Time-resolved measurements of the deposition under turbidity currents
FRANS DE ROOIJ & STUART B. DALZIEL
Department of Applied Mathematics and Theoretical Physics,
University of Cambridge, Silver Street, Cambridge CB3 9EW, UK.
Tel. +44.1223.339737, fax: +44.1223.337918, e-mail: f.derooij@damtp.cam.ac.uk.
30 October 1998
Submitted to the International Association of Sedimentologists for inclusion in the proceedings of the conference on 'Sediment Transport and Deposition by Particulate Gravity Currents', Leeds, 7-9 September 1998.

This paper describes experiments measuring the instantaneous sediment deposition rates for a turbidity current. These measurements were obtained using a recently developed technique capable of very accurate measurements of the layer thickness, from which the concentration in the current could be derived. It was found that turbidity currents from a lock-release form a head, where the particle concentration is highest and under which the largest deposition occurs. The initial decrease in particle concentration within the head is induced by the entrainment of ambient fluid. A maximum in the final layer thickness occurs when the current slows down and the turbulence has decayed to favour detrainment rather than entrainment. Sedimentation dominates the flow at later stages and the concentration decreases. When the current encounters a vertical wall it gets reflected and deposits on top of the deposit formed earlier. A turbidity current from a continuous source attains a steady state when it reaches its run-out length. The data suggest that the concentration in the steady state decays exponentially away from the source leading to a bed thickness with an similar exponential profile.