Northeastern Section (45th Annual) and Southeastern Section (59th Annual) Joint Meeting (13-16 March 2010)

Paper No. 6
Presentation Time: 9:45 AM


TREMBANIS, Art1, SKARKE, Adam1, RAINEAULT, Nicole2, SCHMIDT, Val3 and MAYER, Larry4, (1)Department of Geological Sciences, University of Delaware, 109 Penny Hall, Newark, DE 19716, (2)Geological Sciences, University of Delaware, P.O. Box 3, Newark, DE 19715, (3)Center for Coastal and Ocean Mapping, University of New Hampshire, Chase Ocean Engineering Lab, 24 Colovos Rd, Durham, NH 03824, (4)Center for Coastal and Ocean Mapping, University of New Hampshire, 24 Colovos Road, Durham, NH 03824,

Sorted Bedforms, previously termed Rippled Scour Depressions, are distinct and ubiquitous inner-shelf seabed features possessing alternating sedimentary facies. These features are comprised of 1) a fine well-sorted raised sand beds with anorbital ripples and large-scale hummocks adjacent to 2) a coarse poorly-sorted gravelly sand with pronounced wave orbital ripples. The bedforms (i.e. ripples and hummocks) themselves are quite dynamic yet the overall patch patterns persist over decades despite frequent reshaping of the seabed. We present recent detailed morphological analysis utilizing a series of high-frequency geoacoustic data (side-scan and swath bathymetry) to examine the variations in ripple morphology over the entire coarse sand domain facies. The geoacoustic data was collected from an Autonomous Underwater Vehicle (AUV) configured with a 500 kHz phase measuring bathymetric sonar and 900 kHz side-scan sonar collecting over 20 km of trackline geoacoustic data in depths ranging between 12-18 m. Together these provide high-resolution (O 10 cm) gridded data products of collocated morphology and backscatter measurements of the seabed. Utilizing 2D and 3D Fast Fourier Transform (FFT) spectral analysis techniques over gridded subregions (O 10m) within each facies type the spatial variability of ripple length-scale and orientation is presented. This analysis is particularly useful in examining the changes in bedform geometry near the critical contact between these two distinct facies. Ripples play a fundamental roll in the initiation and maintenance of sorted bedforms and having a detailed understanding of the ripple variability within these features may help us understand why these are such a persistent morphology in shelf settings around the world.