QUANTITATIVE GEOMORPHOLOGY OF THE DRAINAGE BASIN IN SEMI-ARID ENVIRONMENT

Transcription

1 I" QUANTITATIVE GEOMORPHOLOGY OF THE DRAINAGE BASIN IN SEMI-ARID ENVIRONMENT BIMAL GROSE, S. PANDEY AND S SINGH Gentral Arid Zone Research Institute, Jodhpur INTRODUCTION In India Ghose et al (963, 967) have studied the geomorphic characteristics of drainage channels in the Luni Basin in the arid land of Rajasthan. In the present paper an attempt has been made to study the geomorphic cbaracteristics'of streams in 2 randomly selected drainage basins situated in semi-arid environment near Sumerpur (Fig. -2). The region under study comprises an area of 948 sq.km. ' and is situated in between latitudes 25 5' to 25 35' N and longitudes 72 55' to 73 20' E. Thornthwaite moisture index of the region is -36. The average annual rainfall is 500 mm. The mean maximum temperature is 38 C in May and the mean minimum temperature is 9 C in January. The rocks of the region are the Aravalli phyllite, schist and quartzite and Erinpura granite. The Aravallis are folded while the granite has domal format~ons. The Jawai is the main river which flows from east to west. The Ungti Nadi a tributary of tbe Jawai is also important as most of the channels coming from the hills of the region drain their water in it. The Jawai originates from the Sirohi section of AravaUi mountain. The river is ephemeral in nature. MATERIALS AND METHODS For quantitative study of the geomorphic characteristics and their interrelationship of streams in the drainage basins, aerial photographs on the scales of : 3,000 and : 25, 000 have been used. A key map on scale of : 63, 360 showing the streams and drainage basins was prepared by the photogrammetric method described by Ghose and Singh (966). This key map was further reduced to a scale of : 26, 720. The map, thus, prepared was checked by the field surveys. In this paper the streams have been ordered after Strahler's (952. p. 20) adaptation of the Horton's (945. p. 28) scheme of classification. The order number of the basins. number of streams, total and mean stream lengths, longest length of stream, total and mean basin areas, relief ratios, maximum pasin length, constant channel maintenance, drainage density, stream frequency and frequency of first order segment to total basin area have been calculated. The Jog values of the number of streams, mean stream length, total stream length and

2 GEOMORPHOLOGY OF THE DRAINAGE BASINS IN SEMI-ARID ENVIRONMBNT 37 A N f N - fig. I. BASIN NO. I I Z 3 4 5K FIG.Z. ~ASIN NOZ... o I KM. FIG. 3. BASIN NO. I.". o I KM. N 'N {fi;j FIG.4. BASIN.NO '.,0 I KM FIG. 5 BASIN NOS..... o I' KM. FIG. 6. BASIN NO.6... o I KM. N " N f ~ '!G.T tasin NO 7. ~ I KM. "IG.B. BASIN NO.9... o I KM FIG 9. BASIN NO 9 (, ; KM

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4 38 BIMAL GHOSE, S. PANDEY AND S. SINGH basin area have been plotted against each order and the regression lines have been fitted by least square method. The bifurcation ratios, streams length ratios and basin area ratios for each basin have also been calculated. RESULTS AND DISCUSSION (a) Geomorphic characteri,tic8 0/ streams in drainage basins- The quantitative characteristics of the streams for all the selected drainage basins under study have been given in the following table. Their salient features have also been described in detail. Table. Average geomorphic characteristics in three groups of lithologies Geomorphic characteris tics Number of streams Total stream length (kml Mean stream length (km) Largest length of the stream (km) Stream gradient Relief ratio Ma~imum basin length (km) Constant channel maintenance (sq. km) Drainage density (km per sq. km) Stream frequency Basin order Basin area (sq, km) Mean basin area (sq. km) Frequency of first order segment to total basin area Erinp.ura gradlte : ] ] I PhylIite:-schist -quartzite : ] Sandy older alluvium : ( i) Number of streams - The average number of streams in basins of granite is 22 whereas in the basins of phyliite-schist-quartzite and sandy older alluvium these are 2 and 8 respectively. It is obvious that the number of streams is dependant on the type of lithology. ( ii) Total, mean and longest length 0/ the.~tream8 - The average figures for the total stream lengths of the basins in granite, phyjiite-schist quartizite and sandy older alluvium are 24.78, and 6.09 km respectively. As in the granite there are larger number of streams along the joints and fissures than in phyllite-schistquartzite and sandy older alluvium, the total lengths of streams are more than

