1 MECHANICS OF SEDIMENT SUSPENSION AND TRANSPORT WITHIN A FRINGING REEF ANDREW W.M. POMEROY 1 , RYAN J. LOWE 2 , MARCO GHISALBERTI 3 , CURT D. STORLAZZI 4 , MICHAEL CUTTLER 5 and GRAHAM SYMONDS 6 1. The UWA Oceans Institute and The School of Earth and Environment, ARC Centre of Excellence for Coral Reef Studies, The University of Western Australia, Australia, Andrew.Pomeroy@research.uwa.edu.au 2. The UWA Oceans Institute and The School of Earth and Environment, ARC Centre of Excellence for Coral Reef Studies, The University of Western Australia, Australia, Ryan.Lowe@uwa.edu.au 3. The School of Civil and Mining Engineering, The University of Western Australia, Australia. Marco.Ghisalberti@uwa.edu.au 4. U.S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, California, USA, cstorlazzi@usgs.gov 5. The UWA Oceans Institute and The School of Earth and Environment, ARC Centre of Excellence for Coral Reef Studies, The University of Western Australia, Australia, Mike.Cutter@resarch.uwa.edu.au 6. Centre for Australian Weather and Climate Research, CSIRO Wealth from Oceans Flagship, Wembley, Australia, Graham.Symonds@csiro.au Abstract: Large bottom roughness is a characteristic of most coral reef environments and this has been shown to have a substantial impact on hydrodynamic processes in these environments. In this paper, we evaluate suspended sediment concentration (SSC) data as well detailed hydrodynamic data over a coral reef flat in Ningaloo Reef, Western Australia, to understand how this bottom roughness affects these processes. A well-developed logarithmic velocity layer consistently developed above a canopy layer during the experiment. Estimates of bottom stresses from these logarithmic profiles were comparable with estimates obtained directly from turbulent Reynolds stresses, and an order of magnitude greater than those typically reported for sandy beach environments having similar flow. Nevertheless, the sediment grain size distribution of the suspended load was very fine relative to what should be mobilized by these stresses, indicated the large roughness substantially suppressed sediment transport. Introduction The presence of large and complex bottom roughness (or canopies) imposes substantial drag forces on flows generated by waves and currents. These forces have been shown to be substantially larger in canopy environments than in sandy beach environments (e.g., Lowe et al., 2007; Rosman and Hench, 2011; Pomeroy et al., 2012). Although canopies are well known to influence bottom boundary layer hydrodynamics, which are strongly coupled to the sediment dynamics, the physical processes controlling the suspension and transport of sediment in coral reef environments are much less well understood.