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The Barataria barrier coast formed between two major distributaries of the Mississippi River delta: the Plaquemines deltaic headland to the east and the Lafourche deltaic headland to the west. Rapid relative sea-level rise (1.03 cm year-1) and other erosional processes within Barataria Bay have led to substantial increases in the area of open water (> 775 km² since 1956) and the attendant bay tidal prism. Historically, the increase in tidal discharge at inlets has produced larger channel cross-sections and prograding ebb-tidal deltas. For example, the ebb delta at Barataria Pass has built seaward > 2.2 km since the 1880s. Shoreline erosion and an increasing bay tidal prism also facilitated the formation of new inlets. Four major lithofacies characterize the Barataria coast ebb-tidal deltas and associated sedimentary environments. These include a proximal delta facies composed of massive to laminated, fine grey-brown to pale yellow sand and a distal delta facies consisting of thinly laminated, grey to pale yellow sand and silty sand with mud layers. The higher energy proximal delta deposits contain a greater percentage of sand (75-100%) compared with the distal delta sediments (60-80%). Associated sedimentary units include a nearshore facies consisting of horizontally laminated, fine to very fine grey sand with mud layers and an offshore facies that is composed of grey to dark grey, laminated sandy silt to silty clay. All facies coarsen upwards except the offshore facies, which fines upwards. An evolutionary model is presented for the stratigraphic development of the ebb-tidal deltas in a regime of increasing tidal energy resulting from coastal land loss and tidal prism growth. Ebb-tidal delta facies prograde over nearshore sediments, which interfinger with offshore facies. The seaward decrease in tidal current velocity of the ebb discharge produces a gradational contact between proximal and distal tidal delta facies. As the tidal discharge increases and the inlet grows in dimensions, the proximal and distal tidal delta facies prograde seawards. Owing to the relatively low gradient of the inner continental shelf, the ebb-tidal delta lithosome is presently no more than 5 m thick and is generally only 2-3 m in thickness. The ebb delta sediment is sourced from deepening of the inlet and the associated channels and from the longshore sediment transport system. The final stage in the model envisages erosion and segmentation of the barrier chain, leading to a decrease in tidal discharge through the former major inlets. This process ultimately results in fine-grained sedimentation seaward of the inlets and the encasement of the ebb-tidal delta lithosome in mud. The ebb-tidal deltas along the Barataria coast are distinguished from most other ebb deltas along sand-rich coasts by their muddy content and lack of large-scale stratification produced by channel cut-and-fills and bar migration. [ABSTRACT FROM AUTHOR]

Bathymetric surveys conducted before and after the 2005 hurricane season at Little Pass Timbalier in the Mississippi River delta plain, United States, demonstrate that 9.1 (±2.4) x 106 m³ of sediment was eroded from a 47.9 km² area. Between the two surveys, Hurricanes Cindy, Katrina, and Rita passed within 300 km of the tidal inlet. Comparison of before and after bathymetric data sets shows that the distal portion of the ebb-tidal delta (ETD) was the site of 63% of the total erosion, locally resulting in 400 m of shoreface retreat. Shoaling (0.75-1.0 m) in the seawardmost portion of the ebb channel and erosion in the landward portion (∼1.5 m) resulted in a 160 m landward shift of the inlet throat. Collectively, these processes forced the landward migration of the entire tidal inlet and ETD system. There has been considerable discussion about large volumes of mineral sediment deposited on the Mississippi River delta plain interior marsh surface as a result of hurricanes; however, the origin of this sediment is unknown. We identify the distal portion of an ETD as one possible sediment source and hypothesize that ETD and shoreface sediment is mobilized by hurricane waves and transported landward by surge-induced currents. Our results emphasize the role of frequent and intense hurricanes in long-term coastal evolution and as a mechanism for regional sediment retention within the transgressive system beyond typical barrier overwash processes. [ABSTRACT FROM AUTHOR]