Temporal and spatial variability in the flow and dispersal of suspended-sediment on a fringing reef flat, Molokai, Hawaii

A multi-year study was conducted on a shallow fringing reef flat on Molokai, Hawaii to determine the temporal and spatial dispersal patterns of terrigenous suspended sediment. During this study, trade-wind conditions existed for the majority of the year on the reef flat. The trade-wind conditions produced strong currents and resuspended moderate amounts of sediment on the reef flat on a daily basis during the year of study, resulting in an overwhelming contribution to the total sediment flux. The magnitude and direction of the trade winds relative to the orientation of the coastline, the shallow-relief and broad morphology, and tidal elevation, provided the primary control of the physical processes that resuspended and transported sediment on the reef flat over the period of record. Spatial data indicate that much of the terrigenous sediment resuspended on the reef flat is transported predominantly alongshore and is confined to the inner- to mid-reef flat. Evidence for the limited across-shore mixing and transport is provided by the dominantly alongshore wind-driven currents during trade-wind conditions and the well-defined across-shore gradient in percentage calcium carbonate of the suspended sediment. Regions of slightly offshore suspended-sediment transport along the reef flat can be attributed to the circulation pattern set up by the interaction between the trade winds, coastal morphology, and anthropogenic coastal structures (i.e., fish ponds and wharf). The regions in which sediment were seen to move offshore provide the strongest link between the sediment dynamics on reef flat and fore reef, and qualitatively appears to be correlated with low coral coverage on the fore reef. ?? 2005 Elsevier Ltd. All rights reserved.