Surf and Swash Dynamics on Low Tide Terrace Beaches

Low tide terrace (LLT) beaches are characterised by a moderately steep beach face and a flat shallow terrace influencing the local hydro-morphodynamics during low tide. The upper beachface slope (β) and the terrace width (Lt) are the main morphological parameters that define the shape of LTT cross-shore beach profiles. This work aims at better understanding the behaviour of β and Lt and their link with the incoming wave forcing. For this purpose, our results are based on 3.5 years times series of daily beach profiles and wave conditions surveys at two different microtidal LTT beaches with similar sediments size but different wave climate, one at Nha Trang (Vietnam) and the other one at Grand Popo (Benin). While they look similar, two contrasting behaviour were linked to two sub-types of LTT regimes: the first one is surf regulated beaches (SRB) where the swash zone is highly regulated by the surf zone wave energy dissipation on the terrace, and the second is swash regulated beaches (SwRB) acting in more reflective regime where the terrace is not active and the energy dissipation is mainly produced in the swash zone, the terrace becomes a consequences of the high dynamics in the swash zone. Finally, extending the common view of an equilibrium beach profile as a power law of the cross-shore distance, the ability of a simple parametrized cubic function model with the Dean number as unique control parameters is proposed and discussed. This simple model can be used for the understanding of LLT environments but it can not be extended to the whole beach spectrum.

A Coupled Hydrodynamic-Equilibrium Type Beach Profile Evolution Model

An equilibrium beach profile model is developed and coupled with a parametric hydrodynamic model to provide feedback between the evolving morphology and the hydrodynamics. The model is compared to laboratory beach profiles evolving toward equilibrium conditions under constant forcing. The equilibrium model follows the classical approach but uses the bulk sediment transport as the governing model parameter. This approach is coupled with empirically derived and normalised sediment transport functions and a parametric surf zone wave transformation model. The dissipation predicted by the surf zone model controls the cross-shore position of the maxima in the sediment transport functions and hence the cross-shore evolution of the beach profile. Realistic beach profile shapes are generated for both erosive (barred) and accretive (bermed) beach profiles, and predictions of bar and berm position are satisfactory. With more complex normalised sediment transport functions, the model can be applied to conditions with a cyclical wave climate. However, the model concept is better associated with erosive wave conditions and further work is required to improve the link between the modelled dissipation and local transport for accretive conditions.

Equilibrium beach profile on sandy beach of the Mehdya coast of Morocco

The world’s coastlines are shaped by mean sea level, wave conditions and storm surge. Climate change driven variations in these environmental forcing’s will inevitably have a profound effect on the coastal zone. They will result in unprecedented coastal recession, threatening billions of dollars worth of coastal developments and infrastructure. Coastal erosion is observed in some locations along Atlantic alluvial plain (Kenitra coastal (Morocco)) and is an important factor to consider for the coastal zone management. Therefore, for coastal recession estimates are obtained via the simple, deterministic method (Bruun rule) especially, that has been widely used over the last 50 years. It is in widespread contemporary use at a global scale both as a management tool and as a scientific concept. We investigated the potential erosion at the site and the result was very important. The result shows a severe erosion of the 21st century.

ANALYTICAL SOLUTION OF BEACH PROFILE RESPONSE TO SEA LEVEL RISE - APPLICATION FOR TECTONIC MOVEMENT IN SENDAI, JAPAN

Kriebel and Dean (1993) developed a simple approach to quantify the beach profile response to a time-varying sea level. It is based on the equilibrium concept implying that if a beach profile is exposed to a constant wave and water level climate it will attain a specific shape ( i.e., the equilibrium beach profile; EBP). A change in the forcing conditions will make the profile move towards a new equilibrium state, which will be attained if these conditions prevail sufficiently long. For the case of typical sea level rise (SLR), the change in the forcing conditions is slow enough so that the profile has time to adjust towards the EBP at any given time. In this study, new analytical solutions are developed based on the convolution method to describe beach­ profile response to sea water level change.

Local Wave Energy Dissipation and Morphological Beach Characteristics along a Northernmost Segment of the Polish Coast

This paper analyses cross-shore bathymetric profiles between Władysławowo (km 125 of the Polish coastal chainage) and Lake Sarbsko (km 174) done in 2005 and 2011. Spaced every 500 m, they cover beach topography from dune/cliff crests to a seabed depth of about 15 m. They were decomposed by signal processing techniques to extract the monotonic component of beach topography and to perform a straightforward assessment of wave energy dissipation rates. Three characteristic dissipation patterns were identified: one associated with large nearshore bars and 2–3 zones of wave breaking; a second, to which the equilibrium beach profile concept can be applied; and a third, characterized by mixed behaviour. An attempt was then made to interpret these types of wave energy dissipation in terms of local coastal morphological features and the underlying sedimentary characteristics.

VERIFICATION OF DEAN’S EQUILIBRIUM BEACH PROFILE FORMULA FOR LARGE MAN-MADE LAKES

In the paper the possibility of using Dean’s equilibrium beach profile formula for a large man-made lake coastal conditions was studied. A stringent test of its adequate use was made based on mathematical statistics. The calculations were performed for the real bottom profile of the Novosibirsk reservoir beach.