Control of Structure and Tectonics on the Drainage Network Characteristics of Kaveri, Palar and Ponnaiyar Rivers: a DEM-Based Analysis

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Control of Structure and Tectonics on the Drainage Network Characteristics of Kaveri, Palar and Ponnaiyar Rivers: A DEM-based Analysis

Somasis Sengupta

ABSTRACT

O.l.Introduction: The Indian Shield (INS) is one of the ancient and stable parts of the Earth’s crust underlain by Archaean-Proterozoic rocks which have witnessed prolonged denudation for many millions of years (Kale and Vaidyanadhan, 2014). It had formed an integral part of the great Gondwanaland Supercontinent, which stretched as a continuous landmass from South America to Australia till the Mesozoic when it broke up (Kale, 2014). The Dharwar Craton (DC) situated in the southern part of the INS is generally considered to be a stable continental surface and is composed of a mosaic of Precambrian terrains (Valdiya, 2001). Under such circumstances, it was expected that ancient rivers, such as the Kaveri, which drain the DC, display mature relief characteristics and graded profile. However, unlike other cratonic areas of the world, the Kaveri Basin exhibits many geomorphic signatures of rejuvenation and youthful topography (Kale et al., 2014). The river follows an entrenched course across the Biligirirangan-Mahadeswaramalai (BR-MM) Hill Ranges and has carved out a ca 95-km long, deep gorge. The BR-MM Ranges have been identified as horst or block mountains (Valdiya, 2001). Other rivers in the area, such as the Palar and Ponnaiyar Rivers exhibit truncated drainage characteristics. On account of the anomalous drainage and topographic characteristics of the landscape in the DC, it is generally believed that the area is tectonically active (Valdiya, 2001; Ramasamy, 2006a). The control of tectonics, structure and lithology are reflected in the morphological adjustments of the fluvial systems. Surficial geomorphic markers and fluvial responses reveal the nature and degree of litho-structural and tectonic control in an area (Burbank and Anderson, 2001). Hence, geomorphic markers and morpho-tectonic indices have been used by a number of workers across the globe as indicators of active tectonics (Snyder et al., 2000; Goswami et al., 2012 and the references therein). In India, there are relatively fewer studies 25

that have tried to ascertain the tectonic character of an area on the basis muhiple morphotectonic indices and geomorphic markers (Seeber and Gomitz, 1983; Kale and Shejwalkar, 2008). Rather, in most of the studies in India, the substrate characteristics and geophysical attributes have received more attention by the researchers (Lyon-Caen and Molnar, 1985; Bhattacharji et al., 2004; Harinarayana et al., 2006; Malleswari et al., 2012; etc.). The primary aim of this study, therefore, is to systematically investigate whether the much-talked about recent tectonic resurgence is reflected in the relief, drainage network and profile characteristics of the rivers draining this ancient part of the pre-existing Gondwanaland Supercontinent. An attempt has been made to systematically evaluate the control of structure and tectonics on the basin, relief and drainage network characteristics and the channel morphology of the Kaveri, Palar and Ponnaiyar Rivers. The data and results generated from the study could be helpful in understanding the evolutionary history of these ancient rivers draining the Indian Shield.

0.2.The Study area: The area drained by the Kaveri, Palar and the Ponnaiyar Rivers has been selected for the present study. The Kaveri (also Cauvery) River is the largest east-flowing river in South India. It is approximately 800 km long and drains a catchment of about 81,155 km^. The river originates at Talakaveri in the Brahmagiri Ranges of the Western Ghat at an elevation of 1,341 m ASL. From Talakaveri to Shivasamudram Falls, the river flows over the Mysore Plateau, before descending down to the Tamil Nadu Plains, via a -95 km long gorge. SRTM- DEM analysis indicates that the average elevation of the basin is 564 m ASL. About 42 percent of the basin area lies between 650 and 1,000 m ASL. This upland area in the headwaters constitutes the Mysore Plateau. Almost an equal percentage of the catchment area occurs below 400 m ASL. Approximately one-tenth of the basin area is above 2,000 m ASL. The Kaveri Basin, unlike other rivers of Indian Peninsula, displays very high altitudes. The highest elevation in the basin (2,629 m ASL) is found in the Nilgiri Hills, which includes Dodda Betta (2637 m ASL). In the upper and middle reaches, the river flows through the peninsular gneisses and charnockites, respectively with occasional intrusions of Closepet Granite and schist belts of the Dharwar Craton. The lower segment of the river is mostly over Quatemary alluvium with some exposures of Cretaceous sediments (conglomeratic 26

