Re: [GRASS-user] Calculation of Flow Accumulation, FlowPath, and TWI

[Micha Silver]

(keeping on the maillist) On 18/04/2019 19:03, Mehrdad Varedi wrote: Hi Micha, I really appreciate your feedback and thanks for your explanation.  What I am interested to do is finding where the water is accumulated after a rainfall or snowmelt under the ground. It doesn't need to form a river and any path of accumulation under the ground is what I am searching for. I was thinking probably the Flow accumulation or TWI somehow might be a way to find such locations. Now, do you think that r.watershed  is the best way to go or any other solution comes to your mind? In my opinion those are the wrong tools for groundwater flow. But you might have a look at the r.gwflow module. And there are many other software applications designed explicitly for ground water flow: Hydrus or Kineros come to mind. Thank you and kind regards, Mehrdad ᐧ On Thu, Apr 18, 2019 at 4:22 AM Micha Silver <tsvi...@gmail.com> wrote: On 17/04/2019 19:34, Mehrdad Varedi wrote: Hi Everyone, I would like to know how the flow path, flow accumulation, or topographic wetness is calculated in cities versus farms. In other words how to take into account the effect of non-penetrable areas in forming the above-mentioned layers based on a DEM and penetrability score for the study area? No answers yet, so I will give a try: Each of the variables in your question are geomorphology characteristics. They depend only on elevation, slope, aspect. Flow accumulation is  an area, TWI is area divided by tan(slope), etc. These characteristics have nothing to do with infiltration (i.e. penetrable areas). Having said that, the GRASS module r.watershed can take two input rasters: flow and retention, which change the output flow accumulation. If you have spatial data on soil retention properties, or disturbances to surface flow, you can apply them to r.watershed to get a more "realistic" accumulation grid. The defaults are 100 for retention (no infiltration, all water flowing into a cell also goes out) and 1.0 for flow (no disturbances, and no additional contribution for each cell) Thanks for your help, Mehrdad ᐧ _______________________________________________ grass-user mailing list grass-user@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-user -- Micha Silver Ben Gurion Univ. Sde Boker, Remote Sensing Lab +972-523-665918 -- Mehrdad Varedi -- Micha Silver Ben Gurion Univ. Sde Boker, Remote Sensing Lab cell: +972-523-665918

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