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.

由于 2019 年 10 月的台风海贝思（19 号台风），也称为令和 1 号东日本台风，长野县千曲川堤防的许多部分遭到破坏。曾发生过堤防因漫溢而倒塌的事例，一座电气铁路桥也因受侵蚀的护岸破裂而倒塌。在本研究中，对这些灾害进行了调查。

调查同时考虑了地质学——地质力学和堤坝因漫溢而倒塌的水力学。结果表明，堤防坍塌的最重要因素是结构薄弱。有一些案例是通过采取简单的防渗措施来提高堤坝的韧性。研究发现，桥台被冲刷的主要原因是，在高峰后河水位下降过程中，沙洲侵蚀后水路发生变化，使河堤变成了水冲锋。