DRAINAGE BASIN MORPHOLOGY. Morphometric analysis is defined as the numerical

Transcription

1 C H A P T E R 3 DRAINAGE BASIN MORPHOLOGY 3.1 Introduction Morphometric analysis is defined as the numerical systematization of landform elements measured from topographic maps and provides real basis of quantitative Geomorphology {Pal,1972). The major aspects examined are the area,relief,slope,profile and texture of the land as well as the varied characteristics of rivers and drainage basin {Clarke, 1966). For the Ghataprabha basin, the morphometric analysis has been undertaken by employing various methods used in the quantitative and qualitative analysis of landforms with the help of toposheet maps (Scale 1:50,000 and 1:250,000). These studies offer a clue to the interpretation of evolution of the landforms and their development through the ages. Such studies have relevance in prehistoric investigations as they help in the reconstruction of terrain types which were of significance to prehistoric communities and thereby for understanding the man-land relationships during prehistoric times. 3.2 Relief Morphology As the important aspects of landforms, relief and slope offer a clue to the interpretation of the evolution of landforms and their development. Normally, both the aspects are cumulative effects of several factors acting with different intensities at varying periods. Both these morphological aspects seem to be interdependent. Spatially, the parameters express variation due to differences in lithology, structure, drainage and altitude in the basin.

2 3.2.1 Absolute Relief The spatial distribution of absolute relief in the Ghataprabha basin is asymmetric The elevation range is significant from west to east. The western part of the basin has an average altitude of more than 800 in while in the eastern part it ranges between m (Fig. 3.1). The areal distribution of Absolute relief is given in Table 3.1. Table 3.1 Percentage Distribution : Absolute Relief (Ar) Ar in m Percentage below & above The average altitude in the basin is m AMSL with a standard deviation of m which suggests that a large area lies below mean altitude. The correlation analysis shows good association between altitude on one side and morphological properties on the other. Individually the geomorphic variables reveal positive relationship (Table 3.2). Table 3.2 Relationship between Geomorphic Variable Relation of altitude with Correlation Relative relief 0.47 Dissection 0.46 Mean slope 0.47

3 GHATAPRABHA BASIN-ABSOLUTE RELIEF IN METERS BELOW loooctabove FIG;3-1 0 S )0KM 1--1 I

4 The correlation values suggest that altitude is an important factor, that has governed the georoorphic history of the basin Relative Relief Relative relief is the vertical extent of landscape feature, without reference to absolute relief or slope (Evans,1972). Relative relief represents the actual variation of altitudes in a unit area with respect to its local base level. It very well depicts the differences of altitude in a given area. It is closely associated with slopes and is more expressive in understanding morphogenesis. However, it does not take into account the dynamic potential of the terrain and feature of vertical distance from the erosion base. The frequency distribution of relative relief of the Ghataprabha basin has been computed in the grid of 0.4 sq kn) each, which exhibits a marked variation (Fig. 3.2). The basin area may be divided into five categories of relative relief as follows ; a) Extremely low (0-50 m) b) Low ( m) c) Moderate ( m) d) Moderately high ( m) e) High (above 400 m) These five categories are represented with the areal shares of 73.7%, 22.91%, 3.14%, 0.7% and 0.18% of the total basin area respectively (Table. 3.3). The extremely low, low and moderate relief are mainly confined to the eastern parts of the basin, whereas other categories are observed in the western parts.

5 FIG: and above re la tiv e r e l ie f in m e tre s GHATAPRABHA basin

6 Table Percentage Di.stri bution : Relative Relief (Rr) Rr in m Percentage Categories Extremely Low Low Moderate Moderately high above High Relative relief more than 100 m is common in the western hilly terrain of the basin (i.e. upper reaches) due to hills of high altitude and steep slopes. Regarding the present variation of the relative relief, especially over the rugged hilly tracts of the western parts of the basin, no regular or distinct patterns are found to have been evbvled. Few isolated parts have attained maximum values of relative relief (295,299,300 m) in the basin. On the other hand towards the east (mainly the middle and lower reaches), the area displays lower values of relative relief varying between 0 and 150 m representing low and moderate relief. Though, this area is almost plain, some parts have moderate relative relief due to the presence of isolated hill ranges. The development of such particular pattern of isolated higher range of relative relief is scattered in the central and eastern parts of the basin. The frequency distribution of relative relief of the basin (Table. 3.3) shows that the area of high relative relief represent the smallest area (0.18 %) and about 73 % of the total area has been occupied by low relative relief. Thus

