Chapter IV MORPHOMETRIC ANALYSIS AND STREAM NETWORK CHARACTERISTICS IN GADAG DISTRICT 4.1 INTRODUCTION: Streams and rivers are the most dynamic parts of the earth s physical environment. The behavior of streams and rivers is a matter of great interest for a variety of concerns, particularly in case of water resource development. The analysis of streams and their studies have political, social, economic and physical relevance. Rivers usually have well defined spatial boundaries and can usefully be regarded as open systems in which energy and matter are exchanged with an external environment. The character and behaviour of the fluvial system at any particular location reflect the integrated effect of a set of upstream controls, notably climate, geology, land-use and basin physiography, which together determine the hydrologic regime. Downstream controls such as base-level are also important. Climate is of primary significance in that it provides the energy for the most important processes and in combination with vegetation directly influences basin hydrology (David Knighton, 1978). Geological variables can also have far-reaching effects at a variety of scales, 147
particularly in constraining the nature and level of fluvial activity. In addition to these natural controls man s influence is becoming increasingly relevant through river regulation schemes and changing patterns of land use. With the marked increase in dam construction since 1945, up to 20% of total stream run off is regulated in Africa and North America, with comparable figures of 15% and 14% for Europe and Asia respectively (Beaumount, 1978). In the fluvial system the transfer of water and material from land surface to oceans is characterized by a tendency towards increasing concentration and organization. A spatially diffuse input in the form of precipitation and weathered material is combined via a system of hill slopes and a network of channels into a single out put at the mouth of a drainage basin. Available in a hierarchy of sizes, the drainage basin is typically a well-defined topographic and hydrologic entity, which is regarded as a fundamental spatial unit (Chorley, 1969). In the watershed development, the links between slopes and channels in the movement of water through the drainage basin should be recognized at the outset. The links sometimes may tend to become weaker for larger streams with well-developed flood plains. But it is essential to focus on the channel network them. 148
It is for this reason, the morphometric analysis becomes so essential in developing a watershed and hence the researcher has made an attempt to understand the drainage network characteristics in this chapter to choose the favourable spots for water storage. 4.2 MORPHOMETRIC ANALYSIS: Morphometric analysis of a fluvial system involves the study of geometric properties of a drainage system, such as stream segments, numbers, confluences, stream order, bifurcation ratio, lengths, and basin areas etc. The study is planimetric and includes the linear properties, areal (two dimensional) properties and the height/slope properties etc., Irrespective of the width of the channels each stream segment is considered as a line. When the rain occurs the water is guided by the surface depressions. The water lines coalesce at certain points forming the rills, which further form a master rill. When such rills are combined a small stream is formed. The process would continue through the formation of big streams, tributaries and ultimately join the main trunk stream in the concerned area. Each fingertip stream segment is regarded as a first order stream. At the junction of any two first order stream segments a second order stream originates. Similarly at the junction of any 149
two second order streams a third order stream originates and so on. It may be noted that the volume of water, its velocity and energy increases in the channel with increase in the order of streams. Each stream of a specific order has its own basin area from which the stream receives its water through overland flow. The drainage network characteristics of Gadag district have been analyzed in the following pages. 4.3 MAJOR STREAMS AND THEIR BASIN AREAS: Mainly are two rivers in Gadag district viz., the Malaprabha and the Tungabhadra Rivers. The Malaprabha River is the main trunk stream and runs along the northern border of the district. The southern portion of the district has been drained by the Tungabhadra river. About 2767 Sq. Km. area of the district comes under the Malaprabha basin representing 59.43 percent of the total geographical area of the district. Tungabhadra basins cover an area of 1889 Sq.Km or 40.57 percent of the total geographical area of the district. Malaprabha and Tungabhadra rivers receive water from a large number of streams of different order. The stream orders, total segments (numbers), length and density etc., have been analyzed and are as given below. 150