sandstone, fossiliferous limestone and shale) near Tiruchirapally, where the Kaveri starts forming its delta (Pattanaik, et al., 2007). The Palar River rises at the Talagavara Village in the Kolar District of Karnataka at an elevation of 900 m ASL and flows for 370 km over an area of 17,600 km^ before debouching into the Bay of Bengal. The misfit nature of the river is exhibited by the fact that it flows through much wider channel as compared to the valley and basin size. The Ponnaiyar River, sandwiched between the Kaveri and Palar Rivers, originates in the Nandi Hills of Kolar District, Karnataka and drains into the Bay of Bengal at Cuddalore, Tamil Nadu (Pattanaik et al., 2007). The Palar and Ponnaiyar originate over the eastern Dharwar Craton and are underlain by gneisses and granulites before flowing over Quaternary alluvium in the lower reaches (Pattanaik et al., 2007). Monsoonal climate with a pronounced orographic effect dominate the region. Over 75 % of the annual rainfall and runoff and 85 % of the annual sediment load is carried during the rainy season (Vaithiyanathan et al., 1992). The average annual precipitation in the basins varies from ca. 3,800 mm in the Western Ghat zone to ca. 500 mm in the lower reaches. The upper reaches are dominantly under the influence of summer or southwest monsoons but the lower sections receive rainfall from both southwest (summer) as well as northeast (winter) monsoons. The average annual runoff for the Kaveri is about 21.4 km \ which is significantly lower than other large rivers of the Indian Peninsula, such as the Godavari (111 km^), the Krishna (78 km^), the Mahanadi (67 km^) and the Narmada (46 km^), (CWC, 2012) implying very low denudation rates. Hydrologically, the Palar is an intermittent river with abnormally low discharges during the dry season. The highest flow is generally recorded in the months of October to December, the NE Monsoon season.

OJ.Major Objectives of the Study: In the present study, digital geomorphometry supplemented by geomorphic, geological and stratigraphical analysis were carried out to achieve the following objectives: • To identify the major anomalies in the drainage network of the Kaveri, Palar and Ponnaiyar Rivers and to find out if there is any evidence of drainage reorganization. • To ascertain as to what extent, the structure and lithology have exerted a control on the drainage network and channel morphology of these rivers. 27

• To determine whether there is any evidence of control of recent tectonic activity on the channel morphology of these rivers. • To synthesize the geomorphic and geological data and to understand the probable reasons for the present drainage network anomalies in the study basins.

0.4.Methodoiogy:

A combination of geomorphic surveys, digital geomorphometry and DEM analysis, fieldwork, stratigraphical and sedimentological studies and OSL dating was used to reconstruct the geomorphic and tectonic history of the areas drained by Kaveri, Palar and Ponnaiyar Rivers.

