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

Template:Water Overlays 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. Strictly, it is possible to use the overlay without preparing all or any of the data, however the accuracy and usefulness of the model is directly proportional to the preparation of data.

Not all data is equally important. When prioritizing the preparation of data, you may choose to prioritize some data over other, in which case the importances listed below can offer a guideline.

Most data can be loaded in directly in the wizard. Some data should be loaded in separately either before or after stepping through the wizard.

Geographical data

Geographical data needs to be prepared, so that it can be loaded in and used by the water model's calculations. This data will form hydrological features and constructions which interact with the hydrological model.

If a type of data does not exist for your project area, either because the data components do not exist in the project area or because the data is unavailable, it is possible to skip that kind of data while preparing. Generally, the more closely the data (and the water model) resembles the real world situation, the more accurate the model will be. Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist

Calculation properties

Environmental and simulation parameters for the calculation need to be prepared, so that they can be loaded in and the simulation can compute results based on a specific case and intent. This data will influence how the simulation progresses in general.

It's possible to skip any of the configurations and fall back on default values offered. However, in general the results of a better configured overlay will produce more useful results. Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist Template:OverlayChecklist

Result types

A specific idea of what kind of results are relevant as output need to be prepared, so that the overlay can be configured to provide relevant results.

For use with this overlay, there are a number of suggested result types to consider. 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.
6. Start the geo data wizard and load in any additional geographical data not considered during the wizard.
7. When all data is loaded in, recalculate the overlay using refresh grid.
8. 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.

Measurement tool

To get more detailed measurements of the result, you can use the measurement tool to inspect the results of a specific cell. The measurement tool also allows for the saving and loading of locations of measurement, so that comparative measurements can be made between different overlays and different calculations.

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 the configuration wizard is completed, the overlay will automatically recalculate. (If it does not, select refresh grid.)
5. If you have any additional data you wish to load in, open the geo data wizard and follow the steps.
6. If you have any data you wish to modify, select the data in the editor and adjust the properties or attributes accordingly.
7. When all data is loaded in, recalculate the overlay using refresh grid.
8. 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.

• Grid cell size: Due to the complexity of the calculation and the strong impact the level of detail in the data can have, it is possible that an initial calculation yields inaccurate results. One way of increasing the accuracy of the results is to increase the grid cell size.
• 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.
• Input overlays: There is a lot of data which is pre-processed before actually used in the calculations. Some model behaviors can be better explained or reproduced with insight in how the model interprets geographical data in the project. This can be done by adding an input overlay for that type of data.

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. You can then set up a new scenario in your original overlay, and after performing another calculation compare the results of the first and the second situation.