Groundwater Models 101: The Right Model for Your Needs

A guide to choosing the right groundwater model to support critical decision making and promote project success.

Deciding which specific groundwater model meets your unique operational requirements and project objectives can be overwhelming.

Numerous options and choices associated with various groundwater modeling approaches, ranging from simple analytical models to intricate numerical simulations coupling surface and groundwater data, add to the challenge.

Getting the model you need

Each model includes unique assumptions, limitations, and applicability, while the firms creating the models use different methods, tools, and calibration standards as well.

For that matter, groundwater modeling involves a lot of specialized, unfamiliar terms and vocabulary adding to the general confusion around choosing a model.

Terms like “finite difference,” “hydraulic conductivity,” “recharge rates,” and “transmissivity” are just the beginning of the scientific and modeling-specific terminology that may make the whole topic seem opaque and overwhelming. But this industry “jargon” is fundamental to the science of accurate groundwater modeling, and understanding the definitions and use of these terms is essential to making informed decisions about groundwater basin model selection and use.

Determining the right cost for a particular groundwater basin model can be equally challenging. Project complexity and modeling requirements affect the scope of work and expertise needed to produce an accurate model. Competing bids may make the decision more challenging and add more confusion to the model quality and utility evaluation process.

A relatively inexpensive model may look good on paper for saving project funds up front but can result in catastrophic errors and later losses if the project fails to produce the needed outcomes. On the other hand, a model with higher production costs may save significant project expenditures by achieving project objectives and avoiding costly rework, fixes, or potential litigation.

Know your groundwater model

Knowing what kind of model works best for a particular basin, project, or water production challenge empowers utility leaders to effectively address basin management complexities. Groundwater models can be categorized into three primary types: analytical, numerical, and hybrid models.

1. Analytical Models: Using simplified equations to estimate groundwater flow, typically under steady-state conditions, analytical models enable quick assessments for smaller-scale projects where detailed hydrogeological data may not be available. However, their simplicity can also limit efficacy or applicability in more complicated scenarios. Common analytical model examples include the This equation and the Dupuit equation which help estimate aquifer properties based on observed data.
2. Numerical Models: Designed to evaluate intricate hydrological processes, numerical models address complex scenarios involving heterogeneous aquifer characteristics and varying boundary conditions. Numerical models are critical for large-scale basin assessments and complex projects requiring comprehensive detail and accuracy. A leading numerical model, MODFLOW, provides versatility and represents transient groundwater flow and solute transport.
3. Hybrid Models: Combining tools and methods from each modeling approach, a hybrid model may be used for a complex project with extensive accuracy requirements but where detailed hydrogeological data is unavailable for some part of the basin or project area.

Finite difference models, particularly MODFLOW, are essential tools for hydrological studies and provide a robust framework for simulating groundwater flow and transport processes. MODFLOW operates on a finite difference basis, breaking an aquifer into manageable grid cells to enable detailed representation of complex hydrogeological features.

Finite difference models accommodate various spatial scales and geometries, and support a wide range of groundwater management scenarios. These models effectively incorporate various boundary condition types and can accurately simulate variable conditions to model groundwater flow fluctuations at different times and circumstances such as drought or deluge.

Integrated models

Enhancing model reliability requires integrating surface water models that simulate water flow across the basin with a dynamic response to rainfall and other climatic variables. Integrated basin models combine surface runoff, infiltration, and aquifer recharge to represent all water movement within the system.

MODFLOW, developed and supported by the USGS, is a vetted, industry standard software and represents a best practice starting point for a validated and defensible groundwater model. The family of MODFLOW-related programs support simulating site-specific or project-specific items of interest including:

• GSFLOW—coupled groundwater/surface water systems
• MODFLOW-NWT—problems with unconfined groundwater flow
• MT3D-USGS, MT3DDMS—solute transport
• SEAWAT—variable density flow including saltwater
• SUB—aquifer system compaction and land subsidence
• PEST—parameter estimation

Linking groundwater and surface water models provides critical insight into the interactions between surface water and groundwater. Since surface water flow significantly impacts aquifer recharge rates and water availability, accurate groundwater level and flow pattern predictions rely on model integrations and are vital for utility leaders’ ability to deliver effective water resources management.

Groundwater Modeling 101

The first and second installments of our Groundwater Models 101 guide focused on choosing the right partner for your needs and the different groundwater models and their applications.

Our third post explains why groundwater models should be calibrated and outlines potential consequences of using an inadequate model or skipping model development altogether.

Read more about how Geoscience’s integrated groundwater model helped Southern California communities with planning and sustainability: Integrated Santa Ana River Model