0.4.1. Digital Geomorphometry:

The present study is based on the analysis of the 3-arc sec (90 m) Shuttle Radar Topography Mission (SRTM) digital elevation model data (DEM) for the river basins under study. DEM analysis in ArcGIS included the following aspects:

(a) Extraction of Morphometric Attributes: These are the quantitative parameters of the landscape that are derived from the terrain or the elevation surface and drainage network within a catchment (Goudie, 2004). These include: catchment size properties such as drainage area, basin length, main channel length and stream order; relief variables such as absolute relief, local relief and relief ratio; surface attributes viz. slope, aspect and curvature; shape attributes such as circularity ratio, elongation ratio and form factor and the textural parameters viz. drainage density, constant of channel maintenance, stream frequency and bifurcation ratio. (a) Analysis of river longitudinal profiles: The longitudinal profile of a river represents its long-term morphologic adjustment to the varying conditions of climate, lithology and tectonic activity. SRTM data were used in ArcGIS to extract the drainage network of the river basins under consideration. The channel bed elevation and distance data were used to derive the normalized longitudinal profiles and the Hack’s (1957) stream gradient index. The 28

stream profile concavity and steepness indices were estimated from the log-log relationship between basin area and channel slope.

(b) Morphotectonic indices: Morphotectonic indices are quantitative attributes of a drainage basin that reflect the direct response of a fluvial system to recent or past tectonic movements. The most useful and commonly used indices of active tectonic activity, such as hypsometric integral, stream gradient index, drainage basin asymmetry, basin elongation ratio and valley width-depth ratio were derived for the river basins under consideration as well as their major tributaries. These indices were used to classify the basins into three classes of active tectonics.

0.4.2. Identification o f Geomorphic Anomalies: In a fluvial system, some of the most common geomorphic anomalies are linear stream segments, presence of knickpoints and gorges, hanging valleys, outsized channels, sharp deflections in the courses of the rivers, etc. In this study, all the major drainage anomalies in the three rivers have been mapped from DEM data and satellite imageries as well as on the basis of field studies. It is generally expected that the areas affected by tectonic activity are associated with high stream powers and sediment yields. Hence, these parameters were also taken into account. In addition, tidal records at Chennai were also analyzed to detect evidence of tectonic movements in the coastal areas.

0.4.3. Fieldwork: Field work was carried out in all the three basins in order to locate older fluvial records. Older alluvial deposits were located along the Kaveri near Hogenakkal in Tamil Nadu in the middle reach of the river, in a high-gradient barbed tributary at Biligundulu as well as upstream of Shivasamudram Falls near Talakad and Siddapur. Stratigraphical studies were carried out at all these sites. Grain size and XRF analyses of the Biligundulu samples were carried out in the laboratory. About 8-10 samples were sent to the Department of Geosciences, National Taiwan University, Taipei, Taiwan for Optically Simulated Luminescence (OSL) dating. 29

Eleven sites were selected on the Palar River in order to understand the anomalies in this river. Electronic Distance Measurer (EDM) survey was carried out in all the sites in order to obtain information regarding the channel dimensions of this river. The channel cross-sectional data obtained for various sites on the Palar River were compared to those of other rivers in the world in different climatic and hydrological regimes.

0.4.4. Geological and Seismic data: In addition to the above analyses, mapping and analysis of lineaments was carried out using satellite imageries as well as DEM data. The lineament map and the seismicity map of the area were compared to understand their association. Furthermore, the Bouguer Gravity Anomaly map of South India was overlain on the elevation and slope map of the basins to evaluate the nature of relationship.

0.5. Arrangement of the text: The entire thesis has been divided into six chapters. The first chapter deals with the introductory part, and includes the definition of the research problem, the objectives of the study, the description of the Kaveri, Palar and Ponnaiyar River Basins, the methodology used in this work and a brief review of all the previous works related to the research problem. The morphometric properties of the rivers under examination have been presented and discussed in the second chapter. These attributes have been computed from SRTM data. Maps prepared in ArcGIS have been used to represent the data. The next chapter is devoted to the longitudinal profiles of the major rivers in the Kaveri, Palar and Ponnaiyar Basins. The fourth chapter comprises the discussion of the indices of active tectonics derived for the rivers under examination. Basinwise variations in the tectonic indices have also been discussed and the individual morphotectonic indices were grouped into specific clusters of tectonic activity. The results were also compared with the findings of other workers. The fifth chapter deals with various geomorphic evidence of litho-structural and tectonic control on the Kaveri, Palar and Ponnaiyar Rivers such as hanging valleys, knickpoints, gorges, configuration of the delta, etc. The unit stream power, sediment loads and the rate of denudation of the major rivers have also been discussed in this chapter. 30

