How to set up pre-initialized water levels (Water Overlay)
When performing calculations with the Water Overlay, for some use-cases it is necessary to start the calculation with a pre-initialized water levels. In general, water levels can be derived from Water Areas. However, these provide uniform water levels across large areas, meaning for the first moments in the simulation water needs to "settle". Instead, it is possible to provide water levels via a Prequel. This means water can immediately start at the correct levels.
This process is a form of "initialization", and involves using a crude dataset like Water Areas to run a brief simulation until water reaches an equilibrium, and then using those equilibrium results as input for the real simulation.
How to set up pre-initialized water levels and use them in a water calculation.:
- Create a Water Overlay.
- Add Water Areas to the Project to set initial water levels.
- Configure the boundary conditions, such as Inlets and Rainfall, so that the inflow and outflow of the model is more or less in balance.
- Add a Surface last datum result type.
- Recalculate the Water Overlay. and check whether the results resemble a proper initial situation.
- Set the Water Overlay to inactive.
- Add a second Water Overlay.
- Configure the second Water Overlay as desired for the real calculation.
- In the second Water Overlay's configuration wizard, at the step regarding water levels, opt to refer to a different Grid Overlay for input.
- Ensure that the last timeframe is selected.
- Recalculate the second Water Overlay. The resulting simulation has not needed to initialize the water levels, as the input was already initialized.
- The described setup leaves an inactive Water Overlay in the Project which is referenced by the actual calculating Water Overlay. It is also possible to export the results of the initializing calculation as a GeoTIFF, then making that result available via a GeoTIFF Overlay. The actual calculating Water Overlay can then reference that GeoTIFF Overlay for its initial (and initialized) water levels.