Ground water depth formula (Subsidence Overlay)

At the start of a simulation, the ground water depth is initialized with the ground water depth geotiff (if provided) and is optionally overwritten by (managed) water level areas' water level. Furthermore, the ground water level can be managed with drainages (provided as underground buildings), either actively or passively.

Additionally the terrain height can change due to subsidence that occurred in previous years and due to actions taken that raised the terrain. Managed water level areas can react to these changes when indexation is configured. For indexation, see indexation formula.

<math>d_{gw,y} = \begin{cases} d_{d}, & \text{if }n\text{ drainage is larger than 0} \\ max(0.0, d_{a} - \Delta{d_{a,y} - S_{y-1}, & \text{if }n\text{ drainage is smaller than 0} \end{cases}