Remote sensing of wave runup over breakwater slope in field using optical imagery

Abstract

In this paper, wave run-up on the seaward slope of a breakwater in field was measured remotely using optical video imagery and investigated through comparisons with an empirical formula. In order to extract properties of wave run-up and over-topping on the breakwater slope from field videos, individual image frames were sequentially sampled at 3 Hz from a video burst first. Then, the sampled sequential image frames were rectified into real world coordinates. A cross-shore image timestack was generated by collecting an image pixel array, which was defined along the cross-shore transect on the seaward breakwater face of interest. Trajectory of the run-up on the seaward face evolving in time was extracted from the image timestack using a line detection method. The properties of the run-up estimated from field video bursts were combined to the measurements of incident waves, in order to derive an empirical relation between incident waves and run-up. The video-based relative wave run-up height (i.e. R-u,R-2%/ Hs) at a typical armored breakwater with tetrapods was found to be about 2.15. This value is about in the range of the general formula, which was derived from laboratory experiments in earlier studies.