Context and objectives
Hai Phong Bay is characterised by a specific sedimentological regime, influenced by the Red River Delta, the estuaries of several other rivers in North Vietnam, the tides and the monsoons. The rivers discharge an enormous amount of sediments (several hundreds of thousands of tons per month), mainly during the wet season. The transport is visible as ‘sediment plumes’ on the optical images such as SPOT and LANDSAT TM. The deposited sediments are frequently brought back in suspension by typhoons during the monsoon season. This causes filling up (siltation) of the access channel to the harbour, requiring frequent dredging.
Purpose of the study : development of a methodology to study sediment transport and deposition on the basis of satellite imagery, in view of the optimisation of (expensive and tedious) field campaigns. Studies in sediment transport and coastline dynamics are executed as part of preliminary studies for marine and harbour infrastructure works, to update bathymetrical maps and to verify the reliability of available local maps.
Expected scientific results
- The accuracy of maps obtained on the basis of satellite imagery seams to be rather low at first sight. For the survey phase of engineering works in harbours however, these maps are highly valuable and the ‘best possible’ up-to-date information which can be obtained with limited time and budget resources. The study of the evolution of the coastal line facilitates environmental impact studies, such as the evaluation of the impact of a narrowing beach on the coastal tourism sector. In certain parts of Hai Phong Bay the coastline has retreated from 100 m to 400 m between 1952 and 1993 due to strong erosion.
- The images acquired during the wet season show sedimentary plumes at the level of each estuary located in the western part of the bay. The different colours in the water on the satellite images correspond with different values of sediment concentration. It is possible to determine the orientation of sediment transport based on the colour distribution of the spectral values (towards the North).
- On the images acquired during the dry season, no sediment transport is visible. The spectral values are correlated with depth. In the Nam Trieu Channel and the shallow water areas, values of radiance are influenced by the nature of the deposited sediments (sand, mud).
|Project leader(s):||ULg - Laboratoire de Géomorphologie et Télédétection|