GRASS 6.4.0svn (Oregon):/usr4/grassbase > r.watershed -m elev=aber5m
accum=aber5m.ws.accum drain=aber5m.drain basin=aber5m.basin
stream=aber5m.streams visual=aber5m.visual thresh=1500 --o
SECTION 1 beginning: Initiating Variables. 5 sections total.
WARNING: No such file or directory
WARNING: seg_open(): could not write segment file
SECTION 1b (of 5): Determining Offmap Flow.
WARNING: Subprocess failed with exit code 8
WARNING: category information for [aber5m.ws.accum] in [beaver_lake]
missing or invalid
WARNING: category information for [aber5m.drain] in [beaver_lake] missing
or invalid
WARNING: category information for [aber5m.basin] in [beaver_lake] missing
or invalid
WARNING: category information for [aber5m.streams] in [beaver_lake] missing
or invalid
WARNING: category information for [aber5m.visual] in [beaver_lake] missing
or invalid
The warnings at the end must be spurious since these are all output maps
and not created until further along the module run.
The first three WARNINGs look to me to be ERRORs instead. How to I learn
why the module failed?
Also, what guidelines does one apply to determine an appropriate threshold
value for an exterior watershed basin?
GRASS 6.4.0svn (Oregon):/usr4/grassbase > r.watershed -m elev=aber5m
accum=aber5m.ws.accum drain=aber5m.drain basin=aber5m.basin
stream=aber5m.streams visual=aber5m.visual thresh=1500 --o
SECTION 1 beginning: Initiating Variables. 5 sections total.
WARNING: No such file or directory
WARNING: seg_open(): could not write segment file
SECTION 1b (of 5): Determining Offmap Flow.
WARNING: Subprocess failed with exit code 8
WARNING: category information for [aber5m.ws.accum] in [beaver_lake]
missing or invalid
WARNING: category information for [aber5m.drain] in [beaver_lake] missing
or invalid
WARNING: category information for [aber5m.basin] in [beaver_lake] missing
or invalid
WARNING: category information for [aber5m.streams] in [beaver_lake] missing
or invalid
WARNING: category information for [aber5m.visual] in [beaver_lake] missing
or invalid
The warnings at the end must be spurious since these are all output maps
and not created until further along the module run.
Yes.
The first three WARNINGs look to me to be ERRORs instead. How to I learn
why the module failed?
The segment library failed to format a temporary file, it could not write to the file, but I don't know why. What does g.region -p say, and is there enough disk space free where your GISDBASE is?
I can't reproduce with Spearfish or NC sample datasets:
Also, what guidelines does one apply to determine an appropriate threshold
value for an exterior watershed basin?
That depends on your question, how detailed the extracted stream network and basins should be. Given a minimum total catchment area (TCA) to start a stream, the threshold would be TCA / (nsres * ewres), translating catchment area to number of cells.
... and is there enough disk space free where your GISDBASE is?
18G free.
Also, what guidelines does one apply to determine an appropriate
threshold value for an exterior watershed basin?
That depends on your question, how detailed the extracted stream network
and basins should be. Given a minimum total catchment area (TCA) to start
a stream, the threshold would be TCA / (nsres * ewres), translating
catchment area to number of cells.
OK. Please explain 'exterior watershed basin' in the context of
r.watershed.
... and is there enough disk space free where your GISDBASE is?
18G free.
Also, what guidelines does one apply to determine an appropriate
threshold value for an exterior watershed basin?
That depends on your question, how detailed the extracted stream network
and basins should be. Given a minimum total catchment area (TCA) to start
a stream, the threshold would be TCA / (nsres * ewres), translating
catchment area to number of cells.
OK. Please explain 'exterior watershed basin' in the context of
r.watershed.
it is the size (in cells number) of flow accumulation when r.watershed starts delineate streams
OK. Please explain 'exterior watershed basin' in the context of
r.watershed.
it is the size (in cells number) of flow accumulation when r.watershed starts delineate streams
OK. Because I have a vector map of drainage basins I was thinking exterior
to the basin of interest. Now I know better. Thank you.
Now this is interesting: The basin of interest covers about 9,550 ha. When
I try running r.watershed with the DEM resolution of 5m it keeps failing.
