SUSPENDED SAND MEASUREMENTS IN A TURBULENT ENVIRONMENT - FIELD COMPARISON OF OPTICAL AND PUMP SAMPLING TECHNIQUES

Suspended sediment concentrations in and around the surf zone measured from pumped samples were compared to measurements from an optical bac kscatterance (OBS) sensor. At higher values of the eddy diffusivity an d sediment grain size under breaking waves, the pump trapping efficien cy was increased by up to 2.1 times, possibly due to turbulent diffusi on or convection of suspended sediment particles in directions paralle l to the pump inlet. Offshore of the break point, the pump undersample d the suspended sediment in accordance with prior laboratory tests in uni-directional flows. The response of OBS sensors is dependent on the grain size in suspension, and a correction formula for grain size eff ects was obtained.