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Flow dynamics are a key part of the physical processes that drive the sediment transport in an aquatic system, affecting depositional processes and leading to landform evolution. The current asymmetry (CA) noted in Vembanad Lake (VL), India, have a particularly strong influence on the sediment budget and thus shape its geomorphology. In the present study the Coastal Ocean Model - Finite Volume Coastal Ocean Model (FVCOM) was used to compute the lateral current asymmetries and their implications for the long-term morphological changes in VL during different tidal phases. Model results were utilised to calculate the CA using two criteria: (1) Peak flood/ebb velocities with duration, and (2) Asymmetry Index (AIDV). AIDV values suggest the prevalence of ebb dominance over the entire system except at Cherai and Vallarpadam. However, several isolated pockets were noted on the right/eastern bank (shallow depth) of the system where the peak flood velocity exceeded the ebb, favouring accretion. Contrary to the concept of ebb asymmetry, mean velocity and duration asymmetries were prevalent in the asymmetry index (AIDV); hence we adopted peak flood/ebb velocity and its duration asymmetries to improve our understanding of the sediment transport dynamics. Typical flood asymmetry was identified on the right bank and at many of the lateral stations in VL, which switched to the modified ebb asymmetry during substantial river discharge. Analysis of CA enables understanding of the process that influences selective morphological changes, as explained by the model results. This conclusion was well corroborated by results obtained over the past three decades (1973–2008) from analysis of Landsat satellite imagery. Flood/ebb dominance in VL is explicitly substantiated with regions of accretion/erosion derived from satellite imageries. A holistic approach encompassing modelling, observations, remote sensing, and GIS techniques were used to address the erosion-accretion process in VL. |
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