Studies on Locating Sediment Trap for Reducing Dredging in Jellingham Navigational Fairway, Kolkata

Formation of shoals in an estuarine environment creates significant problems such as reduction in depth in navigational channels, decreased discharges and degradation of water quality. One of the widely used solutions to reduce sedimentation is the implementation of a sediment trap by creating a trench or a pit in the submerged bottom at specific locations. A sediment trap is defined as a section of the estuarine bed deepened to a depth greater than its surroundings. The lower velocity allows sediments to deposit in the trap rather than move past over it. Implementation of a silt trap at specific locations in a highly dynamic domain like Hooghly estuary helps to optimize the dredge quantity or the maintenance dredging can be localized to a specific location (the trap) rather over a wide submerged area. This study involves optimization of the location and shape of a silt trap near the Haldi-Hooghly confluence point, West Bengal, India. The trap was designed to reduce the dredging quantity in the downstream Jellingham channel which is a part of the navigational channel en route to Haldia Dock Complex in the Hooghly estuary. Based on a comprehensive numerical study, an option of irregular polygon shaped silt trap of a surface area of 250,000 m2 positioned in such a way to trap the sediments from both the Hooghly and the Haldi rivers near the Haldia anchorage was finalized which was found to perform efficiently in reducing the dredge quantity in the Jellingham channel. The details of the study are reported in this paper.