14 - Mixed sand and gravel beaches

Abstract

Mixed sand and gravel beaches are characterized by a mixture of sand and gravel-sized sediment across and along the beach profile, leading to two, three or even more dominant sediment fractions. They can be found in a wide range of tidal and wave environments geographically, particularly those at higher latitudes, such as New Zealand, the United Kingdom and Spain. Despite their complexity and interest from a management point of view, in the past, these beaches have received less attention from researchers and managers than sandy beaches, and studies into the main physical processes that control their morphodynamics remain limited. These types of beaches, however, have the potential to reduce the effects of sea-level rise on coasts where the presence of different sediment fractions provides the ability to adapt more rapidly than any other beach types to changes in the wave and water-level conditions. Additionally, post-storm recovery rates of mixed sand and gravel beaches are generally faster than those of sandy beaches. Finally, when assessing how the beach will respond to varying forcing conditions in mixed sand and gravel beaches, the total run-up represents a more accurate threshold parameter than just using wave height information alone in determining beach response.