CHAPTER 4 MORPHOMETRICAL FEATURES OF CHITRAVATHI BASIN

Transcription

1 41 CHAPTER 4 MORPHOMETRICAL FEATURES OF CHITRAVATHI BASIN The importance of morphometric studies in general and drainage basin studies in particular is clearly expressed by Christopher Gerrard ( , PP 2-17) in the following words. The drainage basin morphometry of an area is important if an integrative approach to landform studies is to be undertaken. The drainage basin may be thought of as an open system in near steady state conditions, it is likely that the morphometry of a drainage basin will display a recognizable regularity from one neighboring basin to the next. 4.1 MORPHOMETRY The term morphometry was first defined as the numerical systematisation of the forms of the land relief as it can be interpreted from a topographic map. In the words of Clarke (1967) morphometry is the measurement and mathematical analysis of configuration of earth s surface and of the shape and dimensions of its landforms. The main aspects examined are the area, altitude, volume, slope, profile and texture of the landforms as well as the varied characteristics of rivers and drainage basins. Morphometry is not a new concept but its aims and methods have been evolved and modernized in the recent times phase of evolution, morphometric analysis has mainly concentrated on a detailed and intensive analysis of small morphometric analysis units in general and drainage basins in particular. The present study area being a physical unit i.e., a river basin, is well suited to analyse the morphometric aspects. Routine analysis of morphometrical aspects does not serve any purpose and it is to be attempted with a clear objective. This fact is quite explicitly stated by Clarke (1967) in the following words when the quantitative information in the form of statistical dimensionless analysis is derived correctly on proper objective basis, the

2 42 morphometric methods can be a good substitute for the quantities statements by having their meaning in terms of geological history, structure and lithology Drainage basin analysis Middle Ages spanning through seventeenth, eighteenth and even early part of the nineteenth centuries, catastrophism flourished and the landscape created by streams were generally viewed as the result of some severe events. But measurement and quantitative expression of the drainage basin characteristics perhaps began with the ideas of James Hutton, whose Law of Accordant Tributary Junctions was expressed by John Playfair in 1802 in the following words. Every river appears to consist of a main trunk, fed from a variety of branches, each running in a valley proportional to its size and all of them together forming a system of valleys having such a nice adjustment of their declivities, that none of them joins the principal valley, either on too high or too low level; a circumstance which would be infinitely impossible, if each of these valleys were not the work of the stream that flows in it. Subsequently significant developments took place in the practical fluvial hydraulics and in the theory of sediment transport by presenting the concept of a base level of erosion. Subsequently others like Schumm (1956), Strahler (1964) and Chorley (1967) perceived the quantitative expression of drainage basin with varied degree of stress on different elements of drainage basin Methods of stream ordering As the area, and scale of the basins are significant in relation to form characteristics as well as in relation to processes, there has been a search for a method of classifying drainage basins according to their size. This is usually based on stream network. Various methods have been devised for sequential arrangement of tributaries with respect to the main stream. But Strahler (1964, PP 914) has pointed out that

3 43 practical utility is the criterion by which the success of the stream ordering techniques must be judged. Horton (1945) introduced a method of stream ordering based upon, but not the same as, the system of Gravelius (1914, PP 1-3). Hortons method was later modified by Strahler (1964). Gravelius first identified the order-1 stream by tracing it from outlet to source, and at every bifurcation, following the branch assumed to have the greatest width, discharge, head ward branching or junction angle. This process was repeated for each stream which is directly tributary to order-1. Such tributary streams are designated as order-2 streams. The exercise is repeated until the most remote finger tip tributaries are ordered. The main disadvantages of this scheme are (i) the subjective decisions which have to be taken at each bifurcation and (ii) the stream order number is not symmetrically related to the magnitude of a given segment of link. According to Horton (1945, P 281), the main stream should be of the highest order. He defined the first order stream as one receiving no tributaries. A second order stream is formed by the junction of two first order streams, and can receive other first order tributaries. A third order stream is formed by the junction of two second and first order tributaries. Horton s scheme of stream ordering suffers from certain drawbacks. An element of subjectivity exists in the head ward reclassification at bifurcations. Some unbranched finger tip tributaries have order greater than one and that not all the streams of the same magnitude have the same order. Strahler modified Horton s system by allowing his provisional scheme to determine the final ordering so that finger tip channels are designated order-1. Where two first order channels join a channel segment of order-2 is formed. Where two channel segments of order-2 join a segment of order-3 is formed and so on.

