ABSTRACT

The chenier plain coast of southwestern Louisiana has been recognized as the downdrift recipient of fine-grained sediment derived from the Atchafalaya River, to the east. Carried as suspended sediment in the Atchafalaya "mud stream," silts and clays are now accumulating as nearshore deposits of gel-like fluid mud along what has historically been one of the most rapidly retreating shorelines in the United States. The major effect of this sediment is to attenuate incoming wave energy, thus providing conditions favorable for further sedimentation. The initiation of a new cycle of sediment input will provide us with our first opportunity to study the processes that have led to development of the Louisiana chenier plain over the past 5000 years.

Computations based on current and sediment concentration measurements reveal that the volume of sediment carried west from the Atchafalaya River is on the order of 50 x 10⁶ m³/year, a value that represents nearly one-half of the sediment that leaves Atchafalaya Bay. Process-oriented field studies initiated in 1980, together with satellite imagery, color infrared photography, and aerial overflights since 1974, indicate that mudflat sedimentation is increasing to the west. A reversal of the overall pattern of coastal retreat now characteristic of the chenier plain is expected when Atchafalaya Bay becomes sediment filled, thus allowing an even greater volume of sediments to enter the dynamic shelf region seaward of the bay.