Recent Changes in Oyazawabana Sand Spit in Lake Hinuma and Impact of Ground Subsidence due to the 2011 Great Earthquake

Abstract

Ground subsidence by 22 cm occurred in Lake Hinuma in Ibaraki Prefecture during the 2011 Great Earthquake on March 11, 2011. This lake is connected to the Pacific Ocean via the Hinuma and Naka Rivers, resulting in the sudden increase in water level of the lake by 22 cm. This increase in water level was larger than the mean significant wave height of normal waves in Lake Hinuma, and thus large impact to the sandy beach and shoreline vegetation was caused. Field observations were carried out to investigate the impact as well as the impact of a groin constructed before the earthquake.