4 44 Strahler s scheme thus avoids the subjective decisions inherent in the Horton s system. Here all the finger tip tributaries are of order-1. Only one stream segment in the basin will have the highest order, and similar orders have more or less similar geometrical magnitudes. Unlike the Horton s scheme, the Strahler scheme is purely topological, referring only to interconnection and not to lengths, shapes or orientations of the links comprising the network. A serious drawback of the Strahler system of ordering is, its violation of the distributive law by not permitting the junction of lower order segments to change the order of the main stream. Horton s laws of drainage composition Analysing the morphometric properties of the ordered stream segments, Horton derived relationships between order and number of stream segments of a given order. Others following Hortons derived statistical relations of area, relief and slope with order. These are often referred to as Horton s Laws of Drainage Composition shown in Table 4.1. In addition to these laws Horton suggested the concept of drainage density as a measure dissection. Table 4.1 Laws of drainage composition Law Mathematical Expression Source Stream Numbers Nu=Rb s-u Horton (1945) Stream lengths Total stream Lengths Basin Areas Stream Gradients Basin Relief Lu=L 1 RL u-1 Horton (1945) L u =L 1 Rb s-u RL u-1 Horton (1945) Au=A 1 Ra u-1 Schumm (1956) Su=S 1 Rs s-u Morisowa(1956) Hu= H 1 RR u-1 Morisowa(1962) Average fall Yu/Yu+1=Yu+1/Yu+2=Yu + 2/Yu + 3..=1 Yang(1976)

5 45 where Rb = Bifurcation Ratio, Nu = Number of Streams of a given order u, Lu = Average length of the stream of order u, L u = Sum of stream lengths of all streams of order u, Au = Average area of the basin of order u, Su = Average slope of streams of order u, Hu = Average relief of basins of order u, RL = Stream Length Ratio, Ra = Area ratio, RR = Basin/relief ratio; Yu = fall of a segment of order u and Rs=Slope ratio. 4.2 METHODOLOGY The morphometric analysis of the Chitravathi basin is carried out using Survey of India toposheets on scale of 1:2,50,000. As the method suggested by Strahler is comprehensive and convenient, it is employed in the present analysis. According to Strahler (1964, PP ) systematic description of the geometry of drainage basin and its stream channel system requires measurement of linear aspects of the drainage basin and relief (gradient) aspects of the channel network contributing ground slopes. The first two categories of measurement are planimetric, the third category treats the vertical irregularities of the drainage basin forms. The basin is divided into 10 sub basins. The network is ordered as per the Strahlers system in which the order of the segment (u), number of segments in each order (Nu), total length segments (L u ), average length of segments in each order (Lu) and stream length ratios (RL)are calculated on the basis of the number of streams of different orders. The bifurcation ratios (Rb) and means bifurcation ratios are calculated and an attempt is made to test the agreement of the drainage system of the basin with some of the Horton s laws of drainage composition. The morphometric parameters are analysed selectively keeping in mind their relevance in the overall scheme of the study. More emphasis is laid on the relief and gradient aspects, which are studied

