Abstract
AbstractCoastal management and engineering applications require data that quantify the nature and magnitude of changes in nearshore bathymetry. However, bathymetric surveys are usually infrequent due to high costs and complex logistics. This study demonstrates that ground‐based X‐band radar offers a cost‐effective means to monitor nearshore changes at relatively high frequency and over large areas. A new data quality and processing framework was developed to reduce uncertainties in the estimates of radar‐derived bathymetry and tested using data from an 18‐months installation at Thorpeness (UK). In addition to data calibration and validation, two new elements are integrated to reduce the influence of data scatter and outliers: (a) an automated selection of periods of “good data” and (b) the application of a depth‐memory stabilization. For conditions when the wave height is >1 m, the accuracy of the radar‐derived depths is shown to be ±0.5 m (95% confidence interval) at 40 × 40‐m spatial resolution. At Thorpeness, radar‐derived bathymetry changes exceeding this error were observed at time scales ranging from 3 weeks to 6 months. These data enabled quantification of changes in nearshore sediment volume at frequencies and spatial cover that would be difficult and/or expensive to obtain by other methods. It is shown that the volume of nearshore sediment movement occurring at time scale as short as few weeks are comparable with the annual longshore transport rates reported in this area. The use of radar can provide an early warning of changes in offshore bathymetry likely to impact vulnerable coastal locations.
Highlights
Being able to accurately and consistently monitor beach and nearshore processes provides the foundation for understanding beach dynamics (Davidson et al, 2007)
Following the quality control assessment, a comparison between calibrated radar-derived and measured bathymetry showed that 96% of radar-derived values were within ±0.5 m of the measured data and 100% within ±1 m (Figure 6a)
Comparing radar-derived bathymetry (Figure 6c) with the concurrent multibeam survey show an underestimation of radar-derived depths along the beach foreshore south of the radar and an overestimation in an area north of the radar extending south and offshore from the ness (Figure 6d)
Summary
Being able to accurately and consistently monitor beach and nearshore processes provides the foundation for understanding beach dynamics (Davidson et al, 2007). Coastal erosion hotspots have been attributed to the concentration of wave energy caused by complex nearshore geology (Browder & McNinch, 2006; Burningham & French, 2017; Schupp et al, 2006; Williams et al, 2019). These processes are controlled further by changes in the incident wave climate (Hegermiller et al, 2017; Lazarus & Murray, 2011), wave direction bimodality (Burningham & French, 2016; Williams et al, 2019).
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