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

Revision as of 09:38, 14 August 2020

Underground seepage (from (or to) outside the project area) is calculated per cell.

The seepage is calculated using the following formula:

Δ s = \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, calculate the actual amount of water seeping into (or out of) the ground from the bottom.

Δ w = \frac{Δ s}{w s}

Where:

$Δ s$ = The underground seepage which takes place, 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
$c$ = resistance of the separating layer in days
$w s$ = water storage fraction of the soil

$h_{c_{x, y}}$ 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.

@@ Line 14: / Line 14: @@
 * <math>\Delta t</math> = Computational timestep in seconds.
 * <math>h_{x,y}</math> = Ground water head in the grid cell.
-* <math>h_{d,t}</math> = 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>h_{c}</math> = constant ground water level (or head) of the external zone causing the seepage, in meters
+* <math>h_{c_{x,y}}</math> = constant ground water level (or head) of the external zone causing the seepage, in meters
 * <math>h_{v,t}</math> = additional variation of seepage head over time
 * <math>c</math> = resistance of the separating layer in days
 * <math>ws</math> = water storage fraction of the soil
+==Notes==
+* <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.
 ==See also==