New insights into the physical drivers of wave runup from a continuously operating terrestrial laser scanner

Abstract

A dune-mounted terrestrial laser scanner was used to investigate the physical drivers of runup on an intermediate beach under a variety of wave conditions. Specifically, the laser is automated to collect hourly, simultaneous observations of beach morphology and hydrodynamics in the swash and inner surf-zone. A strong tidal signal in de-tided runup statistics is observed such that the 2% exceedence runup elevation and mean swash elevation is higher at high tide than at low tide for the same given wave conditions. This is similar to the significant incident band wave height (Hs in ) at the base of the foreshore, which also showed a similar strong tidal dependence. In fact, our results suggest that mean swash elevation and incident band swash scale well with Hs in , though correlations are slightly improved when beach foreshore slope is included in predictions of incident band swash (r 2 = 0.73 vs 0.69). In contrast, the Stockdon et al., 2006 relationship, which is based on beach foreshore slope, offshore wave height, and wavelength, only explained 53% of the variance in our data even when beach slope was known. Similar to Stockdon et al., we found infragravity band swash was dependent on deep water wave height and wave length. These data suggest that increased or decreased breaking over the sandbar at low and high tides, respectively, may filter the amount of energy left in the incident band to be transferred to runup at the shoreline. The implications of this sandbar filtering are that up-to-date bathymetry or a quantification of dissipation across the surfzone is necessary to produce accurate real-time runup predictions.

Observations of gravel beach dynamics during high energy wave conditions using a laser scanner

“…Only a few field experiments have used laser-scanner technology to perform similar types of measurements as that reported here Brodie et al, 2012;Almeida et al, 2013), and, as a consequence, very little is known about specific aspects, such as behaviour of the laser measurements for different angles of incidence. The variability in the laser-scanner output was investigated for different angles of incidence during a period where no morphological changes occurred to provide insight into the vertical resolution of the data (Fig.…”

“…Recent studies reporting the use of laser-scanners on natural beaches Brodie et al, 2012;Almeida et al, 2013) and laboratories (Blenkinsopp et al, 2012) have demonstrated the ability of the laser technology to measure swash hydrodynamics, as well as bed evolution, on the swash event time scale remotely (i.e., without the need to deploy the instrument within the region of interest). The versatility and precision of 2D laser-scanners have enabled the development of a large range of useful non-contact measurement applications ranging from medicine (e.g., Pallejà et al, 2009), forestry (e.g., Miettinen et al, 2007), to robotics (e.g., Vásquez-Martín et al, 2009).…”

Lidar and Pressure Measurements of Inner-Surfzone Waves and Setup

“…Setup in the swash zone also has been measured using video-based tracking of the water-beach intersection (Holman and Sallenger 1985). More recently, processes in the swash zone have been observed with laser techniques (Blenkinsopp et al 2010;Brodie et al 2012;Almeida et al 2013;Vousdoukas et al 2014).…”

“…The water surface elevation is measured directly, and thus attenuation through the water column need not be considered (as it is for nearbed sensors), and sand-level changes can be measured when the beach is uncovered by swashes. Laser scanners accurately measure the subaerial beach topography in and shoreward of the swash zone in large-scale laboratory (Almeida et al 2013;Vousdoukas et al 2014) and field (Brodie et al 2012) studies. Lidar estimates of swash heights and excursions agree well with pressure and video estimates (Blenkinsopp et al 2010;Almeida et al 2013;Vousdoukas et al 2014).…”

Swash Zone Morphodynamics of Coarse-Grained Beaches During Energetic Wave Conditions

“…Remote sensing methods emerge in this context as the most appropriate solution for this type of field measurement, and recent developments on the use of 2D laser-scanners (Blenkinsopp et al, , 2012Brodie et al, 2012;or Almeida et al, 2013) to perform high frequency measurements of swash zone dynamics (including morpho and hydrodynamics) have demonstrated to be one of the most adequate tool for this propose.…”