Abstract
Existing time variable ripple prediction models have focused on ripple wavelength and height yet have not accounted for the effect of wave directionality on ripple evolution. These models use an equilibrium ripple sub-module that provides the target geometry of the seabed. Temporal variability of the hydrodynamic conditions cause ripple geometry to lag behind and not always agree with that predicted by equilibrium models. In this contribution, previous work is extended through the development of a new 2-D, time variable, spectral ripple model that allows for the estimation of ripple wavelength, height, and orientation. Since ripple irregularity is associated with directionality, the new model also has the ability to predict the irregularity of the rippled seabed. A comparison of the 2-D and existing time-dependent models is carried out using both synthetic and field ripple data that consist of time series representing a variety of wave-forcing conditions. Under strong wave forcing with no orientation changes, the 2-D model predicts ripple wavelength and orientations that agree with those of existing models. During periods of change in wave directions, the 2-D model predicts a significantly smaller ripple height during ripple reorientation. Under weaker energy flows, the 2-D model yields improved estimates especially for relict ripple geometry. In addition, the 2-D model’s spectrum yields a prediction of the seabed irregularity.
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Acknowledgments
Financial support for this work was provided by the National Science Foundation (NSF Awards OCE-0,451,989 and OCE −0,535,893) and the cooperative agreement between the US Geological Survey and the University of South Carolina (the Carolinas Coastal Change Project). The GA dataset was collected with the assistance of the Skidaway Institute of Oceanography and the crew of the R/V Savannah who assisted in the deployment and recovery of the instrumentation. The LB dataset was collected with assistance from the US Geological Survey consisting of three cruises aboard the R/V Dan Moore.
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Nelson, T.R., Voulgaris, G. A spectral model for estimating temporal and spatial evolution of rippled seabeds. Ocean Dynamics 65, 155–171 (2015). https://doi.org/10.1007/s10236-014-0801-y
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DOI: https://doi.org/10.1007/s10236-014-0801-y