Miyazaki University, Japan
Evaluation of beach nourishment works on Miyazaki Coast in Japan
Abstract. Miyazaki Coast has been suffering from beach erosion due to the shortage of sand supply from rivers and the change of waves and nearshore currents by the construction of an offshore breakwater at Miyazaki Port. Some countermeasures, detached breakwaters, seawalls, and gentle slope revetments, have been implemented to control shoreline recession. A beach nourishment project on Miyazaki Coast was employed to supplement the comprehensive sediment control since 2008. This study evaluates the effectiveness of the beach nourishment on Miyazaki Coast with using long-term bottom sounding data. After that, this study discusses the effect of the beach nourishment on longshore sandbar evolution. From the results of the sand volume changes before and after the beach nourishment, a certain degree of effect by beach nourishment can be seen in slowing down the rate of the sand volume change, though the sand volume is still insufficient. The outer sandbar exists stably from the second half of 2000 in Miyazaki Coast, and the multi sandbar system seems to be formed. Also, the sandbar scales, height and distance between sandbar crest and trough, tend to become larger. It seems that the beach nourishment contributes to the longshore sandbar evolution. The effectiveness of the nourishment can be seen in Miyazaki Coast, though the degree of effect varies depending on the area, and the nourishment needs to be continued.
Keywords: Miyazaki Coast; Erosion; Beach Nourishment; Longshore Sandbar