EFFECTS OF THE GEOMETRY OF HETEROGENEOUS HYDRAULIC CONDUCTIVITY FIELDS ON AQUIFER-OCEAN EXCHANGE PROCESSES

Understanding the movement of water, salinity, and nutrients between land and sea through coastal aquifers is vital for the protection of coastal ecology and proper management of water resources. In modeling of coastal groundwater, the estimation of flow exchange processes via numerical methods is in part controlled by the representation of an aquifer’s geology. The objectives of this project are 1) to understand impacts of heterogeneous hydraulic conductivity field geometry on exchanges between fresh water aquifers and the ocean, and 2) to determine the importance of including geologic detail in numerical simulations. We consider three coastal exchange processes: rates and patterns of submarine groundwater exchange, density driven saltwater circulation, and saltwater intrusion. We address two primary questions. First, how does the connectivity of hydraulic conductivity fields impact each process? Second, what are some potential consequences of upscaling these fields using an effective hydraulic conductivity in regard to the quantification of each exchange process?

To answer these questions, hydraulic conductivity fields were created from continental shelf scale geostatistical simulations using borehole data from the Bengal Basin. The geological and flow connectivity of each field was characterized. Variable density flow and transport simulations were conducted using SEAWAT. Model runs included ‘continuous’ and ‘discontinuous’ hydraulic conductivity fields (both with statistics identical to the original data). These heterogeneous models were compared to more simplified homogeneous models with equivalent hydraulic conductivity. Submarine groundwater exchange, density driven saltwater circulation, and saltwater intrusion were calculated and compared across models. The work has implications for predicting exchange processes in different geologic settings and determining the level of geological detail necessary to estimate rates and patterns of land-sea exchange. This provides a framework for understanding exchange processes on smaller scales.