A novel downstream Flood Hazard Grade Index incorporating upstream Hydrograph Characteristics to predict Debris Flow Runoff

The July 2020 debris flow in Japan caused enormous damage, and briefing sessions on disaster prevention have prompted demands for detailed explanations and predictions of such phenomena in high-risk areas. It is necessary to obtain four-dimensional risk information, which considers temporal changes in disaster risk, rather than limiting the analysis to conventionally static information. In this study, we developed a method for setting the boundary conditions necessary for debris flow prediction via a four-dimensional hazard map using various types of digital information. To understand the effects of hydrograph characteristics from the upstream, flow discharge was analysed under different flow conditions, such as topography-driven riverbed shear stress, using a one-dimensional numerical model that considers water and sediment flow. Our results suggested that characteristics of the upstream inflow hydrograph affect flood runoff processes downstream; therefore, we developed a separate downstream flood hazard grade index that uses characteristics of the upstream inflow hydrograph as input

Observations and Modeling of Rainfall and Sediment Runoff in the Lesti River Basin, Tributary of the Brantas River, Indonesia

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

How are fine sediments described in sediment sheet flow?

Stony debris flow transits to sediment sheet flow when the river bed gradient becomes gentle. The sediment sheet flow consists of a water flow layer and a sediment moving layer. Fine sediments are expected to behave as a part of the fluid rather than a solid phase in the sediment moving layer. Further, it can be thought that a part of fine sediment can be suspended in the water flow layer. However, it was not possible to physically express whether the fine sediment behaves as a solid phase or a fluid phase in the numerical simulation model. Here we physically modeled fine sediment behavior in sediment sheet flow. We confirmed the applicability of the new model to describe the longitudinal deposited sediment gradient in flume experiments

Long-term monitoring of sediment runoff for an active sediment control in Joganji River

There were huge sediment yielding and deposition due to debris flows by breaking natural landslide dams which were formed by earthquake in 1858 at upstream reach of Joganji River. Sediment transportation is still active by debris flow and flow with bedload due to rainfall, though a lot of erosion control dams have been constructed. Continuously measuring sediment runoff for long term along a main river is necessary to evaluate the propagation of sediment after the huge events for sediment management in the basin using well hydrological information. Appropriate tools are selected and applied to monitoring in the area managed by Tateyama Mountain Area Sabo Office along Joganji River, using a Reid-type bedload slot sampler, robust-type hydrophone and velocity meter on the bed for bedload and turbidity meter for washload. Monitored data is concentratedly collected at the office to apply risk management for sediment movement due to heavy rainfall and so on. Several typical data and problems to solved were shown because it passed around twenty years since sediment monitoring started, and those are reported in present study

Influence of housing and urban development on debris flow flooding and deposition

Debris flows form deposits when they reach an alluvial fan until they eventually stop. However, houses located in the alluvial fan might affect the debris flow flooding and deposition processes. Few previous studies have considered the effects of houses on debris flow flooding and deposition. This study conducted model experiments and numerical simulations using the Kanako2D debris flow simulator to determine the influence of houses on debris flow flooding and deposition. The model experiments showed that when houses are present, the debris flow spreads widely in the cross direction immediately upstream of the houses, especially when the flow discharge is large or the grain size is small. Houses located in the alluvial fan also influence the deposition area. The presence of houses led to flooding and deposition damage in some places and reduced the damage in others. The simulation also demonstrated the influence of houses. Both the model experiment and the simulation showed that houses change the flooding and deposition areas