CHAPTER 4 THE INFLUENCE OF RIVER BASIN MORPHOLOGY ON RIVER GROUNDWATER INTERACTION

Transcription

1 CHAPTER 4 THE INFLUENCE OF RIVER BASIN MORPHOLOGY ON RIVER GROUNDWATER INTERACTION

2 CHAPTER 4 THE INFLUENCE OF RIVER BASIN MORPHOLOGY ON RIVER-GROUNDWATER INTERACTION 4.0. INTRODUCTION The relationship between the river basin morphology and the hydrologic processes of drainage basin has been an active subject for research in hydrology since early nineteenth century. In such studies, the hydrological response of river basin were interrelated with the morphometric characteristics of the drainage basin, such as size, shape, slope, drainage density, size and length of the streams etc. (Gregory and Walling 1973). Hence, morphometric analyses of drainage basin (quantitative description of the drainage basin geometry) were recognized as an essential first step towards basic understanding of river basin dynamics. The morphometric characteristics of a drainage basin are largely determined by climate and the nature of the geologic materials. Since morpholology and hydrology do not necessarily indicate a cause and effect relationship, the high correlation between them may be because both these factors vary in a consistent way with the underlying climatic and geologic controls (Ritter et al., 1995) PREVIOUS STUDIES The hydrological response of river basins to precipitation events depends on the mechanisms of runoff generation, in particular on the partitioning between surface and subsurface discharge to the channel network (Vivoni et al., 2008). The surface hydrologic 71

3 response to geomorphologic parameters of four river basins has been studied by Sherman (1932), using the classical unit hydrograph concept to describe the hydrologic response and Horton numbers and morphometric parameters to describe the geomorphologic structure of a basin. Patton and Baker (1976) demonstrated predictive relationships between several morphometric parameters and peak flood discharges for streams in several physiographic regions of United States. They found that areal morphometric parameters such as drainage density and stream frequency accounted much to predict peak discharge, along with the relief measure known as Ruggedness number (R) which is the product of relief and drainage density. Similar studies were carried out on the relation of morphmetric character of drainage basins to basin-runoff characteristics (Rodriguez-Iturbe and Valdes, 1979; Gupta et al., 1980; Troutman and Karlinger, 1985; Howard, 1990; Bertoldi et al., 2006). The topographic parameters considered important in these studies were area, channel slope, stream pattern, average basin width, mean length of travel (channel length), and mean relief measured from gauging station. The geomorphologic effects on the groundwater dominance of the river network have also been addressed by many workers (Zecharias and Brutsaert, 1988; Higgins and Coates, 1990; Schumm et al., 1995; Whiting and Stamm, 1995; Sear et al., 1999; Marani et al., 2001). Among the geomorphologic parameters, total length of perennial streams, average basin slope, and drainage density were identified (Zecharias and Brutsaert, 1988) as being relevant to the process of groundwater discharge to the rivers. Schumn et al., (1995) documented that the geomorphic features such as light bulb shape of drainage basins, low drainage density, dendritic drainage pattern, theatre or cirque-like valley heads, steep valley walls and flat valley floors, relatively constant valley width, structural control of 72

4 drainage network, long main valleys and short tributary valleys, high tributary junction angle (55±65) and hanging valley tributaries as the characteristic features of groundwater dominated rivers. In India, the relationship between the morphometric parameters and the hydrology of the drainage basin had been utilized in a number of studies for the prioritization of micro watersheds (Mishra and Nagarajan, 2010), water management (Rao et al., 2010) and for the development of groundwater resources (Sreedevi et al., 2009; Rajarajan and Najeeb, 2008). Even though similar approaches have been applied in Kerala, in the Kuttiyadi (James and Padmini, 1983), Chalakkudy (Babu et al., 2014), Pamba (Rajendran, 1982), Meenachil (Vijith and Satheesh, 2006), Achankovil river basins (Manu and Anirudhan, 2008) and in Muthupuzha watershed (Jobin Thomas et al., 2010), the geomorphologic effects on the river groundwater interaction has not been addressed MORPHOMETRIC ANALYSIS The morphometric analysis (method for quantitative evaluation of the pertinent geomorphic factors) of drainage basin was first developed by Horton (1945). Following the techniques suggested by Horton, several morphometric parameters were developed to describe the various geomorphic characteristic (linear, areal and relief aspects) of drainage basins (Smith, 1950; Schumn, 1956; Strahler, 1957). However, field observations and theoretical considerations indicated that some of these parameters were representing the same aspects of a basin in different ways and not every morphologic parameter was related to a given basin process (Schumn, 1956; Gregory and Walling, 1973, Ebisemiju, 1979). The determination of the geomorphologic parameters 73

