Ground bottom flow formula (Water Overlay): Difference between revisions

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The water level change due to seepage is calculated using the following formula:
The water level change due to seepage is calculated using the following formula:
: <math>\Delta s_{x,y} = \frac{h_{d}(t) - h_{x,y}}{c_{x,y}} \cdot \frac{\Delta t}{24 \cdot 60 \cdot 60}</math>
: <math>\Delta wl_{x,y} = \frac{h_{d}(t) - h_{x,y}}{c_{x,y}} \cdot \frac{\Delta t}{24 \cdot 60 \cdot 60}</math>


The external seepage head is variable over time by the introduction of h<sub>v,t</sub>:
The external seepage head is variable over time by the introduction of h<sub>v,t</sub>:
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Finally, the actual amount of water seeping into the ground from the bottom is calculated as followed:
Finally, the actual amount of water seeping into the ground from the bottom is calculated as followed:
: <math>\Delta w_{x,y} = {\Delta s_{x,y}}\cdot{ws}</math>
: <math>\Delta s_{x,y} = {\Delta wl_{x,y}}\cdot{ws}</math>


Where:
Where:
* <math>\Delta s_{x,y}</math> = The water level change due to seepage, in meters.
* <math>\Delta wl_{x,y}</math> = The water level change due to seepage, in meters.
* <math>\Delta t</math> = Computational timestep in seconds.
* <math>\Delta t</math> = Computational timestep in seconds.
* <math>h_{x,y}</math> = [[Groundwater level formula (Water Overlay)|Ground water head]] in the grid cell.
* <math>h_{x,y}</math> = [[Groundwater level formula (Water Overlay)|Ground water head]] in the grid cell.
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* <math>c_{x,y}</math> = [[Seepage GeoTiffs (Water Overlay)#Seepage resistance|Resistance of the separating layer]] in days
* <math>c_{x,y}</math> = [[Seepage GeoTiffs (Water Overlay)#Seepage resistance|Resistance of the separating layer]] in days
* <math>ws</math> = [[Terrain water storage percentage (Water Overlay)|Water storage fraction]] of the soil
* <math>ws</math> = [[Terrain water storage percentage (Water Overlay)|Water storage fraction]] of the soil
* <math>\Delta w_{x,y}</math> = Seeped in water in m
* <math>\Delta s_{x,y}</math> = Seeped in water in m


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Revision as of 12:14, 4 September 2020

Underground seepage from outside the project area is calculated per grid cell. The formula is based on the formula of Pankow for estimating seepage[1].

The water level change due to seepage is calculated using the following formula:

The external seepage head is variable over time by the introduction of hv,t:

Finally, the actual amount of water seeping into the ground from the bottom is calculated as followed:

Where:

Notes

  • The calculated is essentially the change in groundwater level, inherently taking into account the porosity of the soil. The final is representative of the actual amount of water, i.e. the height of the water, if the relevant quantity of water wasn't in the underground but sat on the surface instead.
  • and can both be provided as spatially variable values.
  • can be provided as a set of values, variable over time.
  • A seepage head lower than the water level in the project is also allowed, resulting in water seeping out to a region outside the project area.

Related

The following topics are related to this formula.

Formulas
Groundwater level formula
Models
Underground model

See also

References

  1. ↑ Estimating seepage, http://grondwaterformules.nl/index.php/formules/ontwatering/kwel-berekenen-pankow, last visited on 2-9-2020
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