The Effects of Nourishments Using the Grain-Size Trend Analysis on the Intertidal Zone at a Sandy Macrotidal Beach

Abstract

Byeonsan Beach is a typical macrotidal beach located at the west coast of Korea, which has been eroded continuously over the past decade since the construction of Saemangeum Dike. Starting from 2011, beach nourishment has been conducted annually on the Beach, with about 8 x 10(3) m(3) of well sorted medium sands over the intertidal flat area. Primary purposes of this study are to understand the pattern of sediment transport using the grain-size trend analysis (GSTA) proposed by Gao and Collins (1992), and to evaluate the effect of nourishment procedures. Because of the monsoonal climate, nourishments were carried out just before the rainy summer season between late May and early Jun. 120 surficial-sediment samples were carefully collected each time in March before nourishment and also in September about 3-month after nourishment. The results of sediment grain-size analysis showed the equilibrium status of transport pattern in the previous winter season and during summer after nourishment, respectively. Beach morphology was also made monthly by using RTK-GPS system. The result showed that most of the nourished sands remained within the intertidal zone of the beach, and thus the nourishment procedures conducted on Byeonsan Beach were considered as successful. Nourishment sediments were transported predominantly landward direction, resulting in 20-cm increase in mean elevation along the upper sand beach. Subsequent amounts of nourished sand were considered to be transported seaward direction showing different transport patterns between 2013 and 2014, especially at the northern and southern parts of the beach. Local factors influencing the transport pattern were the amount of rainfalls and the resulting freshwater discharge from sluice gates, and the climatic conditions such as typhoon events in summer and strong northwesterly winds during winter.