Observations of waves and setup on a steep, sandy beach are used to identify and assess potential applications of spatially dense lidar measurements for studying inner-surf and swash-zone hydrodynamics. There is good agreement between lidar-and pressure-based estimates of water levels (r 2 5 0.98, rmse 5 0.05 m), setup (r 2 5 0.92, rmse 5 0.03 m), infragravity wave heights (r 2 5 0.91, rmse 5 0.03 m), swell-sea wave heights (r 2 5 0.87, rmse 5 0.07 m), and energy density spectra. Lidar observations did not degrade with range (up to 65 m offshore of the lidar) when there was sufficient foam present on the water surface to generate returns, suggesting that for narrow-beam 1550-nm light, spatially varying spot size, grazing angle affects, and linear interpolation (to estimate the water surface over areas without returns) are not large sources of error. Consistent with prior studies, the lidar and pressure observations indicate that standing infragravity waves dominate inner-surf and swash energy at low frequencies and progressive swell-sea waves dominate at higher frequencies. The spatially dense lidar measurements enable estimates of reflection coefficients from pairs of locations at a range of spatial lags (thus spanning a wide range of frequencies or wavelengths). Reflection is high at low frequencies, increases with beach slope, and decreases with increasing offshore wave height, consistent with prior studies. Lidar data also indicate that wave asymmetry increases rapidly across the inner surf and swash. The comparisons with pressure measurements and with theory demonstrate that lidar measures inner-surf waves and setup accurately, and can be used for studies of inner-surf and swash-zone hydrodynamics.

A low-cost multicamera Unmanned Aircraft System (UAS) is used to simultaneously estimate open-coast topography and bathymetry from a single longitudinal coastal flight. The UAS combines nadir and oblique imagery to create a wide field of view (FOV), which enables collection of mobile, long dwell timeseries of the littoral zone suitable for structure-frommotion (SfM), and wave speed inversion algorithms. Resultant digital surface models (DSMs) compare well with terrestrial topographic lidar and bathymetric survey data at Duck, NC, USA, with roor-mean-square error (RMSE)/bias of 0.26/-0.05 and 0.34/-0.05 m, respectively. Bathymetric data from another flight at Virginia Beach, VA, USA, demonstrates successful comparison (RMSE/bias of 0.17/0.06 m) in a secondary environment. UAS-derived engineering data products, total volume profiles and shoreline position, were congruent with those calculated from traditional topo-bathymetric surveys at Duck. Capturing both topography and bathymetry within a single flight, the presented multicamera system is more efficient than data acquisition with a single camera UAS; this advantage grows for longer stretches of coastline (10 km). Efficiency increases further with an on-board Global Navigation Satellite System-Inertial Navigation System (GNSS-INS) to eliminate ground control point (GCP) placement. The Appendix reprocesses the Virginia Beach flight with the GNSS-INS input and no GCPs. The resultant DSM products are comparable [root-mean-squared difference (RMSD)/bias of 0.62/−0.09 m, and processing time is significantly reduced.

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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.