Groundwater Modeling

A groundwater-flow model for the Coastal Plain aquifer system is needed to assess groundwater flow and water levels throughout the Coastal Plain. The model will simulate groundwater flow in all major Coastal Plain aquifers in Maryland, as well as Delaware and the northern part of Virginia. The overall objective of the flow model is to provide a management tool to assist the Maryland Department of the Environment (MDE) in making groundwater appropriation decisions. The model will also provide an improved understanding of the hydrogeologic processes that control groundwater availability. The model will be developed by the Maryland Geological Survey, in collaboration with United States Geological Survey and MDE.

Specific objectives of the model will include estimating sustainable yield for Coastal Plain aquifers, assessing the impacts of groundwater withdrawals on streams, and recommending management tools for evaluating impacts of withdrawals. In order to meet these objectives, the model will require an active water-table layer capable of simulating shallow hydrologic processes, such as recharge, baseflow to streams, submarine groundwater discharge, and evapotranspiration. Because of the large scale of the Coastal Plain model and the number of aquifer layers to be simulated, it will be necessary to use a more detailed model grid (known as a Local Grid Refinement) for selected areas to simulate hydrogeologic conditions at a finer scale than possible with the regional model.

Progress: Model layers and input parameters are currently being assembled.

Water-Supply Management Optimization Modeling

Currently, groundwater managers lack tools for determining optimal patterns and rates of groundwater withdrawals, constrained by the idea of sustainable use. A number of detailed published reports describe the estimated impacts of increased future withdrawal scenarios on water levels in the aquifer system. However, resource managers need improved models and tools that will help them to design optimal withdrawal scenarios under a variety of management constraints such as limitation in drawdown or capture of streamflow. The optimization of future groundwater withdrawals will have to be based on one or more environmental and (or) economic criteria, referred to as objective criteria. Several modeling tools will have to be developed to accomplish the optimization. The first is a regional groundwater-flow model. The second is an optimization model, which would be coupled with the flow model, and used to perform simulations to optimize conditions based on the stated management goals. Optimization models can solve a variety of management problems consisting of different management goals and constraints; for example, drawdown can be minimized, while meeting minimum water-supply demands. Economic criteria, such as the cost of well construction and pumping, can also be included in the optimization simulations.

Progress: The modeling team has begun work to develop management formulations for optimization modeling.