I have a river and a field next to it (with its DEM). I want to determine the water's pathways in the field, when the water in the river reaches a certain level , based on the DEM only.

I am thinking of using r.lake but it only uses one point as a seed?

Obviously a more precise hydraulic modelling of the river inundation is needed but I just want to have an idea of the pathways.

1 Answer 1


By your own admission this is an exercise in futility. What you need is a proper hydraulic model. Consider HEC-RAS (freeware).

Generating a detrended surface models (some call it a relative elevation model) might get you a vague idea of the flow of water at different water heights but again, this is not a peer-reviewed excepted practice filled with potential error. Here a link to detrending in QGIS using IDW interpolation.

You don't ask for it but here is a suit of ArcGIS 10.7 toolbox tools using several different methods for detrending. There is also an transect (IDW) tool for ArcGIS Pro.

  • Thanks for the reply. I was asked to avoid using HEC-RAS due to time constraints and low stakes of the study so I am looking for a tool to get a rough idea of the water pathways in QGIS.
    – user38646
    Commented May 12, 2023 at 15:19

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