NUMERICAL MODEL STUDIES FOR THE DISPERSION OF DREDGED MATERIAL IN OFFSHORE AREA

Abstract

Modern large harbours are faced with the problems of continuous maintenance dredging for maintaining deep access channels. Maintenance dredging constitutes a major portion of the operation expenditure. The cost of maintenance dredging can be minimized by reducing the distance of the disposal ground. A balance has to be struck between the cost of transport of the dredged material and the eventual return of the disposed material to the dredged areas. A consideration of the dredging/disposal process in even such broad philosophical terms readily points out a need for a more comprehensive understanding of the precise nature of the problems and a need to fill numerous gaps in knowledge regarding the significance of known or suspected environmental effects of dredging and spoil disposal. The problem of disposal of dredged spoil related to NMPT Port, attempted in this study and the solution outlined in this report are dedicated to these goals. With the increasing expansion of the Port, a need was felt to have a new dumping ground for the dredged material. At present the quantity of annual maintenance dredging is about 6 million m3 in New Mangalore Port. This is expected to increase with further development in the port due to increase in depth of the approach channel and the lagoon. The radiotracer technique has been widely used to follow the movement of sediments on seabed for last four decades and helps in examining the suitability of the dumping site for dredged material. The studies will also help in selecting right alignments for new navigation channels. In INDIA, these types of studies are generally carried out with the help of Bhabha Atomic Research Centre. BARC report describes results of the two radiotracer investigations carried out at a location north of shipping channel at New Mangalore Port during two different periods i.e. pre south-west and post south west monsoon periods. The investigations were aimed at to evaluate the suitability of the disposal site during two different periods. The first investigation was carried out during October 2007- January 2008 post south-west monsoon period) whereas the second investigation was carried out during January-..