Challenge: To provide an updated, regionally consistent tool for evaluating groundwater availability and supporting water management decisions across north-central Texas.
Solution: The updated Northern Trinity and Woodbine Aquifer Groundwater Availability Model (NTGAM) was developed by INTERA using MODFLOW 6 and represents the aquifer system with an 8-layer hydrostratigraphic framework that captures both aquifers and confining units. The model simulates groundwater flow from predevelopment (1890) through 2020, beginning with a steady-state representation of predevelopment conditions followed by transient simulation. Key inputs include spatially distributed recharge estimated using a Soil-Water Balance approach, historical pumping reconstructed from multiple datasets, and boundary conditions representing streams, evapotranspiration, and lateral flow. We calibrated the model using a Bayesian framework with PEST++ iterative ensemble smoothing (IES), allowing simultaneous estimation of over 100,000 parameters while quantifying uncertainty. History matching incorporated groundwater levels, long-term trends, stream baseflow, and transmissivity observations to ensure consistency with both spatial patterns and temporal dynamics.
Results: The calibrated model successfully reproduces long-term groundwater-level trends across more than a century of pumping, including large regional declines exceeding 1,000 feet in some areas. It is serving as a key tool in supporting multiple groundwater conservation districts and Groundwater Management Area 8 in estimating modeled available groundwater (MAG), informing desired future conditions (DFCs), and guiding sustainable groundwater management and regulatory decision-making.