5 that are most closely associated with a given basin process involves quantitative measure of the effect or influence that each of these parameters exerts on the process. Therefore among the parameters that completely describe the physical characteristics of basins, only few parameters that affect (or are relevant to the process) are considered in a given study. The morphometric parameters considered in the present study to represent the linear, areal and relief aspects of the basin morphology is presented in Table.4.1. Table.4.1. Morphometric parameters considered for the present study Sl.No Parameter Definition Unit References Linear Parameters 1 Stream order Hierarchical ordering Dimensionless Strahler (1957) 2 3 Perimeter (P) Length of the watershed boundary km -- Basin length (Lb) Maximum length of the watershed measured parallel to the main drainage line km -- 4 Stream length (Lu) Length of the major stream km Horton (1945) 5 Stream length ratio (Rl) Rl = Lu/L(u-1), where Lu is stream length of order u and L(u-1) is stream segment length of the next lower order Dimensionless Horton (1945) 6 Bifurcation ratio (Rb) Rb = Nu/N(u+1), where Nu is number of streams of any given order and N(u+1) is number in the next higher order Dimensionless Horton (1945) 74

6 Table.4.1. Contd... Sl.No Parameter Definition Unit References Areal Parameters 1 Area (A) Area of watershed km 2 Dd = Lt / A 2 where Lt is the total km -1 Horton (1945) Drainage density (Dd) length of all the ordered streams Fs = Nu / A 3 Stream frequency (Fs) where Nu is total km -2 Horton (1945) number of stream segments of all orders T = Nu / P Where Nu is the total 4 Drainage texture (T) number of stream km -1 Smith (1950) segments of all orders P is the Perimeter of the basin 5 Infiltration number (IF) IF = Dd X Fs km -3 6 Form factor (Ff) Ff = A/Lb 2 Dimensionless Horton (1945) 7 Circularity ratio (Rc) Rc =4 A/P 2 Dimensionless Miller (1953) 8 Elongation ratio(re) /Re = (1.128 A)/Lb Dimensionless Schumn (1956) 9 Constant of channel maintenance (C) Length of overland 10 flow (Lg) C = 1/Dd km Schumn (1956) Lg = 1/2Dd km Horton (1945) Relief Parameters R = H- h, where H is 1. Bain relief (R) maximum elevation and h is minimum elevation within the basin km Schumn(1956) 2 Relief ratio (Rr) Rr = R/Lb Dimensionless Schumn (1956) 3 Ruggedness number (Rn) Rn = R x Dd Dimensionless Strahler (1958) 75

7 DRAINAGE PATTERN The drainage patterns are good indicators of landform, bed rock type and also suggest soil characteristics of the regions. There are several kinds of drainage patterns. The most common are dendritic, angular, parallel, radial, centripetal, annular, rectangular, trellis, pinnate etc. Moon and Dardis (1988) indicated how the underlying geological structure determines the drainage patterns of rivers. Both dendritic and parallel drainage patterns develop on uniform lithologies and where there are no controlling joints or fractures. Where faults, joints, or other lineaments control drainage it will develop rectangular, while alternating resistant or less resistant strata will promote the development of trellised drainage. In settings where up-doming has occurred annular drainage patterns will be present, and in landscapes where tectonic activity is present, radial and centripetal drainage configurations will manifest. In any catchment one or several of these patterns may be present since these patterns are entirely dependent on the underlying structure (Moon and Dardis, 1988). These drainage manifestations also indicate groundwater discharges characterising a river system (Roets et al., 2008). According to Schumn et al., (1995), the dendritic drainage pattern, is a characteristic features of groundwater dominated rivers LINEAR PARAMETERS Stream orders, Stream number, Perimeter, Stream length, Mean stream length, Stream length ratio and Bifurcation ratio are the linear aspects of channel system in drainage basins. 76

