| On the inner shelf of many coastal seas (depth of 10-20 m) patches of so-called shoreface-connected sand ridges (sfcr) are observed that have a rhythmic structure in the long-shore direction. Typical spacings between successive ridges are 4-8 km, they evolve on a timescale of centuries and they migrate several meters per year along the coast. The formation and evolution of the ridges is attributed to sea level rise (forced response) and to free response, i.e., internal feed-backs between storm-driven currents, waves and the sandy bottom. Knowledge of the joint response of ridges to changes in sea level, wave climate and human interventions is quite limited, because available models either focus on free or forced behavior, and the process-based models ignore wave-topography feed-backs and can not be run for parameter values that are representative for natural shelves. The focus of this project is to remove these limitations, and to gain more fundamental knowledge about the dynamic behavior of sfcr. The specific objectives are: 1. To quantify the characteristics of finite-amplitude sfcr on a shelf with a realistic transverse bottom slope, using a model that accounts for wave-topography feedbacks; 2. To study the nonlinear response of finite-amplitude sfcr to anthropogenic processes on a shelf with a realistic transverse bottom slope; 3. To quantify and understand the relative importance of both external forcing (in particular sea level changes and storm statistics) and internal self-organization (i.e., free behavior) on the formation and long-term evolution of sfcr; 4. To assess and unravel the influence of changes in chronology of mild and severe storms on the long-term evolution of sfcr. For that purpose a model, which already successfully simulates finite-amplitude sand bars in the nearshore zone, will be modified such that it will simulate sand ridges on the inner shelf. First, the model will be configured such that it is consistent with earlier models. After that, the new aspects will be added one after another and their consequences for the nonlinear evolution of sfcr will be systematically explored and explained. |
