1. International Research Journal ISSN-0975-3486 VOL. I * ISSUE—3 &4 RNI : RAJBIL/2009/30097
Research Paper—Geography
THE STUDY OF DRAINAGE NETWORK
AND COMPOSITION OF RYANG BASIN
IN THE DISTRICT OF DARJILING,
WEST BENGAL
Dec.-09—Jan.-2010 * Dr. Moushumi Datta
*Nagindas Khandwala College Mumbai.
Introduction Location of the Study Area
The drainage basin is the most convenient unit for the The leaf shaped Ryang basin comprises of an
study of both geomorphology and hydrology. A area of 63.64 sq. km. It is bound by latitude 260 53’N to
drainage basin is an open system, into which and from 270N and longitude 880 17’E to 880 25’E falling in the
which energy and matter flow, and its boundaries are district of Darjiling, West Bengal, India. The total length
normally well defined. As rivers drain a much of the of the river in the study area is 14.82 km.
terrestrial landscape, drainage basins are a fundamental
unit of geomorphic analysis.
Fig 2
Research methodology
In order to study the
drainage network and
composition of Ryang Basin
Fig 1 the methodology adopted by
Research objectives
To study the drainage network and composition the present researcher is a
of the Ryang basin. rationalistic one
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2. International Research Journal ISSN-0975-3486 VOL. I * ISSUE—3&4 RNI : RAJBIL/2009/30097
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 System Drainage Pattern
The maximum length of the Ryang River is 14.82 Drainage pattern refers to the spatial arrangement
km, originating from an elevation of 2240m (26056’ of stream channels within a drainage basin. Lithology,
04.38" N & 88017’ 29.60" E). The lowest point in this geological structure, topography, relief and geomorphic
basin is 300m (26058’ 38.61" N & 88024’ 47.54" E). The history of the region determine the drainage patterns.
river course in the upper part is not associated with In the area of study we mostly find dendritic drainage
any sediment deposition. However, in the middle and pattern. A notable characteristic of the dendritic pattern
lower part of the study area we can see some boulders, is the presence of tributary streams branching in all
stones and pebble deposition. The width of the river directions. Dendritic drainage is commonly
varies from place to place. encountered in areas of uniform or comparable
lithology.
Drainage Pattern
Fig 4
Parallel pattern of streams are observed around
Fig 3 Lower Mamring. This type of pattern is mostly
It may be due to the local physiographic factors. observed where regional slopes are dominant.
As obtained from the satellite imagery of 26th January Sometimes, topographic features, which are elongated,
2006, the maximum width of the river is 266m (at 26057’ also favour development of such patterns.
16.54" N & 88024’ 48.85" E) while the minimum width is Stream Ordering
56m (at 26067’ 12.33" N & 88023’ 32.49" E). The river River system is made up of a mainstream and its
has a number of curves and that is due to the presence tributaries. The method or system by which streams
of convex ridges. Two sharp curves are observed at are classified into a hierarchy is known as Stream
the east of Lower Mamring and near Lower Kundong. Ordering. In this study, the stream ordering of Strahler
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3. International Research Journal ISSN-0975-3486 VOL. I * ISSUE—3 &4 RNI : RAJBIL/2009/30097
has been followed. 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
Stream Ordering 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
Fig 5 and slope failure. It causes soil erosion as well as slope
Table 1 Stream Orders and Their Respective Parameters
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4. International Research Journal ISSN-0975-3486 VOL. I * ISSUE—3&4 RNI : RAJBIL/2009/30097
deformation at the water shed area near free face slope 28.91sq.km (45.42%) of the basin falls under the
of the water divide. This portion of the basin is the category of 8 to 12 streams per sq. km. whereas only
most problematic part because of higher rate of soil 1.49 sq.km (2.34%) falls under the category of more
erosion and landslide and this area deserves more care than 16 streams per sq.km. High drainage frequency is
for better management. 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.
Drainage Texture Less impact of geological structure on drainage
The character and geometry of the drainage development is marked by the non-distortion of
network is generally evaluated in terms of drainage drainage pattern, which is an indication of
texture, which includes the drainage density and homogeneous lithological character of the basin. The
drainage frequency (Horton, 1945). development of different drainage frequency and
Drainage Frequency density zones of the basin area reflects the nature of
Drainage or channel frequency is the total number variation of relief, soil, rocks with permeable or
of streams per unit area, calculated by the formula impermeable character, hill, slopes, structures, etc.
introduced by Horton (1945). The maximum area of
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