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

Revision as of 11:59, 2 September 2020

Underground seepage from outside the project area is calculated per grid cell.

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

Δ s_{x, y} = \frac{h_{d} (t) - h_{x, y}}{c_{x, y}} \cdot \frac{Δ t}{24 \cdot 60 \cdot 60}

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

h_{d} (t) = h_{c_{x, y}} + h_{v, t} (t)

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

Δ w_{x, y} = Δ s_{x, y} \cdot w s

Where:

$Δ s_{x, y}$ = The water level change due to seepage, in meters.
$Δ t$ = Computational timestep in seconds.
$h_{x, y}$ = Ground water head in the grid cell.
$h_{d} (t)$ = Additional ground water level (or head) of the external zone causing the seepage at time t, in meters
$h_{c_{x, y}}$ = Constant ground water level (or head) of the external zone causing the seepage, in meters
$h_{v} (t)$ = Additional variation of seepage head over time
$c_{x, y}$ = Resistance of the separating layer in days
$w s$ = Water storage fraction of the soil
$Δ w_{x, y}$ = Seeped in water in m

The calculated $Δ s_{x, y}$ is essentially the change in groundwater level. The final $Δ w_{x, y}$ 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 soil but sat on the surface.
$h_{c_{x, y}}$ and $c_{x, y}$ can both be provided as spatially variable values.
$h_{d} (t)$ 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.

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 ==Notes==
+* The calculated <math>\Delta s_{x,y}</math> is essentially the change in groundwater level. The final <math>\Delta w_{x,y}</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 soil but sat on the surface.
 * <math>h_{c_{x,y}}</math> and <math>c_{x,y}</math> can both be provided as spatially variable values.
 * <math>h_{d}(t)</math> can be provided as a set of values, variable over time.