Assessing the Performance of a Low-Cost Method for Video-Monitoring the Water Surface and Bed Level in the Swash Zone of Natural Beaches

Abstract

A method to continuously measure bed and water levels along a cross-shore transect of vertical poles is evaluated. This remote sensing based method uses video imagery of swash flows propagating past an array of vertical poles buried on the beach face. Using datasets collected at two beaches in Chile, the method is compared against measurements obtained with conventional co-localized instruments: LiDAR and ultrasonic distance meters. The present video swash pole technique shows good skill in retrieving swash zone bed level and water levels, while providing the possibility to measure morphological variations at time scales varying from wave groups (tens of seconds) to hours. Discrepancies between video and ultrasonic distance meters are found when short time scales are used, for both depositional and erosion events, but longer duration trends are captured well. Water surface elevations at the wave-by-wave scale proved to be accurate for the backwash phase (root-mean-sqaure-error, RMSE down to 0.028 m, R 2 up to 0.89), when compared against LiDAR. However, discrepancies have been found during the uprush phase (RMSE up to 0.062 m, R 2 down to 0.71), when the influence of the pole on the swash flow generates an overestimation of the water surface. Overall, owing to its simplicity of deployment, low cost and reasonable accuracy, the technique is considered suitable for swash studies.

Non‐hydrostatic, Non‐linear Processes in the Surf Zone

“…Past field studies analyzed the cross-shore transformation of surf zone waves using visual estimates of the free surface obtained from a combination of video cameras and photopoles (Mizuguchi, 1982;Ebersole & Hughes, 1987). The presence of splashes around the poles (Ibaceta et al, 2018) and the errors associated with the pixel resolution limit the accuracy of the measurements to several centimeters in the surf zone. Although generally used in laboratory conditions (Flick et al, 1981), capacitance and resistive types of wave gauges were used very early in the field to estimate surface elevation spectra in the shoaling region (Tucker & Charnock, 1954;Simpson, 1969;Flick et al, 1979) and in the surf zone (Thornton et al, 1976;Gonçalo, 1978;Thornton & Guza, 1983).…”

Assessment of a Smartphone-Based Camera System for Coastal Image Segmentation and Sargassum monitoring

“…Among the coastal video monitoring techniques, ground-sensing approaches by means of camera systems are widely used, allowing the investigation of coastal processes with high temporal and spatial resolution, with optimal accuracy. Numerous alternative or complementary uses are also pursued, with applications related to coastal hydrodynamics [1][2][3][4], morphodynamics [5][6][7], or quality monitoring (e.g., seagrass) [8,9]. Moreover, the use of low-cost devices and public resources has recently become a focus of attention and is being further explored [10][11][12].…”

Convolutional Neural Network and Optical Flow for the Assessment of Wave and Tide Parameters from Video Analysis (LEUCOTEA): An Innovative Tool for Coastal Monitoring

“…Ongoing widespread dissemination of digital systems for video monitoring allowed the development of innovative approaches to automatically obtain and process data along coastal areas. Previous studies have considered the time series of optical images to extract hydrodynamic properties of nearshore waves and currents, swash and runup [4], breaking wave, measures of breaking intensity [5,6], wave period, and wavelength (by monitoring a single pixel in the image over time), wave celerity [7], wave dissipation [8], attenuation [9], and alongshore currents [10]. These studies followed a supervised approach to establish or detect the physical wave parameters.…”