Changing climate has raised attention toward weather-driven natural hazards, such as rain-induced flash floods. The flooding model is an efficient tool used in flash flood warning and hazard management. More and more evidence showed significant impacts of sediment on hydrodynamics and flooding hazard of flash flood. But little information is available regarding flooding hazard sensitivity to sediment characteristics, which hampers the inclusion of sediment characteristics into the flash flood warning system and hazard management. This study used a 1D model to simulate flood hazards. After calibrating and validating the hydrodynamic model, we carried out simulations to test the sensitivity of flood hazard to sediment characteristics like inflow point, size distribution, and concentration. Our results showed that sediment from highly erosive slopes affects the flooding hazard more than sediment from watershed. This is particularly true when sediment particles are fine particles with a medium size of 0.06 mm. When medium particle size of sediment increased above 1 mm, most of the sediment particles are deposited in the river and we see little effect on flooding hazard downstream. Sediment concentration significantly influenced the flooding hazard but was less important than sediment inflow point and medium particle size. Our study suggested considering more characteristics than concentration when including sediment particles into the flash flood warning system.
On August 21, 2020, a landslide occurred in Zhonghai village of Hanyuan County, Sichuan Province, China. The landslide is triggered by two successive rounds of heavy rainfall. This landslide can be clearly divided into an initial landslide and a main landslide. The main landslide is activated by the intense impact and overloading of the initial landslide. The depth-integrated continuum method is adopted to simulate the dynamic process. Due to the complicated failure process, it is found that there is no proper unified parameters in Coulomb model which could well reproduce the two successive landslides. It implies that the dynamic process of landslides is highly associated with the characteristics of sliding bodies. Here, an implement of variable frictional coefficients for different parts is proposed and the parameters are calibrated. It is demonstrated that results from numerical modeling match well with the field investigation. The complicated landslides in two different stage can both be efficiently revealed by depth-integrated continuum modeling.
Warning and evacuation are among the most effective ways for saving human lives and properties from landslide dam hazards. A new warning decision model for landslide dam break is developed using Influence Diagrams to minimize the total losses. An Influence Diagram is a simple visual representation of a decision problem. It analyzes the qualitative (causal) relationships between the variables via a logic diagram and determines the quantitative relationships via conditional probability and Bayes’ theorem. The model is applied for the warning decision-making of the 2008 Tangjiashan landslide dam. The new model unifies the dam failure probability, evacuation, life loss, and flood damage in an Influence Diagram. Besides, a warning criterion is proposed for efficient decision-making. The model is more advanced than the decision tree since the inter-relationships of influence factors are qualitatively analyzed with causality connections and quantitatively analyzed with conditional probabilities. It is more efficient than a dynamic decision-making model (DYDEM) as it can directly calculate the three types of flood loss (i.e., evacuation cost, flood damage, and monetized life loss) and the expected total loss. Moreover, the probabilities of the influence factors leading to known results can be obtained through inversion analysis based on Bayesian theory. The new warning decision model offers an efficient way to save lives from landslide dam breaking and avoid unnecessary expenses from premature warning and evacuation.
Conceptualisation of geo-hydrological characteristic of erosive runoff are of particular importance and has been required in recent soil erosion control. This study aimed to explore the feasibility of applying hydrological attributes to characterize surface runoff pathways in the process of hillslope soil erosion due to rainfall. Combined with sub-millimeter high-resolution laser scanning and computer digital image processing method, three hydrological indicators (i.e., sinuosity, gradient and orientation) were used to investigate the changes of the surface runoff pathways on the slope of three typical southern red soils (i.e., shale (HS), and Quaternary red clay soils (HQ1 and HQ2) under simulated rainfall conditions). The results indicated no significant changes of sinuosity with a mean value of 1.19. After the rainfall with the intensity of 1 mm/min and 2 mm/min, the orientation and gradient changed dramatically. The greatest changes appeared at the first rainfall, which showed that the biggest increase of gradient was 26.78% and it tended to be close to the original slope of the test plot, while the orientation dropped by 5.60–31.44%. Compared with HS and HQ1, the runoff pathway characteristics of HQ2 changed more consistent. The rainfall intensities had a significant impact on the correlation between indicators. The determination coefficients sorting with surface roughness were orientation > graient > sinuosity. And they were significantly linearly related to runoff under 1 mm/min rainfall intensity, while had positive correlation with sediment under 2 mm/min rainfall intensity (p < 0.05). In conclusion, there were more remarkable relationships between orientation, gradient and slope erosion under 1 mm/min rainfall intensity. This provided an innovative idea, that is applying the orientation and gradient to the simulation and prediction model of the rainfall erosion process in the sloping farmland in the southern red soil area.
