The construction of check dams is an important measure to prevent soil erosion on the Loess Plateau and reduce the amount of sediment entering the Yellow River. Based on an analysis of the current ...situation of soil and water conservation on the Loess Plateau and the three major problems faced by the traditional homogeneous soil check dam construction, the study of anti-scouring materials, hydrological calculation methods, dam design and construction technology and soil and water conservation monitoring are carried out in this paper. The results showed that the current soil and water conservation measures on the Loess Plateau have achieved remarkable outcomes. The new design and application concept of check dams with anti-burst and multi-sand interceptions is innovatively proposed in this paper. The new materials of solidified loess have good durability and anti-scouring characteristics and could meet the overflow and anti-scouring requirements of the new check dam. The small watershed high sand content of hydrological calculation can establish the upper limit of the flood sediment boundary for the anti-scouring protection layer of the check dam. The new technology of dam design and construction can achieve no collapse or slow collapse when encountering floods exceeding the standard. Intelligent monitoring systems can realize real-time dynamic monitoring for soil and water conservation on the Loess Plateau. The results will eventually contribute to the national strategy of the Ecological Protection and High Quality Development in the Yellow River basin.
The Ms 8.0 Wenchuan Earthquake has greatly altered the rainfall threshold for debris flows in the affected areas. This study explores the local intensity–duration (I–D) relationship based on 252 ...post-earthquake debris flows. It was found that I=5.25 D-0.76 accounts for more than 98% of the debris flow occurrences with rainfall duration between 1 and 135h; therefore the curve defines the threshold for debris flows in the study area. This gives much lower thresholds than those proposed by the previous studies, suggesting that the earthquake has greatly decreased the thresholds in the past years. Moreover, the rainfall thresholds appear to increase annually in the period of 2008–2013, and present a logarithmic increasing tendency, indicating that the thresholds will recover in the future decades.
Debris flows occur frequently and cause considerable damage in the Wenchuan Earthquake area; however, there has been no systematic real-time monitoring of such events. This study used a monitoring ...system to consider the spatial variation of meteorological and flow processes in a 39.4 km2 watershed. The system comprised three rainfall gauges at different locations, and three hydrological monitoring stations, located on the mainstream and tributaries, with instruments to measure the velocity, height, and density of debris flows. Based on the monitoring data, the debris flow events were categorized and the general runoff velocity, discharge, and density were analysed. We proposed empirical methods for estimating the velocity and the total volume of debris flows based on other easily obtainable parameters, e.g., maximum flow depth and duration. Comparison of the results derived using the monitoring data and empirical formulas with those obtained in other small watersheds worldwide revealed the debris flow characteristics in this relatively large watershed. Rainfall threshold for the debris flows was proposed, which is higher than those proposed for the same region for periods shortly after the Wenchuan Earthquake (2008–2013), and the temporal evolution of the rainfall conditions necessary for debris flows was addressed.
•The debris flow behaviours of small tributaries and the main stream are presented and their differences were addressed.•The empirical methods for estimating the flow velocity and total volume were derived.•The rainfall thresholds for debris flow occurrence were proposed.
In this paper, we analyze the Holocene record of extreme flood events in the upper Minjiang River valley of the eastern Tibetan Plateau, China. Slackwater deposits (SWDs), the fine-grained sediments ...of palaeofloods, were identified within debris flow deposits at a tributary mouth and in channel expansions along the bedrock gorge. Eight palaeoflood SWDs were dated to between 6.0 ± 0.9 ka and 4.6 ± 0.9 ka using optically-stimulated luminescence analysis in combination with the minimum age model and represent at least two phases of palaeoflood events. The palaeoflood history in the upper Minjiang River Valley is consistent with the record of the mid-Holocene flood events in the mainstream of the Yangtze River. These mid-Holocene extreme flood events were closely related to strong ENSO activity and variability of the monsoon climate in the eastern Tibetan Plateau. In our study area, minimum palaeoflood discharges were estimated as 6500–7800 m3/s by the step-backwater method. These estimated discharges are less than the values inferred for the outburst flood that occurred in the upper Minjiang River Valley in 1933. Flood-inundation maps show that palaeoflood SWDs were deposited in low-velocity backwater zones. Our palaeoflood reconstructions are important for improving regional records of maximum flood and help to develop risk analysis for rare flood events.
•Sedimentary characteristics of palaeoflood records in complex environment were identified.•Palaeoflood discharges were estimated to be 6500–7800 m3/s at the three study sites.•Palaeoflood results redefine the envelope curve of the regional maximum floods.•Response of mid-Holocene (6.0–4.6 ka) extreme flood events to climate variability.•Palaeoflood reconstructions help to develop risk analysis for rare flood events.
