r.cn - Generates a SCS curve number map layer
(GRASS Raster Program)
r.cn sg=hy_soil_group lu=landuse_map pr=practice_map
hc=hy_condition_map cn=cn_map amc=AMC_number
r.cn is a command-line interface for generating an SCS CN (Curve
Number) map. The command format is:
r.cn sg=hysoilgroup lu=landusemap pr=practicemap
hc=hyconditionmap cn=cnmap amc=AMCnumber
The command-line ordering can be in any form but all key words must be there
to run the program.
- Hydrologic soil group map name
- Landuse map name
- Practice or management map name
- Hydrologic condition map name
- Output CN map name
- Equivalent AMC condition number for the CN output
r.cn sg=hy.soil.group lu=landuse hc=hy.cond pr=veg.cover cn=cnname
will create a CN map cnname for equivalent AMC condition II
r.cn uses information from the four map layers by reading the
cell layer and its category files. So it is important to update the
category files (text attributes) for all four layers and it expects the
categories of the map layer exactly as shown below:
For the hydrologic soil group map the text categories may be
either "A", "B", "C" or "D". You will reclassify an existing soil type
map using r.reclass or v.reclass.
For the landuse map layer the text categories may be either
"fallow", "row crops", "small grain", "close-seeded legumes",
"rotation meadow", "pasture", "range", "meadow", "woods", "farmsteads",
"roads (dirt)", "hard surface" or "water".
For the practice or management map layer the categories may
be either "straight row", "contoured" or "contoured and terraced".
For the hydrological condition map the categories may be "poor",
"fair" or "good". The rating (good, fair, poor) is based on a
combination of factors that affect infiltration and runoff, which
- density and canopy of vegetated areas
- amount of year-round ground cover
- amount of grass or close-seeded legumes in rotations
- percent of residue cover on the land surface (good is more than 20%)
- degree of surface roughness
AMC is the antecedent moisture condition. AMC I: dry, AMC II: normal, AMC
III (wet). Specify this number during module run.
The category text labels can be applied to above maps using r.support
("Edit category file").
If the combination of the four layers categories does not
exist in the SCS CN table, an error message is printed and
the program quits.
The r.cn program is sensitive to the current window setting.
Thus the program can be used to generate a CN map of any
sub-area within the full map layer. Also, r.cn is sensitive
to any mask in effect.
SCS Curve number method: TR-55, Urban Hydrology for Small Watersheds
Raghavan Srinivasan and Dr. Bernie A. Engel, Agricultural
Engineering Department, Purdue University
Extensions by Markus Neteler, University of Hannover, Germany (fixes for
Last changed: $Date: 2002/03/01 00:08:31 $