ABSTRACT

Stormy conditions associated with periodic winter cold front passages are closely related to transport of suspended sediment to the continental shelf, coastal erosion, and coastal progradation along shoreline sectors where abundant fine-grained sediments are stored on the inner shelf. Cold front passages occur between October and April on three- to five-day cycles. Their typical NW to SE direction of approach, large spatial scales, and numerous yearly occurrences (20 - 30 events/year) drive physical processes that cause significant coastal change.

Both remotely sensed multispectral and high quality photographic data have been collected from altitudes of 0.9 mi (1500 m), 5.6 mi (9000 m), and 13 mi (21,000 m) before and after cold front passages to form a data base for evaluating coastal change and suspended sediment transport pathways. Satellite imagery provide a longer-term perspective on coastal change. Remotely sensed data sets are augmented with ground truth measurements of coastal configuration, sedimentology, and water quality.

Physical processes active in the prefrontal phases of a winter cold front passage are considerably different from those of the post frontal phase. Along the Chenier Plain coast prefrontal stages are characterized by prolonged periods (on the order of several days) of high wave action from the southerly quadrants, water level setup along the coast, and strong alongshore as well as onshore sediment transport. At these times mud from the Atchafalaya River, stored on the nearshore shelf, is transported onshore and alongshore to slightly prograde the Chenier coast. Post-frontal conditions bring dry, cold winds from the northerly quadrants causing water-level setdown along the coast, a significant reduction in nearshore wave energy, and drying of the newly deposited mudflats fronting the Chenier Plain. Rapid drying causes an important increase in sediment strength, mud crack formation, and effective armoring of the mud flats by dried mud clasts that resist erosion in subsequent cycles.