Morphological evolution of beach adjacent to the river mouth after the 2011 tsunami.

Vo Cong Hoang, Hitoshi Tanaka, Yuta Mitobe

Wednesday 1 july 2015

9:00 - 9:15h at Amazon (level 1)

Themes: (T) Water engineering, (ST) River and coastal engineering

Parallel session: 8C. Coastal Engineering

The 2011 Japan Earthquake tsunami, which occurred on March 11th, 2011, caused significant changes to the coastal and estuarine morphology along the coast on the northern part of Japan. Aerial photographs are utilized to demonstrate the severe damage and the subsequent recovery of morphology adjacent to the Nanakita River mouth on Sendai Coast, Miyagi Prefecture. Shoreline on the right bank of the river mouth was getting erosion soon after the tsunami. The erosion was propagating along the beach and causing the completed closure of the river mouth. Coastal structure plays major interruption on the erosion propagation. Analytical solution of one-line model has been utilized to investigate the phenomenon of erosion propagation. The erosion propagation distance, which is the distance along the beach starting from the river mouth to the point eroded shoreline position approaching the initial shoreline position, is proportional to the square root of the corresponded time. A new approach to evaluate value of diffusion coefficient, which is an important parameter in shoreline change simulation, is introduced. This value is utilized in the simulation on the evolution of shoreline on the right bank of the Nanakita river mouth after the tsunami. The good agrrement between measured and simulated data is obtained.