New understandings of the June 24th 2017 Xinmo Landslide, Maoxian, Sichuan, China

On June 24, 2017 (21:39 UTC, June 23rd), a catastrophic landslide occurred at Xinmo village of Mao County, Sichuan Province, China. Soon after the event, some research teams carried out field investigations in order to both support the emergency operations and to understand the failure mechanism and possible evolutionary scenarios. Based on further in-depth interpretation of high-resolution remote-sensing images and detailed field surveys, it is newly found that there are at least six old rockfall deposits in the source area that prove the historic activity of the landslide scarp. Seismic data of the event and morphological evidences along the slope indicate that the landslide was preceded by a significant rockfall. Mechanical calculations show that the surface force due to pore water was far less than the impact force due to the rockfall. It means that the subsequent major rock avalanche was more likely due to the impact of the rockfall on the rock slope below, which broke the rock bridges and caused drop of shear resistance along the fractures. According to these new understandings, a different triggering mechanism for the landslide is proposed

Investigation of vertical velocity distribution in debris flows by PIV measurement

Vertical velocity distribution in some fluid–solid flows such as debris flows has not been well recognized and lacked a commonly accepted form. The particle image velocimetry (PIV) measurement system was employed to investigate the velocity distribution of high-viscosity fluid–solid flows. The velocity distribution was greatly affected by the particles due to the particle-particle collision and momentum exchange between the particle and fluid. Both of them show a similar increasing trend only in the range of the dimensionless flow depth from 0 to 0.7. In addition, based on the log-law model for sediment-laden flows, a modified model was proposed to predict vertical velocity distribution in debris flows. The results indicated that the calculated results were in good agreement with the experimental ones. The coefficient and index for the modified item was about 0.92 and −1/6, respectively

Off-Grid DOA Estimation Based on Compressed Sensing on Multipath Environment

Due to the existence of multipath propagation, the array will receive the multipath propagation signals at the same time while receiving the target signal and the performance of directional of arrival (DOA) estimation will be influenced. In this paper, an off-grid DOA estimation technique based on compressed sensing (CS) on multipath environment is proposed. To deal with the off-grid problem and the multipath propagation problem, we present a compressed sensing based method. This method regards the multipath propagation coefficients vector as a superparameter and the grid as an adjustable parameter. Then, the problem of multipath propagation coefficients estimation is converted to the estimation of an error matrix and the grid is refined iteratively. The simulation results show that the method can achieve off-grid DOA estimation in the presence of the multipath propagation signals

Hydro-climatic characteristics of Yarlung Tsangpo River Basin since the Last Glacial Maximum

Global climate changes significantly impact the water condition of big rivers in glacierized high mountains. However, there is a lack of studies on hydrological changes within river basins caused by climate change over a geological timescale due to the impossibility of direct observations. In this study, we examine the hydro-climatic variation of the Yarlung Tsangpo River Basin in the Tibet Plateau since the Last Glacial Maximum (LGM) by combining δ18O proxy records in Indian and Omani caves with the simulated Indian summer monsoon, surface temperature, precipitation, evapotranspiration and runoff via Community Climate System Model and reconstructed glacier coverage via Parallel Ice Sheet Model. The mean river runoff was kept around a low level of 145 billion cubic meters per year until an abrupt increase at a rate of 8.7 million cubic meters per year in the Bølling-Allerød interval (BA). The annual runoff reached a maximum of 250 billion cubic meters in the early Holocene and then reduced to the current value of 180 billion cubic meters at a rate of 6.4 million cubic meters per year. The low runoff in the LGM and Heinrich Stadial 1 (HS1) is likely attributed to such a small contribution of precipitation to runoff and large glacier cover. The percentage of precipitation to runoff was only 20% during the LGM and HS1. Comparison of glacier area among different periods indicates that the fastest deglaciation occurred during the late HS1, when nearly 60% of glacier area disappeared in the middle reach, 50% in the upper reach, and 30% in the lower reach. The rapid deglaciation and increasing runoff between the late HS1 and BA may accelerate widespread ice-dam breaches and lead to extreme outburst flood events. Combining local geological proxy records and regional simulations could be a useful approach for the study of paleo-hydrologic variations in big basins

Hazard assessment of a pair of glacial lakes in Nepal Himalaya: unfolding combined outbursts of Upper and Lower Barun

AbstractDue to climate change, the future Glacial Lake Outburst Flood (GLOF) risk is more likely in the Himalayas. Despite several GLOF studies, little attention has been given to the combined surge that can result from a pair of upstream-downstream glacial lakes. We chose Upper and Lower Barun glacial lakes as a pilot study due to the region’s increasing population and hydropower investments and the possible outbursts of upper-lower glacial lakes. This study mainly considered four scenarios (100 and 50% breach combination of upper-lower lakes), using a two-dimensional dam break model and inundation propagation. Based on our observations, the glaciers in the study area shrank by 33 km2, and the two glacial lakes expanded by 2.06 km2 between 1976 and 2020. The modeling result suggests that the single flood triggered by Upper Barun cannot travel beyond 50 km; however, the combined flow from the lakes could reach over 85 km. Our results illustrate that at least 60 buildings, motorable bridges, and infrastructures of Arun hydropower along the river course have high damage potential. The study insights can be helpful for effectively planning and formulating various disaster risk reduction initiatives to mitigate the likely effects of glacial lake(s) outbursts

A depth-averaged two-phase model for debris flows over fixed beds

A depth-averaged two-phase model is proposed for debris flows over fixed beds, explicitly incorporating interphase and particle-particle interactions, fluid and solid fluctuations and multi grain sizes. A first-order model based on the kinetic theory of granular flows is employed to determine the stresses due to solid fluctuations, while the turbulent kinetic energy - dissipation rate model is used to determine the stresses from fluid fluctuations. A well-balanced numerical algorithm is applied to solve the governing equations. The present model is benchmarked against USGS experimental debris flows over fixed beds. Incorporating the stresses due to fluid and solid fluctuations and properly estimating the bed shear stresses are shown to be crucial for reproducing the debris flows. Longitudinal particle segregation is resolved, demonstrating coarser sediments around the fronts and finer grains trailing the head. Based on extended modeling exercises, debris flow efficiency is shown to increase with initial volume, which is underpinned by observed datasets