6 46 through Relief and Gradient ratios, profiles and methods of average slope analysis. The shape aspects of the basin are also analysed Bifurcation ratios (Rb) Bifurcation Ratio (Rb) is a ratio of the number of streams of any given order (N u ) to the number in the next higher order (N u+1 ). For a drainage basin of Nth order there will be N-1number of bifurcation ratios. For each basin, single bifurcation ratio (Rb) is obtained as the simple arithmetic mean of the Rbs of the different orders of the basin. Bifurcation ratios characteristically range between 3.0 and 5.0 for watersheds in which the geologic structures do not distort the drainage pattern. The theoretical minimum possible value is 2.0. and it is rarely approached under natural conditions. But the higher order bifurcations usually approach this value. For instance in a drainage basin of 5 th order Rb 4 is the highest and Rb 4, sometimes approaches the theoretical minimum value of 2.0. Because the bifurcation ratio is a dimensionless property, and because drainage systems in homogenous materials tend to display geometrical similarity, it is not surprising that the ratio shows only a small variation from region to region. Abnormally high bifurcation ratios might be expected in regions of steeply dipping rock strata where narrow strike valleys are confined between hogback ridges or other structurally controlled linear basins.the drainage map of Chitravathi basin is shown in figure 4.1. The Chitravathi basin is a 6 th order basin with the total stream segments of 922 and a mean bifurcation ratio of 3.87 shown in table 4.2, which on the whole indicates the unimportant role played by the geological structure in the development of the drainage system. But the different Rbs of the basin range from a minimum of 2.0

7 47 (Rb 5 ) to 4.56 (Rb 3 ) indicating regional variations in the lithological, structural and morphological characteristics of the basin. Fig 4.1 Drainage map of Chitravathi basin

8 48 Table 4.2 Stream segments and bifurcation ratios Stream segments in different orders Bifurcation Ratios Mean Sub basin Total N No. 1 N 2 N 3 N 4 N 5 N 6 Rb 1 Rb 2 Rb 3 Rb 4 Rb 5 bifuraction NU ratio Rb (5+6) Total basin

9 49 Bifurcation ratios at sub-basin level At sub-basin level the Rbs range from a low of 3.19 in Middle chitravathi (Right) sub-basin to a high of 7.88 in Nagasamudram Vanka. It indicates that at sub basin level the development of the drainage network is influenced by the heterogeneity in geological structure and morphology. The upper Chitravathi is a 4 th order sub-basin with mean Rb of The bifurcation ratios of different orders range from 3.37 (Rb 1 ) to 7.0 (Rb 3 ). Vangaperu is a fifth order basin with a mean bifurcation ratio of 3.23 and at different orders it ranges from 2 (Rb 4 ) to 4.23 (Rb 1 ). Nagasamudram Vanka is a third order basin with moderately high mean bifurcation Ratio of 7.88, which is mainly due to high Rb 2 value (12.0). Paleteru is a fourth order basin with mean Rb of But the Rb 2 value of the sub-basin is a little above normal at Maddileru is a fifth order basin with a mean Rb of 3.43 and the Rbs range from a theoretical minimum of 2.0 (Rb 4 ) to a maximum value of 4.35 (Rb 1 ). Jilledubanderu is a fourth order basin with a mean Rb of 4.69 and the Rbs range from 2 (Rb 3 ) to 6.55 (Rb 1 ). The analysis is not carried out for the middle and lower Chitravathi basins as these basins consists of several small streams which are direct tributaries to the Chitravathi and not components of single tributary system. The above analysis indicates that there is not much distortion of the drainage network in sub basins like Vangaperu, Paleteru, and Maddileru. The Upper Chitravathi, Nagasamudram Vanka and Jilledubanderu show some drainage distortions as revealed by abnormal Rb values at different orders Mean segment lengths and stream length ratios The mean length (L u ) of a stream channel segment of order u is a dimensional property and reveals the characteristics of components of drainage network and its

10 50 contributing basin surface. Usually the mean length of channel segments of a given order is greater than that of the next lower order, but less than that of the next higher order. Horton postulated that the length ratio RL, which is the ratio of mean length L u of segments of order u to mean length of segments of the next lower order L u-1, tends to be constant throughout the successive orders of a watershed. According to the law of the stream lengths the mean length of the stream segments of each of the successive orders of a basin tend to approximate a direct geometric sequence in which the first term is the average length of segments of the first order. The stream lengths were obtained based on the toposheets. Total stream lengths and ratios of total lengths in Chitravathi basin are shown in table 4.3. Table 4.3 Total stream lengths and ratios of total lengths in Chitravathi basin Total stream lengths in each order (km) Total stream length Ratios (RL) Sub basin No L 1 L 2 L 3 L 4 L 5 L 6 L u L 1 /L 2 L 2 /L 3 L 3 /L 4 L 4 /L 5 L 5 /L Total basin The total length of the stream segments in the Chitravathi is 2534 km of which the first order streams account for 1373 km with the remaining successive higher order

