Monitoring Beach Face Volume with a Combination of Intermittent Profiling and Video Imagery

Abstract

A methodology for monitoring long-term beach face volume change with a combination of intermittent profiling and video imagery is developed. Intertidal beach morphology can be mapped from video with the use of movement of the waterline over a tidal cycle. Such maps provide detailed information on spatial and temporal evolution of the intertidal area, but no direct information on beach face volume changes as a whole. However, beach face volume might well be correlated with cross-shore changes to a contour located in the intertidal zone. This is significant because such a parameter can be calculated from maps of the intertidal morphology generated with video images. This idea was tested with a series of video images and surveys that were collected over a year and a half on an intermediate beach on the Coromandel Peninsula, New Zealand, over a wide range of conditions. The surveyed profiles show a strong (r2 = 0.95) relationship between the surveyed cross-shore location of the 2-m contour and the surveyed beach face volume, indicating that beach face volume changes are due mostly to intertidal changes. The relationship (r2 = 0.91) between the cross-shore location of the 2-m contour line derived from video and that derived by survey is also strong, demonstrating that the resulting regression parameters can be used to derive beach face (not just intertidal) volume from video. This relationship is unlikely to be universal and must be calibrated with standard (albeit infrequent) profiling at each specific site. The final relationship allows the video images to be used to predict changes to the beach face volume with a success rate of 89% for the test beach used. Such a model is the first step toward providing a robust remote method to coastal managers for assessing day-to-day variations in beach face volume over multiple profile lines on the same beach.