http://www4.ncsu.edu/~hmitaso/gmslab/reports/cerl99/rep99.html
Terrain modeling and Soil Erosion Simulations for Fort Hood and Fort Polk
test areas

Geographic Modeling and Systems Laboratory,
University of Illinois atUrbana-Champaign
Helena Mitasova, Lubos Mitas, William M. Brown, Douglas M. Johnston


 rast=name      raster input file
 vect=name      vector input file containing stream

 output=name    raster output file
 [points=name]  vector output file for adjusted stream points
 [width=value]  width of streams (in meters)
 [depth=value]  additional depth

-q              quiet - do not show progress
-n              no flat areas allowed in flow direction

r.carve does not create a depressionless DEM because many depressions are in
flat areas and not in the streams.

http://www4.ncsu.edu/~hmitaso/gmslab/reports/cerl99/demstr.gif
                                                                                
The program will take the vector stream data, transform them to raster, and
subtracts a defaultdepth + additionaldepth from the DEM. If the given 
width is more than 1 cell it will carve the stream with the given width. 
With -n option it should eliminate all flat cells within the stream, so 
when and if the water gets into the stream it will flow. Vector 
('points') option generates x,y,z for points which define the stream 
with the z value of the bottom of the carved-in stream. These points 
can then be combined with contour points to interpolate a new DEM with 
better representation of valleys.

It has not been thoroughly tested so not all option may work properly - 
but this was the intention.