11 51 having total segment lengths of 575 km, 315km,167 km, 48 km and 56km. In general the sum of the segment lengths decreases with the increasing orders but at sub-basin levels though there is a decrease in length from the first order to second order, at higher orders in some cases like Upper chitravathi, Paleteru and Lower maddileru the total length of fourth order stream is more than the length of third order streams. Mean segment lengths and their ratios are shown in Table 4.4. Table 4.4 Mean segments and their ratios in Chitravathi basin Mean segment Lengths in different orders (km) Sub basin No L 1 L 2 L 3 L 4 L 5 L 6 Mean length Ratios of different orders Mean L u / N RL 1 L 2 /L 1 RL 2 L 3 /L 2 RL 3 L 4 /L RL 4 L 5 /L Total basin RL 5 L 6 /L The mean segment length for the basin as a whole is 2.7 km, which varies from a minimum of 2.0 km for the first order to 56 km for the sixth order. At sub-basin level the overall mean segment length varies from a minimum of 2.1 km in Vangaperu to a maximum of 3.6 km in Maddileru. It is noticed that the mean segment length is lower

12 52 in the sub basins having steeper topography and is comparatively higher in the subbasins with relatively plain topography. The stream length ratios between the mean segment lengths varies from a minimum of 1.29 (RL 4 ) to a maximum of 2.42 (RL 3 ) for the Chitravathi basin as a whole. The values are not in agreement with the law of stream lengths which states that the ratio is constant between mean lengths of different orders. Though in sub basins like upper Chitravathi, Vangaperu and Maddileru the law of stream length holds good to some extent in case of the lower orders, the values are not in agreement with the law in the case of higher orders. The ratios are not at all in agreement with the law in other sub-basins like Nagasamudram Vanka and Jilledubanderu where the ratios differ substantially. This clearly indicates that the law is not holding good either at the micro level or at the macro-level in the Chitravathi basin Degree of dissection To analyse the degree of dissection in basin indices like Drainage density, Drainage frequency and Drainage texture are used. Drainage Frequency (f) = N u /A Drainage Density (d) = L u /A Drainage Texture = f x d Where N u = Total Number of stream segments L u = Total length of stream segments A = Area.

13 53 The Chitravathi basin has a drainage density of 0.48 km/km 2 and a drainage frequency of 0.18 per km 2. The drainage texture is only 0.09 which is a very low value. These values are shown in Table 4.5. Sub basin No Area (km 2 ) A Talbe 4.5 Dissection indices of Chitravathi basin Total Length of the Stream Segments Lu in (km) Total No. of Stream Segments ( Nu) Drainage density d= Lu/A Drainage frequency f= Nu/A Drainage texture d x f Total basin The drainage density varies from 0.36 km/ km 2 in the upper Maddileru basin to a maximum of 0.67 in Paleteru. The drainage frequency varies from 0.10 in Upper Maddileru to 0.27 in the Vangaperu sub basin. Vangaperu, Nagasamudram Vanka, Paleteru, Jilledubanderu and Middle Chitravathi (Right) sub basins are having comparatively high drainage frequency. The drainage texture is relatively high in

