Abstract
Intertidal bars are common features on meso-and macro-tidal sandy beaches with low to moderate wave energy environments. Understanding their morphodynamics is, hence, crucial for enhancing our knowledge on beach processes which is beneficial for coastal management. However, most studies have been limited by assessing bar systems two-dimensionally and typically over the short-term. Morphology and dynamics of an intertidal bar system in a macro-tidal environment have been investigated using bi-annual LiDAR topographic surveys over a period of seven years and along 3.2 km at Groenendijk beach (Belgium). The detected bars demonstrate that a morphology of an intertidal bar is permanently on the beach. However, these individual features are dynamic and highly mobile over the course of half a year. The mean height and width of the bars were 1.1 and 82 m, respectively. The highest, steepest, and asymmetric features were found on the upper beach, while they were least developed in the lower intertidal zone. The bars were evenly distributed over the entire intertidal beach, but the largest concentration observed around the mean sea level indicated the occurrence at preferential locations. The most significant net change across the beach occurs between the mean sea level and mean-high-water neap which corroborates with the profile mobility pattern. The seasonal variability of the bar morphology is moderately related to the seasonally driven changes in storm and wave regime forcings. However, a distinct relationship may be inhibited by the complex combination of forcing-, relaxation time- and feedback-dominated response. This work conducted from bi-annual LiDAR surveys has provided an unprecedented insight into the complex spatial organization of intertidal bars as well as their variability in time from seasonal to annual scale.
Highlights
Meso-and macro-tidal sandy beaches with low to moderate wave energy are commonly characterized by the presence of intertidal bars and troughs known as “ridge and runnel topography”, ‘low amplitude ridges”, or “multiple inter-tidal bars” [1]
The aim of this paper is to investigate the morphodynamics of multiple intertidal bars from seasonal to long-term and on a large scale (>1 km)
The detected bars from the seasonal LiDAR surveys are displayed in Figure 5, which provide a number of insights on large-scale bar morphology over time
Summary
Meso-and macro-tidal sandy beaches with low to moderate wave energy are commonly characterized by the presence of intertidal bars and troughs known as “ridge and runnel topography”, ‘low amplitude ridges”, or “multiple inter-tidal bars” [1]. The development of intertidal bars is conditioned by time-varying interactions of forcing factors between tides and incident wave energy level and variability. The intertidal bar–trough system has a capacity for self-organization and may experience strong morphodynamic feedback on forcing factor condition as well as relaxation time effects [11]. In such a system, the correlation between hydrodynamic forcing and morphological response is weak, while the morphological evolution arises from the internal dynamics of the system including cross- and alongshore process-response function of time. Multiple intertidal bar–trough features must ideally be considered as a 3D morphological system as recently emphasized by [8]
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