NAME

       r.uslek  - Computes USLE Soil Erodibility Factor (K).

KEYWORDS

       raster, hydrology, soil, erosion

SYNOPSIS

       r.uslek
       r.uslek --help
       r.uslek  psand=name  pclay=name psilt=name pomat=name output=name  [--overwrite]  [--help]
       [--verbose]  [--quiet]  [--ui]

   Flags:
       --overwrite
           Allow output files to overwrite existing files

       --help
           Print usage summary

       --verbose
           Verbose module output

       --quiet
           Quiet module output

       --ui
           Force launching GUI dialog

   Parameters:
       psand=name [required]
           Name of soil sand fraction raster map [0.0-1.0]

       pclay=name [required]
           Name of soil clay fraction raster map [0.0-1.0]

       psilt=name [required]
           Name of soil silt fraction raster map [0.0-1.0]

       pomat=name [required]
           Name of soil organic matter raster map [0.0-1.0]

       output=name [required]
           Name for output USLE K factor raster map [t.ha.hr/ha.MJ.mm]

DESCRIPTION

       r.uslek calculates the USLE K factor, that is the Soil Erodibility Factor. It takes  input
       of  soil texture classes (sand, clay, silt) and organic matter, all in range of [0.0-1.0].
       The FAO World Soil CD documentation was used to produce the conversion system between soil
       textures and soil classes. The soil classes are in number of 12 and apparently come from a
       USDA publication of 1951 (p.209). Once the soil classes have been  identified  (by  vector
       cross-products  tests),  a  general  conversion  table  was  applied for transforming soil
       classes into K factor.

NOTES

       r.watershed provides for USLE L, S, LS factors.

EXAMPLE

       Calculate the USLE K factor (synthetic values, North Carolina sample dataset):
       # NC data: simulation
       g.region rural_1m -p
       r.mapcalc "sand  = 0.11"
       r.mapcalc "clay  = 0.47"
       r.mapcalc "silt  = 0.42"
       r.mapcalc "organ = 0.0136"
       r.uslek psand=sand pclay=clay psilt=silt pomat=organ output=usle_k
       r.univar usle_k
       # Result: uslek = 0.25

       Example with small variations (condition: d_sand + d_clay + d_silt => 1.0)
       # NC data: simulation
       r.mapcalc -s "sand_r = rand(0.09,0.13)"
       r.mapcalc -s "clay_r = rand(0.45,0.49)"
       r.mapcalc -s "silt_r = rand(0.40,0.44)"
       r.mapcalc -s "organ  = rand(0.01,0.70)"
       r.mapcalc "temp_sum = sand_r + clay_r + silt_r"
       r.mapcalc "sand = sand_r / temp_sum"
       r.mapcalc "clay = clay_r / temp_sum"
       r.mapcalc "silt = silt_r / temp_sum"
       r.mapcalc "test = sand + clay + silt"
       r.info -r test
       g.remove -f rast name=sand_r,clay_r,silt_r,temp_sum,test
       r.uslek psand=sand pclay=clay psilt=silt pomat=organ output=usle_k
       r.univar usle_k
       # Result: uslek =  variable values

SEE ALSO

        r.usler, r.watershed

AUTHORS

       Yann Chemin, SIC-ISDC, Turkmenistan

       Last changed: $Date: 2014-11-24 18:16:14 +0100 (Mon, 24 Nov 2014) $

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