SUITABILITY OF FEDERAL OFFSHORE SAND RESOURCES FOR ALABAMA BEACH NOURISHMENT: PRELIMINARY RESULTS

Quarterly visits since 2002 to 17 sites yield data on Alabama beach sand quality, which can be compared to previously collected data on offshore sand bodies. Quarterly sampling trips were made in fair weather and after storms, in winter and summer, including both spring and neap tides, to permit comparison of sediment deposited under contrasting conditions. Preliminary data reveal no significant particle-size differences across weather or seasons. Neap-tide samples are coarser, probably because neap-tide windrows are located lower on the foreshore.

Particle-size distributions of Alabama beach sand are compared to those of offshore lithofacies defined by Parker and others (1993). Geometric mean particle size of Alabama beach sand is 331 ± 73 µm (258 to 404 µm). Geometric mean particle size of the Graded Shelly Sand lithofacies is 400 ± 284.5 µm (115.5 to 684.5 µm). Equivalent values for the Shelly Sand and Sand with Mud Burrows lithofacies are 267 ± 33.4 µm (233.6 to 300.4 µm) and 231 ± 30.4 µm (200.6 to 261.4 µm). Graded Shelly Sand is most similar in central tendency to Alabama beach sand, but this lithofacies is so variable that detailed mapping would be required to identify subfacies that are suitable for beach nourishment. If broad sand ridges underlain by the Graded Shelly Sand lithofacies correspond to ancient spits, as is commonly supposed, then spit environmental models should facilitate mapping of subfacies within the Graded Shelly Sand lithofacies. The Shelly Sand and Sand with Mud Burrows lithofacies are finer than the modern beach sand, but geometric mean particle size is within one standard deviation of that of beach sand. It appears, therefore, that until detailed mapping of the Graded Shelly Sand lithofacies can be completed, the Shelly Sand and Sand with Mud Burrows lithofacies should be regarded as primary targets (considering only federal waters) for beach nourishment source material.