Difference between revisions of "Model setup"
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The following describes the typical steps to setup a model for contaminant transport in a fractured limestone aquifer, | The following describes the typical steps to setup a model for contaminant transport in a fractured limestone aquifer, | ||
| − | === Formulation of the modeling objectives | + | === Formulation of the modeling objectives === |
Before setting up a model, it is important to define the modeling objectives. | Before setting up a model, it is important to define the modeling objectives. | ||
The choice of the model concept, model domain, modeling scale and included details should be closely linked to these objectives. | The choice of the model concept, model domain, modeling scale and included details should be closely linked to these objectives. | ||
| Line 16: | Line 16: | ||
* Delineate the capture zone of a well | * Delineate the capture zone of a well | ||
| − | The model scope will, for example, be different for the prediction of the spreading of an entire plume (large scale) | + | === Definition of the model scope === |
| + | The scale is also depending on the modeling objectives. | ||
| + | The model scope will, for example, be different for the prediction of the spreading of an entire plume (large scale) and for the planning of source zone remedial actions (local scale). | ||
An important aspect when choosing the model extent is to have the boundaries sufficiently far away from the most influential features in the area, such as pumping wells. | An important aspect when choosing the model extent is to have the boundaries sufficiently far away from the most influential features in the area, such as pumping wells. | ||
The model extent has to be big enough, so that the boundaries do not influence the results in the area of interest. | The model extent has to be big enough, so that the boundaries do not influence the results in the area of interest. | ||
| + | It should be chosen based on physically meaningful boundaries (f.e. known head isolines or no-flow boundaries). | ||
| − | + | Source zone remediation needs a different scale than the risk assessment of a contaminant plume for water works. | |
| − | + | The following scales can be considered: | |
| − | + | * well scale | |
| − | + | * source zone scale | |
| − | + | * intermediate scale for e.g. pumping tests | |
| + | * plume scale | ||
| − | |||
Based on available data and modeling objectives, the model complexity has to be chosen. | Based on available data and modeling objectives, the model complexity has to be chosen. | ||
A very complex and detailed model is not appropriate if only little field data is available. | A very complex and detailed model is not appropriate if only little field data is available. | ||
Then, a simple model can be applied, which can be refined as soon as new data is measured. | Then, a simple model can be applied, which can be refined as soon as new data is measured. | ||
| − | + | Modeling was an integral part in the limestone project. | |
| − | Initially, a rough model based on first measurements and available data was setup and | + | Initially, a rough model based on first measurements and available data was setup and used for the planning of further field work and measurements. |
| + | These measurements were later on used to improve the model quality. | ||
| − | + | === Conceptualization and setup of a conceptual model including geology and hydrogeology === | |
| − | + | ==== Geologic modeling ==== | |
| − | + | Boreholes can give valuable information about the geology. | |
| − | + | Bits of geologic knowledge can be connected to establish a geologic model, that shows different geologic layers, to which properties can be assigned, and other relevant geologic information. | |
| − | + | [[File:SE-NO_profil.jpg |border|550px|Example geologic profile of a Geoscene3D model.]] | |
| − | |||
| − | |||
=== Data acquisition - measurements to obtain relevant model parameters (see list of parameters for each model) === | === Data acquisition - measurements to obtain relevant model parameters (see list of parameters for each model) === | ||
| − | |||
=== Implementation of parameters for selected units in the model domain (homogeneous/heterogeneous) === | === Implementation of parameters for selected units in the model domain (homogeneous/heterogeneous) === | ||
Revision as of 12:39, 31 January 2017
Contents
- 1 Model setup for fracture flow and transport in limestone aquifers - steps
- 1.1 Formulation of the modeling objectives
- 1.2 Definition of the model scope
- 1.3 Conceptualization and setup of a conceptual model including geology and hydrogeology
- 1.4 Data acquisition - measurements to obtain relevant model parameters (see list of parameters for each model)
- 1.5 Implementation of parameters for selected units in the model domain (homogeneous/heterogeneous)
- 1.6 Choice of boundary conditions
- 1.7 Setup of sources and sinks: Definition of wells
- 1.8 For transient models: definition of initial conditions
- 1.9 Mesh generation
- 1.10 Simulation
- 1.11 Critical evaluation of the modeling results
- 1.12 Model calibration and validation
- 1.13 Model reporting
- 2 Flow chart giving an overview of the individual steps
- 3 Example: Setup of models for a contaminated site with a fractured limestone aquifer (Akacievej, Hedehusene)
Model setup for fracture flow and transport in limestone aquifers - steps
This chapter gives step-by-step instructions for the setup of a model to simulate flow and transport in a fractured limestone aquifer. The following describes the typical steps to setup a model for contaminant transport in a fractured limestone aquifer,
Formulation of the modeling objectives
Before setting up a model, it is important to define the modeling objectives. The choice of the model concept, model domain, modeling scale and included details should be closely linked to these objectives.
