Assessment of siltation processes and implementation of nautical depth in the port of Cochin, India
CEDA Dredging Days 2017 - Sustainable Dredging - Continued Benefits
Ferket B., Heredia Gomez M., Rocabado I., De Sutter R., Van Hoestenberghe T., Kwee J., Werner C., Verwilligen J., Vos S., Nair P., Lamba P., Sharma S., Marthi S., Vantorre M., Manso F.
Abstract: The port of Cochin has the largest siltation rate among Indian ports: +20 million m³/year. Local dynamics are controlled by the two rivers discharging into the port system and the ocean. Siltation occurs mostly during the Monsoon (June-September) when dynamics are high (Naik et al., 1983). The Cochin Port Trust (COPT) has tried to optimize the dredging efforts, i.e. allowing ships to partially penetrate the fluid mud. This project is a comprehensive attempt to tackle this problem by understanding the siltation processes in detail and by determining a minimum water depth, draft and under-keel-clearance at which navigation of ships through fluid mud is “safe” (nautical depth). The project was structured in different stages: 1. Desktop study to understand the existing situation and to determine the required acquisition efforts for the development of a numerical 2D model (TELEMAC7). 2. Data acquisition and fieldwork to gather the key variables to set up and calibrate the numerical model and undertake the navigation studies. 3. Numerical modeling to understand in detail the siltation processes that occur in the area by simulating the hydrodynamics conditions (waves, tides and currents) as well as sediment transport, erosion and siltation processes. After calibration and validation, the model was used for scenario analysis. 4. Navigation studies to determine a nautical depth. Firstly, the navigation conditions were modeled physically by replicating (1) natural conditions under laboratory environment, (2) selecting a number of maneuvers with chosen design ships with different under keel clearance (UKC) levels and (3) determining mud rheology at the towing tank from the Flanders Hydraulics Research (FHR). Secondly, the results obtained in the physical model were compared against the expert judgement of pilots from the Port of Cochin. For this, tests in the 3D navigation simulator from the FHR, replicating Cochin’s hydrodynamic and environmental conditions, were developed. For this project, the nautical depth criterion was defined with a conservative mindset, by assessing “safe navigation” in terms of maneuverability of vessels. Recommendations to support the implementation of this criterion were provided to the client. The combination of all achieved results allowed the COPT to optimize their maintenance dredging strategy, while keeping sufficient nautical depth. In order to reach greater economic success, the nautical depth criterion needs to be fine-tuned in future works.
Keywords: Siltation, rheology, ship maneuvering, modeling, nautical depth