Hi,
is there a simple way to find all the sinkholes in a
raster elevation map? For instance areas where the water will stay in after
a rainfall or after a flood.
Thanks
Johannes Buehler
Hi John
It seems to me that the size of the sinkhole and the resolution of your
dem would have a serious effect on what you could identify.
right, but for my purpose the quality of the data is good enough. perhaps
sinkhole is not the most felicitous word. I mean "Depressed areas".
Valleys with
internal drainages such as bolsons
by the way what are bolsons (my english dictionary does not include this
word)
should show up, but a true sinkhole
such as you see in karst topography might be too small to register,
depending on dem resolution. For bolsons, an hydrological analysis of
drainage patterns for centripetal systems might work to isolate discrete
closed basins.
i just need a simple operation/command like "find all depressed areas"
Nothing complicated.
Johannes
--
-- Johannes Buehler
__O Feldtstr. 45
=`\<, 14789 Greifswald
(=)/(=) johannesbuehler@oderbruecke.de
-----------
Hi Johannes,
Maybe this is a very quick and dirty way but fill the pits, then subtract
your original map from the filled map. That should isolate the depressed
areas. I'm no expert with GRASS thats for sure but I would think that
r.fill.dir / r.mapcalc* fits your purpose. But I'm not so sure if this
works on float point data in grass5... I submitted a question to the list
about the compatiability of floating point rasters and r.watershed with no
response.
Hope this provides some ideas,
bjc
----- Original Message -----
From: "Johannes Bühler" <johannesbuehler@oderbruecke.de>
To: <GRASSLIST@baylor.edu>
Sent: Wednesday, December 04, 2002 8:50 PM
Subject: [GRASSLIST:5150] Re: finding sinkholes
Hi John
> It seems to me that the size of the sinkhole and the resolution of your
> dem would have a serious effect on what you could identify.
right, but for my purpose the quality of the data is good enough. perhaps
sinkhole is not the most felicitous word. I mean "Depressed areas".> Valleys with
> internal drainages such as bolsons
by the way what are bolsons (my english dictionary does not include this
word)
> should show up, but a true sinkhole
> such as you see in karst topography might be too small to register,
> depending on dem resolution. For bolsons, an hydrological analysis of
> drainage patterns for centripetal systems might work to isolate discrete
> closed basins.i just need a simple operation/command like "find all depressed areas"
Nothing complicated.Johannes
--
-- Johannes Buehler
__O Feldtstr. 45
=`\<, 14789 Greifswald
(=)/(=) johannesbuehler@oderbruecke.de
-----------
in high school i was a member of a "cavers" group. we used to locate
caves/sink holes by looking for un-naturally straight tributaries on what
ever maps were availible. the "straight lines" were very good indecations of
fracture zones and shallow faults that would also help form the sink holes in
the limestone.
i'm not sure how to write a program to do this, but it might be a good
starting point.
a "straight line" would have a given probability
a 90 degree bend in a "straight line" would have a higher one
the intersection of multipule straight lines would have a still higher.
if a straight line intersected,but stopped short of, a depression with no
surface drainage then you are approaching 100%
just my .019999
On Wednesday 04 December 2002 20:50, you wrote:
Hi John
> It seems to me that the size of the sinkhole and the resolution of your
> dem would have a serious effect on what you could identify.right, but for my purpose the quality of the data is good enough. perhaps
sinkhole is not the most felicitous word. I mean "Depressed areas".> Valleys with
> internal drainages such as bolsonsby the way what are bolsons (my english dictionary does not include this
word)> should show up, but a true sinkhole
> such as you see in karst topography might be too small to register,
> depending on dem resolution. For bolsons, an hydrological analysis of
> drainage patterns for centripetal systems might work to isolate discrete
> closed basins.i just need a simple operation/command like "find all depressed areas"
Nothing complicated.Johannes
--
Oh, I have slipped the surly bonds of DOS,
and danced the skies on Linux silvered wings.
http://pfrostie.freeservers.com/cad-tastrafy/
http://www.freelists.org/list/cad-linux
On Thu, Dec 05, 2002 at 02:50:13AM +0100, Johannes Bühler wrote:
[...]
i just need a simple operation/command like "find all depressed areas"
Nothing complicated.
Perhaps
http://op.gfz-potsdam.de/GRASS-List/Archive/msg07893.html
helps?
Markus
hi,
thanks to all of you.
r.fill.dir worked fine for finding all depression areas!
after a simple mapcalc and r.null command i got a final map showing all the
depression areas.
Thanks
Greetings
Johannes
--
-- Johannes Buehler
__O Feldtstr. 45
=`\<, 14789 Greifswald
(=)/(=) johannesbuehler@oderbruecke.de
-----------