How to add Subsidence (Water Overlay)

It is possible to include the effects of subsidence in the Water Overlay's calculations by using a Combo Overlay to precompute the resulting Elevation model, and setting the result as the terrain elevation prequel of the Water Overlay.

How to add subsidence to a water simulation:

Add and configure a Subsidence Overlay (or other source which defines amounts of subsidence).
Add a Heightmap Overlay, set to DTM mode.
Add a Combo Overlay, which takes the values of the Heightmap Overlay and subtracts the value of the final result of the Subsidence Overlay.
Open the Water Overlay's configuration wizard, and proceed to the step regarding the Elevation Model.
Opt to select a Grid Overlay to determine the elevation model.
Select the Combo Overlay.
Recalculate the water Overlay.
The calculation has now taken into account the specified subsidence effects.

Notes

The source of Subsidence can be a Subsidence Overlay, but could also be a precomputed result from a GeoTiff Overlay or another Combo Overlay.
The terrain elevation prequel is solely for the terrain elevation and does not include Buildings. Those are added automatically, on top of the terrain elevation, whether that terrain elevation is based on height data or on a Prequel.
By setting up two identical Water Overlays, one taking into account Subsidence and one not, it's possible to investigate in detail the effects of subsidence on the water system.