Perfect Realistic Conceptual Groundwater Models

A groundwater model begins with a realistic conceptual model; a simplified but scientifically accurate representation of the aquifer system. In the Groundwater Modeling System (GMS), the conceptual model guides layer structure, hydraulic properties, boundary conditions, and sources and sinks to be just that, a masterful groundwater model. When the conceptual framework is well constructed, numerical modeling becomes easy, stable, and more defensible; while adding the security to know the conceptual model is a masterpiece.

Below are best practices for mastering realistic conceptual models with GMS, along with common mistakes that reduce reliability.

Best Practices for Mastering and Building a Realistic Conceptual Model

1. Use Multiple Data Sources for Stratigraphy

Build your hydrostratigraphic layers in GMS by incorporating all available subsurface data, including boreholes, maps, cross-sections, geophysics, and well logs. Using GMS tools such as Boreholes, Horizons, and Solids allows you to integrate these datasets into a geologically realistic model without oversimplifying the geology.

Realistic models reflect the actual subsurface, which means representing both the gradual transitions between materials and the abrupt changes, like pinch-outs, erosional surfaces, or faults that your data will reveal inside of GMS.

2. Develop Hydrologic Boundaries that Reflect Actual Conditions

Boundary conditions in GMS should reflect real hydrologic controls, using options like MODFLOW’s RIV, GHB, CHD, no-flow, and recharge only where the data support them and not for modeling convenience. Using GIS and site data in GMS, features such as rivers, lakes, recharge zones, and groundwater divides should come from mapped or measured sources to position the features accurately. 

Doing so preserves realistic processes within GMS, like topographically controlled groundwater divides, rivers exchanging water with aquifers, and  how surface water and groundwater interact while preventing divergence from reality, such as inserting constant head boundaries solely to keep a model stable.

3. Assign Properties Based on Measured or Literature Values

While using GMS, hydraulic conductivity, storativity, and recharge should use measured data or published ranges from aquifer tests, soil and geologic surveys, or published ranges. Property zones should be defined in GMS where the geology indicates changes in material type and follow lithologic changes to maintain realism, rather than applying uniform values across the model. 

Applying a single K value across an entire basin may be convenient, however, it can significantly misrepresent subsurface variability within GMS, as it diverges sharply from realistic subsurface behavior.

4. Ensure Recharge and Discharge Processes Are Physically Defensible

Using GMS recharge and discharge should be grounded in defensible inputs, drawing from climate datasets, land-use information, and regional recharge studies. When tied to real soils and precipitation gradients, recharge patterns become far more realistic and reliable. 

In contrast, assigning a uniform recharge rate across a watershed is a shortcut that often pulls a model away from physical reality, leading to GMS putting out an unrealistic model.

5. Validate the Conceptual Model Before Numerical Simulation

Strengthen your model upfront in GMS by validating conceptual flow directions against real indicators such as regional groundwater gradients, baseflow estimates, and historical hydrographs. GMS models that reflect water moving naturally from higher to lower head and that mirror regional trends, set the stage for reliable simulations.

When flow paths in GMS contradict observed conditions, revisit and adjust before running the simulation, as it is a warning that revisions are needed.

Ready to get going with GMS, Where Better Models Begin?

In GMS, the conceptual model is more than a starting point, it’s the backbone of a credible MODFLOW analysis. Ground your geology and hydrology in real data, and let GMS streamline the process from concept to simulation to set up modeling success. Get modeling with GMS today!