Various fluvial surficial markers were supplemented by geological and geophysical evidence such as lineaments, Bouguer Gravity Anomaly and seismicity in order to ascertain the role of lithology and tectonics on the drainage network of the Kaveri, Palar and Ponnaiyar Rivers and their tributaries. The sixth and last chapter summarizes and explains the major findings of the study. Besides providing suitable explanations for these results, an attempt has been made in this chapter to explain the control of structure and tectonics on the drainage network and the channel properties of the rivers under examination and also the channel adjustment to the tectonic events are explained by synthesizing the information presented in the second to the fifth chapter.

0.6. Major Findings: The chapterwise (Chapter II to VI) major outcomes are summarized below:

0.6.1. Chapter II (Relief and Drainage Network Morphometry): Using SRTM-DEM data, the relief (absolute, relative and relief ratio), surface (slope, aspect, curvature) and the drainage textural parameters (drainage density, constant of channel maintenance, stream frequency and bifurcation ratio) of the river basins have been analysed. The results reveal that the relief parameters register higher values in the Kaveri Basin than in the Palar and Ponnaiyar Basins. From the analyses of the morphometric characteristics of the Kaveri, Palar and Ponnaiyar Basins, one striking observation that can be made is that the middle domain of the Kaveri Basin exhibit higher values of mean elevation, relief ratio and mean slope. Most of the tributaries meeting the Kaveri in this domain, such as Arkavathi, Chinnar, Dodda Halla, Nagavathi and Thattai Halla are characterized by higher values of relief and slope parameters. In the upper domain, although the tributaries display higher elevation (798 - 933 m ASL), the local relief is low as compared to the middle domain. This implies that the higher elevation areas in the Kaveri Basin, which comprise the previously uplifted Mysore Plateau Surface, are characterized by relative subdued erosional rates. This statement is corroborated by the fact that significant negative relationship exists between elevation and 31

the drainage density. This means that the higher elevation areas are comparatively less dissected. This is typically the case associated with the Mysore Plateau.

0.6.2. Chapter III (Analysis o f longitudinal profiles): The longitudinal profile of a river represents its long-term morphologic adjustment to the varying conditions of climate, lithology and tectonic activity. In this study, the 90 m resolution SRTM-DEM data have been processed in ArcGIS to extract the lon^i^dinal profiles of the Kaveri, Palar and Ponnaiyar Rivers and tneir major tributaries. The longitudinal profile of the Kaveri River does not show the typical concave-up form of a steady state river profile of an ancient river. Three distinct channel segments are observed. The upstream segment of the Kaveri over the Mysore Plateau and the lower segment over the Tamil Nadu Plains are characterized by relatively gentle gradients. Along its middle reach, the river is deeply entrenched in bedrock. This reach is steeper by an order of magnitude and exhibits conspicuous breaks. This high-gradient reach coincides with the course across the block mountains (BR-MM Hill Ranges) between Shivasamudram and Hogenakkal (also Hogenakal) Falls. The SL or stream gradient Index (Hack, 1957) of the rivers in the Kaveri Basin (11 to 239) is noticeably higher than the Palar and Ponnaiyar Basins (12 to 130). Highest SL indices are displayed by Dodda Halla (161), Thattai Halla (133), Chinnar (120), Palar (114) and Arkavathi (71). The profile concavity index values range from -0.94 (for Arkavathi) to 2.49 (for Nagavathi). Some tributaries such as the Thattai Halla (-0.24) and Shimsha (-0.12) register negative concavity whereas low positive concavity is observed in the case of Chinnar (0.03), Noyyil (0.05) and Dodda Halla (0.16). Furthermore, the normalized steepness index, calculated by taking the reference concavity of 0.45, registers higher values for tributaries with lower concavities, such as Dodda Halla (60), Chinnar (45), Arkavathi (35) and Suvarnavati (32). Most of these tributaries fall in the middle domain of the Kaveri Basin. Analysis of the longitudinal profiles reveals that the tributaries in the middle domain of the Kaveri Basin display higher values of SL Index and normalized steepness. Also the concavities of these rivers are much lower. Therefore, it appears that the middle domain of 32

