Levee damage and revetment erosion by the 2019 Typhoon Hagibis in the Chikuma River, Japan

Due to Typhoon Hagibis (Typhoon No. 19) in October 2019, also known as the Reiwa 1 East Japan Typhoon, many parts of the Chikuma River's levee in Nagano Prefecture were damaged. There were instances of levee collapse due to overtopping, and an electric railway bridge also collapsed when an eroded revetment broke. In the present study, these disasters were investigated. The investigation considered both the geology - geomechanics and the hydraulics of the levee collapse due to overtopping. The results suggest that the most significant factor in the collapse of the levee was structural weakness. There were cases in which the tenacity of a levee was improved by taking simple measures against seepage. It was found that the bridge abutments washed away mainly because the river levee became a water-colliding front due to changes in the water route following the erosion of a sandbar in the process of river level decline after the peak. (C) 2021 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society.

Automated summary

Typhoon Hagibis in October 2019 caused severe damage to levees and bridges in Nagano Prefecture, Japan, with the main factor of collapse being structural weakness. Simple measures against seepage were found to improve levee tensile strength.