8 Stream order Ordering of streams is the first step in drainage-basin analysis (Horton, 1945) and is a measure of the position of a stream in the hierarchy of tributaries (Leopold et al., 1964). Stream order is also an index of the size of the contributing watershed, to channel dimensions and to stream discharge at that place in the system. In the present study, ranking of streams has been carried out based on the method proposed by Strahler (1964). In this method all the finger tip tributaries are designated as the first order streams, two first order streams produces a second order stream, two second order streams produces a third order stream and so on Stream number The count of stream channel in its order is known as stream number. Stream number is also directly proportional to size of the watershed and channel dimension. It is obvious that the number of streams of any given order will be fewer than for the next lower order but more numerous than for the next higher order Perimeter The perimeter of a drainage basin is defined as the horizontal projection of its water divide and depends on the area and shape of the basin (Zavoianu, 1978) Stream length The length of a stream is a measure of the hydrological characteristics of the underlying rock surfaces and the degree of drainage. Wherever the formations are permeable, only a 77

9 small number of relatively longer streams are formed; in a well-drained basin, a large number of streams of smaller length are developed where the formations are less permeable. Streams of relatively smaller lengths are characteristics of areas with larger slopes and finer textures. Longer length of streams generally indicates flatter gradients (Christopher et al., 2010). The lithology of the area also plays an important role in determining the stream length of various orders (Coates, 1958). According to Horton (1945) the total stream length decreases with increase in stream order while the mean length increases with increase in stream order Mean stream length The Mean Stream Length (Lsm) has been calculated as the ratio of total stream length of order u and the total stream segment of order u. According to Strahler (1964) the mean stream length is a characteristic related to the drainage network and its associated surfaces Stream length ratio Stream length ratio (Rl) is defined as the ratio of the mean stream length of one order to the mean stream length of the next lower order of the stream segment. The length of a stream is a measure of the hydrological characteristics of the underlying rock surfaces and the degree of drainage. Wherever the formations are permeable, only a small number of relatively longer streams are formed; in a well-drained basin, a large number of streams of smaller length are developed where the formations are less permeable. The length ratio gives a general idea about the relative permeability of the rock formations in a basin. More 78

10 specifically, it indicates if there is a major change in the hydrological characteristics of the underlying rock surfaces over areas of consecutive stream orders (Pakhmode et al., 2003). An increasing trend in stream length ratio from lower order to higher order of a river basin indicates mature stage of geomorphic development of the basin (Mishra and Nagarajan, 2010) Bifurcation ratio The ratio of number of segments of a given order Nu to the number of segments of the next higher order Nu+1 is termed as Bifurcation ratio (Rb) (Horton, 1945). Bifurcation ratio characteristically ranges between 3 & 5 for watersheds in which geologic structures do not distort the drainage pattern (Strahler, 1964). Gowd (2004) have attributed the individual high values of Bifurcation ratio to the rock type in the basin. According to Jobin Thomas et al., (2010) high Rb values indicate high overland flow while low Rb values reflect high infiltration rate and less number of channels. The Mean Bifurcation Ratio (Rbm) is defined as the average of bifurcation ratios of all orders AREAL PARAMETERS Basin area, Drainage density, Stream frequency, Drainage texture, Infiltration number, Form factor, Circularity ratio, Elongation ratio, Constant of channel maintenance and Length of overland flow are the areal parameters considered in the present study. 79

11 Drainage density Horton (1932) has defined Drainage density (Dd) as an expression to indicate the closeness of spacing of channels. It is defined as the total length of streams of all orders per unit drainage area. Drainage density is a function of physiographic characteristics of a basin like rock type (Pinchemel, 1957, Strahler, 1964), climate (Chorley & Morgan, 1962) basin shape (Bates, 1981), relief (Slaymaker, 1968) and time (Ruhe, 1952). Drainage density is also a function of precipitation and is highest in area with low annual rainfall, high intensity rains and sparse vegetative cover (Woodyer and Brokfield, 1966). Low drainage density generally results in the area that is highly resistant to erosion, weathering or permeable sub soil materials, dense vegetation and low relief (Nag, 1998). There is also a control between runoff and the drainage density. The peak flow is directly related to the drainage density where as the base flow is inversely proportional (Carlston, 1965) Stream frequency Horton (1932) proposed the stream frequency as the ratio of the total number of streams in a basin to the basin area. A higher stream frequency points to a larger surface runoff and steeper ground surfaces Drainage texture The drainage texture indicates the relative spacing of the drainage lines (Horton, 1945). Drainage lines are numerous over impermeable areas than permeable areas and it is a measure of the total number of segments of all order per perimeter of that area. It gives an 80

