Karst systems are characterized by underground drainage systems formed by the dissolution of soluble rocks. The behaviour of these systems is hard to be conceptualized due to the uncertainty in the location and geometry of these underground caves and its connection with the porous media.

In order to be able to model these systems, the Conduit Flow Process (CFP) package (developed by the United States Geological Survey – USGS) can simulate turbulent ground-water flow by coupling the groundwater flow equation with formulations for a discrete network of cylindrical pipes.

The following tutorial explains how to set up a simple karst conduit system in a previously existing MODFLOW model and the analysis of the results.

Making hydrogeological models can take a long time, from construction, visualization of results and calibration. It is important to use tools that can optimize these tasks and allow the time saved to be used in the analysis of the system.

In this opportunity we will use Flopy to replicate a 2D transport model from a previous post. Flopy is a versatile set of Python scripts which can be used to run MODFLOW and MT3D, amongst other MODFLOW-related groundwater programs in a simple and efficient way. It will be seen how useful this tool is to automate the process of creating groundwater models since modifications of the boundary conditions can be done just by changing the text file.

In addition, MT3D-USGS will be used for the transport modelling. It is an updated release of the groundwater solute transport code MT3DMS, which has new transport modeling capabilities that provide a greater flexibility in the simulation of solute transport and reactive solute transport.

Aquifers can be porous, fractured or karstic. Due to the geological setup and processes related to the formation of the porous media, these acuifers can present a high degree of heterogeneity that affect/impact the groundwater flow patterns and contaminant transport and distribution.

Contaminant plumes for puntual/aerial sources interact with aquifer heterogeneities and anisotropies. Understanding and conceptualizing the distribution of the different hydrogeological units and their properties on the subsurface is a challenge for hydrogeologist, numerical modelers and remediation specalists.

MT3D-USGS is the one of the latest software for contaminant transport developed by the USGS. The initial release was on 2016 as a updated release of MT3DMS. The software has new capabilities for transport modeling coupled with the current MODFLOW packages, it can model unsaturated-zone transport, reactions and remediation schemas.

This transport modeling code is implemented in the pre and postprocessing software for groundwater modeling Model Muse, also developed by the USGS. This tutorial show a basic example of contaminant transport from a point source in a groundwater flow regime controlled by regional flow and discharge to ponds and rivers.

Seawater intrusion is an issue in coastal aquifer management especially on arid environments. Overexplotation of groundwater resources by high production wells on intensive irrigation schemes could lead to an intrusion of saline water from sea and an impact to the quality of water sources.

Available options to assess the behaviour and impact of seawater intrusion are limited in both open source and commercial software; there is also a need of highly skilled groundwater modelers to understand the complex model setup and model output that can provide useful information about the groundwater flow regimen and the risks to water quality posed by seawater intrusion.

Seawater Intrusion Package 2 (SWI2) is a modeling software developed by the USGS and coupled on MODFLOW-2005. SWI2 allows three-dimensional variable-density groundwater flow and seawater intrusion in coastal aquifer systems. This tutorial deals with a basic example of the implementation of SWI2 on a MODFLOW model contructed on Model Muse. The tutorial show the whole procedure of model setup, datasets implementation, conceptualization of boundary conditions and result evaluation.

Assessing the groundwater flow regime in coastal aquifers is a challenge for numerical modelers. In order to have a complete set of parameters and input data for a valuable numerical simulation we need to compile several hydrogeological studies, reconstruct datasets and proof the accuracy of hydraulic tests. Still some parameter would be missing but the experience and criteria of the groundwater modeler would achieve adequate simulations and predictions required by an adaptive sustainable groundwater resources management.

Aquifer modeling requires understanding and expertise on the different boundary conditions available to represent the physical process related to the groundwater flow regime on determined spatial and temporal discretizations. MODFLOW has a set of boundary conditions of specified head, specified flux and mixed. There is a particular boundary condition created for the representation of the interaction between a river and the surrounding aquifer: the River Package (RIV). This tutorial show the implementation procedure of a River Package (RIV) on a regional model with a discussion on the model output and water balance.

On a normal groundwater modeling workflow the hydraulic parameters, observed data and boundary conditions are preprocessed on a GIS software as QGIS, and then imported on a compatible format (vector or raster) into the modeling software. However, Model Muse has a set of different tools to process point, and tabular data into model parameters increasing the speed in the model construction and simulation. This tutorial show the procedure to interpolate hydraulic conductivity from a table into Modflow from a different set of interpolation methods in Model Muse.

MT3DMS, a three-dimensional transport model, will be used in this tutorial to simulate two-dimensional transport in a radial flow field. The example consists on a well which is injecting a solution in a constant rate of 100 m3/d with a contaminant concentration of 10 g/m3 (10 mg/l). This model will run for a total of 27 days.

The following tutorial will explain how the model was build and the conditions considered.