Ripple Sinuosity and Defect Density: Effects of Seabed Objects and Flow Orientation

Abstract:

Ripples are directly influenced by the intensity and direction of near bed flow. Ripple geometric response to unidirectional or oscillatory dominant forcing has definable characteristics respective to each regime, but is less understood in conditions of combined forcing, specifically orthogonal wave and mean current forcing. Previous studies (e.g. Smyth and Li, 2005; Lacy et al., 2007) have suggested that increasingly divergent orientation in wave and current forcing may increase ripple crest sinuosity (meandering). This, in turn, affects ripple migration and ripple defect generation and density (Faraci and Anderson, 2002). In similar fashion, seabed objects, through scour and current steering, may affect ripple morphology, disrupting ripple migration and serving as nodal points for ripple defect generation. With the Fingerprint Algorithm imagery analysis technique (Skarke and Trembanis, 2011), it is now possible to effectively quantify spatial-temporal evolution of ripple morphology from acoustic imagery. Using in situ hydrodynamic and acoustic imagery data from near-shore instrument moorings, this study investigates the influence of combined flow on ripple sinuosity patterns and the relationship of sinuosity to ripple defect location and density. Further, it examines defect density with respect to proximity and orientation to seabed objects, and considers specific characteristics of object influence on ripple migration patterns. Initial findings suggest ripple defect density increases in area of increased ripple crest sinuosity and near seabed objects.