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International Research Journal ISSN-0975-3486 VOL. I * ISSUE—3 &4 RNI : RAJBIL/2009/30097

Introduction

The drainage basin is the most convenient unit for the

study of both geomorphology and hydrology. A

drainage basin is an open system, into which and from

which energy and matter flow, and its boundaries are

normally well defined. As rivers drain a much of the

terrestrial landscape, drainage basins are a fundamental

unit of geomorphic analysis.

THE STUDY OF DRAINAGE NETWORK

AND COMPOSITION OF RYANG BASIN

IN THE DISTRICT OF DARJILING,

WEST BENGAL

Research Paper—Geography

*Nagindas Khandwala College Mumbai.

Dec.-09—Jan.-2010 * Dr. Moushumi Datta

Location of the Study Area

The leaf shaped Ryang basin comprises of an

area of 63.64 sq. km. It is bound by latitude 260 53’N to

270N and longitude 880 17’E to 880 25’E falling in the

district of Darjiling, West Bengal, India. The total length

of the river in the study area is 14.82 km.

Fig 1

Fig 2

Research methodology

In order to study the

drainage network and

composition of Ryang Basin

the methodology adopted by

the present researcher is a

rationalistic one

Research objectives

To study the drainage network and composition

of the Ryang basin.

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Materials and Methods for Study

Data Type Tools/Methods Data Link

Secondary Data Maps 1. Topographical Sheet Survey of India, Kolkata

78 B/5 – 19722.

Topographical Sheet

78 B/5 – 1987

Primary Data Remote Sensing 1.IRS 1C LISS III – 19th National Remote

January, 2002 Sensing Agency, Hyderabad

2.IRS P6 LISS III – 26th

January, 2006

Drainage Pattern

Drainage pattern refers to the spatial arrangement

of stream channels within a drainage basin. Lithology,

geological structure, topography, relief and geomorphic

history of the region determine the drainage patterns.

In the area of study we mostly find dendritic drainage

pattern. A notable characteristic of the dendritic pattern

is the presence of tributary streams branching in all

directions. Dendritic drainage is commonly

encountered in areas of uniform or comparable

lithology.

Drainage Pattern

Fig 4

Parallel pattern of streams are observed around

Lower Mamring. This type of pattern is mostly

observed where regional slopes are dominant.

Sometimes, topographic features, which are elongated,

also favour development of such patterns.

Stream Ordering

River system is made up of a mainstream and its

tributaries. The method or system by which streams

are classified into a hierarchy is known as Stream

Ordering. In this study, the stream ordering of Strahler

Drainage System

The maximum length of the Ryang River is 14.82

km, originating from an elevation of 2240m (26056’

04.38" N & 88017’ 29.60" E). The lowest point in this

basin is 300m (26058’ 38.61" N & 88024’ 47.54" E). The

river course in the upper part is not associated with

any sediment deposition. However, in the middle and

lower part of the study area we can see some boulders,

stones and pebble deposition. The width of the river

varies from place to place.

Fig 3

It may be due to the local physiographic factors.

As obtained from the satellite imagery of 26th January

2006, the maximum width of the river is 266m (at 26057’

16.54" N & 88024’ 48.85" E) while the minimum width is

56m (at 26067’ 12.33" N & 88023’ 32.49" E). The river

has a number of curves and that is due to the presence

of convex ridges. Two sharp curves are observed at

the east of Lower Mamring and near Lower Kundong.

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International Research Journal ISSN-0975-3486 VOL. I * ISSUE—3 &4 RNI : RAJBIL/2009/30097

has been followed.

Stream Ordering

Fig 5

Looking first at the number of segments we find

that the value falls very quickly as order increases.

