NAME

KEYWORDS

SYNOPSIS

Flags:

-b

use stream burning method ; Value of digging in option 'burn'; default is no

-f

use modifying flowdir method ; default is no

-a

use of ascii coordinate point file for basin outlets; file name in option 'file' (see file option for the file format); default is no

-v

use of point vector for basin outlets; vector name in option 'point'; default is no

-c

smoothing corners of subwatershed features; default is no

-i

use stream inlets to create basin; default is no

-s

use stream confluence nodes to create basin outlets; default is no

--overwrite

Allow output files to overwrite existing files

--verbose

Verbose module output

--quiet

Quiet module output

Parameters:

dem=name

Input DEM raster

watershed=name

Input watershed raster

stream=name

Input network vector

sbv=name

Output subwatersheds name

point=name

Input outlet points vector

file=string

Name of ascii coordinate point file for basin outlets (without intitulate column, field separator is 'space', col1 x and col2 y)

burn=float

Value of digging for the burning stream method

area=float

min area (in map units) value for the subwatershed

res=float

raster resolution

col=string

column name for subwatershed identification

percent=float

percentage of zero value accepted for subwatershed creation (area difference with watershed)

snap=float

distance (in map units) to snap outlet point to stream (default is 1)

DESCRIPTION

NOTES

The stream burning method digs the DEM cells which are in contact of the network ( Flag -b is used), then the flow direction raster is computed and subwatersheds created.

The flow direction modified method (use Flag -f ) works directly on the flow direction raster and reorients raster cells which are in contact of the network. For each of these cells, orientation is modified to flag to the network. It's an iterative process which can be slow.

Because of working in cultivated landscapes, the percent value needs to be used for forcing subwatershed creation. In some case of very modified landscapes, subwatersheds creation can fail.

Subwatershed outlets can be submitted from a vector map (use Flag -v and point option), or with an ascii file (use Flag -a and file option). snap option allows the outlet coordinates being snapped on the hydrological network. Using Flag -i allows to use stream inlets for additional outlets. Using Flag -s allows to use confluence points to create additional outlets. Multiple use of different flags can be made to the outlet points creation.

area, col and percent options are compulsories:

- area is the minimum surface value of created subwatersheds (in map units).

- col will be the column name (type INTEGER) in the output map to identify the different subwatersheds.

- percent is the percentage of non value cells resulting of the difference between the whole watershed and the sum of created subwatersheds. As working in modified landscapes where DEM informations aren't the most important for flow directions, an iterative process modifies the flow direction cells in contact of subwatershed boundaries to modify their direction values.

res and snap options are optionals:

- res option allows the user to work with a different resolution of input DEM

- snap option allows the user (if file or point option is used) to snap the outlet points on the line network under this threshold (distance in map units)

EXAMPLES

Subwatershed creation with stream burning method, outlets submitted by point vector map

GRASS 6.3.0 :~ > m.sbw -b -v dem=dem watershed=wshed stream=stream sbv=subwshedB burn=1 col=ident percent=2 area=1000 point=outlet snap=2.5

Subwatershed creation with flow direction modified method, and smoothed corners of subwatersheds

GRASS 6.3.0 :~ > m.sbw -f -c dem=dem watershed=wshed stream=stream sbv=subwshedF col=ident percent=2 area=1000

Subwatershed creation with classical method, and modified DEM resolution

GRASS 6.3.0 :~ > m.sbw dem=dem watershed=wshed stream=stream sbv=subwshedC col=ident percent=2 area=1000 res=50

Subwatershed creation with classical method, and using confluence network for creating outlet

GRASS 6.3.0 :~ > m.sbw -s dem=dem watershed=wshed stream=stream sbv=subwshedC col=ident percent=2 area=1000 

SEE ALSO

REFERENCES

Lagacherie, P., Moussa, R., Cormary, D., AND Molenat, J. 1996. Effect of DEM data source and sampling pattern on topographical parameters and on a topography-based hydrological model. In "HYDROGIS'96. Application of Geographic Information System in Hydrology and Water Resources Management" (K. Kovar and H. P. Nachtnebel, eds.), pp. 191-200. IAHS, Vienna.

Mizgalewicz, P.J., Maidment, D.R., 1996. Modeling agrichemical transport in midwest rivers using geographic information systems. Center for Research in Water ressources Online Report 96-6, University of Texas, Austin, TX, 338pp.

Saunders, W.K., Maidment, D.R., 1996. A GIS assessment of nonpoint source pollution in the San Antonio- Nueces coastal basin. Center for Research in Water ressources Online Report 96-1, University of Texas, Austin, TX, 222pp.

AUTHORS

rabotin@supagro.inra.fr

Last Changed: 23 January 2012

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