93. NUMERICAL SIMULATION OF RAPID EROSION OF SEISHO COAST TRIGGERED BY STORM WAVES DURING TYPHOON 0709

Recovery of Sandy Beach by Gravel Nourishment - Example of Ninomiya Coast in Kanagawa Prefecture, Japan

“…The calculation domain has a length of 1 km including the damaged area of 350 m length between Kinpa and Ginpa Bridges. For the wave conditions, the energy mean wave height of H b = 0.83 m (T = 6.3 s) measured at Hiratsuka wave observatory was employed, similarly to that in Serizawa et al (2009). The normal waves were assumed to be incident from the direction perpendicular to the shoreline (θ w = 0°) of the Yamanishi area where the sandy beach has been gradually recovered by beach nourishment.…”

“…The characteristic grain sizes of the fine and coarse materials are assumed to be d 1 = 0.2 and d 2 = 2 mm, respectively. Serizawa et al (2009) reproduced beach changes owing to the rapid seaward transport of mediumsize sand during storm waves, and the recovery of the foreshore under normal waves by changing the equilibrium slope of medium-size sand depending on the wave conditions. This condition was selected on the basis of the measured beach changes on the Ohiso coast, east of the present study site.…”

“…The beach changes after 10 years were predicted using time intervals of Δt = 0.5 hr. The berm height, the depth of closure and the coefficient of sand transport were the same as those in Serizawa et al (2009). Beach changes after the beach nourishment were predicted under the condition that groins were constructed at both ends.…”

“…In particular, the seawall protecting the Seisho Bypass was severely damaged and collapsed over a length of 1.1 km near the Oiso Interchange, as shown in Figs. 2 and 3, closing the highway to traffic for a long time (Serizawa et al, 2009). Serizawa et al (2009) showed that the erosion of the coast was primarily triggered by the selective discharge of medium-size sand from the beach composed of both sand and gravel by offshore sand transport associated with the storm waves.…”

“…2 and 3, closing the highway to traffic for a long time (Serizawa et al, 2009). Serizawa et al (2009) showed that the erosion of the coast was primarily triggered by the selective discharge of medium-size sand from the beach composed of both sand and gravel by offshore sand transport associated with the storm waves. After the storm, part of the medium-size sand transported offshore returned to the foreshore under normal wave condition.…”