Groundwater (Overlay)

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Revision as of 08:31, 4 January 2019 by Rudolf@tygron.nl (talk | contribs) (Prerequisites)
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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 out output is desired. After that 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. A buffer of at least 1km around your actual project area is recommended.
  • The project's eventual use does not require immediate results. The calculations will take longer than most other calculations in the Tygron Platform, so sessions with live interaction are discouraged.

Data

Before creating and configuring the overlay, it is best to prepare the data you wish to use in your model.

Geographical data

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

Component Importance How to configure Description
Water areas Required for proper water levels Water areas set the water level of all open water in the area they envelop.
Ground water Required for proper water levels The ground water geotiff sets the underground water level.
Weirs Required for proper water flow Weirs connect otherwise separate sections of open water, allowing water to flow over the weir.
Culverts Required for proper water flow Culverts connect otherwise separate sections of open water, allowing water to flow through the culvert.
Pumps Required for proper water flow Pumps connect otherwise separate sections of open water, moving water unidirectionally from the lower terrain level to the higher terrain level.
Inlets Required for proper water flow into and out of the project area Inlets are points in the water model where water is added or removed from the hydrological system.
Sewer areas Recommended for proper water levels Sewer areas intersect with sewered constructions in the area they envelop to form sewers which can store water.
Sewer overflows Recommended for proper water flow Sewer overflows allow water to flow from a sewer out into open water.
Chemical producers Required for modelling chemical flows Chemical producers create some quantity of chloride, phosphorus, or nitrogen.

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:

Component Importance How to configure Description
Simulation time Required How long should the simulation last in total. Groundwater calculations often look at timespans of weeks or months.
Timeframes Recommended How many result snapshots should be generated by the calculation, for inspection after the calculation completes.
Rain Optional How long should rain last at the start of the simulation, and how much rain should fall in total.

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:

Component Importance How to configure Description
SURFACE_LAST_VALUE Required for insight into amount of water The amount of water in any given location.
UNDERGROUND_LAST_VALUE Required for insight into amount of water The groundwater level rise in any given location.
SURFACE_FLOW Recommended for insight into movement of water The flow of water across the land and water in total.
EVAPORATED Recommended for insight into water leaving the system The amount of water which evaporated in total.
UNDERGROUND_WATERTABLE Optional for insight into groundwater The groundwater level in any given location, relative to NAP.
CHLORIDE, NITROGEN, PHOSPHORUS Required for insight into chemical flow and impact The amount of certain compounds present in any location.

Adding and configuring the overlay

Editor→ current situation (header)→ Overlays (bar)→ Groundwater overlay (dropdown)

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.

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.

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.