Mitigation of Sedimentation in Approach Channel and Harbour at Passenger Jetty, Mandwa, Maharashtra

Abstract

Mandwa port is situated on the West coast of India which connects Mumbai to Alibag by establishing inland water transport to reduce travel time and traffic on the road. The port comprises a breakwater of length 360 m and a navigational channel of length 1.8 km, 150 m wide dredged initially to (−) 4.0 m below Chart Datum (CD). The clear depths in the channel are required be maintained at about 2.5–3.0 m below chart datum throughout the year. At present, the port is facing severe problem of sedimentation in the navigational channel. The sedimentation in the approach channel and in the harbour areas occurs mainly due to the deposit of the sea-borne suspended sediments in the dredged areas. There is no significant contribution in the overall sedimentation due to the littoral or river discharges. The annual sedimentation in the approach channel is about 2.0 m, and this would not facilitate availability of clear depth of more than 2.5 m throughout the year in the channel and in harbour area. In order to mitigate this problem of sedimentation two proposed scenarios were studied, namely, proposed condition-I with additional dredging in the channel and harbour areas and other proposed condition-II with modification in the channel alignment (orientation) to align it along the currents to reduce sedimentation in the channel. The MIKE-HD/MT model was utilised for the studies which was calibrated with the collected field data. In second proposal, length of channel slightly reduces by about 100 m. In first proposal, both initial cost and maintenance cost would increase marginally, while in second proposal, initial cost of dredging will be very high as new approach channel needs to be dredged but its maintenance cost will be much less. The detailed findings of this study would be discussed in the paper.