Ken, You "want 14,000 values" of what?? Your original email stated you were "trying to determine flow past a drainage basin outlet" -- r.watershed does NOT do this, if indeed this is what you want. And you say you have "14,000 flow rasters to be used as input" -- what exactly are these 'flow rasters'; what is your goal? I may not understand...
Tom On Thu, Aug 31, 2017 at 2:24 PM, Ken Mankoff <[email protected]> wrote: > Hi Tom, > > I have 1 DEM and 14,000 flow rasters to be used as input. I want 14,000 > values, one at a specific coordinate from each acc output. > > I can do this by running r.watershed 14,000 times. That is slow, unless > I'm missing something (e.g. It works with I.group variables or Time Series > data more efficiently). > > An alternative approach is possible if I knew the complete drainage basin > *and* the fractional value of each cell that contributed to the basin. In > this case I don't need to route. But basins from r.watershed or > r.water.outlet, I think, use SFD not MFD (no cell is ever in 2 basins, are > they?), and I don't know how to get the fractional contribution from each > cell. > > -k. > > Please excuse brevity. Sent from pocket computer with tiny non-haptic > feedback keyboard. > > On 31 Aug 2017, at 19:59, Thomas Adams <[email protected]> wrote: > > 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 <[email protected]> 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 >> [email protected] >> https://lists.osgeo.org/mailman/listinfo/grass-user >> > > > >
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