New Aspects Concerning Hydrodynamics of Turbidity Currents Based on Physical Experiments

Del Rey, Antonio Cosme¹, Rafael Manica², Rogerio Maestri², Ana Luiza de Oliveira Borges², Adriano Roessler Viana³ (1) Petrobras - Petroleo Brasileiro S.A, Vitoria, Brazil (2) Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil (3) PETROBRAS-Petroleo Brasileiro S.A, Rio de Janeiro, Brazil

Over the last decades the turbidite study has been subject of controversy and passionate discussions mainly due to the scarcity of researches related to the mechanisms that involve flow initiation, transport and its deposition. Thus, this work aims to evaluate the potential of physical simulation of turbidity currents to comprehend the internal flow dynamics and its implication on sedimentation process. In order to achieve this objective a three-dimensional model with large dimensions (14m long x 5m wide x 1.20m height) was constructed and a simplified geometry reproducing a channel-basin was implanted inside. Then, a series of 12 simulations of turbidite currents were performed with flows density ranged from 1002 kg/m3 to 1015 kg/m3. Mineral coal sediment (density 1190 kg/m3) was used with grain size ranging between 0.125 and 0.297 mm. The experimental results show new geometrical and dynamical aspects of turbidity currents and their influences on sedimentation process. Essentially, a flow wavy layer was identified close the bottom being originated by internal waves related to vortex detachment in the upper part of the current (head and body). This dynamic process promotes cyclic changes in the current velocity along the flow that are associated with variations on the frequency and amplitude of these internal waves. This behavior also induces changes on the rates of sedimentation/erosion. Hence, the results evidence the complexity of turbidity currents flow evolution involving phases of acceleration and deceleration with alternated erosion, transport and deposition process interaction.