[GRASS-user] Strahler order starting from vector data?

GRASS GRASS user
1

Hi,

I see v.strahler and r.stream.order in addons can assign
Strahler Order to a river network, but how to run that if you
are starting with an existing vector river network with no
raster DEM? could you cross with a matching coastline vector to
extract end nodes at the river mouths? will even a rough DEM
like SRTM data be better than nothing in that case? how good
does it have to be? would etopo1 be ok? (1 arc-minute ~ 2 km
cells)

also, how to get around attaching lake and swamp areas which
split the river vector line in two? convert their boundaries to
lines and treat it as a braided river? fill them in then r.thin
them somehow? otherwise topology would be clean.
how about if the river goes into a cave and out somewhere else? need to trace that gap by hand? (may be too big for the sloppy=
option)

thanks for any tips,
Hamish

2

W dniu 25.01.2011 13:03, Hamish pisze:

Hi,

I see v.strahler and r.stream.order in addons can assign
Strahler Order to a river network, but how to run that if you
are starting with an existing vector river network with no
raster DEM?

Ordering existing river network (without DEM) require topologically correct network I can guarantee that r.stream.order can order a network created by automatic software like r.stream.extract or r.watershed but not about network digitized manually. There are lots of topological and directional checks, but such tool is possible in the feature if really needed

could you cross with a matching coastline vector to
extract end nodes at the river mouths?

With map algebra for example I can cut river network in any place and order it

will even a rough DEM
like SRTM data be better than nothing in that case?

yes, but it not guarantee that river network will be exactly reproduced

  how good
does it have to be? would etopo1 be ok? (1 arc-minute ~ 2 km
cells)

Depending the resolution end extend you need.

also, how to get around attaching lake and swamp areas which
split the river vector line in two?

This is unresolved problem in a general case of network ordering. In general lake is treated as a flat area where stream pass trough. (see r.watershed of GRASS 7 with beautify flat areas for details). There are some early proposition of Mark from early 80s (I do not remember the title but I can search if you interested) how to treat such structures but there are no common agreement about it. On the other hand lake shall be treated as local depression. This is implemented in r.watershed and r.stream.extract for GRASS7

convert their boundaries to
lines and treat it as a braided river? fill them in then r.thin

Same as above. No common ordering system for braided rivers. This problem is commonly called in discussion by hydrologists, but as long as there were no uniform ordering system for braided we can do nothing

them somehow? otherwise topology would be clean.
how about if the river goes into a cave and out somewhere else?

Another unresolved problem. r.stream was created for terrestrial areas not karst system. Modeling of karst system require completely different approach

need to trace that gap by hand? (may be too big for the sloppy=
option)

Probably yes

Jarek

3

I ran into this software (HydroFlow [1]) from Rio de Janeiro State
University that will give you river order (srahler or Shreve) based
only on a vector river network and a basin map. I tested it on a large
basin and it did work fine but, you must have a topologically correct
vector. Hope it helps

Daniel

[1] http://www.fgel.uerj.br/labgis/hydroflow/en/index_ingles.htm

On Tue, Jan 25, 2011 at 10:03 AM, Hamish <hamish_b@yahoo.com> wrote:

Hi,

I see v.strahler and r.stream.order in addons can assign
Strahler Order to a river network, but how to run that if you
are starting with an existing vector river network with no
raster DEM? could you cross with a matching coastline vector to
extract end nodes at the river mouths? will even a rough DEM
like SRTM data be better than nothing in that case? how good
does it have to be? would etopo1 be ok? (1 arc-minute ~ 2 km
cells)

also, how to get around attaching lake and swamp areas which
split the river vector line in two? convert their boundaries to
lines and treat it as a braided river? fill them in then r.thin
them somehow? otherwise topology would be clean.
how about if the river goes into a cave and out somewhere else? need to trace that gap by hand? (may be too big for the sloppy=
option)

thanks for any tips,
Hamish

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