the Kaveri Basin exhibits some characteristics associated with the rivers under recent diastrophism.

0.6.3. Chapter IV (Geomorphic Indices o f active tectonics): Tectonic indices are reconnaissance tools to evaluate the relationship between tectonics and basin morphology and to identify geologically recent deformation. Calculation of these indices for the Kaveri, Palar and Ponnaiyar Rivers and their tributaries was achieved through the analysis of the 90 m SRTM data. The indices include hypsometric integral (HI), stream gradient index (SL), valley width-height ratio (Vf), basin elongation ratio (Re) and drainage basin asymmetry (Af). Hypsometric integral, which describes the distribution of elevation across an area, is below 0.5 for most of the basins. The values of HI are low for the tributaries in the upper and lower domains (0.12 to 0.26 and 0.1 and 0.27, respectively). The tributaries of the middle domain, such as Dodda Halla (0.53), Shimsha (0.41), Arkavathi (0.40), Palar (0.37) and Thattai Halla (0.32) register relatively higher values of HI. These are also the rivers with lower valley width-height ratio (14-49). In the upper domain, the Vf is much higher, in the range of 78 to 133, whereas the lower domain provides still higher values of Vf (223 to 309). All the streams in the Palar and Ponnaiyar Basins are characterized by wide valleys ( Vf 87 to 531). The Elongation Ratio ( R^) of most of the basins is higher. The higher values are observed for Palar (0.75), Dodda Halla (0.74), Shimsha (0.74), Kabbini (0.73) and Chinnar (0.71). The exercise to identify the zones of potential tectonic activity on the basis of ranks and cluster analysis further confirms the earlier observations that the middle domain of the Kaveri Basin is probably the area of moderate to high tectonic activity. Elsewhere, the tectonic activity appears to be insignificant. The morphotectonic indices derived for the study area are nowhere close to the values observed for tectonically active regions, such as Himalaya. Nevertheless, from the above analyses it is evident that most of the morphotectonic indices point to the possibility of active tectonic deformation in the middle domain of the Kaveri River. In comparison, the upper and lower reaches of the Kaveri Basin as well as the Palar and Ponnaiyar River Basins do not provide any evidence of tectonically-induced rejuvenation. 33

0.6.4. Chapter V (Litho-structural and tectonic control on drainage and stream profiles): In order to get a better idea about the nature of tectonic activity in the three river basins under consideration, information regarding the Bouguer gravity anomaly and the distribution of seismic activity in southern India was also obtained from various literary sources. The lineament map reveals that the area of high lineament density occurs between the Kollegal-Shivasamudram Fault and Hogenakkal Fault (Valdiya, 2001). About 18 % of all the stream courses in the Kaveri Basin exhibit a direct control of lineaments whereas the corresponding values for the Palar and Ponnaiyar Basins are 11 and 6, respectively. Two anomalous bends Vaniyambadi and Changam occur in an area of high lineament density. That some of the lineaments are active is indicated by the fact that many of the recent and historical earthquakes in the middle domain of the Kaveri Basin are associated with the faults, viz. Kollegal-Shivasamudram Fault. A good negative relationship exists between Bouguer gravity anomalies and elevation. This implies that higher elevation areas typically exhibit gravity lows (i.e. negative gravity anomaly) and vice versa. The Kaveri River in its middle reach exhibits a number of drainage and channel anomalies, such as, knickpoints, gorges, sharp bends, linear stream segments, hanging valleys, etc. Fault and lineament control on topography is particularly well reflected in the presence of these drainage and channel anomalies. It appears that lithology, to some extent, has also contributed to the development of the knickpoints and gorges on the Kaveri River. For example, the knickpoints at Chuchunakatte and Shivasamudram appear to be lithologically-controlled. Furthermore, at Mekedatu, where the width of the channel is the narrowest, the river has to incise through the resistant Closepet granites. In order to ascertain whether the Kaveri Gorge is of recent age, OSL dating of the fluvial deposits near Hogenakkal was carried out. The OSL dates reveal that these deposits were laid down by the Kaveri River during the late Pleistocene (30 to 40 ka BP). The dates imply that if the gorge is tectonically-induced then the event is not very recent, and the rate of fluvial erosion in this reach is subdued. This observation is further supplemented by data on unit stream power and sediment load at different sites in the Kaveri Basin. Estimates indicate that the unit stream power values within the gorge section are around 325 w W (at Biligundulu and Hogenakkal). 34

