R.stream.* modules
Modules r.stream.order r.stream.basins, r.stream.distance and r.stream.stats are prepared to perform Hortonian analysis in GRASS GIS. Modules can work with outputs data of r.watershed and r.stream.extract being preparing by Markus Metz.
The tutorial/presentation was prepared with North Carolina Dataset.
http://grass.osgeo.org/download/data.php
As a base map elev_ned_30_m was used. Regions setings for analysis:
projection: 99 (Lambert Conformal Conic) zone: 0 datum: nad83 ellipsoid: a=6378137 es=0.006694380022900787 north: 228500 south: 215000 west: 630000 east: 645000 nsres: 30 ewres: 30 rows: 450 cols: 500 cells: 225000
Because r.stream.extract is still in progress analysis will be based on r.watershed results. Stream network has been obtained with r.watershed in MFD mode:
r.watershed -f elevation=elev threshold=700 accumulation=accum drainage=dirs stream=streams convergence=5
Be sure you set the region for analysis before run it.
g.region rast=elev_ned_30_m
For future analysis following map produced by r.watershed are requied: streams with streams network, dirs with flow direction and accum with flow accumulation.
r.stream.order
Module r.stream.strahler may order stream network according four most popular ordering systems. Module can create both all four at once or every order separete
r.stream.order stream=streams dir=dirs accum=accum strahler=strahler shreve=shreeve horton=horton hack=hack
To obtain Scheidegger's stream order is just enough multiply Shreve stream magnitude x2.
r.stream.basins
Module r.stream.basins is prepared to delineate basins and subasins according user rules. I covers (in very small part) funcionalty of r.water.outlet and r.watershed but addationaly has much more posibilities which are presented in this section of tutorial. Module is prepared to delineate number of basins in one step. It requires only two maps direciton and streams. In stream map we can store all information required to proper delineation.
To delinaate all basins with categories of streams simply use:
r.stream.basins dir=dirs stream=streams basins=bas_basins_elem
To delineate all basins definied by outlets, ignoring subbasins use similar code but with - l flag. That flag ignores all nodes and uses only real outlets (in most cases that on image border). That option is very useful to determine major and minor basins in area.
r.stream.basins -l dir=dirs stream=streams basins=bas_basins_last
To delinaeate only one or more particular basin it require to reclass stream basin to theplaned set. The fastest method is r.reclass but also r.mapcalc may repcalce r.reclass. The output is the last (downstream) cell of given stream:
echo '42=42 * = NULL' > tmp1 r.reclass input=streams output=sel_streams_1 <tmp1 r.stream.basins dir=dirs stream=streams basins=bas_basin_1
It is also possible to use more than one stream as an output. If some stream will be tributurary of others it will produce subbasins in main basins. It can be eliminated with -l flag only if streams are in sequence.
echo '42 = 42 252 = 252 188 = 188 * = NULL' >tmp r.reclass input=streams output=sel_streams_1 <tmp1 r.stream.basins dir=dirs stream=streams basins=bas_basin_3
Basin delineated in previous step can be used to cut off streams of that basin. In next step these streams can be used to delinaeate subbasins of given basin
echo 'sel_all_streams_42 = if(bas_basin_1,streams,null())'|r.mapcalc r.stream.basins dir=dirs stream=sel_all_streams_42 basins=bas_elem_42
Do delineate basins of particular order we must use the following procedure:
echo '2 = 2 * = NULL' > tmp r.reclass input=ord_strahler output=sel_strahler_2 < tmp r.stream.basins -c dir=dirs stream=sel_strahler_2 basins=bas_basin_strahler_2
The flag -c must be used because all streams has category 2 (result of reclass operation). If we need basins with category of streams we must use little different approach. First with mapcalc procedure extract that streams with order 2, next use -l flag to creatre basins with category of last (downstream) segments
echo 'sel_strahler_cat_2 =if(ord_strahler==2,streams,null())'|r.mapcalc r.stream.basins -l dir=dirs stream=sel_strahler_2 basins=bas_basin_strahler_2
To determine areas of contribution to streams of particular order we need only use as streams teh result of ordering.
r.stream.basins dir=dirs stream=ord_strahler basins=bas_basin_strahler
