Morphometric analysis of the River Thamirabarani sub-basin in Kanyakumari District, South west coast of Tamil Nadu, India, using remote sensing and GIS

The quantitative analysis of the drainage morphometric system is vital to understand the hydrological and environmental interaction and its processes of an area. The present study deals with quantitative characteristics of morphometry of steep slope and short length sub-basin of R. Thamirabarani in Kanyakumari District, Tamilnadu, India, using geospatial technology. In this study, the digital elevation model data product (ASTER DEM), Landsat ETM+ image and Survey of India topographical map were used to delineate slope, relief and drainage system structures such as drainage pattern, stream order, stream network and stream length of the sub-basin using ArcGIS 9.3 software. The morphometric analysis deals with hydrologic processes such as stream frequency, bifurcation ratio, circulatory ratio and length of overland flow of the sub-basin area and their influences on the local morphologic landforms. The quantitative measurement of these characteristics is used to explore the basin's contribution to the hydrological cycle and the shape, size and formation of the local landscapes in the region. Moreover, the hypsometric analysis and denudation rate were estimated for understanding the quantitative geomorphological characteristics of the sub-basin. The relationship of the morphometric parameters reveals that the drainage network is strongly controlled by geological and geomorphological structures of the area. The geometry of streams exhibits dendritic drainage pattern associated with coarse drainage texture in primary order of streams present on hilly terrain surface and semi-dendritic pattern in higher stream order flow on less elevated surface with gentle slope. The drainage density of the study area ranges from 0.1 to 1.89 km/km(2), and the maximum density value was found along the higher stream order. The mean bifurcation ratio of this area is 4.21 and the high ratio was measured between the third and fourth order of stream segments. The morphometry of this area is depicted by the length of the stream segment, drainage pattern and stream flow direction, which are influenced by relief, steep slope and local geological structure. Furthermore, the sub-basin is found to be strongly elongated in shape with a length of 42.78 km, and the circularity ratio of this area is measured as 0.33 and elongation ratio as 0.57. The textural dissection of the landforms shows low drainage density in the high elevated hilly terrain in the north and high level in the plain areas in the southern part. The values of the circulatory ratio, length of overland flow and elongation ratio are relatively close to one another and the relationship among them shows their influences on the process of surface runoff and sediment deposition along the estuary landforms in the study area. Moreover, it is observed that the hypsometric curve of this study area is characterized by convex-up shape in nature and represents the youth stage (inequilibrium) of landscapes. Consequently, the hypsometric integral value 0.49 reflects the distribution of a major volume of the landmass (435.32 km(2)) at relatively low elevations (< 180 m). The morphometric parameters-induced denudation rate of this study area is 65.14 t/km(2)/year and indicates the occurrence of a wide range of denudation intensities throughout the sub-basin, which is relatively proportional to the suspended sediment yield that is transported in the suspension per unit area. Based on the realistic output, it is proved that remote sensing and GIS are effective tools for morphometric studies of the drainage basin.