A preliminary assessment of wave, current, and sediment interactions on the Louisiana shoreface adjacent to the Isles Dernieres

The Louisiana co;u;t is genera11y characterized as a low w·ave-energy environment where sediment transport i..; dominated by the inftuence or the Mississippi and Atc:haralaya Rivers. Winter cold fronts, however, generate waves and CUrn."nl<; that have a significant impact on a variety of Louisiana's coastal environments, although field data regardini;: their inRuence on the inner shelf are extremely sparse. During a 12-d period that included the pa.o;sage of two cold fronts, waves and near-bed currents were measured on the Louisiana inner-shelf (depth 8 ml using a sophisticated bottom-mounted instrumentation system. Bottom boundary layer parameters were then calcuJated using wave-current interaction models, and sediment transport was predicted by assuming steady state turbuJent difTusion within and above the wave boundary layer. Results indicate that the second front (Jo~ront 2) was the more energetic of the two. A maximum significant wave height of 1.33 m and maximum current speed of 0.21 m s· 1 occurred during this event. Additionally, mean current-induced shear velocity (2.95 cm s·1 and wa"e-current shear \"elocity (4.99 cm s·1) were highest during this event's frontal and prefrontal stages, respe<:tively. During the postfrontaJ stage, currents were strong and weU organized, although combined shear velocities were low as a result of reduced wave height. Predicted sediment transport varied considerably in direction and magnitude throughout the deploy men I, bnt y,·as highest (12.7-16.2 mg cm·' s·' towanl the southeast) during the prefrontal and frontal stages of Front 2. Fair weather transport was low and to the wesL Tha.;, winter i.::old fronts are likely an Important mei.::hanism for sediment movement on the Louisiana inner shelf, although the associated transport direction and magnitude require further quantification. From Che Symposium Recenl Re5ean:h in Caastal Lou.isiaoo: Naiural Sysrem Function and Response 10 Human lnflu.~nce. Rozas. L.P .. J.A. Nyman. C.E. Proffitt. N.N. Rabalais. DJ_ Reed, and R.E. Turner (editors)_ 1999. Pubh•hcd by Lcnusiarrn Sea Grant College Prug:ram.