Abstract
Abstract. Chilika lagoon, one of the largest brackish water lagoons in Asia located along the east coast of India. The rivers draining into the lagoon carry about 13 million tonnes of sediments annually. Because of the cohesiveness properties of the fine sediments, nutrients, heavy metals and other polluted substances tend to bind to the sediment’s surface. Consequently, pollutants can be concentrated in the inlets/estuaries, thus being of great environmental interest. In addition, the mudflats occurring are important biotopes for a large number of micro- and macro-faunal species and act as feeding places for a number of birds. To understand the cohesive sediment dynamics, a numerical model, MIKE 21 Mud Transport (MT) coupled with hydrodynamic (HD) was used. The model simulated the relative bed level height and suspended sediment concentrations. The sediment interchange and accumulation between each sectors and Bay of Bengal were evaluated. The suspended sediment concentration is high in the north-east portion of the lagoon while medium and low suspended loads are observed in the eastern and western portion of the lagoon. Bed thickness is very high in the north-western corner of the lagoon covered with Phragmites Karka which facilitate sediment trap. Total bed thickness change is very much pronounced in the northern sector which receives most of the sediments from the Mahanadi river systems as well along the periphery of the lagoon due to drainage. The eastern lagoon shows a net deposition accumulated fraction (5–15 kg/m2) and hence gives enough indication of the sedimentation processes in the lagoon. Further, the results also warrant immediate attention to check and monitor suspended sediment concentration to find out the net deposition trend in the lagoon environment in order to take decisions in minimizing the sediment load.
Highlights
A coastal lagoon is a distinct dynamic environment where interplay of different energy forces from land-sea-atmosphere operates in a shallow body of water which is partly enclosed by a barrier and which has restricted or ephemeral communication with the sea through one or more inlets
Water quality assessment of the Chilika lagoon using Indian Remote sensing Satellite (IRS) data was attempted by Sudhakar and Pal, (1993) and Pal and Mohanty, (2002) and the results showed significant temporal and spatial variability in the silt load
Hydrodynamics of the lagoon especially the circulation pattern is prerequisite to estimate the other processes in the lagoon
Summary
A coastal lagoon is a distinct dynamic environment where interplay of different energy forces from land-sea-atmosphere operates in a shallow body of water which is partly enclosed by a barrier and which has restricted or ephemeral communication with the sea through one or more inlets. The mudflats occurring are important biotopes for a large number of microand macro-faunal species and act as feeding places for a number of birds (Eisma, 1998). This makes forecast of erosion, transport and deposition of cohesive sediment of great interest in all lagoon systems. Efficient modelling requires the knowledge of several related factors-dynamics / circulatory pattern (Blumberg, 1977; Rao, 1995; Rao et al, 1999) (transport by the moving waters), chemical (decay, reaction between substances), physical (transition between different states) and biological (migration of species), transport of nutrients. The interaction of fresh water, saline water from the ocean and Study Area environmental importance of cohesive sediment transport, accurate simulation of cohesive sediment transport processes in Chilika lagoon are necessary for environmental management, dredging studies, damming projects and even global sea level rise
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