4.4 STREAM ORDERS AND STREAM SEGMENTS: In any drainage network, the streams are classified into different orders according to the number of bifurcations. The advantage of ordering streams is that the stream order is a dimensionless number and hence can be used for the comparison of geometry of drainage network on different linear scales. Various methods of stream ordering were suggested by earlier workers. Davis (1930) proposed a genetic approach to drainage pattern. However the most important quantitative approach to drainage analysis was proposed by Horton (1945) and Strahler A.N. (1952). The drainage map was analyzed by making two different types of measurements, namely dimensionless numbers and linear scale measurement. Dimensionless numbers are usually the ratios of numbers and lengths of streams, whereby shapes of the analogous units can be compared, irrespective of scale. These properties include stream order numbers and bifurcation ratios. If a geometrically similar stream exists in two drainage basins, all corresponding dimensionless numbers will generally be identical but if a significant difference 151
exists between the geometry of the drainage basins, the dimensionless numbers will also be variable. Linear scale measurement, whereby geometrically analogous units of the land surface supporting the drainage system, can be compared as to their size. These include length of a stream channel of a given order, drainage density, constant of channel maintenance, basin parameters and relief. If two drainage basins are geometrically similar, all corresponding dimensions will be in a fixed ratio. The stream network development primarily depends on the geologic structure and time. Davis W. M. (1899) attached the evolutionary significance to the classification of streams as consequent, subsequent and obsequent. A particular drainage pattern development reflects the adjustment of streams with the underlying rock structure. Drainage network composition refers to the topologic and geometric properties of networks. Horton R.E (1945) introduced a modern concept with regard to stream order, which was modified by Strahler A.N (1952). In the present study, the channel segment of the drainage basin has been ranked according to Strahler s (1964) stream ordering system. In this method, the stream originating in the 152
upper reaches are the first order streams; when two first order stream unite, a segment is designated as a second order stream; when two second order segments join a channel segment is a third order stream, and so on. The trunk stream or the main stream through which all the discharge of the water is carried out is the stream of the highest order. The study area i.e. Malaprabha and Tungabhadra are 5 th order drainage basins (Figure4.1) Drainage patterns of stream network from the basins have been observed as mainly dendritic type which indicates the homogeneity in texture and lack of structural control. This pattern is characterized by a tree like or fernlike pattern with branches that intersect primarily at acute angles.though there are number of arguments in this connection, the methods of Strahler A.N. and the Horton s concepts have been employed here to analyze the stream networks of Gadag district. The stream ordering for the two river basins, Malaprabha, and Tungabhadra show a five order stream segments. The table 4.1 shows the stream order, segments and bifurcation ratio, of Malaprabha and Tungabhadra river basins. The Malaprabha River consists of five orders of stream segments. Totally 483 Streams are identified among which 386 are 1st order stream segments, 79 are 2 nd order segments. 14 are 3 rd order, 4 th order segments are only 3 and the Malaprabha river forms the highest 153
order i.e., fifth order segment. The Tungabhadra river basin also consists of five orders of streams. The 1 st order streams are 314, 2 nd order 75, 3 rd order 17, 04 are 4 th order and the Tungabhadra river is a main trunk stream.( Fig - 4.1 ) 4.5 BIFURCATION RATIO (Rb): The bifurcation ratio is the ratio of the number of stream segments of given order to the number of segments of next higer order.it is a dimensionless property and show the degree of integration prevailing between streams of various orders in a drainage basin. Horton (1945) considered the bifurcation ratio as index of relief and dissertation. The mean bifurcation ratios characteristically range between 3.0 and 5.0 for watershed in which geology is reasonable homogeneous and no structural disturbance. The bifurcation ratio (Rb) has been calculated by applying the (Shumn-1956) following equation. Rb Nu Nu 1 Where, Rb = Bifurcation ratio Nu = Total number of stream segments of the order u Nu+1 = Number of segments of the next higher order 154
