FLOW DYNAMICS IN 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 velocities and flow structure were measured utilisi ng an array of miniature Rimco cup anemometers, Gill bi-vane and UVW i nstruments, and wind vanes. Flow measurements indicate that when the w ind approaches the trough blowout parallel to the throat orientation, jets occur both in the deflation basin and along the erosional walls, relative flow deceleration and expansion occur up the depositional lob e, jets are formed over the depositional lobe crest accompanied by dow nwind flow separation on the leeward side of the lobe, and flow separa tion and the formation of corkscrew vortices occur over the crests of the erosional walls. Maximum erosion and transport occur up the deflat ion basin and onto the depositional lobe. Trough blowout morphologies are explained as a function of these how patterns. When the wind appro aches the blowout obliquely, the flow is steered considerably within t he blowout. The degree and complexity of topographic steering is depen dent on the blowout topography. The flow is usually extremely turbulen t and large corkscrew vortices are common. The local topography of a b lowout can be very important in determining flow patterns, 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 remote wind data are used.