The following list gives some examples for modeling objectives:
- Analyze the distribution and potential spreading of a contaminant in an aquifer
- Improve the understanding and predictability of contaminant spreading
- Analyze the influence of transient hydraulic conditions (annual variations, pumping in the area) on plume propagation
- Develop and optimize a remediation strategy for the source zone
- Optimize a remediation strategy for the plume
- Improve risk assessment, e.g. for a drinking water well, in order to assess future actions
- Delineate the capture zone of a well
Definition of the model scope
The scale is also depending on the modeling objectives. The model scope will, for example, be different for the prediction of the spreading of an entire plume (large scale) and for the planning of source zone remedial actions (local scale). An important aspect when choosing the model extent is to have the boundaries sufficiently far away from the most influential features in the area, such as pumping wells. The model extent has to be big enough, so that the boundaries do not influence the results in the area of interest. It should be chosen based on physically meaningful boundaries (f.e. known head isolines or no-flow boundaries).
Source zone remediation needs a different scale than the risk assessment of a contaminant plume for water works. The following scales can be considered:
- well scale
- source zone scale
- intermediate scale for e.g. pumping tests
- plume scale
Based on available data and modeling objectives, the model complexity has to be chosen. A very complex and detailed model is not appropriate if only little field data is available. Then, a simple model can be applied, which can be refined as soon as new data is measured.
Modeling was an integral part in the limestone project. Initially, a rough model based on first measurements and available data was setup and used for the planning of further field work and measurements. These measurements were later on used to improve the model quality.
Conceptualization and setup of a conceptual model including geology and hydrogeology
Geologic modeling
Boreholes can give valuable information about the geology.
Bits of geologic knowledge can be connected to establish a geologic model, that shows different geologic layers, to which properties can be assigned, and other relevant geologic information.
Data acquisition - measurements to obtain relevant model parameters (see list of parameters for each model)
Implementation of parameters for selected units in the model domain (homogeneous/heterogeneous)
Choice of boundary conditions
Setup of sources and sinks: Definition of wells
For transient models: definition of initial conditions
Mesh generation
When working with complex models it is useful to start with a coarse mesh to test the model and the setup with limited time effort. For the real simulations, a finer grid can be employed. Modern grid generators allow a mesh refinement at specific parts of the mesh. Especially at heterogeneities and fractures and at concentration fronts, the mesh should be sufficiently fine to resolve gradients appropriately. This can be tested by a grid refinement study, where the mesh is refined and the results are compared. When the solution does not change with a grid refinement, it is sufficiently resolved.
Simulation
Critical evaluation of the modeling results
Modeling results should be always critically evaluated and tested. It is for example helpful, to have a check the mass balance of a model. It is also important to have a general look at the results, by . f.e. visualizing the hydraulic heads or concentrations in the entire domain. Then, it can be checked, if the boundary conditions are fulfilled and if there are any disturbances in the model domain.
Model calibration and validation
Model reporting
Flow chart giving an overview of the individual steps
ADD FLOW CHART
Example: Setup of models for a contaminated site with a fractured limestone aquifer (Akacievej, Hedehusene)
The setup of a discrete-fracture model in 2D in COMSOL Multiphysics is described in the following document:
The typical workflow for modeling a contaminated site will be demonstrated using an example field site close to Copenhagen.
Example: Setup of models for a field site (Akacievej, Hedehusene)
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