17 Universal Soil Loss Equation RUSLE and Modified Universal Soil Loss
Equation MUSLE etc, which are based on modifications made on USLE. The GIS can also be used as a controlling tool for application ranges of model
parameters, especially the digital elevation model DEM related topographic variables used in erosion modeling.
2.6.1. Revised Universal Soil Loss Equation: RUSLE
The Revised Universal Soil Loss Equation is being developed by the USDAs Agricultural Research Service. The model will be refined and improve
the accuracy of the original Universal Soil Loss Equation USLE to estimate the effects of various conservation systems on soil erosion.
i Model and Components
The RUSLE is an empirical equation that predicts annual erosion tonshayr resulting from sheet and rill erosion in croplands. The USLE is
factor-based, which means that a series of factors, each quantifying one or more processes and their interactions, are combined to yield an overall estimate of soil
loss. It is the official tool used for conservation planning in the US and many other countries have also adapted the equation. The equation is:
A = R K L S C P
where, A =
Annual soil loss tonshectareyr resulting from sheet and rill erosion. This is the predicted value resulting from the execution
of the equation above.
R= Rainfall - runoff erosivity factor.
2.2
18 This factor measures the effect of rainfall on erosion. The R
factor is a summation of the various properties of rainfall including intensity, duration, size etc. It is computed using the
rainfall energy and the maximum 30 minutes intensity EI30 K=
Soil erodibility factor. The soil erodibility factor measures the resistance of the soil to
detachment and transportation by raindrop impact and surface runoff. Soil erodibility is a function of the inherent soil
properties, including organic matter content, particle size, permeability, etc. Because these properties vary within a given
soil, erodibility K values also varies. L=
Slope length factor. This factor accounts for the effects of slope length on the rate of
erosion. S = Slope steepness factor.
This factor accounts for the effects of slope angle on erosion rates. All things being equal, higher slope values have greater
erosion rates. C =
Cover management factor. Accounts for the influence of soil and cover management, such
as tillage practices, cropping types, crop rotation, fallow, etc..., on soil erosion rates.
P = Erosion control factor.
19 Accounts for the influence of support practices such as
contouring, strip cropping, terracing, etc... Once these factors have been determined for a field of interest A can be computed.
Also, the equation can be used to determine the desired cover management factor C or erosion control P if the allowable soil erosion rates are known. Thus, in
this research use the RUSLE to simulate the impact of changes in land use and land cover on soil erosion, anthropogenic impacts on the environment.
Table 2.1: Data Layer and GIS Description for RUSLE Factor
Erosion databases,
factors Data layers
Description of GIS procedures include cross-references
Erosivity R Rainfall
data Spatial interpolation of station EI values; stored as R-
factor map. Erodibility
K Soil data
Assignment of numerical K-values to soil units by reclassification of the soil unit polygon map with the K-
value column from the soil attribute table; stored as K- factor map.
Combining slope length
and gradient LS
Geomorphic If regional geomorphologic relief classes exist, combined
LS-gradient or terrain factor values can be obtained using a 2-Dim table with row wise, relief steepness classes and
column wise the slope length classes, resulting directly in LS-value distribution for the area; stored as an LS-map
file.
Land Cover Land cover,
Farm dbs If necessary pre-processing or spectral classification of
remote sensing data; assignment of C-factor values to land cover RS data classes using cover attribute table; stored as
C- factor map; Conservation
Practice Farm
Land cover For land use types with soil conservation practices,
reclassify C-factor map with P-factor values of land cover attribute table, using P=1 for non-conservation areas.
20
2.6.2. Difference between RUSLE and USLE
