquifer, recharge, and surface-water impacts (rivers, streams, wetlands). This reduced-order modeling approach is capable of predicting current and future water levels and salinity profiles in the aquifers with much lower computational effort than traditional fully coupled variable density modeling approaches and is therefore suitable for rapid simulations and large regional domains. A second objective is to develop an efficient graphical representation of inundation caused by extreme water levels that are associated with storm surge and astronomical high tides coupled with sea-level rise. The numerical modeling platform will be integrated into a well-established commercial groundwater modeling graphical user interface, that will be optimized for application to DoD installations using sea-level change and extreme water level scenarios obtained from the Defense Regional Sea Level (DRSL) database.
The project team plans to develop a new saltwater intrusion modeling approach that is based on the reduced order SWI2 (Seawater Intrusion package for the MODFLOW computer program) package, implemented in the latest unstructured grid version of MODFLOW (– computer program for groundwater modeling), MODFLOW-6 (most recent version of MODFLOW computer program for unstructured grids). The Aquaveo’s Groundwater Modeling System (GMS) graphical user interface will also be updated to run the reduced order flow code. The project team will develop full support and documentation for conceptual model, numerical model, and Geographical Information System (GIS) based input of the key SWI2 parameters, including subprograms for building the needed ocean boundary condition and starting elevations for the subsurface salt concentration zones. The ocean boundary condition will be designed to directly use the output from the DRSL sea-level database scenarios. The combined scenario extreme water level inundation maps will be constructed by using available GIS-based information on Navy installation infrastructure, and the GMS software to download digital elevation maps that can be contoured and manipulated to show the impact of different total water level or saltwater intrusion scenarios on flooding of critical surface and subsurface infrastructure. The combined software package will be tested by application to several (3 to 4) representative coastal installations, with comparison to field data.
The new modeling approach will result in a rigorous yet easy-to-use simulation tool for assessing the impacts of global sea level rise and extreme water level events on coastal installations. The software will be designed to allow installation managers and other stakeholders with limited mathematical modeling experience to quickly and easily perform simulations of groundwater saltwater intrusion and land inundation under different DRSL scenarios. This capability will facilitate the planning and decisionmaking process related to actions necessary to mitigate the effects of future global sea level rise and extreme water level events.