14 54 Vangaperu, Nagasamudram Vanka, Paleteru, jilledubanderu and Middle Chitravathi (Right) indicating higher degree of dissection. But the indices as such independently viewed convey a picture of highly sub-dude relief a characteristic of old stage of geomorphic cycle. 4.3 SHAPE ASPECTS OF THE BASIN The shape or outline form of drainage basin, as it is projected upon the horizontal datum plane of a map, may affect stream discharge characteristics. Long narrow basins with high bifurcation ratios would have attenuated flood discharge periods, whereas round basins of low bifurcation would have sharply peaked flood discharges. For studying the geometry of different special shapes many shape index formulae have been derived by different researchers by employing shape parameters like area (A), Perimeter (P), Longest axis (L), radius of inscribing Circle and radius of the smallest circumscribing Circle (R). The shape indices are manipulated in such a way that they give a value of 1.0 for circle. Horton s Form Factor (1932), reciprocal of Form Factor used by U.S. Army of Corps of Engineers (1949, 54), Compactness Factor of Gravelius (1914), Elongation Ratio of Schumm (1956), Circularity Ratio of Miller (1953) are some of the indices particularly useful to study the shapes of drainage basins. The inappropriateness of a circle as the standard figure of reference on comparison with the pear shaped drainage basin, which has sharply defined point at the mouth, Chorley used the Lemniscate function (K) as a model, which is a ratio between the perimeter of the lemniscate and the actual perimeter of the basin, to study the drainage basin shapes. In the present study Schumm s Elongation Ratio Re, defined as the ratio of diameter of a circle of the same area as the basin to the maximum basin length,

15 55 Miller s Circularity Ratio (Rc), defined as the ratio of basin area to the area of the circle, having the same perimeter as the basin, and Chorley Lemniscate function are used to analyse the shape of the basin. Elongation Ratio (Re) =1.13 A/L Circulatory ratio (Rc) = 4 A/P 2 Lemniscate function (K) = L 2 /4 A Where, A = Area of the Basin; L = Longest axis of the basin from the mouth; P = Perimeter of the basin. Shape indices of standard shapes are shown in table 4.6. Table 4.6 Shape indices of standard shapes Standard S. geometrical No shape Shape parameters Shape indices Area Perimeter (A) (P) (km 2 ) (km) Longest Circularity Elongation Axis (L) Ration Ratio (Re) (km) (Rc) 1 Triangle Square Hexagon Circle Lemniscate function (k) The Chitravathi basin is almost a pear shaped basin with a narrow elongated lower part. The distance along the longest axis of the basin is 119 km and the width at the widest part is 74 km. The ratio between the width and length is 1:1.6, and it indicates the relatively compactness of the basin. The shape indices of the basin are shown in table 4.7.

16 56 Table 4.7 Shape indices of Chitravathi basin Sub Shape Shape indices basin Area Perimeter Longest Circularity Elongation Lemniscate No (km 2 ) (km) axis(km) ratio (Rc) ratio (Re) function (k) Total basin The shape indices indicate that the Chitravathi basin has got a moderately efficient shape. The basin circularity ratio of Miller (0.41) indicated that the shape of the basin is elongated. The elongation ratio of Schumm (0.7) shows that the shape is moderately efficient when compared with the circle. Of these three indices selected for the present study elongation ratio gives relatively high values for the less efficient shapes. For instance for the equilateral triangle elongation ratio is 0.74 where as the circularity ratio is 0.6. The K values are least for the circle (0.31), 1.0 for Lemniscate shape and greater than 1.0 for the elongated shapes. Among the sub basins Nagasamudram Vanka sub basin is the least efficient (Rc=0.31, Re=0.42, K = 1.84) or it is the most elongated shape and so it will have attenuated discharge of runoff. The lower Chitravathi has comparatively more

17 57 compact and efficient shape when compared to circle. The K values show that the Paleteru sub basin (k=0.94) and lower Maddileru sub basin (k=0.98) and Middle Chitravathi (Right) (k=0.98) are almost pear shaped basins. It may be inferred that the Paleteru and lower Maddileru and Middle Chitravathi (Right)sub basins will have concentrated peak run off with their pear shaped shapes. 4.4 RELIEF OF THE BASIN Relief is a qualitative description of the amount of change in elevation per unit distance. It is the difference between the highest point and the lowest point in elevations on a map. Low relief means little change in elevation with change in position, high relief means lot of change in elevation with change in position. The relief aspects of the basin are studied through (i) Relief map (ii) Relief ratios (iii) Stream gradients and slope analysis Relief map The elevation of the Chitravathi basin above msl varies from 197 m at the confluence of Chitravathi with Pennar River to a maximum of 960 m in the Mallappakonda hills of the upper Chitravathi with an overall relative relief of 763 m. But 85 per cent of the area lies between 300 m and 700 m with an affective relative relief of 400 m. Table 4.8 shows basin area in different relief categories. In Chitravathi basin the area above 700 m is a mere 4.3 percent while the area below 300 m is 9.1 per cent. The highest area of 1359 km 2 lies in m relief zone, which forms about 25.3 per cent of the total area.

