Mark Kulp

Impacts of Rising Sea Level to Backbarrier Wetlands, Tidal Inlets, and Barrier Islands: Barataria Coast, Louisiana

The Barataria barrier system within the Mississippi River delta plain, is experiencing some of the highest relative sea-level rise (SLR) rates in the continental USA (0.94 cm/yr). This has led to substantial wetland loss in Barataria Bay (16.9 km 2 /yr, from 1935-2000). This conversion of wetlands to intertidal and subtidal environments results from several linked processes including subsidence, marsh front erosion, and catastrophic scour during large magnitude hurricanes. Increasing open water within Barataria Bay has amplified tidal exchange with the ocean. Between 1880 and 2006, an increase of 400% took place in the combined cross-sectional areas of the major tidal inlets of Barataria Bay, associated with the enlarging tidal prism. This expansion of the inlets has been at the expense of the adjacent barrier islands, evident in the concomitant progradation of the ebb-tidal deltas. Since the 1880s the ebb delta at Barataria Pass built seaward more than 2.0 km, sediment cores show that sand constitutes the upper 1-2 m of the ebb delta. Movement of sand offshore, regional subsidence and increasing bay tidal prism produce segmentation of the barriers, forming new inlets such as Pass Abel. Acceleration in eustatic sea level rise will lead to further wetland loss and thus ultimately barrier disintegration. The Barataria barrier chain will be transformed into an island-only system similar to the Isle Dernieres and Timbaliers.

1880 to 2005 Morphologic Evolution of a Transgressive Tidal Inlet, Little Pass Timbalier, Louisiana

Abstract The majority of changes to barrier island shorelines can be attributed to the influence of tidal inlets, and therefore an understanding of inlet processes is important to effectively manage barrier systems. High rates of relative sea-level rise within the Mississippi River delta plain have resulted in a highly transgressive coastal regime and a rapid landward-migration of barrier island and tidal inlet systems. Moreover, ongoing conversion of back barrier and interior wetlands to open water increases tidal exchange. Enlarging bay-tidal prisms together with the landward migration of the barrier systems results in a dynamic environment within which tidal inlets undergo vast changes in position, geometry, and shoreline morphology. Historic bathymetric maps (dating to the 1880s) and newly acquired bathymetric data for Little Pass Timbalier are used to construct a series of digital elevation models and ultimately an evolutionary model for the area. The evolution of Little Pass Timbalier is complex and has encompassed periods of landward and lateral channel migration (43 m/yr and 23 m/yr, respectively) and avulsion to breaches along the adjacent barrier shoreline. The breaching event widened the inlet throat from 1.5 km in 1890 to 8.6 km by 1930. The increasing bay tidal prism resulted in inlet widening and the formation of multiple channels separated by ephemeral shoals. During the same time, the ebb tidal delta grew in size and prograded seaward while the adjacent barriers migrated landward.