Hurricane Katrina Splay Deposits: Hydrodynamic Constraints on Hyperconcentrated Sedimentation and Implications for the Rock Record


W.R. Barnhart

A breach of the London Avenue Canal levee in New Orleans’ Lower Ninth Ward during Hurricane Katrina created a unique opportunity to compare flow conditions with the resulting bedforms. Those deposits are examined and correlated to probable hydrodynamic conditions during deposition, including the fluctuating causes for repetitive bedforms and changing conditions within the continuous unidirectional current through the breach. Flow depth was determined mathematically from clast size and is examined as a limit on bedform thickness. Characteristics of the splay deposits point to deposition under hyperconcentrated conditions in a high-velocity current, leading to a remarkably high depositional rate. This study suggests a mechanism for the simultaneous deposition of multiple laminae as a single set under hyperconcentrated conditions. Clay and clay drapes in the deposit indicate fluctuations in flow, not a cycle of active/passive sedimentation.