By using the water course systems in SPRING it is ensured that the upstream quantities of the groundwater are considered downstream in the exchange balance. This ensures that when a water section dries up only so much water can trickle away, as the existing upstream amount, for example seasonally, allowed.
The basic formula for the simplified derivation of the water level in the water course is:
The formula is valid only at a ratio of b >> h.
With:
Water level (over bottom oft he water course) h
outflow q
bottom slope I
Manning/Strickler coefficient kSt
Wetted perimeter b
If the attributes (VINZ, VGRD, VSYS) for the water course system calculation are assigned in the model file, an additional input block appears when selecting the module SITRA:
Maximum change [m³/s]
In determining the groundwater runoff at a node, the quantities which flow from the upper section to this node are taken into account. These leakage rates are at each iteration added together from the upper course to the considered node, to evaluate how much water can trickle away at the appropriate potential (< water level).
This in turn causes a change in the leakage rates and thus a change in the groundwater runoff. This iteration is limited by specifying a maximum volume change.
Maximum number of iterations
The iteration of the leakage rates can lead to a very high number of calculation steps before the max. (volume) change is achieved. In extreme cases, no convergence is achieved at all. Therefore, at this point, the number of iterations is limited.
Once a restriction (max. volume rate or max. number of iterations) is reached, the iteration of the groundwater runoff stops.
Extended settings in the module GEONEU