The river Mahanadi is one of the major inter-state east flowing 
rivers in peninsular India. It originates at an elevation of about 
442 m. above Mean Sea Level near Pharsiya village in Raipur 
district of Chattisgarh. During the course of its traverse, it drains 
fairly large areas of Chhatisgarh and Orissa and comparatively 
small area in the state of Jharkhand and Maharashtra. The total 
length of the river from its origin to confluence of the Bay of 
Bengal is about 851 km., of which, 357 km. is in Chattisgarh 
and the balance 494 km. in Orissa. During its traverse, a number 
of tributaries join the river on both the banks. There are 14 
major tributaries of which 12 are joining upstream of Hirakud 
reservoir and 2 downstream of it. Approximately 65% of the 
basin is upstream from the dam. The average annual discharge 
is 1,895 m 3 /s, with a maximum of 6,352 m 3 /s during the 
summer monsoon. Minimum discharge is 759 m 3 /s and occurs 
during the months October through June. 
Fig. 1. Location of Study Area (Mahanadi river basin) 
Mahanadi basin enjoys a tropical monsoon type of climate like 
most other parts of the country. The maximum precipitation is 
usually observed in the month of July, August and first half of 
September. Normal annual rainfall of the basin is 1360 mm 
(16% CV) of which about 86% i.e. 1170 mm occurs during the 
monsoon season (15% CV) from June to September (Rao, 
1993). The river passes through tropical zone and is subjected to 
cyclonic storms and seasonal rainfall. In the winter the mean 
daily minimum temperature varies from 4°C to 12°C. The 
month of May is the hottest month, in which the mean daily 
maximum temperature varies from 42°C to 45.5°C. 
3. METHODOLOGY 
Basin boundary and drainage characteristics of the watershed 
were derived in HEC -GeoHMS module in ArcView 3.2a 
software using 1 km resolution GTopo30 USGS Digital 
elevation model (DEM) as major input. A fill grid map was 
generated after correcting the DEM for sinks. Flow direction 
map was derived from this fill sink map and subsequently a 
flow accumulation map was derived from it. Stream definition 
was derived from this flow accumulation by specifying the 
maximum threshold area for delineating drainages. A sub-basin 
for each delineated stream is then extracted. To extract the basin 
boundary, an outlet at Mundali station in the Mahanadi river 
basin was defined. Finally, a basin for the defined outlet was 
delineated along with the river network. It was further 
subdivided into desired number of sub-basins by specifying 
various outlets where the gauging station exists along the 
extracted drainage. A square grid of area 25 x 25 km 2 was 
generated over the study region. There were in all 267 such 
grids falling in the basin. This extracted grid network for the 
basin was used to overlay with the other thematic layers and 
hence define the distribution of various parameters and 
properties in the basin. VIC model requires the definition of 
input parameters for each grid distributed uniformly over the 
area. 
Remote sensing based satellite images being most reliable and 
offering synoptic views of large areas were the viable option to 
study landcover dynamics on a regional scale. LANDSAT MSS 
images of 1972-73 were downloaded, preprocessed and 
mosaiced to create a seemless image of the whole basin. Since 
the individual images were of different dates, classifying the 
mosaic into landcover types was not feasible. So, the individual 
images were classified using unsupervised classification 
(Isodata clustering) technique into several classes (200) and 
they were merged based on their spectral signatures into 7 
landcover types namely Water body, DF/moist deciduous forest, 
SF/dry deciduous forest, Agriculture, Built up/settlement, 
Barren land and River bed (dry). The preliminary classified 
layer was then improved using visual interpretation approach. 
Thus, an integrated digital and visual classification was 
attempted to map landcover since a single technique would not 
have been feasible for regional mapping. The individual 
classified images were then mosaiced and clipped by the basin 
boundary. Landcover mapping for 1985 was done using NOAA 
AVHRR images (1 km resolution) whereas AWiFs (56 m 
resolution) was used to prepare for the year 2003. The same 
approach of unsupervised classification and visual interpretation 
technique was followed to perform the task. The landuse/ 
landcover maps of Mahanadi basin for 1972, 1985 and 2003 are 
shown in Fig. 2. GCP’s (ground control points) were used to 
improve and validate classification scheme. Classification 
accuracy of more than 70% was achieved using this approach. 
Four major input files are required to make the VIC model input 
database. They are Vegetation parameter file, Vegetation 
Library file, Soil parameter file and Forcing files. The data in 
these files were stored in the ASCII format. A soil parameter 
file describes the characteristics of each soil layer for each grid 
cell. This is also where other basic grid cell information is 
defined like grid cell no., lat-long of the grids (which serves as a 
link to other parameter files), mean elevation etc. Mean 
elevation values for each grid were derived from Digital 
elevation model. The primary data source to prepare this input 
was digital soil texture map prepared from NBSS & LUP 
(National Bureau of Soil Survey and Landuse Planning, 
Nagpur) soil maps (scale-1:50,000). Soil texture map was 
rasterised and overlaid with the grid map to extract dominant 
soil type in each grid. The second soil layer was taken as FAO 
global soil map of the world. All other parameters except c, 
elev, depth, offgmt, rough, and annual prec are a function of 
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