Erosion Control of Scour During Construction. Report 3: Experimental Measurements of Refraction, Diffraction, and Current Patterns Near Jetties

Source: https://erdc-library.erdc.dren.mil/jspui/ ; Effective, comprehensive, and low cost procedures do not exist for eliminating scour during construction in the nearshore environment. Determination of potential alternative procedures is seriously hampered by the inability to predict the extent of potential scour. The objectives of this research program are to develop techniques to minimize and control scour during nearshore construction and to predict the probable magnitude of scour that may result as a function of currents and wave climate. One phase of the research effort is the development of numerical techniques (incorporating both refraction and diffraction effects near the structure) for computing wave-induced velocities and tidal currents in the vicinity of structures and applying these results to determine sediment transport of the bottom material at the particular site. The purpose of this study was to obtain detailed and precise experimental data regarding wave-height variations and currents (patterns and magnitudes) downwave from a shore-connected breakwater or jetty under the simultaneous effects of refraction and diffraction. This information provides insight into the phenomenon of combined wave refraction and diffraction and can be used to verify numerical models that simulate this phenomenon. The experimental investigation was conducted in a wave basin that was molded in cement mortar and consisted of an area 50 ft x 60 ft with a water depth of 1 ft in the open-ocean region. A vertical, impermeable breakwater (shore-connected) extending perpendicularly from the shoreline was installed on a beach slope of 1V on 20H. In the neighborhood of the breakwater, currents existed that affected the wave heights. The magnitude of these wave-induced return currents is a function of incident wave characteristics. The effect of varying the incident wave height on the wave-height amplification factor, H/H?, was investigated and it was determined that the greatest variation in H/H? occurred in the deep shadow ...