FINDING SAND IN A SAND-DEFICIENT ENVIRONMENT: SAND RESOURCES, REGIONAL GEOLOGY, AND COASTAL PROCESSES FOR THE RESTORATION OF THE BARATARIA BARRIER SHORELINE, SOUTHEASTERN LOUISIANA

The barrier coastline of Barataria Basin (Louisiana) has undergone significant retreat and reduction in size during the past 100 years. This shoreline protects the Barataria Bay ecosystem that provides enormous productivity, economic benefits, and storm protection. The most practical restoration method to rebuild these shorelines is sand replenishment. Understanding the recent geologic framework allows for the identification of sand-rich features that can serve as sand sources. A dense survey of high-resolution seismic data (CHIRP and Boomer), vibracores and borings were used to identify available resources. Previous studies using less dense surveys greatly over-estimated sand resources available in this area. This study shows that, contrary to common opinion, not all deltaic subsystems have abundant sand resources.

The western and central sections of the study area are composed of a low barrier beach in the form of a thin continuous washover sheet (~1 m). This area is part of the Bayou Lafourche erosional headland. Erosional reworking of the Lafourche headland has released limited sand to the barrier shoreface, starving potential nearshore sand resources. The primary sand deposits in these sections are ebb-tidal deltas of Caminada (2.9 to 3.9 x10⁶ m³), Barataria (14.2 to 20.1 x10⁶ m³), and Quatre Bayou (15.2 to 20.3 x10⁶ m³). Older deposits include buried ebb tidal deltas of Barataria (26.8 to 35.7 x10⁶ m³) and Quatre Bayou (71.7 to 102.4 x10⁶ m³), and buried incised channels. Sediment analysis from core samples indicate most of the sand to be fine to very fine in size (2 to 4 phi).

The eastern section consists of the Plaquemines delta lobe between Barataria Bay and Sandy Point. The sand resources found here consist of isolated sandy channel-fill deposits. The largest deposit in the study area is the Sandy Point sand body with an area of ~44 km², a thickness of 6.1 to 9.2 m and an estimated sand volume of 170.4 to 227.2 x10⁶ m³. Geometry, location, and textural description from sediment cores suggest deposition within a distributary mouth-bar environment.