12 idea of the infiltration rate of an area. Smith (1950) classified the drainage density into five different textures. They are very coarse (<2), coarse (2-4), moderate (4-6), fine (6-8) and very fine (>8) Infiltration number The infiltration number (IF) of a drainage basin is the product of drainage density and stream frequency. It is a parameter that gives an idea of the infiltration characteristics of the basin. The higher value indicates low infiltration and high runoff whereas its lower value indicate higher infiltration and low run off with shallow depth to water table (Das and Mukherjee, 2005) Form factor The Form Factor (Ff) is the ratio of the basin area (A) to the squared value of the basin length (L) (Horton, 1932). Form factor is used to predict the flow intensity of a watershed of a defined area and this has a direct linkage to peak discharge (Horton 1945, Gregory and Walling 1973) Circularity ratio Circularity Ratio (Rc) is defined as the ratio of the basin area to the area of a circle having the same perimeter as that of the basin (Miller, 1953). Rc is influenced by the length and frequency of streams, geological structures, land use, climate, relief and the slope of the sub basins. Its low, medium and high values are indicative of the youth, mature and old stages of the life cycle of the tributary basins (Magesh et al., 2013). 81

13 Elongation ratio The elongation ratio (Re) is defined as the ratio between the diameter of the circle of the same area as the drainage basin and the maximum length of the basin (Schumn, 1956). Values close to 1 are the typical regions of low relief, whereas the values in the range of are usually associated with high relief and steep ground slope (Strahler, 1964). These values are grouped into three categories a) circular (> 0.9) b) oval ( ) c) less elongated (< 0.7) Constant of channel maintenance Constant of channel maintenance (C) is a measure of texture similar to the drainage density. It is equal to the reciprocal of drainage density and is a measure of the minimum area required for the development of a drainage channel (Schumn, 1956). Constant of channel maintenance depends on basin relative relief, lithology and climate. It decreases with increasing erodibility Length of overland flow Horton (1945) defined the term length of overland flow (Lg) as the length of flow of water over the ground before it becomes concentrated in definite stream channels. The average length of overland flow is equal to half the reciprocal of the average drainage density (1/2 Dd). The Lg averages the down slope flow paths, from the drainage divide to the nearest channel and also points to the efficiency of the drainage in the basin. 82

14 RELIEF PARAMETERS Relief aspects of a drainage basin have great influence on the hydrologic response, and depend on the channel type and relative gradient of the basin. Basin relief, relief ratio, slope and ruggedness number are the important relief aspects of a drainage basin Basin relief Basin relief (R) is the difference between the maximum and minimum elevation of a drainage basin (Schumm, 1956). Importance of Basin relief as a hydrological parameter has been recognized long before (Sherman, 1932, Horton, 1945; Strahler, 1964). Basin relief is an important factor in understanding denudational characteristics of the basin. It is a parameter that determines the stream gradient and influences flood pattern and volume of sediment that can be transported (Hadley and Schumm 1961) Relief ratio The relief ratio (Rr) is defined as the ratio of maximum relief to horizontal distance along the longest dimension of a basin parallel to the main drainage line (Schumn, 1956). It measures the overall steepness of the drainage basin and is an indicator of the intensity of erosion processes operating on the slopes of the basin Slope Slope is an important terrain parameter and it affects the land stability. Slope is defined as the loss or gain in altitude/unit horizontal distance in a direction. Slope of any terrain is one of the factors controlling the river- groundwater interaction. 83

15 A uniformly steep watershed would favor rapid transfer of water out of the watershed, while a uniformly flat watershed may not contain sufficient subsurface storage volume to sustain high base flows. In gently sloping areas, the surface runoff is slow allowing more time for groundwater to percolate, whereas, high slope areas facilitates high runoff allowing less residence time for rainwater and hence comparatively less infiltration (Prasad et al., 2008) Ruggedness number The ruggedness number is expressed as the product of basin relief and drainage density (Strahler 1958). The high ruggedness value implies that the river basin is more prone to soil erosion and have intrinsic structural complexity in association with relief and drainage density (Vijith and Satheesh 2006). 84