Coastal survey data for Perranporth Beach and Start Bay in southwest England (2006–2021)

Records of beach morphologic change and concurrent hydrodynamic forcing are needed to understand how coastlines in different environments change over time. This submission contains data for the period 2006 to 2021, for two contrasting macrotidal environments in southwest England: (i) cross-shore dominated, dissipative, sandy Perranporth Beach, Cornwall; and (ii) longshore-dominated, reflective gravel beaches within Start Bay, Devon. Data comprise monthly to annual beach profile surveys, annual merged topo-bathymetries, in addition to observed and numerically modelled wave and water levels. These data provide a valuable resource for modelling the behaviour of coastal types not covered by other currently available datasets

High‐Energy Surf Zone Currents and Headland Rips at a Geologically Constrained Mesotidal Beach

International audienceWe analyze Eulerian and Lagrangian measurements of wave-induced circulation collected during a 3-week field experiment at a high-energy mesotidal barred beach with the presence of a 500-m headland and a submerged reef. Small changes in wave and tide conditions were found to largely impact circulation patterns. Three main regimes were identified depending on offshore wave obliquity: (1) Under shore-normal configuration, the flow was dominated by cross-shore motions, except for moderate waves at low tide, with the presence of a quasi-steady circulation cell on the reef. (2) Under shadowed configuration, an onshore-directed current flowing away from the headland and a weak oscillating eddy were present outside and inside the shadow region, respectively. (3) Under deflection configuration, a deflection rip flowing against the headland and extending well beyond the surf zone was present, with activity maximized around low tide for moderate waves. Under 4-m oblique waves, the deflection rip was active regardless of the tide with mean depth-averaged velocities up to 0.7 m/s 800-m offshore in 12-m depth, with energetic low-frequency fluctuations. Our results emphasize the ability of deflection rips to transport materials far offshore, suggesting that such rips can transport sediment beyond the depth of closure. This study indicates that a wide variety of wave-driven circulation patterns can occur and sometimes coexist on beaches with prominent geological settings. Changes in the dominant driving mechanism can occur as a result of small changes in wave and tide conditions, resulting in more spatially and temporally variable circulation than along open sandy beaches. Plain Language Summary Most field experiments about wave-induced circulation patterns have been conducted along open sandy beaches, while experiments in geologically constrained environments are scarce. We performed intensive field measurements at a high-energy beach with the presence of a 500-m headland and a submerged natural reef. Three main circulation patterns were identified depending on the offshore wave obliquity. For shore-normal waves, cross-shore motions dominated the nearshore region, while oblique wave configurations resulted in more complex horizontal circulation. In particular, under intense headland-directed longshore current, the flow was deflected seaward against the headland. This deflection resulted in an intense seaward flowing jet (deflection rip) extending well beyond the surf zone edge, particularly during storm conditions. Such findings highlight the ability of these deflection rips to dominate water and sediment exchanges between the nearshore and the inner shelf region. Our study further outlines the more spatially and temporally variable circulation patterns occurring along geologically constrained beaches compared to open sandy beaches, ranging from small recirculating cells across the reef to a large deflection rip extending hundreds of meters beyond the surf zone

Lagrangian observations of circulation on an embayed beach with headland rip currents

This study describes the first comprehensive measurements of nearshore current patterns across the entire extent of an embayed beach bounded by headland rip currents. A field experiment at Whale Beach, NSW, Australia provides valuable insights into: (i) embayment-wide spatial and temporal flow behaviour; (ii) rates of cross- and alongshore water exchange; and (iii) the influence of geological control by headlands on morphology and circulation. Lagrangian flow data was obtained using 34 GPS drifters with 293 individual deployments, over a single ebbing tidal cycle during moderate-low energy (H_s=1m) oblique wave forcing. In-situ wave and current data, and bathymetric data were also collected. Beach morphology was dominated by a large mid-beach rip channel with lesser headland rip channels. Mean flow rates were 0.6ms⁻¹ in the mid-beach channel and 0.4ms⁻¹ in the headland channels, with the majority of cross-shore water volume flux (~60%) through the central channel. A weak alongshore current O (0.1ms⁻¹) was forced by the oblique offshore wave angle. Rip current velocities, flow variability, and rate of surfzone exits by Lagrangian drifters increased as water level decreased. Transient currents on a planar bar along the northern half of the beach, with mean speeds velocity standard deviation up to 0.2ms⁻¹, were not tidally modulated. Lagrangian time series were used to differentiate four current regimes (rip cell, rip head, planar bar and offshore low energy zone) based on mean velocity, velocity variability and degree of tidal modulation. An increase in surfzone exit rates by drifters was observed from south (upwave) to north (downwave), with exit rates per drifter deployment of 22% at the south headland rip, 65% at the mid-beach open rip, and 80% at the north headland rip. The high rate of drifter exits contrasts previous observations on open coast beaches. Observed flow behaviours are attributed to wave shadowing at the upwave (protected) end of the beach, and longshore currents forced by oblique waves deflected offshore at the downwave headland. These field observations are in good agreement with recent numerical modelling. A relationship between bathymetric variability and current intensity was determined, with cross-shore average mean velocity correlating with a parameterisation of bathymetric alongshore non-uniformity. This study demonstrates that flow behaviour and exchange rates can vary along the length of an embayed beach due to geological control. This research has implications for transport of organisms, nutrients and pollutants, is relevant to beach safety practitioners, and can be used in calibration of numerical models

Wave, Tide and Topographical Controls on Headland Sand Bypassing: Model Files

This archive contains model input files in support of the publication "Wave, Tide and Topographical Controls on Headland Sand Bypassing" by King et al. (2021)

Wave, Tide and Topographical Controls on Headland Sand Bypassing: Dataset

This dataset is in support of the article "Wave, Tide and Topographical Controls on Headland Sand Bypassing" by King et al. (2021). This dataset contains: All model input files for calibration, validation, and testing scenarios. A .xlsx file with headland morphometric parameters. A .csv file with all headland names and associated numbers as used in the manuscript. A .xlsx file with wave data from the WaveHub buoy used to characterise the wave climate. A NetCDF file with processed DTM's showing the derivation of sediment coverage along the North Coast of Cornwall, UK. A NetCDF file with modelled headland bypassing rates for all headlands and scenarios. A NetCDF file with parameterised headland bypassing rates for all iterations of the parameterization. A NetCDF file with environmental and topographical parameters associated with each headland and modelled scenario as used in the headland bypassing parameterisations

COMBINED EFFECTS OF PHYSICAL AND BIOLOGICAL PROCESSES ON COASTAL DYNAMICS AND RECOVERY: THE BLUECOAST PROJECT APPROACH

Poorly constrained uncertainties limit the prediction of medium-term to long-term regional sediment budgets and morphological change, and thus hinder coastal management decision-making. We present a multi-disciplinary approach that aims to address this challenge and is implemented in the BLUEcoast project. The approach brings together scientists and coastal stakeholders across a range of scientific disciplines. Quantifying all processes at all scales is not feasible and our approach uses targeted representative case studies, which are carefully selected to allow subsequent upscaling and ensure transferability. We illustrate this approach with specific examples from the BLUEcoast consortium