Rapid Erosion of A Cohesive Shoreline, Sargent Beach, Texas

ABSTRACT One of the areas of highest coastal erosion along the Texas coast is located in the deltaic headland coastal segment of the Brazos River in the vicinity of Sargent Beach. Because of this erosion, a section of the Gulf Intracoastal Waterway (GIWW) from Cedar Lakes to East Matagorda Bay is in danger of intrusion from breaching of the narrow (less than 300 m wide) shorefront. Owing to its deltaic origin, the beach is composed of cohesive fine grained clay and silt material, overlain by a narrow layer of coastal peat and topped by a thin veneer of fine grained quartz beach sand with a high percentage of shell fragments. The northeastern half of the study area has an average erosion rate of 6.7 m/yr and has a thin sandy flat sloping beach over the clay deposit. The southwestern section has up to a meter high clay bluffs outcropping into the surf zone and has an average 11 m/yr erosion rate. It is speculated that this high erosion rate is a result of intermittent wave cutting of large chunks of the clay bluff material. The overall erosion rate along this coast is due to a general lack of sand.