7 the low relief as its rnaximura expansion over the basin indicating maturity of the basin. Fluvial processes, nature and structure of rocks are the two main agents which determine the nature of relief development. In the Ghataprabha basin, low relief is associated with mature drainage whereas high relief is found to be the characteristics of youthful drainage. However, the basic cause of contrast in relative relief seems to be the variation in lithological formations. As stated in the previous chapter, the study area is characterized by different geological formations such as Archaeans, Kaladgis,Deccan Traps, laterites etc. Relative relief more than 150 m is invariably associated with Deccan traps and laterites of the Western Ghats region and also with the patches of the Kaladgi quartzites and sandstones which are found in the western parts of the basin. On the other hand, the eastern and central area of the basin is occupied mainly by the Deccan Traps and Kaladgis formations. In this part harder formations of the Kaladgis like quartzites and sandstones are responsible for a few isolated patches of moderate relief (more than 100 m) in almost plain area. Also in the middle reaches of the basin due to the hard granite and granite gneisses a few parts show moderate relief. Thus selective weathering in the normal course of the denudation processes particularly in the zone of different geological formations have played a decisivfj role in the development of such variation of re 1«11vi=i 1it=!f.

8 3.2.3 Dissection Index As the relative relief does not consider the vertical distance from the erosion base, it is not useful for understanding the degree of erosion. Dissection, as an expression of the degree of erosion, is the ratio between the relative relief and absolute relief. It is an important parameter of drainage basin and useful in the study of '10 terrain and drainage basin dynamics as well as stage of basin development. -j-j^ In the Ghataprabha basin dissection displays spatial variation giving rise to five major categories of dissection (Table 3.4) (Fig 3.3). Table 3.4 Geomorphic Index for Dissection Dissection in % Category Stage of morphoevolution 0-5 Low Peniplain 5-20 Moderate Old age or youth Moderately high Late maturity High Maturity above 70 Very high Early maturity (Mukhopadhyay,1982).

9 GHATAPRABHA BASIN d issec tion INDEX IN PERCENTAGE ElllU 20-i'o Z.O g a b o v e P'lG; KM

10 These five categories of dissection share the total area of the Ghataprabha basin in decreasing order (Table. 3.5). The low and moderate dissection categories are mainly confined to middle and lower reaches while the high and very high dissection categories are restricted to upper reaches of 41 the basin. The varying degree of erosional potential, due to differences in aspects like lithology, slope, relative relief, vegetation growth and rainfall distribution is the main cause for the spatial variations of dissection in the basin. The dissection index in the basin ranges between 0 and 93. The average percentage of dissection in the Ghataprabha basin is 5.32 with standard deviation. Table 3.5 Percentage Distribution : Dissection Index Dissection Category Percentage to in % the total area 0-5 Low Moderate 15, Moderately high High 1.05 above 70 Very high 0.35

11 3.2.4 Hypsometric Analysis 42 Hypsometry is the measurement of the interrelationships of area and altitude. This concept of the area-height analysis of the drainage basin was first introduced by Horton (1945). Hypsometric curve relates the cross-sectional area of a drainage basin to relative height above the basin mouth (Strahler, 1952). It is an ogive or cumulative frequency curve which indicates the stage of georaorphic cycle of the basin and the proportion of the area of the surface at various elevations. The hypsometric integral is the This indicator of the stage of development of the basin. integral is large in youthful stage and decreases as the landscape is denuded towards maturity or old stage. The hypsometric integral for the Ghataprabha basin is 62.36% which indicates that the landform is in the stage of maturity (Fig.3.4). According to Strahler (1952), hypsometric integral above 60% indicates an early stage of inequilibrium of landscape development. It jnay be called as sub-maturity stage with extensive divide areas as yet not entirely transformed into the stage of maturity (Strahler,1952). The comparison between hypsometric analysis and other morpheme trie parameters shows^ that the high integral associated with low relative relief, gentle slopes, is low dissection,low stream gradient and low drainage density. All these parameters indicate the mature stage of landform development in the study area.

