• Ratheesh Ramakrishnan

      Articles written in Journal of Earth System Science

    • Simulation of suspended sediment transport initialized with satellite derived suspended sediment concentrations

      Ratheesh Ramakrishnan A S Rajawat

      More Details Abstract Fulltext PDF

      Suspended sediment transport in the Gulf of Kachchh is simulated utilizing the suspended sediment concentration (SSC) derived from Oceansat OCM imagery, as the initial condition in MIKE-21 Mud Transport model. Optimization of the model mud parameters, like settling velocity and critical shear stress for erosion are realized with respect to the sediment size distribution and the bottom bed materials observed in the Gulf. Simulated SSCs are compared with alternate OCM derived SSC. The results are observed to be impetus where the model is able to generate the spatial dynamics of the sediment concentrations. Sediment dynamics like deposition, erosion and dispersion are explained with the simulated tidal currents and OCM derived sediment concentrations. Tidal range is observed as the important physical factor controlling the deposition and resuspension of sediments within the Gulf. From the simulation studies; maximum residual current velocities, tidal fronts and high turbulent zones are found to characterise the islands and shoals within the Gulf, which results in high sediment concentrations in those regions. Remarkable variability in the bathymetry of the Gulf, different bed materials and varying tidal conditions induces several circulation patterns and turbulence creating the unique suspended sediment concentration pattern in the Gulf.

    • Sediment dispersal pattern along an engineered micro-tidal tropical estuarine beach

      DIKSHA KARAPURKAR V S HEGDE RATHEESH RAMAKRISHNAN

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      To evaluate the annual sediment dispersal pattern, a year-long beach profile monitoring and granulometric analysis were adopted along the Kundapura estuarine beaches of coastal Karnataka. The river mouth is bounded by breakwaters and the coast is armoured by seawalls and groins. Beaches adjacent to the breakwater showed progradation as a result of the shadow zone created due to the sheltering effect from incident waves. Evidence also comes from the replacement of coarser mode sediments by finer. Those away from the shadow zone, however, experienced extensive erosion. They are subjected to along-shore drift and minimal replacement from the same. It was also observed that despite being tropical estuarine beaches, sediments did not show any affinity towards a Cuvial-derived character. These points towards transport of fine sediments further offshore and retention of coarser fraction in the surf zone that is to be carried shoreward. Breakwaters in turn facilitate this by channelising the river discharge farther in the sea. Evidence towards the same is also provided by the well-sorted to moderately well-sorted nature of the sediments. Breakwaters were thus observed to highly influence the sediment dispersion and distribution along an estuarine coast. This study will provide knowledge on the role of coastal structures in sediment dispersion while framing future coastal protection strategies for the conservation of the coast.

      $\bf{Highlights}$

      $\bullet$ Progradation of beaches adjacent to the breakwaters due to sheltering from direct waves whereas erosion of beaches away from the influence of these structures is observed.

      $\bullet$ Extensive engineered coast has resulted in the narrowing of the natural beach width making it reflective with a high-energy environment thus accelerating further erosion. Due to this, the beach has lost its recreational value.

      $\bullet$ The along-shore drift directions derived considering beach morphology, beach volume change and beach sedimentology, along with the mode of transport and environmental affinity of sediments provide a comprehensive understanding of sediment dispersal pattern along the coast.

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