Turbulence is important to sediment transport, whether in air or water. Linkages between turbulent events and pulses in aeolian sediment transport have been difficult to establish, however, especially in non-laboratory environments. One deficiency with field-based studies is that none measured wind velocity and saltation (sediment "jumping," the primary mode of sand transport by wind) with precisely and tightly controlled time and space synchronization. Turbulence has large temporal and spatial gradients, so it seems illogical to expect strong correlations between wind speed and transport rates with instrument separations at meter scale. The goal of this doctoral dissertation research project is to establish and quantify the spatial and temporal scales of unsteadiness in wind and saltation fields; to identify the nature of turbulence causing transport pulsing; to characterize the spatial and temporal dimensions of wind and transport unsteadiness; and to design, build, and deploy a new sensor for the detection of saltating sand grains. Arrays of instruments will be deployed to simultaneously measure the horizontal and vertical dimensions of sediment transport and wind speed. Saltation sensors and anemometers will be placed 2 cm apart to ensure tightly controlled space synchronization. Linkages between turbulent wind events and pulses in sediment transport will be established using variable interval time averaging (VITA), enhanced VITA, and autocorrelation methods. Traps will be deployed to obtain samples of transporting sand to determine their grain size characteristics and moisture content. The research will be conducted in an Australian coastal dune system, but the results will be applicable to sediment transport processes occurring in wind and water at a broad range of settings.
This project will provide a fundamental understanding of the response of sand to fluctuating (turbulent) wind conditions. This understanding is a necessary precursor to understanding the deficiencies of wind-blown sediment transport rate models. This research may have implications to coastal managers because they are interested in sediment transport rates. Coastal dunes built by blowing sand also provide a defense against flooding; a characteristic that is especially important in a time where the average global sea level is rising. An increased understanding of aeolian processes and the resultant landforms will improve capabilities to manage or preserve coastal environments. It is essential that fundamental relationships between wind and sand are understood to improve the ability to predict sediment transport rates. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.
