Heterogeneity and Dynamics on a Shoal during Spring-Winter Storm Season, South-Central Louisiana, USA

Ship Shoal, a shore-parallel elongate sand shoal and a remnant of a late Holocene active delta has a unique heterogeneous sedimentary feature strongly affected by winter storms and fluvial sediment input from the Atchafalaya River. The interaction between fluvially derived sediment and subsequent deposition on the shoal has not been quantified; implications for hydrodynamic modeling are profound given that the shoal surface vacillates between sand and fluid mud. Thus, attenuation effects on waves and currents vary greatly. The results of a field survey undertaken during spring flood and winter storm periods showed that during fair weather, river-borne sediments transported to the shoal, forms a distinct fluid mud layer. Bottom sediments were re-suspended and transported by storm-induced waves and prevailing northerly/southerly trends of currents over the shoal during the period. Data presented here suggest that the high sediment transport during the storms and the ephemeral deposition of fine-grained sediments could form transient sediment distribution on the shoal without leaving any modern sedimentary records, as reported by recent core surveys.