Dickson, M.E, Hicks, D.M., and Coco, G. 2007. A Holocene-Scale Numerical Model of Shore Profile Evolution on an Eroding Alluvial Fan Coast, JCR SI 50 (Proceedings of the 9th International Coastal Symposium), 821 – 826. Gold Coast, Australia, ISSN 0749.0208

The Holocene evolution of beach, cliff and substrate on an idealized sand/gravel shoreface is investigated using a newly developed numerical model. The model describes a geomorphic system in which a gently sloping alluvial fan composed of sand and gravel is eroded by wave action under stable relative sea level. In this system landward erosion into the sloping surface produces cliffs that increase in height with time. Beneath water level, wave orbital motions impart stress on the seabed, which gradually lowers as a result. Excavation of the alluvial fan, both at the shoreline and in the nearshore, releases sediment that is transported onshore by wave asymmetry, building beaches. With no abrasion of the beach sediment, the beaches build to an elevation and volume that prevents erosion of the backshore, and the system progresses to a steady state where the nearshore has been excavated to closure depth. By contrast, with abrasion of the beach sediment (producing fine material that is assumed to be transported offshore and lost from the system), the beach volume reduces until the beach only provides intermittent protection against backshore erosion, leading to the formation of cliffs which, when they erode during storms, recharge the beach with sediment. In this situation, a translating shoreline develops. Depending on the various rates assumed for abrasion, seafloor lowering and cliff recession, beaches of various sizes and shapes emerge, and these provide a feedback in terms of the frequency of erosion events.