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SGS evaporation and infiltration

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Using soil parameters we can simulate infiltration, and with negative rainfall we can simulate evaporation.

How do these losses interact with SGS when only part of a cell may be inundated?

For example using the attached image, SGS may determine there is a narrow channel equivalent to half a cell. Will evaporation/infiltration be calculated based on the full area of the cell, or the area calculated by SGS?

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Section 3.2.9 of the release notes available here provides the following:-

"Treatment of Infiltration and Negative Rainfall with SGS Enabled

With SGS enabled, cells that are partially wet the treatment of infiltration and direct rainfall is as follows. See Section 3.2.4 above for details on the SGS Infiltration Approach and SGS Negative Rainfall Approach options.

• For positive rainfall, i.e. rainfall on to the 2D cell, the volume source for each cell is the total cell area times the rainfall irrespective of whether the cell is partially wet or not.
• For negative rainfall (evaporation), the volume of evaporation is factored by the wet area fraction of the cell. That is, if the cell is only 10% wet, only one tenth of the cell’s total area contributes to the negative source term.
• For models with soil infiltration the infiltration rate is proportional to the wet area fraction of the cell. However, initial infiltration losses are based on the total area of the cell (i.e. infiltration will proceed at the maximum possible rate until the cumulative infiltration – also based on total cell area - equals the initial loss value) even if the infiltration occurs with the cell partially wet. This approach is adopted to conform with that required for direct rainfall, which assumes the rainfall is applied over the entire cell irrespective of whether the cell is partially wet or not. Likewise, soil capacity is based on the total cell area (i.e. infiltration will cease once the cumulative infiltration equals soil capacity), and the cumulative wet time for the Horton model will also increment for cells that are partially wet."

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