THE EFFECTS OF SEDIMENTATION ON NAVIGATION ENVIRONMENT IN A TIDAL DOMAINTED ESTUARY THROUGH NUMERICAL MODELING STUDY

摘要

An improved knowledge of marine environmental conditions is very vital for port planning and operation purposes. Sedimentation is a major issue in certain ports requiring periodic maintenance dredging and deepening of navigational channel. The depths of navigation channel gradually decrease over time due to high sedimentation rates behaving as sediment traps. Hence maintenance cost is a critical element concerning economic feasibility of a port, in particular when long access channels require frequent dredging. The Kolkata Port Trust (KPT) and Haldia Dock Complex (HDC) located in the Hooghly basin, India experiences serious sedimentation problems. It is an important estuary and presently under increasing stress due to the port activity, maintenance dredging and discharge of sewage outfalls. The Hooghly is a tide dominated estuary and tidal effects are noticed upstream up to nearly 200 Km from estuary mouth located near the Sagar Island. To address the problem of sedimentation a comprehensive knowledge of bottom boundary layer (BBL) dynamics, suspended sediment concentration (SSC) and spatio-temporal varability of bottom stress is an essential pre-requisite. Hence numerical modeling of BBL and SSC requires integration of various numerical models viz; hydrodynamic models, near-shore wave models and sediment transport models. Realistic estimates require geographical distribution of bottom sediments, its size and properties. The work reports on the sedimentation issues in the Hooghly basin and the role of various hydrodynamic forcing responsible to alter sediment transport mechanisms prior to and after the dredging activity. Assessment of navigational environment in the Hooghly basin based on modeling study is discussed.