12 1-0 -p- HYPSOMETRIC GHATAPRABHA CURVE BASIN

13 3.2.5 Altimetric FrequencF Analysis 4 3 Altiraetric frequency analysis is based on the geomorphic principle that hilltops offer the last refuge for vanishing relief (Miller,1953). The aim of this analysis is to demonstrate the existence of erosional surfaces or levels and to correlate them from area to area. This analysis shows the numerical frequency of certain levels and is useful to identify the high level erosional surfaces which have originated by denudational processes. The altimetric frequency graph (Fig. 3.5) drawn for the Ghataprabha basin is based on grid method of frequency distribution which according to Clarke (1966) is useful in the area of multiple cycle than in uplifted or structural platforms. The peaks on this histogram represent the remnants of that height of erosional surfaces. The altimetric frequency graph (Fig. 3.5) of the Ghataprabha basin shows two major surfaces. The higher surface over 914 m occupy least area whereas surfaces between m dominate the landscape. 3.3 Slope Morphology Like relief, slope is also one of the significant parameter of the evolution of landforms and their development. Slopes are important aspect of surface forms, since surfaces are entirely composed of slopes and their angles controls the gravitaional force available for geomorphic work (Strahler,1956). Slopes are thus fundamental unit of landscape, so they need careful study.

14 GHATAPRABHA BASIN a l t im e t r ic f r e q u e n y h is t o g r a m 55« KM FIG:3-5

15 Slopes develop as a result of interaction between the various geomorphic processes over a region and the nature and structure of rocks. As such, slopes have a genetic significance and their study is imperative in the final analysis of the georaorphology of the area Mean Slope Mapping of the average slopes for the Ghataprabha basin shows their spatial variation and reflects that the available gravitational force for geomorphic work varies significantly in the basin (Fig. 3.6). The distribution of slope angles in the Ghataprabha basin (Table. 3.6) shows that there are five categories of slopes in the basin. The Fig. 3.6 exhibits the variation of slope angles in different reaches of the Ghataprabha valley. The upper reaches of the river is characterized by moderate to steep o o slopes ranging between 15 to 25 due to the presence of Table 3.6 Percentage Distribution : Mean Slope Mean slope in degrees Category Percentage to the total area below 1 Level Gentle Moderately steep Steep Very steep 0.15

16

17 Western Ghats. However, steep slopes are found in pockets and these follow the trend of high relative relief and high dissection index. The elevated sections of the rugged hilly ti'acts and mountainous terrain lying above 800 ni show o the attainment of above 20 slope. 45 The middle and lower reaches of the river Ghataprabha are o characterized by very low slope angles varying between 0 o to 10. This region is marked by almost plain area. However, occasional isolated hills in this plain area is o o marked by moderate slope ranging between 5 to 10. The representative (average) slope angle for the o o Ghataprabha basin is 0 82' with standard deviation of 1 83'. Areal distribution of mean slope (Table. 3.6) shows that the basin is dominated by level surface with slope of less than 1 o and the area occupied by steep slope is very low. According to Young (1972), low frequency of steep slopes and predominance of gentle slopes suggests a recent rejuvenation.

18 3.3.2 Slope and Lithology The distribution of slopes like relative relief depends on lithology of the area. The variation of slope angles depend upon whether they occur on resistant or non-resistant rocks. As stated in preceding chapter, geologically the basin is covered by three formations, namely the Archaeans, the Deccan traps and the Kaladgis. However, major portion of the Ghataprabha basin is covered by the Deccan traps and the Kaladgi formations. The Deccan trap region show high frequency of steep slopes o o in the basin ranging between 15 and 25. The low gradient is associated with the Kaladgi formations. However, presence of quartzites, limestones gives rise to isolated patches of moderate to steep slopes in otherwise plain area in the lower reaches of the Ghataprabha basin Slope and Relative Relief Slope primarily is a function of relative relief and hence it increases with it (Strahler, 1950). High relative relief in the upper reaches of the Ghataprabha basin is responsible for steep slopes. The correlation value (r = 0.99) between relative relief and slopes indicates that they are positively related. The spatial distribution and the correlation coefficient of mean slopes and relative relief indicates that there is greater degree of uniformity in the intensity of the geomorphic processes in the Ghataprabha basin.

