Subsidence Overlay
What is the subsidence overlay
How the subsidence overlay calculates
Subsidence is currently composed of 2 forms of reduction of peat: oxidation and subsidence. 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.
Settlement
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 settlement, 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.