However, the values of unit stream power of these sites do not match with those obtained for rivers draining actively uplifting areas, such as the Himalaya, obtained by previous workers. Further, the annual sediment load of the Kaveri River (1.5 * 10^ tons/yr) as well as the rate of denudation (40.5 tons/km^/yr) are modest in comparison with other Peninsular rivers (Singh et al., 2008; Panda et al., 2011). All these observations indicate that the area is not undergoing rapid tectonic deformation at present. The Palar River over the Tamil Nadu Plains reveals some unusual characteristics - a) the river displays abnormally high rate of change in the channel width with catchment area, and b) the drainage network reveals very sharp bends and truncated nature of the drainage. These anomalies have been explained in terms of large floods on Palar, river capture and drainage reorganization. The unusually wide channel of this river does not imply active tectonic deformation in this part of the Tamil Nadu Plains.

0.7. Major Conclusions: Several conclusions may be drawn from the data and analysis presented in Chapters II to V. Only the salient ones are listed below:

• The morpho-tectonic indices of active tectonics, the longitudinal profile parameters and various geomorphic markers provide sufficient evidence to infer that the middle domain of the Kaveri Basin, coinciding with BR-MM Ranges, is tectonically active. Indisputable evidence such as hanging valleys, bedrock gorges, multiple knickpoints, etc. suggest rapid ongoing erosion by the Kaveri River and its tributaries in this domain. • In comparison, various lines of evidence indicate that the upper and lower reaches of the Kaveri River as well as the Palar and Ponnaiyar Basins are areas of relative tectonic stability. Unusually wide channel of the Palar River, absence of any trend in the tidal gauge data during the last six decades and lower values of the morphotectonic indices of active tectonics are suggestive of only relative stability of the landscape for a long time. 35

Although the drainage, relief and valley characteristics in the upper domain do not provide any indication of geological recent tectonically-induced rejuvenation, the higher elevation of the Mysore Plateau (ca. 700-900 m ASL) implies that it an old and relict landscape that was previously uplifted, sometimes before Miocene (Gunnell, 1998a). Notwithstanding the fact that the middle domain of the Kaveri Basin displays signs of intense fluvial erosion in response to active tectonic deformation, the rates do not appear to be unusually high as expected. The luminescence ages (30-40 ka BP) of the ancient alluvial deposits preserved near Hogenakkal not only suggest a major phase of deposition in the late Pleistocene, but also that the river has not actively incised its bed since this phase. The OSL dates of sediments of the Kaveri Delta ftirther imply that the present delta region has received only modest amounts of sediment from the upper catchment in general and the Kaveri Gorge in particular during the last ~ 100 ka. In addition, very modest values of sediment yield and specific stream power in the gorge section of the Kaveri River only indicate that the tectonically-driven rejuvenation in this domain does not appear to be as geologically recent as postulated by earlier workers.