ABSTRACT

The Caminada-Moreau beach-ridge plain is located within an abandoned distributary system of the Mississippi River, and its formation is closely related to shifts of the active delta. The most recent of these changes, the shift to the present bird-foot delta (800 years B. P.), has placed a dynamic stress on the beach system by changing the effective wave climate and by cutting off the sediment source. The system response to this dynamic stress is a redistribution of sediments to reduce longshore power gradients.

Despite the moderate wave climate found in the Gulf of Mexico, extremely high erosion rates have resulted in long-term shoreline retreat as high as 20 m/yr and a net volumetric loss of 5.3 x 10⁵ m³/yr over a 20-km shoreline section. The sediment movement is dominated by longshore transport, as evidenced by longshore gradients in erosion rates, which decrease from west to east, and occurs primarily during high-energy events (storms) rather than seasonally. Of the material transported downdrift, 41 percent is captured on the Grand Isle barrier. The sediment crosses Caminada Pass through lateral migration of interchannel shoals.

The Caminada-Moreau beach system displays several levels of form-process variability. On a large scale, the coastline is undergoing reorientation toward the dominant wave approach. On a smaller scale, sediment is being eroded, transported, and redeposited as sediment envelopes as opposed to a continuous sediment flow. The tidal inlet represents an important sediment redistribution point where some of the sediment passes laterally across the inlet and the remainder is either lost offshore or incorporated into the tidal delta complex.