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

Revision as of 12:01, 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:

\Delta s_{x,y}={\frac {h_{d}(t)-h_{x,y}}{c_{x,y}}}\cdot {\frac {\Delta 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:

\Delta w_{x,y}={\Delta s_{x,y}}\cdot {ws}

Where:

$\Delta s_{x,y}$ = The water level change due to seepage, in meters.
$\Delta t$ = 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
$ws$ = Water storage fraction of the soil
$\Delta w_{x,y}$ = Seeped in water in m

The calculated $\Delta s_{x,y}$ is essentially the change in groundwater level, inherently taking into account the porosity of the soil. The final $\Delta w_{x,y}$ 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 underground but sat on the surface instead.
$h_{c_{x,y}}$ 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.

@@ Line 22: / Line 22: @@
 ==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.
+* The calculated <math>\Delta s_{x,y}</math> is essentially the change in groundwater level, inherently taking into account the porosity of the soil. 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 underground but sat on the surface instead.
 * <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.
 * 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.
 ==See also==