[GRASS-user] r.watershed, blocking, and max_slope_length

[Ken Mankoff]

Hi again,

On 2016-03-25 at 19:50, Ken Mankoff <mankoff at gmail.com> wrote:
> I can't seem to get blocking or max_slope_length to work as I would
> expect. I see no change to the output when I use them.

Perhaps some MWEs with the NC data set will help demonstrate what I'm doing and presumably doing wrong...

Here I'm setting max_slope_length to 15 (g.region -p shown the resolution is 10) so I would expect flow to only move ~1 grid cell. But the accumulation map is identical to running r.watershed w/o the max_slope_length setting.


r.mapcalc "rain = 1"
r.watershed -s -a --v elevation=elev_srtm_30m accumulation=acc drainage=fdir flow=rain
r.watershed -s -a --v elevation=elev_srtm_30m accumulation=acc.len drainage=fdir.len flow=rain max_slope_length=15
g.gui.mapswipe first=acc second=acc.len


And here, I'm trying to block flow from crossing the 30 m elevation contour:



r.contour input=elev_srtm_30m at PERMANENT output=z_30_v levels=30
v.to.rast --overwrite --verbose input=z_30_v type=line output=z_30_r use=z --overwrite
r.mapcalc "rain = 1"
r.watershed -s -a --v elevation=elev_srtm_30m accumulation=acc drainage=fdir flow=rain
r.watershed -s -a --v elevation=elev_srtm_30m accumulation=acc.block drainage=fdir.block flow=rain blocking=z_30_r
g.gui.mapswipe first=acc second=acc.block


  -k.