The influence of wave-, wind- and tide-forced currents on headland sand bypassing – Study case: Santa Catarina Island north shore, Brazil

Abstract

Investigations of headland sand bypassing is still an under-reported subject in the literature. This paper aims to understand the contribution of currents forced by different mechanisms such as tides, winds (i.e. local wind acting over the ocean surface generating currents, without considering wave generation) and waves (as they approach/break on the coast) to headland sand bypassing. The study was carried out in an area comprising a series of seven headlands with varying wave exposure due to changes in shoreline orientation and increasing tidal influence close to a relatively large bay. This paper uses a calibrated and validated processbased model (Delft3D) to simulate a series of scenarios including spring and neap tides during flood and ebb conditions and a range of wind and wave scenarios that encompass both average and extreme conditions. The results indicate that waves are the main driving force for the headland bypassing as they transport sand at rates two orders of magnitude higher than tide-or wind-driven sediment transport. The tide-driven currents can only transport sediment during spring tides in locations where the currents are intensified. It is also demonstrated that the wave direction plays an important role in sediment transport. In exposed areas with larger headlands a combination of wave directions is required to first transport sediment offshore (out of the beach) and secondly to transport sediment alongshore and back to the next beach.Whereas in areas with little variation in wave direction exposure, the same oblique wave direction is responsible for the entire headland bypassing process. This is the first time the contribution of tide-, winds-and wave-generated sediment transport to headland bypassing have been studied.

High‐efficiency gravel longshore sediment transport and headland bypassing over an extreme wave event

“…While it is relatively straightforward to predict bypassing rates around groynes and other near‐idealized structures (e.g. Pelnard‐Considere, ; Larson et al ., ), it has proven far more difficult to predict bypassing around the complex morphology of natural headlands (George et al ., , ; Vieira da Silva et al ., , ; McCarroll et al ., ), and no generalized formula exists for predicting headland bypass rates. Given the underdeveloped state of research in this area and the near absence of robust observations of headland bypassing rates, the measurements described here are of significant value.…”

“…While transport rates on long, open stretches of coastline may be amenable to a simple function of sediment characteristics and wave power, transport on embayed and rocky coastlines is often impeded by headlands and limitations in sediment supply. Although there has been recent interest in headland bypassing on sandy beaches (Goodwin et al ., ; George et al ., ; Vieira da Silva et al ., , ; McCarroll et al ., ), little effort has been applied to understanding the bypassing of gravel. Presently, there are no quantitative observations of gravel headland bypassing rates and no methods for estimating bypassing in gravel environments.…”

Wave and Tidal Controls on Embayment Circulation and Headland Bypassing for an Exposed, Macrotidal Site

“…The wind and pressure forcing models were linearly interpolated and applied as spatially varying inputs across the WAVE and FLOW domains. We do not examine wind variation in detail, and it is noted that [40] determined that local winds contribute minimally to total bypassing rates.…”

“…Hydro-morphodynamic modelling, using a validated numerical model, of a group of adjacent natural headlands has been undertaken [12], with quantification of predicted bypassing of individual headlands for a given year. Additionally, an examination of the impact of varying wave, wind, and tidal conditions on bypassing for this same group of headlands [39,40] found that for a micro-tidal climate, waves were the greater driving force by two orders of magnitude; however, the effect of tide in a macrotidal climate has not been examined. While [40] described the broad impact of wave-tide controls across multiple nearby headlands, it did not examine detailed circulatory controls across any individual embayment or provide a means to predict bypassing for the observed headlands.…”

“…Additionally, an examination of the impact of varying wave, wind, and tidal conditions on bypassing for this same group of headlands [39,40] found that for a micro-tidal climate, waves were the greater driving force by two orders of magnitude; however, the effect of tide in a macrotidal climate has not been examined. While [40] described the broad impact of wave-tide controls across multiple nearby headlands, it did not examine detailed circulatory controls across any individual embayment or provide a means to predict bypassing for the observed headlands. Several recent efforts [12,31,41] have concluded that many coastal embayments previously assumed to be closed cells may in reality experience some degree of headland bypassing, making them open systems.…”