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IAPRS & SIS, Vol.34, Part 7, “Resource and Environmental Monitoring", Hyderabad, India, 2002 
and width measurements were recorded to calculate the values 
of various shape indices viz., lemniscate ratio, compactness 
coefficient and form factor. 
RESULTS AND DISCUSSION 
The extent and status of gully control structures in a 
representative catchment (Tablel) shows 
Table 1. Extent and status of gully control structures installed in Barahamanawala catchment 
  
  
Type of gully Number of % damaged structures Yosilted structures* 
Structure structures installed Partial ' Complete25-50 50-75 100 
Loose rock dams 4 25 75 50 50 nil 
Gabions 6 17 83 nil 65 35 
Permanent 3 30 30 nil 30 70 
that nearly all the structures were a failure in one or the other 
way. About 75, 83 and 33 per cent of loose rock dams, gabions 
and permanent structures, respectively, were damaged 
completely whereas 25, 17 and 30 per cent of these respective 
structures were damaged partially. About 70 per cent of 
permanent structures had been silted up completely to the crest 
level and the gully being still active. This situation could be 
considered as more dangerous than if these structures were not 
there. The runoff water now will have to fall from an additional 
height of the crest structure, thereby increasing its velocity and 
kinetic energy tremendously, resulting in more erosion. Almost 
all these structures were installed in the highest-order gully at 
upper, middle and lower slope segments. No effort was made to 
tackle the lower-order gullies. 
Gully erosion indices 
Gully density (length of gullies per unit area) varied from 28.1 
to 54.6 km km?, whereas gully texture (number of first-order 
gullies per unit area) ranged from 1629 to 4423 km? in the 
three catchments (Table 2). It has been shown that gully density 
and gully texture are virtually uncorrelated and probably are 
related to different controlling mechanisms (Morgan, 1976). 
High values of gully density are associated with runoff 
production from regular moderate rainfalls whereas gully 
texture is the result of high intensity rainstorms. 
Table 2 Gully erosion indices and soil erosion severity in the study catchments 
  
  
Catchment Gully density Gully texture Peak runoff Sediment density 
(km km?) (No. km?) (1 s'ha”!) (tha) 
I 28.1 ‘1629 103.0 22 
II 34.8 2908 182.9 5.4 
III 54.6 4423 187.9 12.9 
  
Both gully density and gully texture were greatest in catchment 
III followed by II and I. Catchment III was expected to have the 
highest value of gully density and gully texture due to its 
compact shape, greatest average slope steepness and sparse 
vegetation. This was also reflected by the highest peak runoff 
(187.9 1s! ha") and sediment density (12.9 tha!) in catchment 
III. 
Gully patterns 
About 76 per cent of the total gullies in the catchments 
represented first-order gullies, followed by 21.6 per cent as 
second-order and 0.3 per cent as fourth-order (Table 3). 
Table 3. Distribution of number, length and mean length of 
different-ordered gullies 
Gully Number Length Mean length 
  
order (%) (%) (m) 
First 23:8....65.6 9.4 
Second 21.6 19.9 9.8 
Third 2.3 5.0 14.6 
Fourth 0.3 8.8 352.8 
  
739 
Similarly about 66 per cent of the total length of gullies 
constituted the first-order, followed by 20 per cent as second 
and 5 per cent as third order gullies. The number of gullies 
decreased with increasing order, whereas the average length of 
gullies increased with increasing order. It was 9.4 m for first- 
order and 349.5 m for fourth-order gullies. Lower-order gullies 
were receiving runoff at a lower velocity, which increased the 
length of higher-order gullies at a faster rate (Nakano et al 
1985). Also the longer gullies grow at a faster rate than the 
shorter gullies (Burkard and Kostaschuk, 1997). The overall 
distribution of number of gullies on the either side (facing 
north-east and south-west directions) of the main gully was in 
the ratio of 1.3:1 irrespective of their order whereas the 
corresponding ratio for the length of gullies was 1.1:1 (Table 
4). The ratio of distribution for the number of gullies was 1.3:1 
for first-order, 1.5:1 for the second-order, 2:1 for the third-order 
and 1:1 for the fourth-order gullies. This may be attributed to 
the local variations in the slope steepness of the catchments. 
Gully formation is largely controlled by the generation of a 
sufficient volume of runoff and by a sufficient level of relief 
energy, which depends on the slope gradient (Vanderkerckhove 
et al., 1998). Desmet et al. (1999) indicated that the landscape 
positions where gullies start are more controlled by slope 
gradient.