Geomorphological and Drainage Morphometrical Relationship of Gem Potential Alluvial Deposits in Upper Kalu Ganga Basin, Sri Lanka: A Remote Sensing and GIS Based Approach

Several alluvial deposits in the Kalu Ganga basin are the most prominent secondary gem deposits in Sri Lanka. The quantitative morphometric analysis of watersheds is necessary to understand the hydrological setup of an area and the spatial distribution of alluvial formations. Since the processes involved in weathering, erosion, and sediment transport are directly imprinted on the land surface, an attempt was made to study drainage morphometry and morphology of the Upper Kalu Ganga basin to understand hydrologic processes that influenced the formation of secondary gem deposits. Digital Elevation Model (DEM) with GIS application and field observations were applied for the present study. Calculated linear, areal, and relief morphometric parameters of the basin indicate surface runoff, potential energy, susceptibility for soil erosion, denudation rate, sediment yield, and discharge rate are likely to be much higher in Kalu Ganga Head-watershed, Rath Ganga, and Hangamu Ganga while sediment deposition is higher in Kuru Ganga and Katugas Ella. The surface roughness studies enable to identify the localities of alluvial deposits that may carry gem-bearing sediments. Among the several methodologies used, multivariate analyses of morphometric parameters are the most viable and cost-effective for evaluating possible gem-bearing alluvial deposits on a regional scale, despite their limitations.