Bedload Transport by density underflows: an experimental approach

MILANA, J. P

Santa Bárbara, CA, USA

Workshop; Slopes Consortium Annual Meeting; 2009

UC Santa Bárbara - Slopes Consortium

Bedload Transport by density underflows: an experimental approach Questions: a) How does the tractive transport occurs actually b) What are the basic bedforms that can be generated c) How does bedding occurs and how valid is the “traction carpet” theory d) How much bedload is delayed with respect to suspended load (this has an important geological implication on canyoning cycles). e) Is it possible to model bedload transport?   Objective of the research: If we can understand the process, then it would be possible to model transport and deposition on bedload dominated depositional systems. Areas of application: All systems, particularly proximal ones, and bypass dominated ones as Rosario (study was motivated after the field study of Rosario Fm conglomertaes) CONCLUSION 1: Gravel clusters could explain well the “traction carpet” deposition without the need of any frictional freezing CONCLUSION 2: bedload transport at the base of density flows seems to be quite comparable to open flow channels. This explains many similarities. However it needs to keep in mind that the shear velocity is usually higuer in gravity flows and therefore, suspended-load fractions are coarser and could be misinterpreted as bedload. In such a case, the presence of structures (bedding, xbedding) or fabric, should help to recognize the dominant depositional mode. CONCLUSION 3: Turbidity flows subjected to variations on suspended load are prone to generate “pressure waves” that help bedload transport. These pressure waves would be sacled to the flow and might be related to the hydraulic fracturing and downward sand injection. CONCLUSION 4: There is a significant delay of bedload in bedforms as they act as sediment buffers. While suspended load travels AT the flow velocity, bedload travels significantly slower, but speed varies according to the mode at which bedload occurs.