Ground bottom flow formula (Water Overlay): Difference between revisions
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: <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_{c,tf}</math> = [[Bottom resistance prequel (Water Overlay)#Bottom resistance|Resistance of the bottom boundary]] in days at [[Timeframes (Water Overlay)|timeframe]] <math>tf</math> and cell <math>c</math>. | : <math>c_{c,tf}</math> = [[Bottom resistance prequel (Water Overlay)#Bottom resistance|Resistance of the bottom boundary]] in days at [[Timeframes (Water Overlay)|timeframe]] <math>tf</math> and cell <math>c</math>. | ||
: <math>ws_{c}</math> = [[Terrain water storage percentage (Water Overlay)|Water storage fraction]] of the soil. | : <math>ws_{c}</math> = [[Terrain water storage percentage (Water Overlay)|Water storage fraction]] of the soil at cell <math>c</math>. | ||
: <math>\Delta s_{c,t}</math> = The amount of ground bottom flow through the bottom boundary from deeper ground layers, in m, at time <math>t</math> and cell <math>c</math>. | : <math>\Delta s_{c,t}</math> = The amount of ground bottom flow through the bottom boundary from deeper ground layers, in m, at time <math>t</math> and cell <math>c</math>. | ||
{{article end | {{article end | ||
|notes= | |notes= | ||
* The calculated <math>\Delta wl_{c}</math> is essentially the change in groundwater level, inherently taking into account the porosity of the soil. The final <math>\Delta s_{c}</math> 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 ground but sat on the surface instead. | * The calculated <math>\Delta wl_{c,t}</math> is essentially the change in groundwater level, inherently taking into account the porosity of the soil. The final <math>\Delta s_{c}</math> 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 ground but sat on the surface instead. | ||
* <math>p_{c,tf}</math> and <math>c_{c,tf}</math> can both be provided as spatially variable values using [[Prequels (Water Overlay)|prequel overlay]]s. These prequels can have multiple timeframes, as indicated by the formula, allowing changing head and resistances over time. | * <math>p_{c,tf}</math> and <math>c_{c,tf}</math> can both be provided as spatially variable values using [[Prequels (Water Overlay)|prequel overlay]]s. These prequels can have multiple timeframes, as indicated by the formula, allowing changing head and resistances over time. | ||
* <math>h_{v}(t)</math> can be provided as a set of values, variable over time. | * <math>h_{v}(t)</math> can be provided as a set of values, variable over time. | ||
Revision as of 13:04, 27 February 2024
Ground water flowing in from deeper ground layers through the bottom boundary, due to head pressure from water bodies situated outside the project area is calculated per grid cell. The formula is based on the principles used in the formula of Pankow for estimating this ground bottom flow[1].
The water level change due to ground bottom flow 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 flowing into the ground from the deeper ground layers through the bottom boundary is calculated as followed:
where:
- = The water level change due to the ground bottom flow at time and cell , in meters.
- = Computational timestep in seconds.
- = Ground water head at cell and time .
- = Additional global pressure at time , in meters.
- = Ground water level (or head pressure) in meters at timeframe and cell .
- = Additional variation of bottom head pressure over time.
- = Resistance of the bottom boundary in days at timeframe and cell .
- = Water storage fraction of the soil at cell .
- = The amount of ground bottom flow through the bottom boundary from deeper ground layers, in m, at time and cell .
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 ground but sat on the surface instead.
- and can both be provided as spatially variable values using prequel overlays. These prequels can have multiple timeframes, as indicated by the formula, allowing changing head and resistances over time.
- can be provided as a set of values, variable over time.
- A head pressure lower than the water level in the project is also allowed, resulting in ground water lowering and flowing into the deeper ground layers and out of the project area.
How-to's
Related
The following topics are related to this formula.
See also
- Bottom pressure prequel (Water Overlay)
- Bottom resistance prequel (Water Overlay)
- Ground bottom flow result type (Water Overlay)
- Ground bottom pressure m (Water Overlay)
References
- ↑ Estimating ground bottom flow, http://grondwaterformules.nl/index.php/formules/ontwatering/kwel-berekenen-pankow, last visited on 2-9-2020
- Models
- Surface • Ground • Rain • Evaporation • Infiltration • Elevation • Breach • Sewer • Storage • Tracer flow • Border • Order
- Model formulas
- Timestep • Season • Surface water level • Groundwater level
- Flow formulas
- Surface flow • Surface infiltration • Ground flow • Ground infiltration • Surface evaporation • Ground evaporation • Ground bottom flow
- Hydraulic structure formulas
- Culvert • Weir • Breach growth • Breach flow • Pump • Sewer Overflow • Inlet • Drainage
- Related