Table - 4.1 Gadag District: Stream order, Stream Segments and River basin Malaprabha Basin Tungabhadra Basin Stream order Bifurcation Ratio Stream segment Bifurcation ratio 1 st 386-2 nd 79 5.89 3 rd 14 6.64 4 th 03 5.66 5 th 01-1 st 314-2 nd 75 5.19 3 rd 17 5.41 4 th 04 5.25 5 th 01 - Total/Average 894 5.67 5.67 Mean Bifurcation ratio 18.19/3 = 6.06 15.85/3 =5.28 The bifurcation ratio for the successive orders of the Malaprabha river basin is given in the table 4.1. For every second order stream there are approximately 5-6 first order streams. Similarly for every third order stream there are 6-7 second order streams and for fourth order it is 5-6 streams of third order stream segments. The bifurcation ratio for the successive orders of the Tungabhadra river basin from 1 st to 4 th order is 1:5.19, 1:5.41 and 1:5.25. The mean bifurcation ratio for Malaprabha river basin is 1:6.06 and Tungabhadra river basin is 1:5.28. 155
Figure 4.1 156
However the mean bifurcation ratio value is 5.67 for the study area (Table.4.1) Bifurcation ratios characteristically range between 3.0 and 5.0 for basins in which the geologic structures do not distort the drainage pattern (Strahler, 1964). Strahler (1957) demonstrated that bifurcation ratio shows a small range of variation for different regions or for different environment dominates. The mean bifurcation ratio value is 5.67 for the study area (table-4.1) which indicates that the geological structures are less disturbing the drainage pattern. The significance of bifurcation ratio with reference to watershed development in Gadag district is highly positively acceptable. The bifurcation ratio 5.67 is most favourable for the watershed development under semi-arid conditions in Gadag district. Under the drought conditions the number of stream segments will be more or less 6 to 7 in general (Waugh, 2000). 157
Plate-18: Over flow of Gaddihalla a second order stream in between Gadag and Hataleger. Plate-19:Magadi Tank : constricted across the third order stream 158
Plate-20: Bennihalla (Malaprabha Basin) 4 th order stream Plate-21: Hirehalla in Tungabhadra Basin a 4 th order stream 159
4.6 STREAM LENGTH (Lu): Every stream segment has its own length. Stream length is one of the most a significant hydrological feature of the basin as it reveals surface runoff characteristics streams of relatively smaller lengths are characteristics of areas with larger slopes and finer textures. Longer lengths of streams are generally indicative of flatter gradients. Generally, the total length of stream segments is maximum in first order streams and decreases as the stream order increases. The numbers of streams of various orders in the basin are counted and their lengths from mouth to drainage divide are measured with the help of optometer. The mean length can be found out in the following manner: Where, Lsm =Lu/Nu Lsm =Mean stream length Lu = Total stream length of order Nu = Total number of stream segments of order u The length ratio is calculated as follows: RL =Lu/Lu-1 Where RL = Stream length ratio Lu = The total stream length of the order u Lu-1 = The total stream length of its next lower order 160
The stream lengths plays a significant role in deciding the watershed spots as it gives an idea about surface run off and the volume of water flow through the channel to be collected in the proposed spot. The stream length ratio has been calculated for all orders of streams in Gadag district. It may be noted that each stream order has a characteristic number of channels, length and drainage area. The stream length aspects have been given in the table 4.2 for two river basins of Gadag district. In Malaprabha River the 1 st order streams have a total length of 835 Km and with a mean length of 2.16 Km and a ratio of 1:0.47. The figures for the 2 nd and 3 rd order streams are, total length 321 Km means length 4.06 Km, ratio1:0.48, and 111 Km length, 5.84 Km mean length and ratio 1:0.67 respectively. The total length of 4 th order streams is 72 Km with a mean length of 24 Km. It is observable that the mean length of all streams increases with increase in order. The total length of the main trunk stream the Malaprabha has a length of 35 Km in Gadag district. The total length of all streams of Malaprabha River is 1364 Km. (Table.4.2) The Tungabhadra river basin has a total length of all streams to an extent of 1293 Km. Out of which 813 Km length 161
