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The relative contribution of processes driving variability in flow, shear, and turbidity over a fringing coral reef: West Maui, Hawaii

January 1, 2008

High-frequency measurements of waves, currents and water column properties were made on a fringing coral reef off northwest Maui, Hawaii, for 15 months between 2001 and 2003 to aid in understanding the processes governing flow and turbidity over a range of time scales and their contributions to annual budgets. The summer months were characterized by consistent trade winds and small waves, and under these conditions high-frequency internal bores were commonly observed, there was little net flow or turbidity over the fore reef, and over the reef flat net flow was downwind and turbidity was high. When the trade winds waned or the wind direction deviated from the dominant trade wind orientation, strong alongshore flows occurred into the typically dominant wind direction and lower turbidity was observed across the reef. During the winter, when large storm waves impacted the study area, strong offshore flows and high turbidity occurred on the reef flat and over the fore reef. Over the course of a year, trade wind conditions resulted in the greatest net transport of turbid water due to relatively strong currents, moderate overall turbidity, and their frequent occurrence. Throughout the period of study, near-surface current directions over the fore reef varied on average by more than 41?? from those near the seafloor, and the orientation of the currents over the reef flat differed on average by more than 65?? from those observed over the fore reef. This shear occurred over relatively short vertical (order of meters) and horizontal (order of hundreds of meters) scales, causing material distributed throughout the water column, including the particles in suspension causing the turbidity (e.g. sediment or larvae) and/or dissolved nutrients and contaminants, to be transported in different directions under constant oceanographic and meteorologic forcing.