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

International Research Journal      ISSN-0975-3486       VOL. I * ISSUE—3&4          RNI : RAJBIL/2009/30097
International Research Journal   ISSN-0975-3486      VOL. I * ISSUE—3 &4       RNI : RAJBIL/2009/30097
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International Research Journal         ISSN-0975-3486         VOL. I * ISSUE—3&4           RNI : RAJBIL/2009/30097
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  1. 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 8
  2. 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 çÚUâ¿ü °ÙæçÜçââ °‡ÇU §ßñËØé°àæÙ 9
  3. 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 10
  4. 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 (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 (2.34%) falls under the category of more erosion and landslide and this area deserves more care than 16 streams per 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 (40.73%) falls under the category of 2.2-3.3 km per sq. km. High Drainage Density group includes 8.38 which is 13.17% of the Ryang Basin. Low Drainage Density group includes 1.48, 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 R E F E R E N C E · 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. çÚUâ¿ü °ÙæçÜçââ °‡ÇU §ßñËØé°àæÙ 11