View source for How to generate an initialized groundwater situation

When working with the [[Ground model (Water Overlay)|complete groundwater model]] of the [[Water Overlay]], it is very likely that any initial configuration for groundwater is not actually the state of the groundwater "at rest", meaning that during the initial period of the simulation the groundwater will always flow to a different location into a more stable configuration. For example, an initial groundwater dataset may have a consistent groundwater level defined for a large plot of land, while the more natural situation may be that the water follows a curve due to the way water flows into and out of the ground.

The consequence of this phenomenon, especially for short simulations, is that groundwater will not yet have reached a natural state by the the time the main event of the simulation takes place, or even when the simulation ends. To compensate for this, it is possible to prepare the groundwater data by setting up and running a stationary calculation for groundwater, allowing it to settle, and using the (more natural and stable) result as the initial groundwater state for the actual calculation.

{{howto|title=initialize a groundwater file
| Ensure that the Water Overlay has the [[Ground water (Water Overlay)|groundwater mode]] set to "Complete".
| Ensure that the Water Overlay has [[Groundwater_depth_prequel_(Water_Overlay)|data for groundwater]] set, if one is available.
| Ensure that the Water Overlay has a [[Ground last value result type (Water Overlay)|ground last value]] output.
| Configure the rainfall for the model to run stationary, for a period of multiple weeks. 
| Recalculate the Overlay.
| Export the ground last value output of the Overlay as a GeoTIFF.
| Open the Water Overlay configuration wizard, and proceed to the groundwater step.
| Upload the exported GeoTIFF and set it as the groundwater data for the Water Overlay.
| Repeat the recalculate, export, and upload steps as often as desired, until the groundwater's stabilization time and effect is acceptable for your use-case.
}}

{{howto|title=initialize a groundwater prequel
| Ensure that the Water Overlay has the [[Ground water (Water Overlay)|groundwater mode]] set to "Complete".
| Ensure that the Water Overlay has [[Groundwater_depth_prequel_(Water_Overlay)|data for groundwater]] set, if one is available.
| Ensure that the Water Overlay has a [[Ground last value result type (Water Overlay)|ground last value]] output.
| Configure the rainfall for the model to run stationary, for a period of multiple weeks. 
| Recalculate the Overlay.
| Add a new Groundwater Overlay
| Open the Water Overlay configuration wizard for this new overlay, and proceed to the groundwater step.
| Select the option "Select a Groundwater Depth Grid Overlay"
| Select the Ground water overlay you have calculated before.
}}

{{article end
|notes
* There is no single way to configure a model to run in a stationary mode. However, a good rule of thumb is that water flowing into the model should be matched by water flowing out of the model. For example: if your model features 2 [[Inlet (Water Overlay)|Inlet]]s both configured to remove 0.01m³ of water per second from the model, you can set a linear rainfall which introduces 0.02m³ of water per second into the model.
* It's very likely that at the start of the actual calculation's simulation, the groundwater will still take a moment to settle. However, through these steps the time it takes and the margin of difference is greatly reduced.
* If the prequel ground water overlay is good as it is, it is advised to put it on inactive to prevent it being recalculated unnecessarily.
}}