19 3.3.4 Slope and Drainage Density 47 According to Strahler (1950), the interrelationship between mean slope and drainage density is always positive. Following this principle, the correlation coefficient value of the Ghataprabha basin is 0.89 which indicates the mature stage of the basin. In brief, the variation in mean slope angles is the result of differences in the lithology, relief and hydrology Analysis of Hillside Slopes Being a region of diverse rock types, differing in lithological and structural characteristics, the Ghataprabha basin represents different slope elements. Wood (1942) has distinguished four elements that appear in fully developed slope and they are as follows from the top :the waxing slope or crest, the free face or scarp, the debris or talus slope and the pediment. The evolution of these four elements of the hillside slopes in different geological formations of the Ghataprabha basin has been analysed. It is observed that in the Deccan trap region, the development of four elements of hillside slopes as suggested by Wood (1942) is not very clear. In this region, the second element i.e. scarp is not distinctly seen and below the scarp the whole slope is covered by debris. On the other hand, the Kaladgi hills have shown all the four elements in well-developed form. It has been observed that the crest of the Deccan trap hills are more flat than the those of the Kaladgi hills.

20 Also due to the intense chemical weathering and flat crest from which less material is lost, the Deccan trap hill 48 crest has a thicker deposit of weathered material than Kaladgi hills. The second element of the hillside slopes is the free face which is well developed in the Kaladgi hills especially where the capping rocks are hard like quartzites and sandstones. However in the Deccan trap hills the free face is missing and the whole surface between the crest and the pediment is covered by debris. There is a distinct difference between the thickness of the debris of both the Deccan trap and Kaladgi hills due to difference in resistance capacity of these rock types. The thickness of the debris on the free face of the Deccan trap hills is thin and the material accumulated here is very fine. However, on the crest and on the debris slope the thickness of debris is considerable and on the pediment the thickness decreases rapidly. In case of the Kaladgi hills, the thickness of the debris on the free face is more and on the pediment it increases rapidly and the weathered material accumulated here consist of angular to sub-angular pebbles. 1 The fourth element namely the pediment surfaces is the most important and conspicuous of all the landforms both in the Deccan trap and the Kaladgi region.

21 3.4 Dralnag* Basin Morphologjr Rivers and river systems are one of the most important georaorphio systems operating on the earth's surface. Drainage system forms a major feature of the landscape and provides valuable information about the denudational history of the region. The quantitative evaluation of georaorphio characteristics of the drainage basins is the main objective of fluvial georoorphology as it helps in understanding the interrelationship between norphological system and process-response system (Chorley,1969). It Is possible to study the dynamic characteristics of the drainage basin with the help of morphometric analysis. Basin morphometry is the measurement and mathematical analysis of drainage form, its characteristics, shape and network. A number of methods of describing drainage basin morphology have been proposed by many scholars. Among these Horton (1945) was the pioneer who established different laws to study the interrelationships between various parameters. Following Horton's pioneer work, many scholars have made significant contribution in this field namely Strahler (1950,1952,1971), Schumm (1966,1977), Gregory and Walling (1973), Gardiner (1982) and in India by Pal (1973), Singh (1980,1982), Dikshit (1976), Mukhopadhyay (1980,1982) and others.

22 However, no major attempts have been made to study the drainage network aspects of the Qhataprabha basin. The 50 studies carried out by Kulkarni and Sinha(1969) and Pappu (1974) are noteworthy. But these investigations are restricted to some aspects of the drainage system of the river. Against this background, an attempt has been made here to give an comprehensive account of the drainage system of the river Ghataprabhaf Drainage System The main river of the study area is the Ghataprabha which is a major southerly tributary of the river Krishna. The river Ghataprabha originates on the eastern slopes of the Western Ghats at an elevation of 884 m above mean sea level at Ramgad in Chandgad taluka of Kolhapur district, Maharashtra state. It has a total course of about km and it follows an easterly course and in the lower reaches takes abruptly north-eastern turn to meet the main river Krishna at an elevation of 500 m. The river Ghataprabha shows major irregularity in its course in the form of waterfall near Gokak town where it falls over sandstone cliff of about 63 m high. Major tributaries of the Ghataprabha river are the Hlranyakeshi, Tamraparni and the Markendeya which also originate in the Western Ghats (Fig.3.7). There are also a number of small streams which have their sources in the nearby isolated hills.

