In-Situ Observations of Mudbanks of Southwest Coast of India and Mapping of its Extent in 2016

Formation of mudbanks in Alleppey, south-west coast of India is an annual phenomenon which is widely discussed, and many hypotheses have been proposed on its formation. The presence of fluid mud in a levitated condition in the bottom is believed to be the cause of the formation. In this study, in-situ measurements of the Suspended Sediment Concentration (SSC) were carried out for five months in the year 2016 during the monsoon using the Laser interferometry instrument (LISST 100X). This observation was to determine the variations in the SSC in the water column and to delineate the zone of mudbank. One station inside the mudbank (M2) and other two stations outside the mudbank (M1&M3) were considered. During the monthly observations, huge difference in the near bottom SSC from 600-700 mg/l in the mudbank region and 300-400 mg/l in the outer regions indicates the extent of the mudbank region. The particle sizes were ranging from clay to sand. The concentration of clay particles has abruptly reduced from 50 mg/l to 15 mg/l in surface waters at the outer regions of mudbank. It was also found that these suspended particles have settled back after the monsoon. Observations for periphery demarcation was carried out during the mid of the monsoon (26 July 2016) with 30 stations in five different transects covering both inside and outside regions of the mudbank. Based on the variations in the concentration and the particle sizes, mudbank periphery was demarcated. The mudbank periphery was identified here with the presence of high concentration of clay particles near the sea bottom. The total particle concentration level at near bottom varied from 600 mg/l in the mudbank stations to 200 mg/l at outside regions. Fivefold increase in the concentration of clay particles at the near bottom in mudbank stations revealed the extent of mudbank region. The presence of clay particles was more than fifty percent of the total concentration. The concentrations of clay near the bottom in stations 11, 12 and 29 have increased from 50 mg/l to 250 mg/l, 20 mg/l to 100 mg/l and 40 mg/l to 200 mg/l respectively. This abrupt increase showed the presence of mudbank and was used to demarcate its periphery.