Full text: Technical Commission VIII (B8)

2. STUDY AREA 
The Indravati is one of the northern tributaries of the Godavari 
in its lower reach. The Indravati catchment lies between 
latitudes 18 27' N to 20 41' N and longitudes 80° 05" E to 83° 
07° E (Figure 1). The river Indravati rises at an altitude of about 
914 m near Thuamal Rampur village in the Kalahandi district 
of Orissa on the western slopes of the Eastern Ghats and joins 
Godavari at an altitude of about 125 m. The main river flows 
for a length of about 477 Km. The Indravati basin with a 
catchment area of 41285 Km? constitutes 13.32 % of the total 
Godavari basin. The basin has high hills, deep valleys and large 
plateaus. The mean annual rainfall in of this area is about 1288 
mm, most of which occurs between May and September. 
Average potential evaporation rates are 6.5 mm per day, while 
average minimum and maximum temperature are 13°C and 39 
‘C respectively. There are no major irrigation projects existing 
in the study area. The major land covers in the catchment are 
forest (68 %), followed by agriculture (22 96). Agriculture is the 
main occupation of the people in the area. 
  
Basin-sub basin map of India 
Godavari Basin 
  
  
XC NS 
60 km 
  
  
  
  
  
  
Figure 1. Location map of Indravati Catchment 
3. METHODOLOGY 
3.1 Soil Erosion Model - USLE 
Techniques for prediction of soil loss have evolved over the 
years. The most widely used equation for soil loss prediction of 
the catchment is the Universal Soil Loss Equation (USLE). The 
USLE equation computes average annual soil loss (A) which is 
a product of five different factors that affect soil loss, and is 
given by: 
A-RKLSCP (1) 
  
     
    
   
     
    
    
   
    
  
  
  
   
   
    
    
   
  
  
    
  
  
  
   
    
   
  
  
  
  
  
  
  
    
   
  
   
    
  
    
   
   
     
   
   
  
  
    
  
   
   
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B8, 2012 
XXII ISPRS Congress, 25 August - 01 September 2012, Melbourne, Australia 
Where, À = average annual soil loss in tons per hectare, R = 
rainfall-runoff erosivity factor (MJ/ha.mm/h), K = soil 
erodibility factor (t.ha.h/ha/MJ/mm), LS = topographic or slope 
length/steepness factor, C = cover and cropping-management 
factor, P = supporting practices (land use) factor. All of the 
factors are dimensionless, with the exception of R and K. The 
preparation of spatial data base for this model is explained 
below. 
3.1.1 Rainfall Erosivity Factor (R): The erosivity factor 
R is often determined from rainfall intensity if such data are 
available. In majority of cases rainfall intensity data are very 
rare, consequently attempts have been made to determine 
erosivity from daily rainfall data (Jain er al., 2001). In River 
Indravati catchment, no station has rainfall intensity data. 
Therefore R is determined using mean annual rainfall as 
recommended by Morgan and Davidson (1991). The expression 
is given below. 
R=P*05 Q) 
Where, P = mean annual rainfall in mm and R = rainfall 
erosivity factor in MJ/ha.mm/h. A 20-year time series of 
monthly girded average precipitation dataset from the Climatic 
Research Unit -Average Climatology 2.0 (CRU-CL 2.0) 
(http-//Www.cru.uea.ac.uk/cru/data/tmc.htm) from 1982 to 2002 
is used in preparing R factor layer. Inverse distance method, 
which is very fast and efficient weighted average interpolation 
method in ILWIS, is used to show spatial distribution of mean 
R factor values in Indravati catchment. 
3.1.2 Soil Erodibility Factor (K): The soil erodibility 
factor (K) represents both susceptibility of soil to erosion and 
the amount and rate of runoff, as measured under standard plot 
condition. In the study area no detailed soil map in the large 
scale is available. The soil map prepared by National Atlas and 
Thematic Mapping Organization, Department of Science and 
Technology, Government of India on 1: 2 Million scale is used 
to prepare K factor. 
3.1.3 Slope length and steepness factor (LS): The 
topography affects the runoff characteristics and transport 
processes of sediment on a watershed scale. A 90 m resolution 
DEM from the Shuttle Radar Topography Mission (SRTM) is 
downloaded from ftp;//eOmss21u.ecs.nasa.gov/srtm/ , and gaps 
of no data is filled with coarser Gtopo 30 DEM 
(http/pdaac.usgs.gov/etopo30/hvdro/index.asp).This rectified 
90 m resolution DEM is used to prepare the LS factor as 
discussed below. 
Slope Length Factor (L); Mc Cool et al. (1987) presented 
the following relationship to compute the slope length or L 
factor: 
L = (W22.1)" (3) 
where L = slope length factor; À = field slope length (m); m = 
dimensionless exponent that depends on slope steepness, being 
0.5 for slopes exceeding 5 percent, 0.4 for 4 percent slopes and 
0.3 for slopes less than 3 percent. A grid size of 100 m is used 
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