An Integrated Approach to Study Mud Banks of Alleppey Kerala using the Autonomous Vertical Profiler (AVP)

Abstract

Mud Banks of Kerala are areas of the sea adjoining the coast that have a special property of dampening the waves and creating clearly demarcated areas of calm water during the roughest monsoon conditions of the sea. It is believed that these areas have a muddy bottom and suspended muddy sediments in the water column. The mere existence of mud in an area is not enough to form mud banks. However the mud of the right texture needs to get consolidated at the right depth where wave action could churn it up into a thick suspension (Gopinathan, C. K. et al. 1974). The mud banks are of socio-economic importance for the fisheries industry. A consolidated effort was made from April to August 2014 to understand the evolution and properties of the Alleppey Mud Banks of Kerala. The Autonomous Vertical Profiler (AVP) developed at the National Institute of Oceanography was used to obtain high resolution profiles of conductivity, temperature, dissolved oxygen, PAR, chlorophyll and turbidity at 3 locations M1, M2 and M3. These profiles are presented in this paper. This effort was complemented by deploying a surface mooring with an identical AVP profiling on a taut line at a fixed location, M2 at about 6m water depth. AVP was programmed to perform 4 dives per day and transmit data to the laboratory using a cellular network. During this deployment period the mooring AVP was subjected to wave break action and extreme monsoonal and cyclonic conditions, high waves and strong wind gusts. The in-situ AVP and the AVP on the mooring was successfully deployed to obtain high resolution data of the Mud Banks. A total of 115 missions were executed, out of which about 44% achieved the required dive depth. Using the Mooring AVP, the variations of turbidity in the surface layer, mid-waters and bottom layer of the Allepey Mud Bank were studied over a period of 38 days. The Mud Bank was studied for the first time using an autonomous profiling unit.