Research on Sediment Transport Processes in Mountainous Rivers Based on Geomorphic Analysis

Abstract

In recent years, floods with sediment have occurred often in Japan, causing serious channel changes and bed deformation in mountainous rivers. In this study, we investigated a flood event caused by heavy rainfall due to Typhoon Hagibis in 2019, which produced tremendous damage to the Uchikawa River basin in Miyagi prefecture, and determined the characteristics of the flood event and processes of active landform deformation by focusing on the sediment transport capacities of the channels. The flood mainly occurred in the transition zone between the mountains and the alluvial plain in the lower Uchikawa River basin. The flood flowed down the back marsh and former channel along the Uchikawa and Gofukuya Rivers, which resulted in massive sediment deposition with longitudinal sediment sorting. The sediment transport capacities of the main channels were calculated based on the sediment transport by floodwaters. The results showed that the flooding occurred due to a decrease in the sediment transport capacity, and each event of flooding along the Uchikawa River and other main channels occurred separately. We also calculated the sediment transport capacities of the Sozu, Tenchi, and Oyaokawa Rivers, which flooded due to the 2018 torrential rainfall in the western part of Japan. With these additional cases, we confirmed that the sediment transport capacity can be an indicator to explain the process of sediment transport and deposition, and detect areas that are likely to be affected by active landform deformation.