Call For Paper Volume:4 Issue:6 Jun'2017

Effect of Turbulence on Deposition of Cohesive Sediments

Publication Date : 28/02/2015

Author(s) :

Mr. Anurag Subhash Kale , Dr. Trimbak M Parchure.

Volume/Issue :
Volume 2
Issue 2
(02 - 2015)

Abstract :

Depositional characteristics of marine sediment occupy a paramount position in the field of Coastal Engineering and Environmental Engineering. The knowledge of Deposition, Transportation and Consolidation of fine sediment is very essential in design and dredging of navigation channels and development of ports for sustainable growth of any country. Deep water ports have played a significant role in improving the economy of all the rich countries in the world. One would intuitively think that that the rate of deposition of sediment would be higher under still water condition than under turbulent condition. Turbulence is expected to bring bottom sediment in suspension and keep it in suspension for longer duration. This is true for non-cohesive sediments. However, fine sediments flocculate and form larger and heavier flocs due to increased inter-particle collision rate resulting from low turbulence. Hence the micron-sized cohesive sediment flocs settle faster under low turbulence than under static condition. The results of experiments reported in this paper provide experimental proof for this interesting phenomenon. Laboratory facility in the form of Jar Test apparatus was used in the present study. In addition, another set-up in the form of twelve glass cylinders of 250 ml capacity was also used. Borosilicate beakers of 1 litre capacity were used in the jar test apparatus to evaluate the effect of turbulence on cohesive clay minerals as well as natural sediment. Varying suspensions of sediment concentrations were prepared by using a) Sea water, b) Tap water, and c) Reconstituted Sea water. Natural sediment obtained from Rohini Port, located on the west coast of India was used for experimental work. This sediment prevailing in saltwater of the ocean contained about 50 percent of clay particles with size less than 12 microns. Experimental results with 1 litre beakers kept in the quiescent condition showed that the minimum sediment concentration needed for forming an interface was 3 gm/l for natural sediment. Effect of low turbulence generated in 1 litre capacity beakers gave very important conclusions. When the vanes were rotated at varying low speeds, effect of turbulence on cohesive sediments and natural sediment gave clear and defined results indicating that lower the RPM for rotating vanes, higher was the sediment settlement rate. Also rotation speeds varying between 5 and 20 RPM, 5 RPM gave the highest rate of sediment settlement. Graphs of % deposition with and without turbulence were plotted for the cohesive sediments as well as for the natural sediment with varying concentration. This paper is an Interim stage of research work, which has been undertaken and only the results available as of now are reported

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Effect of Turbulence on Deposition of Cohesive Sediments

February 24, 2015