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 wl_{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,tf}} \cdot \frac{\Delta t}{24 \cdot 60 \cdot 60}</math>


The external bottom head pressure is variable over time by the introduction of <math>h_{v}(t)</math>:
The external bottom head pressure is variable over time by the introduction of <math>h_{v}(t)</math>:
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: <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.
: <math>h_{d}(t)</math> = Additional ground water level (or head) of the external zone causing the seepage at time t, in meters
: <math>h_{d}(t)</math> = Additional ground water level (or head) of the external zone causing the seepage at time t, in meters
: <math>p_{x,y,tf}</math> = [[Bottom pressure prequel (Water Overlay)#Bottom pressure|Ground water level (or head) of the external zone]] causing the seepage at [[Timeframes (Water Overlay)|timeframe]] <math>tf</math>, in meters
: <math>p_{x,y,tf}</math> = [[Bottom pressure prequel (Water Overlay)#Bottom pressure|Ground water level (or head) of the external zone]] in meters at [[Timeframes (Water Overlay)|timeframe]] <math>tf</math>.
: <math>h_{v}(t)</math> = [[Ground bottom pressure m (Water Overlay)|Additional variation of bottom head pressure]] over time
: <math>h_{v}(t)</math> = [[Ground bottom pressure m (Water Overlay)|Additional variation of bottom head pressure]] over time
: <math>c_{x,y}</math> = [[Bottom resistance prequel (Water Overlay)#Bottom resistance|Resistance of the separating layer]] in days
: <math>c_{x,y,tf}</math> = [[Bottom resistance prequel (Water Overlay)#Bottom resistance|Resistance of the separating layer]] in days at [[Timeframes (Water Overlay)|timeframe]] <math>tf</math>
: <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 s_{x,y}</math> = Seeped in water in m
: <math>\Delta s_{x,y}</math> = Seeped in water in m

Revision as of 15:47, 25 January 2024

Hoe is kwel geïmplementeerd in het Tygron Geodesign Platform? (Dutch only)

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

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

The external bottom head pressure is variable over time by the introduction of :

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

where:

= The water level change due to seepage, in meters.
= Computational timestep in seconds.
= Ground water head in the grid cell.
= Additional ground water level (or head) of the external zone causing the seepage at time t, in meters
= Ground water level (or head) of the external zone in meters at timeframe .
= Additional variation of bottom head pressure over time
= Resistance of the separating layer in days at timeframe
= Water storage fraction of the soil
= Seeped in water in m

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.

How-to's

Related

The following topics are related to this formula.

Formulas
Groundwater level formula (Water Overlay)
Models
Underground model (Water Overlay)

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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