Groundwater Overlay

The groundwater overlay is an implementation of the Water model optimized for calculating the flow of underground watertables. This implementation focuses on water flowing at a low speed, and on the functioning of the water system without calamitous events such as breaches.

Use cases

The groundwater overlay can be used and is recommended when exploring the following use-cases:

• Modeling a static, low-speed water system
• Modeling the long-term effects of excessive rain or excessive drought on the water table
• Modeling the spread of chemicals through the underground, carried along by water

Preparing to use the overlay

To use the overlay, it is recommended that the project meets a number of prerequisites. Next, data can be prepared which define the functioning and flow of the water model. This includes a clear idea of what kind of output is desired. After the data is prepared, you can begin the actual steps of adding the overlay.

It is important to model a fully functional static water system for any relevant use of the groundwater overlay. After setting up the static water model, additional effects can be modeled to account for special circumstances. This has the added benefit of creating a control-state, to which results of modifications or calamities can be compared.

Prerequisites

When creating your project, make sure it meets the following criteria:

• Your project has been loaded in with a high-resolution DEM. This can be configured during the new project wizard.
• Your project is large enough to account for edge effects.

Data

It is advised to prepare the data you wish to use in your model before creating and configuring the overlay.

Geographical data

The following data needs to be prepared, so that it can be loaded in and used by the water model's calculations: Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist

Calculation properties

Consider the duration you want your simulation to last, and whether you wish to account for rainfall in your model. The following environmental data needs to be prepared, so that it can be configured and used by the water model's calculations: Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist

Result types

After the calculation completes, consider what kind of output is relevant to your use-case. The following result types can be considered, so that it can be configured and used by the water model's calculations: Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist

Adding and configuring the overlay

The groundwater overlay can be added to the project, either by using the overlays dropdown in the editor ribbon, or by selecting the overlays editing option in the ribbon, and then opting to add it via the left panel. The overlay can then be configured using the configuration wizard. In general, if all steps in the configuration wizard are followed, no further editing outside of the wizard is required to configure the overlay.

How to use the groundwater overlay:

1. Check that your project sufficiently matches the stated prerequisites
2. Make sure that you have prepared all data you wish to use
3. Add the groundwater overlay to your project
4. Start and follow the steps in the configuration wizard
5. When the configuration wizard is completed, the overlay will automatically recalculate. (If it does not, select refresh grid.)
6. When the recalculation has completed, you can inspect the results

Data analysis

When the calculation has completed, results of the calculation inspected by selecting the overlay in the session interface. The quickest means of inspecting the results are listed here. For a more complete overview, see result analysis.

Overlay map

To check directly whether the model functions as expected, you can activate the overlay, and see the end-results directly. If multiple timeframes have been recorded, the results can be replayed, to see the progression of the results over time.

Measure tool

While inspecting the overlay, you can use the measure tool to get a detailed view of exact values in specific locations. By saving the point of measurement, it's possible to rerun the model after adjusting the calculation parameters and see the effects on the exact same location.

Water balance

Besides directly inspecting the results geographically, when verifying the functioning of a hydrological model it can be insightful to check the water balance. This option allows a net tally of where water ends up in the hydrological system.

Refining the model

Based on the results from the initial calculation, you can tweak your data to refine your model. You can update your relevant datasets, and then step through the configuration wizard again.

How to refine the groundwater overlay:

1. Reopen the configuration wizard of the overlay
2. In any step where you want to update your data, either change the individual values or clear, and reupload the data
3. Skip through all steps which concern data you do not wish to change
4. When you finish the configuration wizard, the overlay will automatically recalculate. (If it does not, select refresh grid.)
5. When the recalculation has completed, you can inspect the results

Every step where no data has changed can be skipped, and the dataset which has been uploaded can be reuploaded in the relevant step. Alternatively, you can do this directly by changing the relevant data in your project. For example, it is possible to directly change the attributes of constructions.

Common refinements

This section is a stub.

• Ground water: The functioning of groundwater is commonly strongly influenced not only by the groundwater level but also the assumed distance to the impenetrable layer below ground. That layer is effectively the lowest the groundwater level can be.

Saving the results

If the results of the calculation provide a proper baseline hydrological model, the result of the overlay can be saved as an inactive copy. This means that the overlay, including its direct settings and its results, are duplicated into a new overlay. The duplicate is then set to "inactive". This means the data in that overlay won't change as further changes are made. This means you can set up a new scenario in your original overlay, and after performing another calculation compare the results of the first and the second situation.