23 GHATAPRABHA BASIN-RtVERS

24 51 The river Ghataprabha and ita tributaries occupy narrow valleys in the source hilly region and are characterized by youthful features such as presence of potholes, knick points in the form of rapids and waterfall, the dominance of boulders and cobbles in the modern as well as the old river beds. As the rivers make further advance, the valleys are relatively broad and well developed flood plains are common. The river Ghataprabha in ita lower reaches shows the characteristic features of fully mature stream. It follows sinuous path and displays classic example of well developed meandering pattern. The braiding of the river course is the common characteristic feature observed. The Ghataprabha drainage system is controlled by lithology and structure. Dendetric pattern is common in the Deccan trap region which can be attributed to the lithological homogeneity and absence of structural control. On the other hand, the region covered by the rocks of the Kaladgi series have shown sub-parallel drainage pattern. Here, the control of structure over drainage system is clearly noticeable. In the area around Yadwad-Lokapur towns, small streams follow the northerly direction to meet the Ghataprabha river due to the presence of north-south fracture zone (Awati and Kalaswad, 1978).

25 3.4.2 Analysis of Longitudinal Profiles 5 2 The longitudinal or long profile is a graph of distance versus elevation. A critical study of the long profiles of the river Ghataprabha and its tributaries indicate that all the rivers have steep gradients in their source region where they have a drop of nearly 200.to 300 m within a short distance of 5 to 8 km course. In the middle and lower reaches the gradient decreases. This marked difference in gradient between the upper and lower reaches of these rivers result in strong vertical erosion in the upper reaches with heavy deposition in the middle and particularly lower reaches. The long profiles of the tributary rivers Tamraparni and the Hiranyakeshi are similar in form (Fig. 3.8). Both are concave upwards and very much regular and smooth. On the other hand, the profiles of the Ghataprabha and the Markendeya (Fig. 3.8) have different forms. These profiles are not perfectly concave upwards and appear to be convex in their middle and lower reaches. Major irregularities are represented by knick points and waterfalls such as Gokak falls (Plate 4 a)on the river Ghataprabha which is located in the middle reaches at a distance of 125 km form the source. Near the Gokak falls number of potholes are developed. (Plate 4 b). Besides this major irregularity, there are a number of minor knick points which are marked by a sudden increase in the gradient of the river Ghataprabha. Though the rapids and barriers are not seen on the profiles drawn, field observations show that such features are present in the middle and lower reaches of the river Ghataprabha.

26 LONG PROFILES FIG:3-8

27 At a number of places these rivers have not only cut through the alluvium but have entrenched the bed rock 5;^ below, thereby indicating the rejuvenated nature of these rivers. Breaks or knick points are more prominent in case of the tributaries (Plate 1 b) and this shows that they are ot fully adjusted with the base level Basin Network Analysia Basin network analysis includes mainly three aspects of the drainage basin morphology and they are as follows : a. Linear aspects b. Areal aspects c. Relief aspects These aspects are helpful in understanding the basin morphology. The basin network analysis for the Ghataprabha basin has been carried out for the upper, middle and lower reaches. a. Linear Aspects a.i. StreaiB Order The firat step in drainage basin analysis is designation of stream order. Strahler's (1971) modified method of ordering the streams is followed in the present work. According to this method, the fingertip tributaries of a river are named as order one. These are the streams which have no tributaries. When the two first order streams join, they form second order and so on with streams of higher order. As per this ordering of streams, the trunk stream of any watershed bears the highest order number in the entire system. Accordingly, the Ghataprabha river is found to be of fifth order stream.

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29

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31 For detail analysis the Ghataprabha basin has been divided into three regions i.e. upper, middle and lower reaches. 5 ^ Stream ordering in these three reaches (Fig.3. 9 a,b,c) shows that in the middle reaches number of streams are less as compared to other two reaches (Table 3,7). Following Horton's (1945) first law,the relationship between sliream order and stream number is straight line geometric relationship (Fig. 3.10) i.e. with an increase in order the number of streams increases. Table 3.7 Strean Order No. of streams in Stream Upper Middle Lower order reaches reaches reaches *- a. ii. Bifurcation Ratio a It is defined as the ratio between the number of streams of a given order and the the number of streams of the next higher order. The bifurcation ratio for upper, middle and lower reaches of the Qhataprabha river has been calculated (Table. 3.8). These values are more or less normal according to Horton's (1945) law as they range between 3 and 5. However, variations in these values are due to the differences in topographic characters, mainly surface runoff, the degree of integration of streams (Sidu and Pande, 1974).