The ratio of number of segments of one order to the

next is also calculated. This ratio is called the

Bifurcation Ratio. It may differ from one river to the

other, depending upon the topography and the speed

of the river. Looking at the values, we can see that the

bifurcation ratio varies from 2.0 to 6.0 and the average

value is 4.06. Turning now to average stream length,

we anticipated that the average length of stream

segments increases with stream order. The table 1

confirms this fact, with mean lengths for the Ryang

River ranges from 0.60 km for first order segments to

7.78 km for fifth order segments. Here we find that the

average length ratio is RL=2.05. Fig 7 depicts that

44.56% of the basin area is secured by the first order

channels. These channels are extending in length by

headword erosion and are being assisted by slumping

and slope failure. It causes soil erosion as well as slope

Table 1 Stream Orders and Their Respective Parameters

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deformation at the water shed area near free face slope

of the water divide. This portion of the basin is the

most problematic part because of higher rate of soil

erosion and landslide and this area deserves more care

for better management.

Drainage Texture

The character and geometry of the drainage

network is generally evaluated in terms of drainage

texture, which includes the drainage density and

drainage frequency (Horton, 1945).

Drainage Frequency

Drainage or channel frequency is the total number

of streams per unit area, calculated by the formula

introduced by Horton (1945). The maximum area of

28.91sq.km (45.42%) of the basin falls under the

category of 8 to 12 streams per sq. km. whereas only

1.49 sq.km (2.34%) falls under the category of more

than 16 streams per sq.km. High drainage frequency is

found in the southern part of the basin area.

Drainage Density

Drainage Density is the sum of stream length per

unit area; express the closeness of spacing of stream

channels. The maximum area of 25.92 sq.km (40.73%)

falls under the category of 2.2-3.3 km per sq. km. High

Drainage Density group includes 8.38 sq.km which is

13.17% of the Ryang Basin. Low Drainage Density

group includes 1.48 sq.km, which is about 2.33% of

the area under study.

Conclusion

From the above study of the Ryang Basin it can

be concluded that in the Ryang Basin the development

of the stream is greatly natural, irrespective of

geological or structural influences on which they flow.

Less impact of geological structure on drainage

development is marked by the non-distortion of

drainage pattern, which is an indication of

homogeneous lithological character of the basin. The

development of different drainage frequency and

density zones of the basin area reflects the nature of

variation of relief, soil, rocks with permeable or

impermeable character, hill, slopes, structures, etc.

· Basu, S.R., 1968: Landscape evaluation – A Methodology. Geographical Review of India, Calcutta, Vol.30, No .4. pp. 9-

13. · Basu, S.R. & Sarkar, S., 1987: Eco-system vis-à-vis Landslides – A Case Study in Darjeeling Himalayas, Impact of

Development on Environment, Calcutta, Vol.2: pp. 45-53. · Basu, S.R. & Sarkar, S., 1990: Development of Alluvial Fans in

the Foothills of the Darjeeling Himalayan and their Geomorphologic and Pedological Characteristics. In Rachoeki, A.H. and

Church, H. (eds) Alluvial fans – A Field Approach. John Wiley & Sons Ltd., pp.321-334. · Carson, M.A., 1969: Models of Hill

slope Development under Mass Failure, Geographical Analysis, Vol. 1: pp. 76-100. · Chorley, R.J., 1969: The Drainage Basin

as the Fundamental Geomorphic Unit, In Chorley, R.J. (ed.), Water, Earth and Man, Methun & Co. Ltd., GB, Vol. 2, pp. 77-99.

· Doornkamp, J.C. & King, C.A.M., 1971: Numerical Analysis in Geomorphology – An Introduction, Edward Arnold, And

GB: pp.3 –73. · Horton, R.E., 1970: Erosional Development of Streams: Quantitative Physiographic Factors, In Dury, G.H.

(ed) Rivers and River Terraces. Macmillan & Co, Ltd., GB: pp.117-216. · Kale, V.S. and Gupta, A., 2001: Introduction to

Geomorphology, Orient Longman Ltd. (ed), pp. 82-98. · Leopold, L.B., Wolman, M.G. and Miller, J.P., 1964: Fluvial

Processes in Geomorphology, Eurasia Publishing House (Pvt.) Ltd., New Delhi: pp. 131-149. · Thornbury, W.D., 1984:

Principles of Geomorphology, Wiley Eastern Ltd., pp. 16-17. Zernitz, E.R., 1932: Drainage Patterns and their Significance

Journal of Geology, Vol. 40: pp. 498-521.

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