Traversing the Qinghai–Tibetan Plateau, the Sichuan–Tibet Railway is by far the most difficult railway project in the world. The Qinghai–Tibetan Plateau features the most active crustal dynamics on ...earth, the strongest coupling effects of endogenic and exogenic dynamics, and the environment most sensitive to global climate change. The project area is characterized by extremely cold climate, high elevation and relief, high seismic intensity, high geothermal activity, and high tectonic stress. Consequently, the threat of various disaster risks is ever-present at different stages of the entire life cycle of the Sichuan–Tibet Railway. There is urgent need to systematically study these problems at various levels from the fundamental science to the development of key technologies. This article investigates the different disaster risks recognized during the various stages of construction of the Sichuan–Tibet Railway project, and summarizes the scientific challenges and technical problems faced in relation to disaster risk prevention and control. This work also introduces the scientific deployment and relevant research progress of the Sichuan–Tibet Fund special project initiated by the National Natural Science Foundation of China. Here, we also aim to solve the major fundamental scientific challenges in terms of long-term risk prevention and control during the construction of the Sichuan–Tibet Railway, and lay a theoretical foundation to promote breakthroughs in the bottleneck of key technologies. The scientific challenges addressed in the study of disaster risk associated with the Sichuan–Tibet Railway include the following: The quantitative assessment of the activity of deep-large faults and strong earthquake prediction, the evolution of physical fields in areas of strong tectonic activity, the development mechanisms of tunnel hazards, the slope evolution processes under coupled endogenic and exogenic dynamics in alpine gorges, the impact of climate change on the formation and evolution of surface hazards, and the evolution of extreme wind fields in deep-cut canyons. The technical problems faced in disaster risk prevention and mitigation in relation to the Sichuan–Tibet Railway are as follows: Advanced identification, monitoring, and early warning of geological disasters in mountainous areas with steep and complex terrain; risk analysis, prevention, and control of railway engineering disasters based on their dynamic processes; tunnel engineering hazard monitoring, early warning, risk analysis, prevention, and control technologies; key technologies for emergency response; and the green and resilient railway system and lifecycle risk management. The Sichuan–Tibet Fund special project will include five key research topics: (1) the interior geological structure and dynamic evolution of the eastern plateau; (2) the hazard-inducing mechanisms of coupled internal and external forces in canyons and gullies within plateaus; (3) the cataclysm mechanics of deeply buried long-distance tunnel engineering; (4) risk identification and projection of major disasters affecting the railway; and (5) the integrated management of scientific innovations and super large-scale railway construction. Systematic research is expected to reveal the evolution of earth surface movements and coupled engineering-disturbance related disasters. It will also enable the formation of a comprehensive risk analysis method for major engineering disasters, and promote the development of green, safe, efficient, and resilient engineering disaster risk reduction technologies that will support the disaster risk management during the entire lifecycle of the Sichuan–Tibet Railway.
•Investigated the natural and anthropic disaster risks in different construction stages of the Sichuan–Tibet Railway.•Identified the scientific challenges and technical gaps faced in disaster risk reduction of the Sichuan–Tibet Railway.•Proposed fundamental research and technologies development directions for a safe and resilient Sichuan–Tibet Railway.
•Massive sand beds and lateral gravel bars induced by outburst floods are identified.•Modern flood hydrographs provide potential scenarios for megaflood simulations.•Our new geomorphic evidences ...provide key constraint on megaflood age and magnitude.•Potential flood erosion and depositional area were predicted in the Grand Canyon.•Geomorphic impact of outburst flood events was assessed from 104 to106 m3/s.
Catastrophic floods from breaching of natural dams on the Namche Barwa and Giala Peri play an important role in shaping high-mountain landforms in the eastern Himalayan syntaxis. However, there is limited knowledge of geomorphologic evidences and magnitude of outburst flooding in the Yarlung Tsangpo Grand Canyon. In this paper, geomorphic impacts of high-magnitude outburst floods (104–106 m3/s) were analyzed using palaeoflood hydrology technology. Well-preserved 2018 Sedongpu (SDP) flood and 2000 Yigong (YG) flood sand bars are charactered by grey sands with parallel laminations, whereas megaflood geomorphic evidences in the Grand Canyon are dominated by massive slackwater deposits and lateral gravel bars. The palaeoflood events were dated to 4.3–2.4 ka, corresponding to the known Holocene megafloods in the lower Yarlung Tsangpo River. These flood ages are obviously younger than most of remnant lacustrine deposits during the late Pleistocene, but consistent with the ages in the top part of palaeolake and glacial moraines of the Namche Barwa. The chronological data help to confirm the highest probability phases of outburst floods from moraine-dammed lakes. The repeated megaflood peak discharges range from 0.5 to 1.1 × 106 m3/s, which are approximately 5–10 times greater than the maximum peak discharge of 2000 YG flood (9.5 × 104 m3/s) and 20–40 times than that of 2018 SDP flood (2.5 × 104 m3/s) in the Medog reach. Megaflood waters are always deepest (∼200 m) and fastest (∼50 m/s), which are at least twice times larger than 2000 YG flood. Higher shear stress (>3.3 kPa) and stream power per unit area (>168 kw/m2) occurred in narrower channel and sharp bend with higher velocity. Our model also predicts some potential erosion and deposition landscapes resulted from floodwaters routing through the Grand Canyon. These results address the geomorphic impacts of catastrophic flood events with magnitudes (104–106 m3/s) in the Yarlung Tsangpo Grand Canyon. Our new palaeoflood geomorphologic evidences provide a key constraint on the age and magnitude of Holocene megafloods in the largest Himalayan River.
