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 | * 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.
- Wunsat = 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.
- WLunderground = The groundwater level, relative to datum.
- Hsurface = The terrain height in the cell, relative to datum.
- RD = The ROOT_DEPTH_M of the construction if present, the ROOT_DEPTH_M of the surface terrain otherwise.
- GBDM = The GROUND_BOTTOM_DISTANCE_M of the Water Overlay. (effectively available height in the underground).
- Eweather = The evaporation rate of the weather.
- Etop = The WATER_EVAPORATION_FACTOR of the construction if present, the WATER_EVAPORATION_FACTOR of the surface terrain otherwise.
