I have to model the dispersion from a river towards the aquifer. I have to estimate the flux towards the aquifer during a flood event.
I use 1D linear interpolation for interpolating linearly along a line: one map with point geometry provides the data for interpolation (flood hydrograms from hydraulic model) and a second map with line geometry (shapefile of the river) is used for linear interpolation.  The wet area of the river changes during the flood.
I assign the condition to all the nodes of the river (maximum flooded area) but I would like the condition to be active only on the wet nodes (where h_river> pc).

1) Can I use the hh (hydraulic head) BC with a min flow rate constraint (= 0 m3/d)? I this way feflow allows only inflow (positive) but I think that this BC is also assigned to the nodes with elevation > hh, it isn’t? What is the impact in the rate budget of the nodes of the river (maximum flooded area)?

2) Can I use the fluid transfer condition with a minimum hh constrained (river bed elevation)? I have read that this solution is used for:
• river that goes dry (https://52.136.242.250/index.php/topic,18273.0.html)
So, setting hmin equal to the elevation of the river bed, when h_river < h_min the flow would be outgoing (from the aquifer to the river) but with out transfer rate = 0, it will be = 0. It is correct?

3) can I use the lake plugin? What’s the difference with fluid transfer condition + hh constrained?

Thanks for the replies.
1) Yes, using this configuration at nodes outside the currently flooded area (and with hh in gw lower than river water level) you will still get infiltration. The only way to limit the area in this case would be to use different time series on all nodes, depending on the time they are flooded. This is not easy to set up and hard to maintain for different scenarios for river levels.

2) Yes, this can be done at least in the last few FEFLOW releases, and it is definitely the preferred option. In one or two older versions, though, (maybe 6.x or 7.0, not sure) FEFLOW will reverse the flow in case that the river water level (transfer bc value) is LOWER than the river bed elevation (head constraint) as the differential between water level and constraint becomes negative. In even older versions FEFLOW will ignore the constraint in this case, hereby possibly creating way too much inflow from the river where none should occur. So if you're not using 7.2 or 7.3, please check with a simple test example.

3) I guess you could (as far as I know it supports limiting the BC area to the flooded area), but the main reason for using this is normally the need for keeping a balance within the lake / river.

How visualize 3rd BC nodes during simulation when riverbed minimum head constraint get active?

I have used  the fluid transfer condition with a minimum hh constrained (river bed elevation):  in case that the river water level (transfer bc value) is LOWER than the river bed elevation (head constraint) the water flux is equal to zero.
The problem is to visualize the wet area: in view components – fluid transfer BC the visualized nodes are only nodes in which the constraint is NOT activated (i.e. the saturated nodes). The same happens if I create an expression = Fluid Trasfer Bc – elevation.
Is there any way to view the evolution of the wet area?
It is possible to add this parameter (h river – hh constrained)  in the visualization?
Showing "Rate Budget" nodal parameter may be the easiest way to visualise simulation results here (i.e. it will be zero when BC is inactive).
I agree with Durchlässigkeitsbeiwert - the rate budget is probably the easiest option. In general it would be nice, though, if FEFLOW could - in a future version - show active contraints in a way different from the swapped BC (for example well in case of an active constraint on a head BC) or from just removing the icon (as for the head constraint on transfer BCs).

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