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8 GEOMORPHOLOGY OF TH B DRAINAGE BASINS IN SBMI-ARID ENVIRONMENT 4 j 'i"o I- ~I S (oj...j L /-0 -< ~ 0 5 '"...J 0 ~ o l- Cl 9 FIG. IS. Loe; 2 J ORDER TOTAL STREAM LENGTH PLOTTEO 7 a AGAINST 9 OR DEft ~,~ ~_~ 0 5 o t OaDER 6 7 ~~I ~ 0::.J 9 0 II 2 I FIG. 6. LOG BASIN AREA PLOTTED AGAINST ORDER? o () &4 & ~'88 ~.9;.95 ;"3 ~ 5 FIG.I? BASIN AREA RATIO (Rb) ~2 5 I- -< "'2 0 ~ 5 a: -<, 0 z ~0'5 '" o FIG. 8. BIFURCATION RATIO (lib)

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11 BIMAL GHOSE, S. PANDEY AND s. SINOH 4. The bifurcation ratios in three groups of lithologies vary from each other. The values in the basins in granite, phyllite-schist-quartzite and saudy older alluvium are 4.50 to 9.83, 4.33 to 9.66 and 4.50 respectively. 5. The relationship exist between bifurcation ratios and basin area ratios and also between basin area ratios and stream length ratios but there is no significant correlation between bifurcation ratios and stream length ratios. The correlation coefficient values for first two types of relationship are and respectively at 5% level. 6. The average values of basin order, basin area. number of streams, total stream length, relief ratio and contant of channel maintenance are varying in three groups of lithologies. The values are higher in granite followed by phyllite-schist-quartzite and sandy older alluvium. The values of mean basin area, mean stream length, longest length of the stream and maximum basin area are larger in sandy older alluvium while the values of drainage density, stream frequency and frequency of first order to total basin area are higher in phyllite schi st-quartzite. ACKNOWLEDGEMENT Authors are grateful to the Director and Head of the Divi~ion of Basic Resource Studies for providing facilities and valuable suggestions during the c9urse of study. Thanks are also due to Shri M. B. Jain, Statistician for necessary advice. REFERENCES Coates, Donald R Quantitative geomorphology of small drainage basins of Southern Indiana. Tech.. Rep. 0. Office of Naval Reaearch, Dept. Geol. Oolumbia University, New York. Chose, B. and Pandey, S Quantitative geomorphology of drainage basin. J. Ind. Soc. Soil. Sci. : Ghose, B., Pandey, S., Singh, S. and Ghees Lal Quantitative geomorphology of the drainage basins in the Central Luni basin in Western Rajasthan. Zeit. fur Geomorph. : 46-60, Ghose, B. and Singh, S Quick method of aerial photogrammetric mapping of geomorphic features, soils and vegetation community. Ind. J. Geog. : Horton, R. E Erosional development of streams and their drainage basins; hydro-physical approach to quantitative morphology. Geol. Soc. America Bull. 56 : Maxwell, J. C. 955; The bifurcation ratio in Horton's law of stream numbers (Abstract). Am. Geophys. Union Trans. 36 : 520. Strahler, A. N Hypsometric (area altitude) analysis of erosional topography. Geol. Soc. America Bull. 63: 7-42.