Application of X-band radars for deriving intertidal bathymetries and characterising coastal behaviours

Lyddon, C.E.; Bird, C.; Brown, J.M. ORCID: https://orcid.org/0000-0002-3894-4651; Plater, A.J.. 2021 Application of X-band radars for deriving intertidal bathymetries and characterising coastal behaviours. Southampton, National Oceanography Centre, 48pp. (National Oceanography Centre Internal Document, No. 23)

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Abstract/Summary

Coastal monitoring techniques aim to capture the relationship between physical forcing factors and morphological change, at a range of timescales to understand ongoing coastal processes and identify areas prone to erosion and flooding hazards posed by storms. Standard marine radar provides temporally and spatially continuous monitoring data over a wide area in all conditions, and images can be processed to generate intertidal bathymetries to assess morphological change across event (days-years) timescales. This research applies a series of intertidal bathymetries derived from a standard marine radar deployed at Camber Sands, southeast England in XBeach, a process-based, storm response model, to assess wave runup hazard at the coast during a high energy storm event from the deployment period. Wave runup is dependent on offshore wave climate and beach slope and used here as a proxy to explore the influence of nearshore morphological variability, represented by different processing techniques to derive intertidal bathymetries from the marine radar images, on a coastal hazard. XBeach is used in combination with beach survey data from the site to first demonstrate reasonable skill in reproducing wave runup observations. Intertidal bathymetries are derived from the marine radar images using either a local or regional water level signal, and an average of 1, 5, or 10 days of images preceding the storm event. Modelled wave runup shows up to 0.32 m sensitivity to input intertidal bathymetries, which could be important for overwash predictions. The slope and resolution of the radar-derived intertidal bathymetries is sensitive to the water level time series used. This research is the first time that radar-derived intertidal bathymetries have been used to assess a coastal hazard in a process-based model, and results show that ideally users would have a locally measured water level to accurately generate intertidal bathymetries, and extended beach surveys for ground truthing.