Dredged Material Dumping Site Selection Using Mathematical Models

Siltation is a big hurdle in maintaining the required depth in and around port. Dredging is required in order to maintain the desired depths in the port. Dumping of dredged material has its own impact in the surrounding area and in turn its cost effectiveness. Studies for identification of dredged material dumping ground for development of a multipurpose terminal at Karanja were carried out. Four sets of dumping grounds were initially identified and their impact was observed at three different locations. MIKE 21HD with flexible mesh setup was used for the studies. Since the capital dredging would be going on for a period of six months, model simulations with MIKE 21 HD were done for a period of one month and then extrapolated for six months period. The impact of each dumping location for continuous dumping for a period of one month was assessed using the model simulations. The time required to restore the ambient conditions once the dumping is stopped was also examined. A comparison of the suspended sediment concentration was done at some locations in the vicinity of the dumping site. A comparison on the suspended sediment concentration and the bed thickness change at different points for the different dumping ground were observed. It was found that the suspended sediment concentration will fluctuate with the tide and will attain the lowest value of 5 ppt at the dumping location. The change in bed thickness is expected to be very marginal with maximum being of the order of 5 cm and the time required restoring the ambient conditions after the dumping ceases would be about 10 to 15 days. Based on this information location of the dumping ground could be finalised which has the minimum impact on the relevant area and is cost effective.