Ground evaporation formula (Water Overlay): Difference between revisions

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* W<sub>unsat</sub> = The amount of water in the saturated zone. The height of the water column if the equivalent amount of water was placed on the surface.
* W<sub>unsat</sub> = The amount of water in the saturated zone. The height of the water column if the equivalent amount of water was placed on the surface.
* WL<sub>underground</sub> = The [[Groundwater level formula (Water Overlay)|groundwater level]], relative to [[Datum|datum]].
* WL<sub>underground</sub> = The [[Groundwater level formula (Water Overlay)|groundwater level]], relative to {{datum}}.
* H<sub>surface</sub> = The [[Terrain height (Water Overlay)|terrain height]] in the cell, relative to datum.
* H<sub>surface</sub> = The [[Terrain height (Water Overlay)|terrain height]] in the cell, relative to {{datum}}.
* RD = The [[Root depth m (Water Overlay)|ROOT_DEPTH_M]] of the construction if present, the [[Terrain root depth m (Water Overlay)|ROOT_DEPTH_M]] of the surface terrain otherwise.
* RD = The [[Root depth m (Water Overlay)|ROOT_DEPTH_M]] of the construction if present, the [[Terrain root depth m (Water Overlay)|ROOT_DEPTH_M]] of the surface terrain otherwise.
* GBDM = The [[Ground bottom distance m model attribute (Water Overlay)|GROUND_BOTTOM_DISTANCE_M]] of the Water Overlay. (effectively available height in the underground).
* GBDM = The [[Ground bottom distance m model attribute (Water Overlay)|GROUND_BOTTOM_DISTANCE_M]] of the Water Overlay. (effectively available height in the underground).

Revision as of 08:15, 14 June 2019

Underground evaporation is calculated per cell.

For all underground evaporation, the height of the unsaturated zone is used.

Hunsat = Hsurface - WLunderground

First the capacity for saturated evaporation is calculated, based on how much of the saturated area is in contact with the roots.

Csat = max( 0 , min( RD , GBDM ) - Hunsat ) * WSP

Next the height of the unsaturated zone, and based on that the capacity for unsaturated evaporation is calculated.

Cunsat = max( 0 , min( RD , Hunsat ) ) * ( Wunsat / Hunsat )

Finally, the actual evaporation is calculated:

Δwunsat = min( Cunsat , Δt * Eweather * Etop )
Δwsat = min( Csat , (Δt * Eweather * Etop) - Δwunsat )
Δw = Δwunsat + Δwsat

Where:

  • Δw = The total amount of evaporation which takes place.
  • Δt = Computational timestep.
  • Δwunsat = The amount of evaporation which takes place from the unsaturated zone.
  • Δwsat = The amount of evaporation which takes place from the saturated zone.
  • Csat = The amount of evaporation that can take place from the saturated zone.
  • Cunsat = The amount of evaporation that can take place from the unsaturated zone.
  • Hunsat = The height (column) of the unsaturated zone.

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