function. Stream links were used for stream order calculation by 
giving input of flow direction. The resulting stream order grid 
was converted into ESRI line format by using raster to feature 
conversion tool. Sub-watersheds were delineated by giving an 
outlet or pour point, which is the lowest point along the 
boundary of the watershed. The cells in the source raster are 
used as pour points above which the contributing area is 
determined. The drainage systems of 94 tributaries of 
Valapattanam river basin have been extracted and analyzed 
(Figure 1). 
i 
  
  
   
   
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Legend 
ud 
River 
E Sur boss koundary 
OO. DE FE 
  
  
  
264820"E 76a00"E 7841 a0"E 78-SYA07E 
Figure 1. Map showing location and sub-basins of valapattanam 
river. 
3.1 Geomorphic indices 
Geomorphic indices applicable to fluvial systems in different 
regions and of varying size correlate with independently derived 
uplift rates (Kirby and Whipple, 2001) and are applicable to a 
variety of tectonic settings where topography is being changed 
(Bull and McFadden, 1977; Azor et al, 2002). The present 
study is based on the calculation of five geomorphic indices: 
Stream-length gradient index (SL), asymmetry factor (AF), 
hypsometric integral (Hi), drainage basin shape (Bs) and valley 
floor width-to-height ratio (Vf) for 94 sub-basins of the 
Valapattanam river basin. All the measurements have been 
carried out by using drainages and contours extracted from 
SRTM DEM in GIS environment. 
4. RESULTS AND DISCUSSION 
The results of analyzed geomorphic indices of the Valapattanam 
river basin are discussed in the following sections. 
4.1 Stream length-gradient index (SL) 
The SL index is a practical tool for measuring perturbations 
along stream longitudinal profiles, as it is sensitive to changes 
in channel slope (Burbank and Anderson, 2001). Furthermore, 
SL index may be used to detect recent tectonic activity by 
identifying anomalously high index values on a specific rock 
type (Chen et al., 2003; Zovoili et al., 2004). The SL index of 
each segment of the river was calculated by the equation (1) 
SL- (AV/A) L (1) 
The SL index was calculated for all the 94 sub-basins covering 
the whole study area and the spatial distribution of SL map was 
prepared by Inverse Distance Weighted (IDW) interpolation 
method (Figure 2). High SL values are observed in sub-basins 
     
   
  
located at the upper part of the river. Several locations along the 
head water regions of the river basin show anomalous SL values 
where the river crosses the fault planes, but in the downward part 
of the river, SL values are found to be distributed uniformly. The 
values were classified into three categories: SL 2500; 300< 
SL«500; and «300. The anomalous SL values that are observed 
in uniform lithological conditions are due to tectonic activities, 
The SL index value will increase as rivers and streams flow over 
an active uplifts, and may have lesser values when they are 
flowing parallel to features such as valleys produced by strike- 
slip faulting (Keller and Pinter, 2002). 
  
dT 1840" 
12508 
1453208 
High : 4524 
    
Low : 0.0321 
  
  
  
BEE 75°3007E TS4ŸA0"E 7553 20°E 
Figure 2. Spatial distribution of SL values. 
4.2 Asymmetry factor (Af) 
Af is an areal morphometric variable used to detect the presence 
or absence of regional tilt on basin or regional scale. The Af is 
determined by using the equation (2) (Keller and Pinter, 2002). 
Af=Ap/A1<100 (2) 
where, Ag is the area of the basin to the right (facing 
downstream) of the trunk stream, and Ay is the total area of the 
drainage basin. An Af factor above or below 50 may result from 
basin tilting, resulting either from active tectonics or 
lithologic/structural control, for example the stream slipping 
down bedding plains over time. The asymmetry factor was 
computed for selected 94 sub-basins with well developed 
drainage network. The difference between calculated Af values 
and neutral value i.e. 50 of the sub-basins vary between 0.17 and 
49 (Figure 3). Higher values of Af in the NE-NW regions of the 
river basin are due to tectonic activity, whereas those near the 
estuary are due to lithological control. The values were classified 
into three categories: AF >16; Af <16Af>7; and Af <7. 
4.3 Hypsometric curve and Integral (Hi) 
The hypsometric integral is an index that describes the 
distribution of elevation of a given area of a landscape. The 
integral is generally derived for a particular drainage basin and is 
an index that is independent of basin area. It corresponds to the 
area below the hypsometric curve and therefore is correlated with 
the shape of the curve (Keller and Pinter, 2002). We have used 
an extension called CallHypso (Perez-Pena et al., 2010) of the 
software ArcGIS 9.2 and a DEM with 90 m resolution for 
drawing hypsometric curves and calculation of hypsometric 
integral. Computed Hi values of the sub-basins range from 0.14 
to 0.86 (Figure 4). Most of the sub-basins especially those 
situated 1 
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