Sediment Dynamics of Beach Cells under Oblique Swell Waves

Abstract

Property development along the west coast of Barbados has led to an increasing pressure on the coastline as property owners desire to have their residences close to the sea. The addition of new coastal structures including revetments, breakwaters, and groynes, changes the dynamics of the natural littoral system. The sediment transport mechanism(s) between the beach cells characteristic of the west coast is not fully understood, so accurately predicting the effects of additional structures is difficult. Additionally the potential effects of sea level rise and a healthy reef on the mechanics and stability of the system is un-researched. Recent increases in interest of the design of multi-purpose reefs (MPR) and artificial surfing reefs (ASR) has further led to the desire for insight into the sediment dynamics at headland-reef-bay systems. This study evaluates the response and interaction mechanism(s) acting at a beach cell system with a focus under swell conditions and oblique waves typical of the west coast of Barbados. Using the Delft3D numerical model and a schematized section of coastline, a sensitivity analysis is conducted on parameters of interest to determine their effects on the sediment transport in the system. Delft3D was determined to be a valid tool to examine sediment transport in this type of system. Model results indicated that the most important parameters governing the sediment behaviour are the significant wave height, direction, and sediment diameter. Other factors of importance included reef size, reef shape, reef asymmetry, and reef roughness. Perhaps surprisingly, sea level had little effect on overall transport rates but was the most important factor affecting the location and type of transport. These changes to the mode of transport are important as they govern the public perception of what is occurring. The transport associated with elevated sea levels, although not a problem from the system perspective, becomes an issue from the beach user and public opinion perspective as erosion takes place at the beachface where it is highly visible and has significant effects on beach usability.