GfsDischargeElevation is typically used in GfsRiver simulations to compute the water elevation corresponding to a given discharge along a boundary. This is done by recursively adjusting the water level above a reference level (along boundaries where a Dirichlet condition for the fluid depth
P is imposed) until the given discharge is obtained (to within 1% by default).
This elevation value can then be used to impose the water level on the boundary (and thus impose the given discharge).
The syntax in parameter files is
[ GfsConstant ] [ GfsFunction ] [ GfsFunction ]
where the first GfsFunction is the discharge (which can be a function of time but not space). The second GfsFunction is optional and can be used to specify the reference water level (which is flat by default).