However, running the module on the 10m resolution DEM is working. There's
still 18G of free space on that partition; could the temporary file be
greater than that?
For a drainage basin of 9,550 ha, would there be meaningful differences in
r.watershed output between 10m and 5m cell size?
it is the size (in cells number) of flow accumulation when r.watershed
starts delineate streams
Jarek,
Now that I have a successful run I'd like to learn how to interpret the
output maps. For examples, the accumulation map is a solid rectangle of color
and the stream output has scattered short line segments, and the visual is a
bunch of color. I've read the descriptions on the man page but still have
not grasped how to interpret the results in terms of what they tell me about
the area modeled.
it is the size (in cells number) of flow accumulation when r.watershed
starts delineate streams
Jarek,
Now that I have a successful run I'd like to learn how to interpret the
output maps. For examples, the accumulation map is a solid rectangle of color
and the stream output has scattered short line segments,
???
and the visual is a
bunch of color. I've read the descriptions on the man page but still have
not grasped how to interpret the results in terms of what they tell me about
the area modeled.
Pointers and suggestions greatly appreciated.
TIA,
Sorry but I cannot understand you. What type of help you expect?
you have problems interpret results of basic hydrological modeling? , or rather result you received are far from expected.
in general r.watershed with basic parameters do not nothing what do not other hydrological modeling tools like taudem, saga, TAS, TNT watershed, and others. So please be precise what is your problem. If the first (hope not) I suggest rather some manulas at the begining (www.geomorphometry.org) if the second try to explain differences.
Stream accumulation map:
Have you set a reasonable threshold? If your threshold value is to
low then you will have scattered lines. Say at 10m resolution you set
the accumulation threshold to 1- you will be generating streams that
are derived from a watershed area of 100m. I don't know if this makes
sense or not.
hth,
Stephen
On Wed, Feb 10, 2010 at 12:50 PM, Rich Shepard <rshepard@appl-ecosys.com> wrote:
On Wed, 10 Feb 2010, Jarek Jasiewicz wrote:
Sorry but I cannot understand you. What type of help you expect?
Hydrological modeling I've done in the past have been strictly numeric,
not graphic. I've not used GRASS before for modeling basins.
... do not nothing what do not other hydrological modeling tools like
taudem, saga, TAS, TNT watershed, and others.
I'll take a look at those.
I'm used to numeric output, not maps. Interpreting the latter is not
within my professional experience. That's what I need to learn.
Let's not spend our time and resources thinking about things that are
so little or so large that all they really do for us is puff us up and
make us feel like gods. We are mammals, and have not exhausted the
annoying little problems of being mammals.
Stream accumulation map:
Have you set a reasonable threshold?
Stephen,
I've no idea. I set the minimum basin size at 5 acres, so using 10m x 10m
cell resolution I came up with a threshold of 21780.
Attached is a small region showing the output accumulation map (10m cell
size) overlaid with the three project points of interest (the small x's).
The topmost x is on the purple stream line, the one below it represents a
dam with the channel behind it covered by the reservoir storage.
Using the wxPython GUI display window, querying the uppermost point gives
me the geographic coordinates of the point, nothing about the underlying
accumulation map cell value.
I'll read the ESRI docs, and a tutorial I found from MicroImage on their
TNTMips (which I vaguely recall from when I last ran Windows more than a
dozen years ago).
WARNING: Subprocess failed with exit code 8
WARNING: category information for [aber5m.ws.accum] in
[beaver_lake]
missing or invalid
WARNING: category information for [aber5m.drain] in
[beaver_lake] missing
or invalid
WARNING: category information for [aber5m.basin] in
[beaver_lake] missing
or invalid
WARNING: category information for [aber5m.streams] in
[beaver_lake] missing
or invalid
WARNING: category information for [aber5m.visual] in
[beaver_lake] missing
or invalid
The warnings at the end must be spurious since these
are all output maps
and not created until further along the module run.
yeah, they are. It's setting itself up to write out new metadata and
command line history and it doesn't know about the errors so it tries
anyway. It's been known for a while and we should fix it, but it's
pretty harmless.