18 58 Table 4.8 Subbasin wise area indifferent relief zones Sub basin name Relief categories <200m m m m m m >700m Area(km 2 ) Total basin Area Upper Chitravathi (14.8) 75(9.8) 400(52.4) 175(23) 763 Vangaperu (4.2) 169(37.1) 137(30) 131(28.7) 456 Nagasamudram Vanka (33.5) 125(47.5) 34(12.9) 16(6.1) Paleteru (26.1) 209(51.5) 66(16.3) 25(6.1) Upper Maddileru (3.5) 375(42.9) 413(47.2) 56(6.4) 875 Lower Maddileru (24.4) 119(22.1) 251(46.6) 37(6.9) Jilledubanderu (17.1) 194(44.3) 81(18.5) 88(20.1) Middle Chitravathi (Right) (55.8) 125(33.9) 22(6) 16(4.3) Middle Chitravathi (Left) - 38(7.7) 437(88.5) 19(3.8) Lower chitravathi 16(2.1) 437(56.9) 297(38.5) 19(2.5) Note:Figures in brackets are percentages to total area

19 59 Areas under different relief categories are shown in figure 4.2. Fig 4.2 Relief zones of Chitravathi basin

20 60 A look at the relief map reveals that the m relief zone is markedly narrow on the left side of the basin particularly in sub-basins of Upper chitravathi and Nagasamudram vanka. But on the right side of the basin covering the sub basins of Maddileru the m relief zone is comparatively wider than the relief zones on either side. In Maddileru which is the largest of the tributaries and covers about onethird of the total basin area 44.3 percent of the area is in m relief zone. The middle chitravathi (Left) basin is a nearly monotonous plain with 88.5 percent of the area having less than 100m of relative relief and lies in the relief zone of m. On the whole and the table 4.8 reveals that in all the sub basins the available relief is very low. In lower chitravathi mostly covered by Cuddapah and Kurnool formations the relative relief is only 263m Relief ratios It is a non dimensional index and is the ratio between the relative relief and the longest axis (L) of the basin. This index gives a fair picture of the terrain characteristics of a region. Table 4.9 reveals that the Chitravathi basin as a whole is having a relief ratio of which is very low value associated with old stage of geomorphic cycle. Stated otherwise the fall in height is only 6m per km.

21 61 Table 4.9 Relief ratios Sub basin No Longest axis in km Maximum height of the basin(m) (H) Minimum height of the basin(m) (h) Relative relief R=H-h (m) Relief ratio R/L Total basin At the sub basin level the relief ratio varies from a minimum of in Middle Chitravathi (Left) sub basin to a maximum of in Jilledubanderu sub basin. Middle chitravathi (Right), Lower Maddileru and Upper Chitravathi are other sub basins with relatively high values. But in general all the sub basins depict a low relief Stream gradients The stream gradient is another index used for analysing the terrain characteristics. It is the average fall in the height along the stream course per unit distance. The gradient ratio is a non dimensional index analyzing the slope element of the terrain.the gradients and gradient ratios for a Chitravathi main stream and the important tributaries like Vangaperu, Nagasamudram vanka, Paleteru, Maddileru and Jilledubanderu are shown in Table 4.10.