Mass movements in mountainous areas are capable of damming rivers and can have a lasting effect on the river longitudinal profile. The long profile is commonly used to retrieve regional tectonic information, but how much dams may compromise geomorphometry-based tectonic analysis has not been systematically researched. In this study, we investigate the relationship between river dams and the longitudinal profile of the upper Indus River basin, based on interpretation and analysis of remote sensing imagery and digital elevation models (DEMs) and local field work. We identified 178 landslide, glacier and debris flow dams. Using TopoToolbox, we automatically extracted the river longitudinal profile from the 30 m SRTM DEM, determined the location of convex knickpoints and calculated the channel steepness index. One hundred and two knickpoints were detected with heights above 148 m, of which 55 were related to dams. There is good spatial correspondence between dams, convexities in the river longitudinal profile and relatively high steepness index. Different dam types have different impacts on the river profile; on the upper Indus, debris flow dams have a greater impact than landslide and glacier dams and can form knickpoints of up to 900 m. Therefore, dams may have a significant influence on the river longitudinal profile, knickpoints and steepness index, and should be considered when extracting information on regional tectonics using these indices.
In recent years, landslide lake disasters occur frequently in southwest mountainous areas of China. Considering the influence of dam size and discharge channel location, three large-scale field tests were carried out in a natural river to study the failure process and mechanism of non-cohesive soil landslide dam, and the process and mechanism of non-cohesive landslide dam breach were analyzed. The results show that the dam size and discharge channel location have a significant influence on the breach mechanism of the landslide dam. The dam failure process can be divided into three stages: the initiation stage, the development stage and the failure stage. When the discharge channel is located close to the bank, the width of the breach is smaller, and the volume of the residual dam body is larger. The more stable the dam body is, the longer the breach process time is, and the smaller the peak discharge is. This study can provide a scientific reference for the emergency disposal and risk assessment of landslide dam.
Space-time image velocimetry (STIV) is a promising technique for river surface flow field measurement with the development of unmanned aerial vehicles (UAVs). STIV can give the magnitude of the velocity along the search line set manually thus the application of the STIV needs to determine the flow direction in advance. However, it is impossible to judge the velocity direction at any points before measurement in most mountainous rivers due to their complex terrain. A two-dimensional STIV is proposed in this study to obtain the magnitude and direction of the velocity automatically. The direction of river flow is independently determined by rotating the search line to find the space-time image which has the most prominent oblique stripes. The performance of the two-dimensional STIV is examined in the simulated images and the field measurements including the Xiasi River measurements and the Kuye River measurements, which prove it is a reliable method for the surface flow field measurement of mountain rivers.
Both global climate change and human activities are continuously impacting the abruptness and frequency of water-related natural disasters such as flash floods, debris flows, and landslides in mountainous areas, greatly threatening the safety of lives and properties. A recent rainfall-induced debris flow event happened on July 6, 2020 in the Chenghuangmiao Gully, in Sichuan Province, China, resulting in severe damage to buildings at the outlet. An integrated analysis of the consequence and triggering mechanism of this debris flow event was conducted with hydrologic information, topographic details, vegetation regimes, and drone aerial imagery. The result shows that the entire runout of the debris flow differs from that of common ones (debris flow and rainfall were highly related and synchronized), which happened 4 h after the stop of the rainfall. The hysteretic feature increases the difficulty of the prediction and warning of the debris flow due to lack of a responsible triggering mechanism. The hillslope surface is well covered by vegetation, hindering regular observation and cleaning up of long-term deposited wood and sediment debris. This effect increases the crypticity and abruptness of potential debris flows. With field evidence and analysis, it is speculated that long-term accumulative processes of dead wood sand sediment deposition formed a small-scale debris dam, and the continuous water release from the watershed led to dam breaching, subsequently triggering the initiation of the debris flow. Multiple steps distributing along the gully of an average slope of 15.65° contributed to the amplification of the debris flow once the breach of the upstream wood and sediment dam occurred. Along the gully, small-scale landslide scars can be observed, possibly amplifying the scale of the debris flow and disaster impact. This debris event gives a lesson of necessary demands of predicting and managing the risks of a low-frequency debris flow non-synchronized with rainfall events.
Frontiers in Microbiology
Reviews in Molecular Evolution of Infectious Agents and Diseases