In a groundwater model, situations can arise where it is known that a certain number of nodes must have the same potential head, but the value is unknown. This occurs, for example, with:

• open water in a horizontal or 3D model,

• along the saturated part of a vertical well in a vertical model,

• as a boundary condition for the transition from a 2D to a 3D area,

• at the interconnected well nodes in a 3D model.

If the nodes are specified under the data type GLEI in the mesh file, the same potential head value results for all these nodes in the flow calculation. This is realised numerically by adding the equations of the corresponding nodes; so that they are treated as one unknown.

In the case of a vertical well in a 3D model, there is no need to distribute the abstraction rate to the vertical nodes (unless, for example, different rates are actually extracted by several pumps over the depth). If the nodes below each other are equated, the entire well abstraction can be applied to any of these nodes.

Realization in SPRING