FLOW DYNAMICS AND GEOMORPHOLOGY OF A TROUGH BLOWOUT

The dynamics and geomorphological development of a trough blowout loca ted at Fiona Beach in the Myall Lakes National Park in NSW, Australia, are examined. Wind speeds, velocities and flow structure were measure d utilizing an array of miniature Rimco cup anemometers, Gill bivane a nd UVW instruments, and wind vanes. Flow measurements indicate that wh en the wind approaches the trough blowout parallel to the throat orien tation, jets occur both in the deflation basin and along the erosional walls, relative flow deceleration and expansion occurs up the deposit ional lobe, jets are formed over the depositional lobe crest accompani ed by downwind flow separation on the leeward side of the lobe, and no w separation and the formation of corkscrew vortices occur over the cr ests of the erosional walls. Maximum erosion and transport occurs up t he deflation basin and onto the. depositional lobe. Trough blowout mor phologies are explained as a function of these flow patterns. When the wind approaches tile blowout obliquely, the flow is steered considera bly within the blowout, and the degree and complexity of topographic s teering is dependent on the blowout topography. The how is usually ext remely turbulent and large corkscrew vortices are common. The local to pography of a blowout can be very important in determining overall san d transport and blowout evolutionary conditions and paths. Estimates o f potential sand transport within the blowout may be up to two orders of magnitude lower than actual rates if remotely sensed wind data are used.