22 62 Sub basin name Table 4.10 Average gradient of important streams Height at stream source H 0 (m) Height at stream mouth H e (m) Fall in height (H 0 -H e ) Stream length L(km) Average gradient (m/km) Gradient Ratio Vangaperu Nagasamudram vanka Paleteru Maddileru Jilledubanderu Chitravathi The fall in height for the entire 160 km course length of Chitravathi river is only 500m with an average gradient of 3.1m/km. Such a low gradient is the proof of stream in old age. For the tributary streams the gradient ranges from 4.5m/km for Maddileru to 8.4m/km for Nagasamudram vanka. Jilledubanderu (8.0 m/km) and Vangaperu (7.3m/km) are other streams with comparatively high gradients. The gradient ratio is for the Chitravathi river and it varies from for Maddileru to for Nagasamudram vanka. For Chitravathi main stream at different points stream lengths and the corresponding elevations are determined and tabulated in table Table 4.11 Elevation of the stream at different points S.No Stream Elevation Stream S.No length L(km) (m) length L(km) Height(m) 1 Beginning

23 63 A graph is plotted between stream length (km) and elevation (m) for entair Chitravathi river as shown in graph 4.1. Graph 4.1 Elevation Vs Length of Chitravathi river 4.5 SLOPE DISTRIBUTION The average slope of the drainage basin is determined as per the following procedure. The horizontal equivalents are calculated for the predetermined slope values of 2 0, 5 0 and 10 0 as per the scale of the map. By matching the horizontal equivalents with the distance between two contours the slope categories are determined and adjacent similar slope categories are clubbed together viz., (i) 2 0 (ii) (iii) and (iv) 10 0 as shown in figure 4.3.

24 64 Fig 4.3 Slope map of Chitravathi basin

25 65 Sub basin wise areas in different slope categories are measured and tabulated in table A look at the slope map and table 4.12 reveals that the Chitravathi basin has very gentle slopes. Of the 5371 km 2 of the total Chitravathi basin area as much as 89 percent (4781 km 2 ) is having less than that 2 0 of slope. Only 4.6 percent of the area is having over10 0 slope. Table 4.12 Areas in km 2 in different slope categories Sub basin No Slope categories < >10 0 Total sub basin area (km 2 ) (86.8) 22 (2.9) 59 (7.7) 20 (2.6) (93.4) 27 (5.9) - 3 (0.7) (95.8) 8 (3.0) 3 (1.2) (96.6) 6 (1.5) 6 (1.5) 2 (0.5) (86.2) 30 (3.4) 31 (3.5) 60 (6.9) (91.3) 8 (1.5) 14 (2.6) 25 (4.6) (82.0) 19 (4.3) 7 (1.6) 53 (12.1) (66.9) 25 (6.8) 17 (4.6) 80 (21.7) (99.8) 1 (0.2) (91.7) 48 (6.2) 11 (1.4) 5 (0.7) 769 Total 4781 (89.0) 194 (3.6) 148 (2.8) 248 (4.6) 5371 Figures in brackets are percentages to sub basin areas. At sub basin level in all the sub basins except Jilledubanderu & Middle Chitravathi (Right) sub basin over 85 percent of the area is having less than 2 0 of slope. In Jilledubanderu also 82 percent of the area is having less than 2 0 of slope. The only exception is Middle Chitravathi (Right) sub basin in which also 66.9 percent of the area is in less than 2 0 slope category but the peculiarity is that 21.7 percent of the area is having more than 10 0 of slope. The sub basins with substantial areas with steep slopes are Jilledubanderu with 12.1 percent of the area and Upper Maddileru

26 66 with 6.9 percent of the area. In some of the sub basins like Vangaperu, Nagasamudram vanka and Paleteru nearly 95 percent of the area and in Middle Chitravathi (Left) sub basin 99.8 percent of the area is having less than 2 0 slopes. 4.6 SUMMARY The morphometric analysis of the basin is carried out using the scheme suggested by Strahler. The basin is divided into 10 sub basins and the analysis is done at sub basin level. The Chitravathi basin is a 6 th order basin with a mean bifurcation ratio of 3.87 indictating uniformity in the geological controls on the development of drainage but regional variations are noticed at the sub basin level. The stream length ratios are not in agreement with the law of stream lengths. The drainage density, drainage frequency and texture ratio indicate a low degree of dissection. The shape indices indicate that the basin has moderately efficient shape. But some sub basins like Nagasamudram Vanka have elongated shapes. The relief ratio and gradient of streams indicate that the Chitravathi basin is in the old stage of the geomorphic cycle. From the slope analysis it is inferred that more than 85 per cent of the area is suitable for agricultural purposes as the slope is less than 2 0.