Subsidence Overlay

This article is a stub.

What is the subsidence overlay

The subsidence overlay is a grid overlay, and part of the subsidence collection of overlays. It shows which places in the 3D world are subject to subsidence due to oxidation and/or compaction of peat.

How the subsidence overlay calculates

Subsidence is currently composed of 2 forms of reduction of peat: oxidation and compaction. These forms of subsidence are both relevant for the complete picture of subsidence, but are, in principle, calculated via separate formulas. The results of these formulas are added together to get the total amount of subsidence.

Oxidation

Peat, when exposed to oxygen, can oxidize. In this process the peat combines with the air to form CO2, reducing the total mass and volume of the peat. The amount of oxidation depends on the clay thickness, because clay may insulate the peat, preventing it from oxidizing. It also depends on the (lowest) ground water level in relation to the surface of the land.

For information on the exact calculation of subsidence due to oxidation, see the article on Subsidence calculation.

Compaction

Peat is a porous and relatively soft terrain type, meaning it can be compressed. Based on the amount of peat in the ground, the density of the top layer, and the net height increase.

For information on the exact calculation of subsidence due to compaction, see the article on Subsidence calculation.

Multi-year calculations

Subsidence is calculated in 1-year steps. For each year, the amount of subsidence is calculated. That amount is then used to recalculate the input parameters for the overlay. The next 1-year step is then calculated.

For more information on the way the multi-year calculation is performed, see Subsidence calculation.

How to configure the subsidence overlay

When the subsidence overlay is added to a project, there is some minimum information required for a calculation.

Peat soil

The calculation will only work when the terrain is sensitive to subsidence. By default, peat is the only terrain sensitive to subsidence. If your project does not yet have a peat soil, you can either set a different soil type to be sensitive to subsidence, or add peat to your project.

How to change soil sensitivity to subsidence:

1. Hover over the 3D world and click to find the underground soil type
2. Select that underground soil type in the left panel
3. In the right panel, switch to the attributes tab
4. Add the attribute "SUBSIDENCE" with value 1

How to change the soil type:

1. Select "peat" in the left panel
2. Select the "General" tab in the right panel
3. Draw the terrain in the 3D world

Water level areas

Subsidence is only calculated within water level areas, regardless of what data is present in the project. These areas are defined by the fact that they have a WATER_LEVEL attribute.

There are 2 ways of getting this data into your project: by importing it (i.e. your own data) into the project as areas with attributes, or by manually drawing the appropriate areas and adding attributes to those.

How to import water level areas:

1. Drag your GeoJSON file into the editor
2. Select "Import as areas
3. Rename the water level attribute to "WATER_LEVEL"
4. Select "Send"

How to create a water level area manually:

1. Add a new area to the project
2. Draw the area into the 3D World
3. Add the attribute "WATER_LEVEL" to the area, with a value of, for example, "-10"
4. Select "refresh grid"

Refresh overlays

When data has been loaded in or changed in the editor, the grid is not updated automatically, so you will not immediately see your changes. To force the grid to update, you can refresh the grid.

Further data

It's possible to configure the overlay further with additional data.

Ground water levels

By default, the ground water levels are loaded in from a publicly available geotiff automatically. Under the "Keys" tab in the right panel, you can change the selected geotiff by selecting a different one at "Include Ground Water Tiff". You can also disable the ground water geotiff, and use a ground water level attribute of areas instead.

How to add your own ground water data:

1. Select the overlay
2. In the right panel, select the "keys" tab
3. Uncheck the "Include Ground Water Tiff" checkbox
4. Select or create an area, part of the 3D world
5. Add the attribute "GLG" to the area, with a value of, for example, "-1"

Clay thickness

By default, no data about clay thickness is available, and is considered to be "0". It's possible to add this attribute to areas to further influence the amount of subsidence taking place.

How to add clay thickness data:

1. Select the overlay
2. Select or create an area, part of the 3D world
3. Add the attribute "CLAY_THICKNESS" to the area, with a value of, for example, "0,4"

Oxidation

The following data must be added to a project for the oxidation calculation:

Attribute	Description	Name to import as
Water level	The areas with the relevant data must have a water level attribute to mark them as water level areas.	WATER_LEVEL
Ground water level	A ground water level, in meters from the surface of the land. The larger the value, the dryer the soil is. Should be greater than 0. (Can also be 0, but there will be no subsidence then.)	GLG
Clay thickness	The thickness of the layer of clay on the top of the soil, in meters. The thicker the layer, the less subsidence occurs. Should be 0, or greater than 0.	CLAY_THICKNESS

It is possible to load in your own GeoJSON file with information which is relevant to the oxidation calculations. When this data is loaded in, results of the calculations will become visible in the 3D world when the overlay is selected.

To import you own file, you must prepare a GeoJSON file with the specified data in the correct format. The file should contain the data listed above. When the file is prepared, it can be imported via the option in the ribbon, or by dragging the file into the Engine. The file must be imported as areas. When importing, the attributes must be renamed to the attribute names listed above.

How to configure oxidation subsidence by importing data:

1. Drag your GeoJSON file into the editor
2. Select "Import as areas
3. Rename the ground water level attribute to "GLG"
4. Rename the clay thickness attribute to "CLAY_THICKNESS"
5. Rename the water level attribute to "WATER_LEVEL"
6. Select "Send"
7. Select the subsidence overlay
8. Select "refresh grid"

When creating the data manually in the editor, you must add at least one area to the project, and to the 3D World. The appropriate attributes (listed above) must be added to the area.

How to configure oxidation subsidence by drawing areas:

1. Add a new area to the project
2. Draw the area into the 3D World
3. Add the attribute "WATER_LEVEL" to the area, with value "-10"
4. Add the attribute "GLG" to the area, with value "-0,9"
5. Add the attribute "CLAY_THICKNESS" to the area, with value "0,1"
6. Select the subsidence overlay
7. Select "refresh grid"