r.watershed & blocking

[mankoff]

I'm not sure if this is a bug, but I think so. When I set the blocking}} option to {{{r.watershed, I see no difference in the accumulation map.

The example below, which should work on the NC data set, creates a "blockage" at 30 m, runs r.watershed with and without the blockage, and compares results.

r.contour input=elev_srtm_30m@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

Also discussed at ​https://www.mail-archive.com/grass-user@lists.osgeo.org/msg31665.html and ​https://gis.stackexchange.com/questions/187310/what-does-the-blocking-option-do-in-grass-r-watershed

[mmetz]

Replying to mankoff:

I'm not sure if this is a bug, but I think so. When I set the blocking}} option to {{{r.watershed, I see no difference in the accumulation map.

The blocking option only affects RUSLE-related outputs length_slope and slope_steepness. Slope lengths are calculated from drainage paths through the terrain. Path tracing stops as soon as a blocking cell or a stream cell is encountered.

[martinl]

Can we close, update manual, or?

[mmetz]

Replying to martinl:

Can we close, update manual, or?

It is already mentioned in the manual.