Dredging of sand from a creek adjacent to a sand-spit for reclamation: Its impact on spit stability and coastal zone

Abstract

A quantity of about 17 + 10 sup(6) m sup(3) sand had been dredged from the Jatadharmohan creek (JMC) 15 km south of Paradip Port (east coast of India) in 2000, and a quantity of 14 + 10 sup(6) m sup(3) sand will be dredged again from the same creek bed as fill material for reclamation of a low lying land. MIKE 21 hydrodynamic model was run to evaluate the change in flow pattern due to altered bathymetry, and GALENA to analyse the stability of a spit adjacent to the creek. JMC is a region of divergence, and favours deposition, and this has been confirmed by subsequent monitoring and bathymetry studies. The pre- and post dredging bathymetry of 2000 when compared with the bathymetry of 2005 revealed accumulation of sediments of the order of 2.11 + 10 sup(6) m sup(3) in an area of approx. 4.22 + 10 sup(6) m sup(2). The sediment from the bed to a depth of 3.3 m consists of very loose sand, silt and clay. These materials could be recent deposit transported by flood or static liquefaction during dredging operation. Medium sand is found upto R.L. - 8.15 m below bed level and thereafter a deep deposit of predominantly fine sand upto the 20.0 m. The slope stability results show that the dredged region will be stable, even if it is dredged to a depth of 12.0 m by maintaining a slope of 1:6. The modeling results indicate that there will be no remarkable change in flow pattern when the dredging depth is increased from 3.5 m to 12.0 m, and the spit will also be stable with a safety factor of 3.0 and a slope of 1:6.