Behind the zebra's stripes: ripple morphodynamics and implications for seabed object detection

Trembanis, Arthur C.The complex morphodynamics of the inner continental shelf present challenges to investigations of sediment transport, bedform dynamics, and seabed object detection. The reactive nature of seabed morphology to hydrodynamic forcing, and in turn, influence of morphology to near-bed hydrodynamics, results in spatially variable and often rapidly evolving morphology, such as ripple bedforms. As ubiquitous morphological expressions of the inner continental shelf, ripple bedforms influence seabed roughness and sediment transport on spatio-temporal scales that are only just becoming clear. Due to this wide-spread influence, ripple bedforms have been the subject of decades of research. While progress has been made on predicting time-varying ripple morphology such as wavelength and orientation, the contributions of ripples to seabed roughness, and the modifiers to ripple roughness (i.e. mechanisms for ripple erosion such as bioturbation), remain poorly understood. Compounding this issue, ripple bedforms introduce challenges to seabed object detection. Of particular concern are legacy munitions and explosives of concern (MEC), often referred to as unexploded ordnance. In the dynamic inner continental shelf, smaller MEC may become buried or obscured in ripple bedform fields, rendering traditional survey techniques ineffective. Further, the interactions between ripple bedforms and seabed objects have not been investigated fully. While ripples complicate object detection, the influence of seabed objects on near-bed flow may similarly influence both the fate of objects in ripples, as well as the ripple bedforms themselves. As such, this dissertation investigates the relationship between seabed morphodynamics and seabed objects with implications for seabed object detection. First, ripple bedform morphodynamics are investigated, with specific focus on dynamics that complicate ripple modeling, including ripple eccentricities. This investigation is expanded into ripple roughness and erosion, including both physical and biological modifiers to bedforms. Towards object detection, a process is discussed for synthesizing information and optimizing sensor technology and methodology for MEC detection, with consideration given to the complications of MEC detection with existing geophysical sensors in dynamic settings. This examination is expanded to investigate the fate of MEC during energetic events, and the application of ripple morphology, object scour burial, and object mobility models to aid in the detection of seabed objects in complex morphology typical of the inner continental shelf. The results of this dissertation highlight the importance of morphodynamics as modifiers to sediment transport, seabed roughness, and seabed object detection. Further, this dissertation demonstrates the importance of morphodynamics in determining the fate of MEC in the inner continental shelf and illustrates the significance of morphodynamic modeling as a tool to adapt and improve MEC detection methodology.University of Delaware, School of Marine Science and PolicyPh.D