OPTIONS

-z

Creates zero-value background instead of NULL. For some reason (like map algebra calculation) zero-valued background may be required. This flag produces zero-filled background instead of null (default).

stream

Stream network: name of input stream map on which reduction will be performed produced by r.watershed. r.stream.extract has deleting short stream procedure build-in. Because streams network produced by r.watershed with SFD and MFD may differ it is required to use both stream and direction map produced by the same operation. Stream background shall have NULL value or zero value. Background values of NULL are by default produced by r.watershed and r.stream.extract. If not 0 or NULL use r.mapcalc to set background values to null.

dir

Flow direction: name of input direction map produced by r.watershedRegion resolution and map resoultion must be the same. Also stream network map must have the same resolution. It is checked by default. If resolutions differ the module informs about it and stops. Region boundary and maps boundary may be differ but it may lead to unexpected results.

threshold

Integer vaule indicating the minimum number of cell in first-order streams (sensu Strhahler) to leeve it in the network.

OUTPUTS

The module produces new stream map where streams shortrer than threshold are deleted. To keep file consistent, when short stream is deleted the next stream segment is joined with previous one by asigning its category.

BEFORE:

      |2
___1__|____3____

AFTER:
      
___1______1____

DESCRIPTION

Module r.stream.del is prepared to removing short streams from stream network. The short streams are undesired outcome of networks delineated from DEMS in stream ordering and basin delinating. In stream ordering very short stream may increase network order, when two short stream of first order will increase order of next streams. The second situation is connected with network delineated with more complex criteria than only accumulation threeshold like Montgomery's method or weighted method (r.stream.extract) It may produce a scope of very short streams on vallyes slopes. Such streams may lead to wrong results in stream ordering and basin delination so removing short streams to simplify the network. It also may have great impact on Horton's statistics: r.stream.stats.

NOTES

r.stream.extract has option to delete shot stream, so r.stream.del is preperad only for use with r.watershed output network. So this module will be probably depreciated in the nearest future. Module can work only if direction map, stream map and region map has same settings. It is also required that stream map and direction map come from the same source. For lots of reason this limitation probably cannot be omitted. this means if stream map comes from r.stream.extract also direction map from r.stream.extract must be used. If stream network was generated with MFD method also MFD direction map must be used.

EXAMPLES

Strahler stream ordering before and after removing short streams

r.watershed elevation=elev_ned_30m@PERMANENT threshold=100 d8cut=infinity mexp=2 stream_rast=stream_mont direction=stream_dir
r.stream.order stream=stream_mont dir=stream_dir strahler=streahler_before 

r.stream.del stream=stream_mont dir=stream_dir threshold=10 reduced=stream_out
r.stream.order stream=stream_out dir=stream_dir strahler=streahler_after

SEE ALSO

AUTHOR

Last changed: $Date$