[GRASS-user] Repeated r.watershed runs

[Thomas Adams]

Ken,

I'm confused about what you are trying to do with r.watershed, because the
output from the module is:

accumulation=name
Name for output accumulation raster map
Number of cells that drain through each cell
tci=name
Name for output topographic index ln(a / tan(b)) map
spi=name
Stream power index a * tan(b)
Name for output raster map
drainage=name
Name for output drainage direction raster map
basin=name
Name for output basins raster map
stream=name
Name for output stream segments raster map
half_basin=name
Name for output half basins raster map
Each half-basin is given a unique value
length_slope=name
Name for output slope length raster map
Slope length and steepness (LS) factor for USLE
slope_steepness=name
Name for output slope steepness raster map
Slope steepness (S) factor for USLE

I think you want a hydrologic model, and r.watershed is NOT that. What are
you trying to obtain?

Tom




On Thu, Aug 31, 2017 at 1:47 PM, Ken Mankoff <mankoff at gmail.com> wrote:

> Hi List,
>
> I'm trying to determine flow past a drainage basin outlet. The
> complicating factor is that I need to do this each day for 40 years. If I
> do "r.watershed" ~14,000 times I'll get the results, but it will take 3
> days. It seems that r.watershed is likely calculating many things each time
> through the loop. Is there a more efficient way to this? A flag to
> r.watershed that isn't documented? Something with time-series?
>
> Alternatively, because I only need the flow at the outlet, I could
> calculate the basin, not route the flow, and instead sum the values in the
> basin. I assume this would take seconds or minutes rather than days. In
> this case I'm not sure of the best way to define the basin. I tried doing
> r.water.outlet upstream from the outlet, but I think this uses SFD, which
> means the basin may be significantly underestimated.
>
> I also tried inverting/flipping the DEM and then running r.watershed with
> convergence=1, and a flow equal to 0 everywhere except 1000 at the outlet
> (now the source due to the inversion) to see where it flooded upstream (now
> downstream due to the inversion). This didn't seem to work... because
> basins are filled and flow routes to the edge of the DEM, I could not pick
> out the
>
> Any advice how to either a) efficiently route 14,000 FLOW rasters over 1
> DEM or b) determine the full basin will be much appreciated.
>
> Thanks,
>
>     -k.
>
> _______________________________________________
> grass-user mailing list
> grass-user at lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/grass-user
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/grass-user/attachments/20170831/8de0afe0/attachment.html>