Can Dissolved Material Replace Cohesive Sediment in Turbidity Current Physical Modelling? Experimental Inferences Based on Cohesive, Non-Cohesive and Mixed Low-Density Flows

Ducker, Richard Eduard¹, Rafael Manica¹, Ana Luiza de Oliveira Borges¹, Rogério Dornelles Maestri¹ (1) Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil

This work presents an experimental investigation of low-density turbidity currents using cohesive (bentonite), non-cohesive (mineral coal) and mixed sediments in order to evaluate their cinematic, geometric and depositional behaviour. Beyond that, it was investigated use of dissolved material (salt) replacing cohesive sediment in these flows. Hence, two sets of experiments were conducted in a bi-dimensional channel with five different sediment ratios ranged from cohesive (100% bentonite), mixed (25:75; 50:50; 75:25) to non-cohesive (100% coal) flows. The second set used the same setup but with salt instead of bentonite. The bulk density (Cvol < 2%) and volume were kept constant in order to compare both sets. The results were evaluated regarding the flow-deposit properties (head velocity, head and body height and grain size distribution). First, it was verified that presence of more bentonite in the flows changed, but not significantly, the general trends of each property. It was principally expressed in terms of depositional patterns where it was detected same trends of deposition (thinning downstream) only with a slight modification of flow transport capacity (coarser grains reaching distal zones). After that, these same analyses were carried to the second set of experiments (salt) and the results were cross-correlated. Again, similar trends of results were verified presenting good correlation between the data proving be possible the use of salt replacing sediments (simplifications of experimental procedures and further analysis). Moreover, the low-concentration used in this work can be explanation for such flow-deposit similarities among cohesive, non-cohesive and mixed turbidity currents.