Factors Affecting the Supply and Distribution of Sediment in Some Tropical Ports

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A brief review has been made of five hydraulic investigations of port siltation carried out by various international laboratories. The ports studied are distributed throughout the tropics from South America to Indonesia and the factors affecting sediment supply and distribution either directly or indirectly have been summarized. In spite of local variations, the similarity of many features suggests the existence of a common mechanism of sediment transport.Twenty months of field measurements at one of the ports demonstrated that turbidity in the water column is low from surface to 0.15 m above the bed. These measurements, together with those from flume tests on the behavior of local mud in currents, indicated that siltation is not solely due to deposition of silt suspended in the main body of flow. Further wave flume tests showed that under certain conditions, a shallow, highly turbid layer forms on the bed, capable of being transported by weak tidal currents without significant vertical mixing. Supplementation of field measurements of water movement with more detailed hydraulic model measurements permitted the formulation of a siltation mechanism.Appraisal of results suggests the most important immediate source of the silt to be the shallow coastal mud banks. Waves produce the turbid, near-bed layer which is transported by littoral currents into port approach channels for redistribution by the prevailing residual current, itself a function of fluvial/tidal interaction.Key words: siltation, dredging, silt movement, flocculation, waves, tides, river flow, residual currents