32 UPPER REACHES ORDER MIDDLE REACHES LOWER REACHES REGRESSION LINES:-STREAM ORDER, VS. STREAM NUMBER. FIG: 3-10

33 Horton (1945) considered the bifurcation ratio as an index of relief and dissection. According to Shreve (1966), 5^: bifurcation ratio on mature surface tend to have values between 3 and 5, with an usual value around 4, The average bifurcation ratio of the Ghataprabha basin is 4.38 indicating the mature stage of the basin, which has also been confirmed by the hypsometric analysis described earlier. The Kaladgi quartzite and limestone region shows value of bifurcation ratio as 5.63 and the value 3.29 is confined to the area where both granite and Archaeans are well developed (Table. 3.8). The lower reaches of the river Ghataprabha river is exception (Table. 3.8) to the hypothesis proposed by Giusti and Schneider (1966) which states that the bifurcation ratios within a region decrease with the increasing order. This is due to the fact that here geology and relief have affected the branching of streams. a.ill. Stream Length The second law of Hortonian model (1945) which concerns with the stream length, states that the mean length of stream segments of a given order increases exponentially with the increasing order. This has been observed in the Ghataprabha basin (Table. 3.9) and the graph (Fig. 3.11) shows a positive exponential function. In case of total length, a negative exponential function is found (Fig.3.12) where the total stream length decreases with an increase in stream order (Table ).

34 UPPER REACHES MIDDLE REACHES LOWER REACHES REGRESSION LINES: STREAM ORDER VS. MEAN STREAM LENGTH FIG:3-I1

35 UPPER REACHES MIDDLE REACHES LOWER REACHES REGRESSION LINES: STREAM ORDER VS. TOTAL STREAM LENGTH r s - : ^ i 2

36 5G Table 3.8 Bifurcation ratio (Rb) a. Upper reaches stream order stream number Rb Average = 3.97 b. Middle reaches Average = 3.99 c. Lower reaches Average = 5.63

37 57 The length ratio from mean stream length has a higher values in comparison to length ratio from total stream length (Table. 3.9). The stream length of various orders help in identification of terrain characters and is associated with slope, sediment type, rainfall and basin area. In the lower reaches of the Ghataprabha river, the stream length is more where limestone is prominent rock type. However, in the quartzitic terrain streams are shorter because of the less effective permeability and weathering. b. Areal Aspects b.i. Basin area Basin area is a dimensional parameter which is mainly associated with factors like stream length, lithology, slope, stream frequency and drainage density. Coarsegrained sediments and resistant beds are also associated with basin area as these factors increase the surface runoff. Horton's (1945) law of basin area states that the first order basin have the smallest mean basin areas and the successive higher orders show increase in the basin area resulting in the largest area of the highest order stream i.e. the trunk stream, thus showing a geometric or positive function.

38 Table 3-9 Strean Length 58 a.upper reaches Stream Total Length Mean Length Order stream ratio stream ratio length length Average = 1.82 b. Middle reaches Average = 2.06 c. Lower reaches Average = 2.99

39 However, Table shows that all the three regions i.e. upper reaches, middle reaches and lower reaches of the 5 0 river Ghataprabha follow the Hortonian law of basin area though they are situated in different geological formations. Strahler (1971) stated that the law of basin area as the "mean basin areas of successive increasing orders form a geometric series beginning with the mean area of the first order basin and increasing according to constant area ratio But in all three regions i.e. upper, middle, and lower reaches, there is some variations in area ratio within the orders whereas the law requires a constant area ratio which is not possible in nature. b- ii. Stream Frequency Stream frequency is defined as the number of streams per unit area within the drainage basin. It is a dimensional parameter and is used as supplementary measure of the fineness of the texture of topography and also of extent of dissection. Stream frequency is more in the upper reaches of the Ghataprabha basin (2.39 / sq km ) than the middle reaches (0.70/sq km ) and lower reaches (0.89/sq km). These differences in the values of stream frequency are mainly due to mainly topography, lithology, porosity of rock, slope, rainfall and vegetational cover.

