High-resolution, large-scale laboratory measurements of a sandy beach and dynamic cobble berm revetment

Abstract

High quality laboratory measurements of nearshore waves and morphology change at, or near prototype-scale are essential to support new understanding of coastal processes and enable the development and validation of predictive models. The DynaRev experiment was completed at the GWK large wave flume over 8 weeks during 2017 to investigate the response of a sandy beach to water level rise and varying wave conditions with and without a dynamic cobble berm revetment, as well as the resilience of the revetment itself. A large array of instrumentation was used throughout the experiment to capture: (1) wave transformation from intermediate water depths to the runup limit at high spatio-temporal resolution, (2) beach profile change including wave-by-wave changes in the swash zone, (3) detailed hydro and morphodynamic measurements around a developing and a translating sandbar.

Fig. 1

(a) Schematic of flume setup showing primary instrument locations (see Table 1). The yellow shaded area represents the sand volume and the dark grey shaded area is the permanent 1:6 impermeable slope. The black solid and dashed horizontal lines indicate the minimum (z_wl = 4.5 m) and maximum (z_wl = 4.9 m) water levels. (b) Close up of the dynamic cobble berm revetment geometry after construction corresponding to the grey box in (a). The minimum water level used for revetment testing (z_wl = 4.6 m) is shown as a solid horizontal line and the dashed line indicates the maximum water level. The light grey region indicates the constructed dynamic revetment and the dot-dashed line shows the beach profile prior to revetment construction. (c) Photograph of the constructed dynamic revetment on the underlying sand beach. The yellow line indicates the initial line of the revetment crest.

Fig. 2

Example wave measurements. (a) Timestack of water depth measured by the Lidar throughout the surf and swash zones. (b) Timeseries of water surface elevation at x = 225 m as indicated by the vertical dashed line in (a). (c) Measured free- surface profile through the surf and swash zone at the time indicated by the horizontal solid line in (a). Note that the measurements capture the splash-up generated by a breaking wave at x = 235.5 m.

Fig. 3

Example morphology data. (a) An example beach profile as measured by the mechanical profiler (black) and the swash zone profile obtained from the Lidar data (blue). (b) Separation of bed (black dots) and swash data at x = 253.8 m (blue), x = 255.3 m (red) and x = 256.8 m (orange) for an example section of data. The mean bed elevation between each swash event is shown in white. (c) Bed elevation change relative to the initial profile in the swash zone at the wave-by-wave timescale. (d) Beach profile data showing the evolution of the sand beach and dynamic revetment modified from Bayle et al.. The revetment surface is marked with a thicker line.

Fig. 4

Timeseries data from surf zone rig 1, x = 226.5 m. (a) Water depth derived from pressure transducer data, (b) cross-shore flow velocity measured 5 cm (blue) and 10 cm (red) above the bed using EMCMs, and (c) suspended sediment concentrations 5 cm (blue) and 10 cm (red) above the bed measured using OBS.

Fig. 5

Example swash data. (a) Video timestack extracted from the high definition video. (b) Timestack of water depth extracted from the Lidar data with the timeseries of shoreline position added in red.