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Energy Condition of Deposition and Source of Sediments in the Bengal Basin from Grain Size Analysis

Dilip K. Datta*
Environmental Science Discipline, Khulna University, Khulna 9208, Bangladesh

V. Subramanian
School of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110067, India

Abstract/ Executive Summary:

The annual sediment discharge of the Ganges-Brahmaputra–Meghna (G-B-M) river system– estimated in the Bengal basin–is one of the highest globally, and more than 60% of this sediment load is delivered in the delta itself. The sediments typically consist of fine to very fine sand, silt and clay. The sediments are poorly sort ed and positively skewed suggesting dominance of the finer-grained portion relative to the mean size. The distribution is mostly leptokurtic. A relatively high-energy hydraulic environment affects their deposition which takes place mostly under a graded (for bed sediments) and uniform suspension (for suspended sediments) condition. The riverbank and flood plain sediments show close similarity in size with the riverine sediments of the Bengal drainage basin, and could be a major source of river sediments. Sediments transported by the Himalayan rivers are relatively fine grained compared with that of the sediments transported by the Peninsular rivers to the Bay of Bengal.

Keywords: Grain size analysis; Energy condition of deposition; Bengal basin; Bangladesh

Location: In the Bengal Basin

Start Date:

End Date:

Program Area: Resource Development and Management

Commodity: Land degradation

Objectives:

No study has yet been made that has considered the grain size distribution of the total Bengal basin with respect to other major river sediments of the subcontinent. Moreover, because of the mere catastrophic volume of the sediments annually delivered to the basin, the sediments deserve an integrated grain size study. We report here our results on the grain size distribution of the riverine sediments of the Bengal Basin and we applied the statistical parameters as a tool for discriminating depositional processes.

Methodology:

Bed and suspended sediments were collected during 1991-94 at different stations throughout the basin in different seasons. The bed sediments were collected from the top few centimeters of the river channel, and the suspended sediments were decanted out of 10-liter water samples collected at a depth of 50-100 cm from the water surface approximately at the middle of the channel. The grain size distribution was determined by a sieve shaker (Fritsch Analysette 03.502) and Laser Particle Sizer after treating the samples with 25% H2O2. The statistical parameters of bed sediments were derived by the graphic method (Folk and Ward, 1957) and that of the suspended sediments were derived by the method of moment.

Source of Information: Khulna University Studies 2(1): 63-70

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Since the sediments are mainly derived from a floodplain which is important globally for the concentration of population (more than 400 million) and intensive agricultural activities (Crow, 1995), they might carry anthropogenic contaminants capable of polluting the natural aquatic system. Thus this sediment mass offers a good opportunity for studying their various geochemical components. Moreover, the mere amount of the sediment flux through the basin to the Bay of Bengal is significant enough to influence a tropical marine system such as the Bay of Bengal.

Knowledge Management: Journal