Lama et al.

The bifurcation ratio (R _b ) is an index of relief

of weak and impermeable subsurface material with

and dissections (Horton 1945) and lower values

sparse vegetation and mountainous relief (Chopra

are characteristics of structurally less disturbed

et al. , 2005). Smith (1950) had classified drainage

watersheds without any distortion in drainage

density into three classes i.e. low (D<1.5 km.km -2 ),

pattern (Nag 1998). According to Strahler (1964), R _b

medium (1.5-2.5 km.km -2 ) and high (>2.5 km.km -2 ).A

values of 3-5 indicated that the geological structures

high drainage density of 6.22 km.km -2 suggested that

do not have a dominant control over the drainage

the region was composed of weak and impermeable

pattern of the watershed. In the present study, the

subsurface

materials,

sparse

vegetation

and

meanbifurcationratioof1.71indicatedtheabsenceof

mountainous relief with high runoff potential.

strong structural control on the drainage pattern and

A perusal of Table 2 reveals that lower values of form

that the watershed was structurally less disturbed.

factor and elongation ratio, as well as, circularity

Similar finding has also been reported by Subba Rao

ratio indicated the watershed to be elongated in

(2009). Higher values of R _b between the first and the

shape having flatter peak flow of longer duration.

second order streams (Table 2) indicated that the

Flood flows of such basins can easily be managed

steeper slopes of the watershed is more prone to soil

than those of a circular basin (Sharma et al. , 2012,

erosion. Kumar et al. , (2012) observed that higher

Wandre and Rank 2013). Ruggedness number (R )

n

values of bifurcation ratios for the first and second

of 3.11 indicated that the area has very rugged

order streams indicated more chances of erosion in

topography. It also implied that the area is prone

the upper reaches of a mountainous watershed in

to soil erosion. The stream frequency (F ) is closely

s

Uttarakhand, India. In our study also, we observed

related to the permeability, infiltration capacity and

higher bifurcation ratios for the first and second

relief. The value of F for the watershed was found

s

order (I/II =2.22 and II/III = 1.88) streams, which

to be 26.97, which indicated high relief and low

highlighted susceptibility of the upper reaches in the

infiltration of the bed rock and consequent high

watershed to erosion.

runoff. As a result, despite of having flatter peak

Relief ratio (R _h ) is the ratio of the maximum relief to

flow, the runoff potential of the watershed is high,

the horizontal distance along the longest dimension

which is further supported by the fact that it has a

of the basin parallel to the principal drainage

high drainage density (6.22 km.km -2 ). High value

line (Schumm 1956). It is a measure of the overall

of infiltration number (167.61) suggested that there

steepness of a drainage basin and is an indicator of

is adequate scope for surface and ground water

the intensity of the erosion processes operating on

development (Singh 2006).

the slopes of the basin. Its value normally increases

with decreasing drainage area and size of a given

Conclusion

drainage basin. For Um Shipra watershed the value

The watershed exhibited a dendritic drainage pattern

of R _h was found to be 0.04.

with high drainage density indicating that the area

The drainage density (D) expresses the closeness

is composed of weak and impermeable subsurface

of spacing of channels and is affected by factors

materials with sparse vegetation and mountainous

which control the characteristic length of streams

relief having high runoff potential. Relatively lower

like resistance to weathering, permeability of rock

value of bifurcation ratio indicated the absence of

formation, climate, vegetation, etc. It also provides

strong structural control on the drainage. A plot

a numerical measurement of land dissection and

of the logarithms of the stream length of a given

runoff potential. In general, low value of D is

order against the order showed a linear relationship

observed in regions underlain by highly resistant

indicating the watershed has developed over a

permeable material with vegetative cover and low

homogeneous rock material. Lower values of

relief. High drainage density is observed in regions

form factor, circularity ratio and elongation ratio

34