Summary

Studying the weathering and erosional processes within fluvial systems has become very importance because stream sediment data is often required when we utilize the natural resources in the physical environment. However, the high cost prevents the monitoring and collection of these data from for all the rivers and tributaries in the world. Therefore, sediment data are predicted for ungauged streams from rating curves or through hydrological modeling. These modeled data are not applicable world-wide because sediment transportation patterns vary both spatially and temporally. Therefore, the first objective of this research is to analyze the sediment generation and delivering patterns in space and time in a small watershed, which is being developed as an experimental catchment at the University of Peradeniya, located in the humid tropical Climate. The natural weathering and erosional rates have been measured in the Central Highlands of Sri Lanka using the advanced analytical method of applying cosmogenic nuclides and chemical mass balances. The second objective is to unravel the causes of low weathering and erosional rates and identify mechanisms that operate in the prevailing climatic and topographic settings.

The Ma Oya, a tributary of the Mahaweli River, originating from a catchment area of about 5.4 km2 in the Hantana Mountain Range has been selected for this study. At present, this catchment is being developed as an experimental watershed of the University of Peradeniya and the installition of automatic atmospheric and hydrological observation systems are under way. In this ongoing project, funded by the University of Peradeniya, the Ma Oya catchment will be continuously monitored and hydro-meteorological parameters will be collected at a higher resolution (at 15 minute intervals). In the proposed (new) project, the concentration of suspended sediment loads will be monitored in four mini-catchments within the larger Ma Oya Catchment for an entire hydrological year. These mini catchments have been selected such that they represent a diverse range of topographic and land use patterns. The chemical constituents in surface water of the streams in the four min-catchments and groundwater in ten selected wells will be monitored on regular basis. Mineralogical and chemical characteristics of representative regolith profiles within the catchment and suspended loads in the stream will also be analyzed extensively in the new project. The spatial variation of chemical weathering intensity within the catchment will be studied with magnetic susceptibility measurements of sediments and soils.

One M. Phil. student will also be trained in the proposed project. The instrumentation of the Soil Science Laboratory of the Department of Geography will also be upgraded. Weathering and erosional processes in the Experimental Ma Oya Catchment will be better understood and results will be documented. Besides the M. Phil. thesis, two research articles will be written and published in indexed journals.

Objectives

1. To determine spatial and temporal variation in transportation of sediment loads in monsoon rain-fed streams in tropics
2. To determine the suspended load transportation pattern across the stream profile
3. To derive geological, morphological and environmental control in sediment generating and delivering process in tropical catchments
4. To study geochemical behavior of chemical constituents and mineralogical transformation in the process of chemical weathering in tropics

Major Equipment Facilitated by Grant