Leakage coefficients for receiving water courses

Attributes: LEKN (node wise), LERA (polyline wise), LEEL (element wise, horizontal and 3D models only)

These data types define the leakage coefficient, which represents a linear relationship between the difference from the receiving water course to the groundwater level hvorf -h and the leakage rate Q.

 


Schematic representation (1) of the leakage parameters

 

 


Schematic representation (2) of the leakage parameters

 

The calculation modules require a transformed leakage coefficient α in the time unit [TU] of the model file:

L [m²/TU]= α A [s/TU]

With the help of this value, the leakage rate (per TU) can be computed directly from the potential difference. A represents the area in the bottom of the receiving water course where the water flows through. The term "[s/TU]" transforms the time unit second (s) into the time unit of the model file (TU). The plot generation can represent both the original input values (LEKN, LERA, LEEL) and the corresponding transformed values for L.

 

 

The leakage coefficient α [1/s], the input values (LEKN, LERA and LEEL) and L have the following relationships between each other:

Nodes (LEKN):

LEKN [m²/TU] = α A [s/TU] i.e. L = LEKN

 

Polylines (LERA):

LERA [m/TU] = αb [s/TU] i.e. L = l * LERA

 

The corresponding length (l) for each node of the polyline/receiving water course is computed in the model checking. It is defined as the sum of half the distances to the adjacent nodes. Therefore, the leakage coefficients with regard to a polyline must be put in in the correct order.

 

Elements (LEEL):

The meaning of LEEL depends on the data for UNDU. There are two different meanings:

UNDU defined at any nodes of the element or at all nodes = 0:

LEEL [1/TU] = α [s/TU] i.e. L = A * LEEL
The element area A is computed in the model checking.

 

UNDU with values > 0 at minimum at one node of the element:

LEEL [m/s] = kv [m/s].

 

The input value represents the vertical permeability in m/s for the covering layer. The value UNDU is averaged from all nodes in the element, where no input value means UNDU = 0. The average value represents the thickness of the covering layer. The final leakage coefficient L requires the element area A which is obtained in the model checking:

 

L = LEEL / UNDU A [s/TU]

 

Leakage coefficients always have to use the time unit from the model file (TU) except for LEEL combined with UNDU.

The leakage calculation always requires the definition of a receiving water course (VORF). Otherwise, the leakage data are ignored.