[GRASS-user] floodplain creation

Vaclav Petras wenzeslaus at gmail.com
Thu Oct 4 20:11:26 PDT 2018

Based on what we have discussed (including some off-list), the best shot
seems to be using directions based on r.watershed on the carved DEM
together with the given (not computed) streams for HAND (streams are also
used for the carving and r.lake steps).

An alternative is using streams from r.watershed, but only those which fall
into a buffer around the given streams (for more context, see some of my
previous emails when I already mentioned this).

Getting the directions for a stream, as I suggested, is of course useless
except for using it for updating the direction raster which may or may not
bring a minor improvement (probably not worth complicating the workflow).


On Wed, Oct 3, 2018 at 5:46 PM Shane Carey <careyshan at gmail.com> wrote:
> Hi Vaclav,
> I have checked the output from r.watershed with what you have calculated
and I do see differences in the value obtained by both. Could it be a
rounding issue perhaps? The only other difference I see is that the output
from r.watershed is a complete raster as opposed to just the river network.
See image attached to explain what I mean. Does that make any difference?
> Le gach dea ghui,
> Shane Carey
> GIS and Data Solutions Consultant
> On Tue, Oct 2, 2018 at 12:07 PM Shane Carey <careyshan at gmail.com> wrote:
>> Ok cool. When I I try to run the r.stream.distance with this new new
stream direction layer (that I calculated with  r.mapcalc
"streams_direction_8 = int((streams_direction + 45) / 45)" ),
>> it just hangs on the part that says: "caclulating downstream
parameters". So I am not sure what is going on here - have you any ideas on
>> Also, could you explain a little about what this expression is doing:
(streams_direction + 45) / 45)
>> Thanks Vaclav
>> Le gach dea ghui,
>> Shane Carey
>> GIS and Data Solutions Consultant
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