TY - JOUR

T1 - Sediment deposition from turbidity currents in simulated aquatic vegetation canopies

AU - Soler, Marianna

AU - Colomer, Jordi

AU - Serra, Teresa

AU - Casamitjana, Xavier

AU - Folkard, Andrew Martin

N1 - This is the peer reviewed version of the following article Soler, M., Colomer, J., Serra, T., Casamitjana, X. and Folkard, A. M. (2017), Sediment deposition from turbidity currents in simulated aquatic vegetation canopies. Sedimentology, 64: 1132–1146. doi:10.1111/sed.12342 which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1111/sed.12342/abstract This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving.

PY - 2017/6

Y1 - 2017/6

N2 - A laboratory flume experiment was carried out in which the hydrodynamic and sedimentary behaviour of a turbidity current was measured as it passed through an array of rigid obstacles. The obstacles were intended primarily to simulate aquatic vegetation canopies, but could equally be taken to represent other things, for example forests or offshore wind turbines. The turbidity currents were generated by mixing naturally-sourced, poly-dispersed sediment into a reservoir of water at concentrations from 1 to 10 gL-1, which was then released in the experimental section of the flume by removing a lock gate. For each initial sediment concentration, runs with obstacle arrays with solid plant fractions of 1% and 2.5%, and control cases with no obstacles, were carried out. The progress of the current along the flume was characterized by the array drag term, CDaxtoe (where CD is the array drag coefficient, a the frontal area of cylinders per unit volume and xtoe the current toe position along the flume). The depositional flux of sediment from the current as it proceeded was measured at thirteen traps positioned along the flume. Analysis of these deposits divided them into fine (2.2–6.2 μm) and coarse (6.2-104 m) fractions. At the beginning of the development, the gravity current proceeded in an inertia dominated regime until CDaxtoe =5. And for CDaxtoe > 5, the current transitioned into a drag-dominated regime. For both fine and coarse sediment fractions, the rate of sediment deposition tended to decrease gradually with distance from the source in the inertial regime, remained approximately constant at the early drag-dominated regime, and then rose and peaked at the end of the drag-dominated stage. This implies that, when passing through arrays of obstacles, the turbidity currents were able to retain sufficient sediment in suspension to maintain their flow until they became significantly influenced by the drag exerted by the obstacles.

AB - A laboratory flume experiment was carried out in which the hydrodynamic and sedimentary behaviour of a turbidity current was measured as it passed through an array of rigid obstacles. The obstacles were intended primarily to simulate aquatic vegetation canopies, but could equally be taken to represent other things, for example forests or offshore wind turbines. The turbidity currents were generated by mixing naturally-sourced, poly-dispersed sediment into a reservoir of water at concentrations from 1 to 10 gL-1, which was then released in the experimental section of the flume by removing a lock gate. For each initial sediment concentration, runs with obstacle arrays with solid plant fractions of 1% and 2.5%, and control cases with no obstacles, were carried out. The progress of the current along the flume was characterized by the array drag term, CDaxtoe (where CD is the array drag coefficient, a the frontal area of cylinders per unit volume and xtoe the current toe position along the flume). The depositional flux of sediment from the current as it proceeded was measured at thirteen traps positioned along the flume. Analysis of these deposits divided them into fine (2.2–6.2 μm) and coarse (6.2-104 m) fractions. At the beginning of the development, the gravity current proceeded in an inertia dominated regime until CDaxtoe =5. And for CDaxtoe > 5, the current transitioned into a drag-dominated regime. For both fine and coarse sediment fractions, the rate of sediment deposition tended to decrease gradually with distance from the source in the inertial regime, remained approximately constant at the early drag-dominated regime, and then rose and peaked at the end of the drag-dominated stage. This implies that, when passing through arrays of obstacles, the turbidity currents were able to retain sufficient sediment in suspension to maintain their flow until they became significantly influenced by the drag exerted by the obstacles.

KW - gravity current

KW - inertial regime

KW - drag-dominated regime

KW - sediment deposition

KW - canopy

U2 - 10.1111/sed.12342

DO - 10.1111/sed.12342

M3 - Journal article

VL - 64

SP - 1132

EP - 1146

JO - Sedimentology

JF - Sedimentology

SN - 0037-0746

IS - 4

ER -