40 GO a. Upper reaches Table 3.10 Mean Basin Area Stream order Mean basin area (sq kto) b. Middle reaches !. Lower reaches

41 b.iii. Constant of Channel Maintenance (CCM) g COM is defined as the ratio of the area of the basin to the total length of streams of all orders. In other words, it is inversely related to the drainage density and has the dimension of length {Schumm, 1956). It is an expression of the surface area required to support one km of channel (Leopold at ax 1969). It signifies the relative size of the landforra units and increases with the size of landform units. Streams in the Ghataprabha basin require an area of 0.97 sq km to survive in the middle reaches. However, it require more area (1.24 sq km ) in the lower reaches of the basin. The factors like lithology and climate seem to be more important in this case. b. iv. Drainage Texture Drainage texture is defined as the product of drainage density and stream frequency. The drainage texture values for the Ghataprabha basin (Table. 3.11) shows that it has coarse drainage texture. Texture ratio i.e. the ratio of total number of streams to perimeter of the same basin indicates the relative spacing of drainage lines. Texture ratio is high in the lower reaches of the Ghataprabha basin, mainly due to the factors like infiltration capacity, climate and rock structure.

42 c. Relief Aspects c. 1. Average Gradient Average gradient is obtained by dividing the total fall by total length of each order. Hortonian law (1945 ) states that the low order streams have steep gradient and thus having a negative exponential function. Once again a straight line geometric relationship is strongly established in the Ghataprabha basin {Fig. 3.13). c. ii. Relief Ratio It is a ratio between the total relief of a basin and the longest dimension of the basin parallel to principle drainage line (Schumm, 1956). The relief ratio of the middle reaches of the Ghataprabha basin is more where contrasting relief features are present (Table 3.11). Schumm (1956) has stated that as the relief ratio increases, the drainage basin becomes more elongated. It can be seen from the map of the Ghataprabha basin (Fig.1.1) that it is more elongated as its relief ratio is higher due to contrasting relief features. c. ill. F o m Factor The form factor suggested by Horton (1932) is the ratio of the basin area to the square of the basin length and it indicates the shape of the drainage basin. The form factor

43 o\ 2 (- zi LU no Q< Ct CD (S> < cd UJ >< o \ 'A ^ \ \\ ^ \ w \ T' \ O \ \ 10 7^ \ ip \ O \ \ \ (P \ H \ ^ \ " V -r \ \ o \ R= \ > R \ R = ^ h ORDER UPPER REACHES MIDDLE REACHES LOWER REACHES REGRESSION LINES: STREAM ORDER VS. AVERAGE STREAM GRADIENT FIG:3*13

44 Table 3.11 Drainaffo Network Analysis Stroara COM Drainage Texture Average Relief Forra Frequency Texture Ratio Gradient Ratio Factor (sq km) (m/km) Upper reaches Middle reaches Lower reaches

45 64 for the Ghataprabha basin is 0.61 which indicates that the basin has a elongated shape. c. iv. Drainage Density Drainage density is defined as the ratio of the total length of all the streams within a single river system and is calculated by dividing the total length of the streams by the area drained (Robinson,1986). According to Morgan (1976) drainage density is an index of gross landform. It can be useful for the classification of drainage basin for the spatial prediction of drainage basin processes. Drainage density is associated with interchannel distance (Horton,1945) and ruggedness of terrain (Strahler,1950). Various factors which affect the drainage density have been studied by many geomorphologists. On the basis of these studies. Morgan (1976) states that drainage density appears to be both in response to the factors controlling run-off, and control of the run-off itself. Drainage density is an important characteristic of river system as it reflects the combined effects of topographic, lithological, pedological and vegetational control. The drainage density map of the Ghataprabha basin (Pig. 3.14) shows the spatial distribution of drainage density. The Ghataprabha basin shows very low drainage density ranging between 0 to 2 per sq km. Similar to other morphological parameters, drainage density varies spatially with relief,

46 GHATAPRABHA BASIN drainage d e n s it y m KM/SQ KM FIG ;3K Y A* 31 V C

47 lithology and precipitation. The upper reaches of the basin 65 shows slightly more value of drainage density (more than 1.5 km /sq km) due to high relief, steep slope, harder rock type, heavy rainfall and impermeable soils. On the other hand the area covered by sandstone shows very low drainage density. Here permeability and poor supply of rain water have restricted the branching of the river and their tributaries, 3.6 Overview The study of draitiage basin morphology reveals that the morphometric parameters vary spatially in the basin. The area of low category of relative and absolute relief, dissection index and mean slope are mainly confined to middle and lower reaches of the basin whereas high category of the above mentioned parameters are restricted to the source region. Geostatistical analysis for 1234 quadrats indicates that the Ghataprabha basin has lower average values of relief (absolute and relative), mean slope and dissection. This fact implies that the landforms in the basin are more mature. The study of drainage network have shown that the Ghataprabha basin reflects mature characteristics and an advanced stage of drainage network development.