Ultrasonic measurements of suspended sediment concentrations at Harris Bayou, Mississippi

Abstract

The use of ultrasonic acoustic technology to measure the concentration of fine suspended sediments has the potential to greatly increase the temporal and spatial resolution of sediment measurements while reducing the need for personnel to be present at gauging stations during storm events. A laboratory investigation by Carpenter et. al (2009, 2014) was undertaken by the National Center for Physical Acoustics in cooperation with the USDA-ARS National Sedimentation Laboratory. In these experiments, two immersion transducers were used to measure attenuation from 20 MHz acoustic signals propagated through suspended clay (smectite and kaolinite) and silt particles (i.e. clays and silts ranging from 0.03-14 micrometer particle size diameter) for a wide range of concentrations (0.3-14 g/L). Attenuation curves for each particle classification were compared to the theoretical attenuation curves developed by Urick (1948) and Sheng and Hay (1988) for scattering as presented by Landers (2010), and a model for estimating concentration was created. Subsequently, a customized field deployable system was developed using the laboratory transducer design parameters and deployed as an acoustic surrogate monitoring fine sediment particles in suspension at Harris Bayou, in cooperation with personnel from the U. S. Geological Survey. Using the laboratory and field systems concurrently, the calibration measurements show good agreement between the laboratory grade equipment and the new prototype system. The results of laboratory calibration and testing of the prototype system at Harris Bayou will be presented.