International Journal of Science and Research (IJSR) ISSN (Online): 2319-7064 Index Copernicus Value (2013): 6.14 | Impact Factor (2013): 4.438 Volume 4 Issue 8, August 2015 www.ijsr.net Licensed Under Creative Commons Attribution CC BY A Geomorphological Analysis of the Longitudinal Profile of Tambraparni River, Agasthyamalai Sub- Cluster, South Western Ghats Karthika Krishnan 1 , S. Mohana Kumar 2 1 School of Earth & Atmospheric Sciences, Madurai Kamaraj University, Madurai, India 2 Department of Geology (Retd.), University College, Trivandrum, India Abstract: This paper is a part of the author’s research work dealing with the geomorphometry and geomorphology of the Tambraparni River Basin (Kanyakumari district), located on the Western flank of South Western Ghats. The Western Ghats mountain chain running parallel to India’s western coast extends from the state of Gujarat in the north up to Tamil Nadu in the south, over a distance of 1600 km uninterruptedly. The present work endeavors to interpret the geomorphology of the Tambraparni River through longitudinal profile approach. The study of longitudinal profile shows a smooth, parabolic curve, gently concave to the sky, practically flat at the mouth and steepening towards the source for the Tambraparni River that helped the classification of the river channel into four reaches namely lower, middle, upper and higher reaches. Moreover, a notable irregularity that affected the gradient of the longitudinal profile of the stream has been identified as knickpoints enabling further detailed study in the linear distribution pattern and the genetic relationship of waterfalls in the southern tip of Western Ghats mountain chain. Keywords: Geomorphology, Longitudinal profile, River basin, Western Ghats, Knickpoints 1. Introduction The simplest morphological expression that contains the greatest amount of information on the Geomorphology of a river system is the study of longitudinal profile of the river. A river longitudinal profile or long profile shows the shape of the river's course from its source to its mouth. It shows the changing width, depth and gradient of the channel from upstream to downstream. The long profile shows how, in the upper stage of a river’s course, the river’s gradient is steep but it gradually flattens out as the river erodes towards its base level. The most striking observable fact related to long profiles is their form. The plotting of these profiles displays altitude (from amsl) against distance (from stream mouth) and resulting form is a curve more or less regular, the concavity of which increases towards the source region of the stream. The stream profile concavity is assumed to be a common, most obvious and persistent feature and it is considered as a universal feature, regardless of the climatic condition, length of the river or the nature of the country rocks over which the river flows. This, largely generalized observation on long profiles of the streams is a fascinating topic of research for geologists, geomorphologists and geographers everywhere. Gilbert in 1877 provided a significant explanation for the form of the long profile for the first time. Numerous laboratory studies conducted during the subsequent years showed that the slope of the long profile is inversely proportional to the discharge of the associated stream. Further studies were made to assess the influence of variables other than discharge, on long profiles. These variables included the nature of the river bed material, the stream load (suspended or bed load), the type of the rock forming the stream channel etc. These studies led to the conclusion that the variation of the discharge (Q), the mean diametre of the river bed material and the sediment load are the most important factors influencing shape of the long profile of streams. However, studies also revealed the fact that a number of other factors, such as the erodibility of the rocks, presence and proximity of tributaries, neotectonic movements and structural discontinuities etc., also account for any deviations from the general form of the long profile, without fundamentally modifying it. The concavity in the long profile of rivers has traditionally been explained through the introduction of the concept of grade, in which the slope declines downstream as a consequence of the interplay between discharge, bed material size, sediment load and morphological characteristics of the channel (Mackin, 1948). Subsequently, the concept of equilibrium profile was introduced in place of the term graded profiles. The term equilibrium profile is defined as a smooth curve without important discontinuities. In natural conditions, many rivers with long profiles with no discontinuities, deviates strongly from the supposed equilibrium curve, because of local influences of the tributaries, changes in the quality of river bed material, the influence of vegetation, neotectonism, base level changes and so on. The form of longitudinal profile or long profile of rivers and their scientific descriptions began to appear in geomorphology during 1950s - 70s (Shulits, 1941; Yatsu, 1955; Hack, 1957 and Brush, 1961). In 1990s the study of river profiles were resumed with new arguments and new research methods (Snow and Singerland, 1987; Ohmori, 1991; Scheidegger, 1991; Susan Rhea, 1993 and Morris and Williams, 1999). Paper ID: SUB157456 963