The occurrence of landslides is affected by various environmental factors. When predicting landslides, conventional neural networks optimize parameters using global connectivity, which limits their ...efficiency in extracting features of contributing factors. In this study, we developed an attention-constrained neural network with overall cognition (OC-ACNN) to focus on important features from the complex data. The method has four steps: (1) extract the overall cognition as the prior input based on historical landslide distribution and contributing factors, (2) embed an attention mechanism in hidden layers to allocate more weight to noteworthy features, (3) update weights and fit the nonlinear relationship by the back-propagation neural network (BPNN), and (4) generate prediction results using a classifier. This model was applied to the Sichuan-Tibet Highway, considering 10 predisposing factors and 1449 historical landslides. The evaluation results indicate that OC-ACNN (0.822) had a higher predictive capability than multiple linear regression (MLR, 0.734) and BPNN (0.789) in terms of the area under the receiver operating characteristic curve (AUC). Further, we compared different attention patterns and score functions for use with the proposed model. The results show that OC-ACNN offered greater predictive performance than Self-ACNN (without OC, 0.803) and that the improved cosine (0.822) score function had better results and stability than others (0.819 highest).
•A framework that combines SPP, DSC, and ML classifiers was proposed for more accurate LSM the first time.•Spatial and response features were fused as high-level features by considering different ...dimensions.•Samples considering landslide scales could improve performance for LSM.•ML can classify features more effectively than FC layers.
Reliable landslide susceptibility mapping (LSM) is essential for disaster prevention and mitigation. This study develops a deep learning framework that integrates spatial response features and machine learning classifiers (SR-ML). The method has three steps. First, depthwise separable convolution (DSC) extracts spatial features to prevent confusion of multi-factor features. Second, spatial pyramid pooling (SPP) extracts response features to obtain features under different scales. Third, the high-level features are fused into prepared ML classifiers for more effective feature classification. This framework effectively extracts and uses different-dimension features of samples, explores ML classifiers for beneficial feature classification, and breaks through the limitation of fixed input sample sizes. In the Yarlung Zangbo Grand Canyon region, data on 203 landslides and 11 conditioning factors were prepared for availability verification and LSM. The evaluation indicated that the area under the receiver operating characteristic curve (AUC) for the proposed SR and SR-ML achieved 0.920 and 0.910, which were 6.6% and 5.6% higher than the random forest (RF, with the highest AUC in ML group) method, respectively. Furthermore, the framework using 64×64 size inputs had the lowest mean error of 0.01, revealing that samples considering landslide scales could improve performance for LSM.
Many glacier dams on major rivers at the southeastern edge of the Tibetan Plateau had been previously determined through remote sensing and glacier terminal position calculation. It was hypothesized ...that such damming substantially impeded river incision into the plateau interior. Investigation on the large glacial-dammed lake at the entrance of Tsangpo gorge is critical for understanding this hypothesis. So far, the issues, such as age, lake surface elevation, and stages of this dammed lake, are still in debate. Our field survey of lacustrine deposits and loess distribution along the middle Yarlung Tsangpo River and its tributary, Nyang River, suggested that the lake surface elevation was at about 3180masl. The 23 quartz optically stimulated luminescence (OSL) and 4 organic AMS 14C ages all fall into the Last Glacial period (~41–13ka). The OSL and 14C ages are in general agreement with each other where applicable. There might be only one long damming event because the ages of lacustrine deposits from 2970 to 3100masl are similar, and every lacustrine section is sustained for a long time. The estimated lake surface area was 1089km2, and the volume was ~170km3, which differ from previous estimations which suggested two-stage (about early Holocene and 1.5ka) lakes, and the largest lake surface elevation reached 3500m.
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