Characterizing beach intertidal bar systems using multi‐annual LiDAR data

Abstract

Intertidal bars are common in mesotidal/macrotidal low‐to‐moderate energy coastal environments and an understanding of their morphodynamics is important from the perspective of both coastal scientists and managers. However, previous studies have typically been limited by considering bar systems two‐dimensionally, or with very limited alongshore resolution. This article presents the first multi‐annual study of intertidal alongshore bars and troughs in a macrotidal environment using airborne LiDAR (light detection and ranging) data to extract three‐dimensional (3D) bar morphology at high resolution. Bar and trough positions are mapped along a 17.5 km stretch of coastline in the northwest of England on the eastern Irish Sea, using eight complete, and one partial, LiDAR surveys spanning 17 years. Typically, 3–4 bars are present, with significant obliquity identified in their orientation. This orientation mirrors the alignment of waves from the dominant south‐westerly direction of wave approach, undergoing refraction as they approach the shoreline. Bars also become narrower and steeper as they migrate onshore, in a pattern reminiscent of wave shoaling. This suggests that the configuration of the bars is being influenced by overlying wave activity. Net onshore migration is present for the entire coastline, though rates vary alongshore, and periods of offshore migration may occur locally, with greatest variability between northern and southern regions of the coastline. This work highlights the need to consider intertidal bar systems as 3D, particularly on coastlines with complex configurations and bathymetry, as localized studies of bar migration can overlook 3D behaviour. Furthermore, the wider potential of LiDAR data in enabling high‐resolution morphodynamic studies is clear, both within the coastal domain and beyond. © 2019 John Wiley & Sons, Ltd.

Autonomous monitoring of nearshore geomorphology and hydrodynamics to assist decision making in coastal management, using shore-based radar systems: A case study on the Fylde peninsula, UK

“…In addition to this system of bars, the larger sedimentary feature indicated accretes, expanding northwards by around 200 m. This confirms local anecdotal knowledge, scientific observations and modelled predictions about this system with the dominant longshore current driving sediment northwards and migration of sediment onshore under typical conditions. See Miles et al (2019) for a description of these intertidal bar systems along the Fylde coast that closely aligns with the radar-derived characteristics. Further analysis aims to show the effect of storms and changes in wave direction on sediment migration at this site.…”

Predicting Morphodynamics for Beach Intertidal Systems in the North Sea: A Space-Time Stochastic Approach

“…In contrast, the method employed to build the model described in this article can be applied to any morphological data set with sufficient measurements or any study site where such measurements can be carried out. Additionally, the model's poor prediction of long-term large volume change challenges the significance of studies using low measurement frequency (e.g., a survey per year) [46].…”

“…Morphodynamics of beaches with multiple intertidal bar-trough systems have been well documented over the past (e.g., [35,46,47,54,55]). They mainly occur on restricted coasts with a surplus of sand, exposed fetch-limited waves, and large tidal range above 3 m [56].…”

Coastal morphodynamics: nearshore, beach and dunes

“…Miles et al . () also working on longer‐term morphodynamics examined nearshore bar movements in three dimensions using light detection and ranging (LiDAR) within a macrotidal environment in the UK. Over a 17‐year period the (3–4) bar positions were characterized for a 17 km stretch and showed distinct alignment with the predominant wave approach direction.…”

“…However, their findings showed that establishing the relation between forcing and response is not a straightforward task due to the complexities of that control of coastal morphodynamics. Miles et al (2019) also working on longer-term morphodynamics examined nearshore bar movements in three dimensions using light detection and ranging (Li-DAR) within a macrotidal environment in the UK. Over a 17year period the (3-4) bar positions were characterized for a 17 km stretch and showed distinct alignment with the predominant wave approach direction.…”