Geosciences Seminar Fri, 02/19/2016 - 13:13 "Negative diffusion in Shoreline Sand Waves and its implication on the long-term fate of nourishments" by Jaime Arriaga, UPC, will be held at room Aula of Institut de Ciencies del Mar (ICM - www.icm.csic.es). ABSTRACT: Shoreline sand waves are dynamic coastal features expressed in the shoreline as rhythmic undulations with a wavelength of kilometres and a characteristic growth time of years. These large scale features are believed to be driven by an instability in the longshore transport in the presence of High-angle wave incidence (HAWI), this instability is caused by strong refraction effects and manifests as an unbalance between the wave height and wave angle at breaking. In order to predict its appearance and behaviour a simplified model approach is necessary due to computational costs and because more complicated models tend to have an important chaotic behaviour in the long run. A quasi two dimensional model is presented, which is able to reproduce and to capture the complex dynamics and growth of these features. A theoretical case is analysed where instability occurs and a real/pragmatic case where the diffusion of a mega-perturbation (Dutch coast) is analysed over 20 years.