Terrain water storage percentage (Water Overlay)

Icon	Attribute	Unit	Layer	Range	Description
	WATER_STORAGE_PERCENTAGE	fraction (m³/m³)	Ground		The percentage (as a fraction) of the ground layer volume which can be filled with water. A lower percentage means the ground layer will be able to store less water, and the saturated zone will rise higher with the same amount of water in the ground layer.

Based on the properties of the terrain, water may infiltrate into the ground layers. Two ground layers are distinguished; the unsaturated zone and saturated zone.

The speed at which water can infiltrate from the surface to the unsaturated zone is dependent on both the GROUND_INFILTRATION_MD of the surface terrain, as well as the GROUND_INFILTRATION_MD of any building in that location, if present. Of the infiltration values of the building and the surface terrain, the lowest value is used. If either has an infiltration value of 0, water cannot infiltrate into the unsaturated zone.

The maximum amount of water which can be stored in the saturated zone is based on the WATER_STORAGE_PERCENTAGE of the ground terrain.

Ground flow, also known as horizontal infiltration, is also dependent on the infiltration properties of the ground layer, unless an aquifer exists the same location.

Notes

Contrary to its name, the WATER_STORAGE_PERCENTAGE should always be a fraction.
The groundwater level reduction is related inversely to the WATER_STORAGE_PERCENTAGE, as the contribution of a given volume of water to the groundwater level increases when the capacity for water storage in the ground layer decreases.