EFFECT OF SEDIMENT SIZE ON SANDBAR MORPHOLOGY IN DIFFERENT COMPACTION CONDITIONS

抄録

 This study presents the effect of sediment size on the morphological change of a sandbar under loose and medium-dense compaction. An artificial cross-shore beach profile was designed with a small-scale sandbar on the offshore side of a 2D wave flume. A total of 12 regular wave cases were tested on two different sandbars setup using medium sand (D₅₀ = 0.33 mm) and very fine sand (D₅₀ = 0.08 mm). Experimental results revealed that very fine sand was more susceptible to erosion than medium sand in the mechanism of wave breaking to impinging. The maximum erosion zone for medium and very fine sand was found at the offshore sharp edge of the sandbar and at the impinging point, respectively. In loose compaction, a strong inverse correlation (R² = 0.80) was found between the net erosion volume and wave steepness for the medium sand, whereas a sharp peak of net erosion volume existed at the medium wave steepness in very fine sand. In medium-dense compaction of very fine sand, the reduction of net erosion volume was 67 %, 57 %, and 82 % at low, medium, and high wave steepness, respectively. At the middle depth of the sandbar, very fine sand yielded an average increase in shear strength that was five times higher than medium sand. At this depth, a strong inverse correlation (R² = 0.84) was established between the change in average shear strength and wave steepness under loose compaction of medium sand, however, similar to net erosion volume, a sharp peak was found at the medium wave steepness of very fine sand. Furthermore, datasets assessed in the laboratory would be useful for numerical simulation.