is represented by 1 st order streams, 234 Km by 2 nd order, 112 Km by 3 rd order streams, 69 Km by 4 th order streams and the main trunk stream i.e., Tungabhadra has 45Kms of length. The total length of all streams including two river basins in Gadag district is 2637 Km. The mean length of all streams (excluding trunk streams) is 8.46 Km. The mean stream length ratio with each increase in order has some fluctuations. The proportion of length increase ratio will generally be constant for a given drainage system. But chance variations may be expected in the configuration of any drainage system. These may produce inequalities of observed length ratio from one order to the next. The length ratio for two basins streams has no constant values to form a geometric series. This is mainly due to variations in the nature of rock and terrain conditions. The Tungabhadra river basin has a total length of all streams to an extent of 1273 Km. Out of which 813 Km length is represented by 1 st order streams, 234 Km by 2 nd order, 112 Km by 3 rd order streams, 69 Km by 4 th order streams and the main trunk stream i.e., Tungabhadra has 45Kms of length. 162
Table - 4.2 Gadag District: Stream Length and Length Ratio Mean stream Length ratio Stream Stream length Length (Km) River basin RL=Lu/Lu-1 order (Kms) Lsm = Lu/Nu Malaprabha Basin 1 st 835 (708 Cms) 2.16 2 nd 321 (272 Cms) 4.06 1:0.47 3 rd 111 (94 Cms) 7.92 1:0.48 4 th 72 (61 Cms) 24.00 1:0.67 5 th 25 (21 Cms) - Tungabhadra Basin 1 st 813 (689Cms) 2.59 2 nd 234 (198Cms) 3.12 1:0.16 3 rd 112(95Cms) 6.59 1:0.53 4 th 69 (58 Cms) 17.25 1:0.62 5 th 45 (38 Cms) - Total 2637 (2234 Cms) 8.46 Total length of all streams = 2637 Kms Mean length of all streams = 8.46 Kms (Excluding trunks streams) 163
Plate-21 (a) Muradi M.I.Tank: Constructed across the third order (Shirahatti halla) stream. 4.7 DRAINAGE DENSITY AND BASIN AREAS: Drainage density is one of the important linear aspect of the drainage basin. Drainage density defined as the closeness of channels. It is expressedin units like km/km2 or mi/mi2. The measurement of Drainage Density (Dd) is a useful numerical measure of landscape dissection and runoff potential (Chorley, 164
1969). On the one hand, the Dd is a result of interacting factors controlling the surface runoff; on the other hand, it is itself influencing the output of water and sediment from the drainage basin (Ozdemir and Bird, 2009). Dd is known to vary with climate and vegetation (Moglen et al., 1998), soil and rock properties (Kelson and Wells, 1989), relief (Oguchi, 1997) and landscape evolution processes. Every stream or channel segment of any order has its own basin area. In each first order stream basin all ground surface of the basin contributes directly to the first order channel. In each second order basin, considered in its entirety, only part of the overland flow enters the first order channels directly. The area of an entire second order basin is the sum of the first order basins and contains all inter basin areas within its perimeter (Strahler, A.N.). As the stream order increases the basin area enlarges and contributes more volume of water to the channel. This study helps in the watershed development and the planner may choose the most favorable spot for the water storage. The total basin area of two basins in Gadag district (viz., Malaprabha, 2767 Sq.Km, and Tungabhadra 1889 Sq.Km) is 4656 Sq.Km. 165
Drainage density is a measure of the length of stream channel per unit area of drainage basin. Mathematically it is expressed as: equation: Horton (1945) expressed drainage density by the following Where Drainage Basin Dd = Lu/A Malaprabha River Basin Tungabhadra River Basin Dd = Drainage density Lu = Total stream length of all orders A = Area of the basin (km2 Table-4.3 Gadag District - Drainage Density Total area ( Sq. Km) Total stream length (Km) Drainage density A L (Km/Km 2 ) 2767 1364 0.48 1889 1273 0.66 Total 4656 2637 0.56 The basin area, stream length and the drainage density have been depicted in the table - 4.3.The average density of drainage for the entire Malaprabha and Tungabhadra river basin in Gadag district is 0.56 Km per Sq. area. When the individual 166
basins are considered, it is observable that there is slight variation in the drainage density between two basins. The Tungabhadra basin has a drainage density of 0.66 Km. Per Sq, and Malaprabha river basin has a drainage density of 0.48 Km. per Sq.The drainage density may be described as having course texture (DD < 5 Km Length per km2 /area;), medium texture (DD =5-10 Km Length per km2 /area;), fine texture(dd =10-20 Km Length per km2 /area;), and ultra fine texture etc., The drainage density in Gadag district (i.e, 0.56 Km/Km2 area) is a coarse texture. This is a characteristic feature of dry regions particularly in semi-arid regions like Gadag district. The coarse drainage density attracts the watershed development for various economic activities. The streams in the Gadag district are non-perennial and flow only during rainy season. Hence it is very essential to store the rainwater during rainy days. 167