Effect of Submergence Condition and Overtopping Depth on Gully Scour Dimensions: Observations from the 2011 Great East Japan Tsunami

Abstract

When a tsunami reaches a shore, it propagates along river channels with tremendous energy and overtops river levees. It causes severe damage to the levee structures through scouring along levee slope. In the present study, gully scours created along the levee slopes of two rivers (Omotogawa and Sakarigawa Rivers) in Iwate Prefecture and three rivers (Nanakitagawa, New Kitakamigawa, and Abukumagawa Rivers) in Miyagi Prefecture were investigated after the 2011 Great East Japan tsunami. The energy head during levee overtopping for each location was calculated from post-tsunami surveys. The relationship between the energy head and gully scour dimensions (length, width, and depth) was analyzed. The analyses clarified that gully scour dimensions were greatly dominated by two important phenomena: (i) overflow type (free overflow or submerged overflow), and (ii) soil texture at the scoured region. The present study results can be utilized to obtain the overtopping flow height for post-tsunami analysis.