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

Revision as of 09:04, 28 August 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

$h_{c_{x,y}}$ 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 4: / Line 4: @@
 : <math>\Delta s_{x,y} = \frac{h_{d}(t) - h_{x,y}}{c_{x,y}} \cdot \frac{\Delta t}{24 \cdot 60 \cdot 60}</math>
-The external seepage head is variable over time by the introduction of h<sub>v,t</sub>
+The external seepage head is variable over time by the introduction of h<sub>v,t</sub>:
 : <math>h_d(t) = h_{c_{x,y}} + h_{v,t}(t)</math>