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IAPRS & SIS, Vol.34, Part 7, “Resource and Environmental Monitoring", Hyderabad, India, 2002
were computed as a raster layers. The rainfall erosivity (R-
factor) was calculated from average monthly rainfall of 5
raingauge stations in and around the study area (IMD, 1971)
following Fournier's index (Fournier, 1960). The soil
erodibility factor (K) was calculated using the data on soil
properties and the monographs of Wischmeier and Smith
(1978) and Hamer (1981) The physical and chemical
properties of different soil series of Nagpur district
(Anonymous, 1990) were used for the estimation of soil
erodibility (K) factor. Slope length in meters (L) was calculated
from the slope steepness in percentage (S) following of
established relationship (Desmet and Govers, 1996). Potential
soil erosion at sub basin level was estimated based on the
integration of the rainfall erosivity (R), slope length (LS) and
soil erodibility (K) factors in GIS. The actual soil erosion was
estimated by integrating of potential erosion with cover (C) and
management practices (P) factors. The quantum of potential
and actual soil loss at sub basin level was calculated based on
the multiplication of the area by mean value of the respective
erosion class. The areal extent of actual soil erosion under
different erosion classes was worked out at sub basin level.
Based on estimated areal extent of potential and actual erosion
under different erosion classes at sub basin level, the compound
values were estimated. Based on quantitative morphometric
parameters, the compound values of potential and actual soil
loss the ranks of sub basins were worked out. The sub basins
priority zone map was generated based on the ranks of
estimated actual soil loss parameters. The multi-criteria
weighted overlay analysis was performed considering potential
erosion, slope, soil depth, texture and land use/land cover layers
as input to find out the priority areas to suggest appropriate soil
conservation measures. In the final composite map based on the
range of cumulative values, nine mapping units have been
identified to suggest various soil conservation measures.
Rainfall data Field Survey data SOI toposheets IRS-ID-LISS HI Data
Monthly Iso-hytel maps Soil depth, texture & OC maps Morphometric anlysis DEM LU/LC map
Rainfall erosivity (R) factor Soil erodibility (K) factor Slope length (LS) P-factor | Cover (C)
i I factor factor
Y Y |
Ranking of morphometric parameters Potential erosion | Actual soii erosion
Y Y
Quantification of soil loss & ranking of sub basins
Y
Prioritization of sub basins based on compound values
Y
Weighted overlay in GIS for Identification of soil conservation units
Y
Suggested conservation measures for soil and water conservation
Fig.1 Methodology flow chart
RESULTS AND DISCUSSION
Estimation of Potential and Actual soil erosion
The raster layers of rainfall erosivity (R), topographical factor
(LS), soil erodibility (R), cover (C) and management (P) factors
of USLE were computed in GIS. Based on the integration of
rainfall erosivity, slope length and gradient and soil erodibility
factors, potential soil erosion classes like slight, moderate,
moderately severe, severe, very severe and extremely severe
were identified. The area analysis reveals that slight, moderate,
moderately severe, severe, very severe and extremely severe
potential soil erosion were noticed in 36.63, 12.69, 7.62,
8.21,5.33 and 24.86 per cent of the total area. The estimated
potential soil erosion shows the soil loss of the terrain without
the influence of the cover and management factors. The
integration of rainfall erosivity, slope length and gradient and
soil erodibility, crop cover and management factors reveal
655
negligible (7.69%), very slight (26.57%), slight (18.62%),
moderate (8.54%), moderately severe (4.01%), severe (6.97%),
very severe (6.15%) and extremely severe (16.74) classes of
actual soil erosion. The analysis reveals that the cover and
management factors are influencing the degree and extent of
soil erosion.
Prioritization of Sub Basins
Quantitative morphometric parameters approach: The
values of drainage density, bifurcation ratio, stream frequency,
texture ratio were directly proportionate to the status of erosion.
The highest value of these parameters is considered as the
highest priority, next higher value is the next priority and so on.
The values of the form factor, circulatory ratio and elongation
ratio properties were inversely proportionate to the status of
erosion. The lowest value of these parameters is considered as
the highest priority, next lower value as the next priority and so
