Landslide damming of valleys may have a significant effect on the evolution of fluvial landscapes. The southeastern Tibetan Plateau is highly prone to landslide damming due to its deeply incised ...valleys and young, active geology. Here we present a sedimentological investigation of a landslide-dammed lake in the upper reach of Lulang River on the eastern Himalayan syntaxis. Detailed interpretation of lacustrine varve, lakeshore, and subaqueous delta sediment shows that Lulang landslide-dammed lake (LLDL) had a surface elevation of 3360 m a.s.l., an area of 3.3 × 106 m2, and a volume of 6.5 × 107 m3. Radiocarbon dating of six organic clay lacustrine samples demonstrate that LLDL formed before 24.2 ka cal. BP and persisted for at least 8.8 ka. Sediment infill reached full capacity soon after 15.4 ka cal. BP and fluvial conditions then prevailed. Sedimentary evidence and morphological analysis of cross sections along the LLDL outlet channel revealed a larger, earlier lake with a total volume of 4.3 × 109 m3 and water surface elevation at 3570 m a.s.l. that failed catastrophically; the resulting outburst flood drained 98.5% of the impounded lake. The remnant lake maintained a relatively stable water level of 3360 m a.s.l. for its lifetime of at least 8.8 ka. Long profile and steepness index analysis indicate that the location of the catastrophic dam failure and subsequent long-term blockage is associated with a knickpoint. The origin of the knickpoint may have been polygenetic, however, the landslide damming seems to have increased its distinctiveness and persistence. The relatively wide valley and low channel slope characteristic of reaches upstream of LLDL is likely to have resulted from glacial activity, rather than backwater aggradation which had only a local influence.
•Lulang landslide dammed lake persisted from 24.2 ka cal. BP. to 15.4 ka cal. BP.•Sedimentary evidences show that It drained catastrophically in the very beginning.•The remnant lake maintained stable without significant fluctuations of lake level.•The sediments infilling reached its full capacity eventually.•The breach channel of landslide dam corresponds to a knickpoint of river profile.
•A model is proposed to predict the longitudinal profile of velocity inside vegetation patches.•The proposed analytical model was verified by twenty groups of velocity data.•The predicted velocity ...profiles agree well with the measured velocities.•Velocity profiles can evaluate the deposition of fine sediment inside vegetation patches.
This paper proposes an analytical model for predicting the longitudinal profile of depth-averaged streamwise velocities in a channel with an emergent array of rigid cylinders. The governing equation of the analytical model was derived from the momentum equation and flow continuity equation. The longitudinal transect through a flume with a vegetation patch was divided into four regions based on two length scales of flow adjustment upstream of and inside the array, and analytical solutions were proposed for the four regions. Laboratory experiments demonstrated that the array length does not influence flow adjustments near the upstream edge of the array, so the model can predict the longitudinal profile of streamwise velocity for either short or long arrays. Twenty groups of velocity data from different sources were used to verify the proposed model. The predicted velocities agreed well with the measured velocities, indicating that the model is capable of predicting the longitudinal profiles of the velocity upstream of and inside a model patch. The predicted velocity profile can be further employed to estimate regions of enhanced or diminished deposition of fine sediment or organic matter inside model patches.
The Chapecó River Basin (CRB) is located in the west of Santa Catarina State (South Brazil) and has a relief modelled by a large basalt lava outpouring that occurred in the Paraná Sedimentary Basin. ...The CRB is characterised by two plateau compartments resulting from regional denudation and associated with a river network that was formed after the basaltic lava completed its flow phase in the Lower Cretaceous. Elements of structural geology together with weathering of rocks and its products, such as regolith, have been commonly used to analyse and interpret the landforms in CRB, whose fluvial landscape is shaped by bedrock channels and incision valleys. Nevertheless, there is a lack of detailed studies about such structural factors in terms of type and origin, and to what extent they may be proxies of tectonic tensions of an intra-plate character. In the lack of guide levels and deposits that allow a better interpretation of recent tectonic deformations, in this work we aimed to evaluate tectonic-structural factors involved in the landscape evolution of the CRB through measurement and analysis of morphometric indices derived from the ALOS PALSAR DEM. We analysed the following morphometric parameters for 43 sub-basins: the basin asymmetry (FA), hypsometric integral (HI), elongation, local relief, slopes distribution, Hack index for the two main river channels (Chapecó and Chapecozinho), and concavity index of the main channels of sub-basins. The results obtained from the morphometric analysis of the river network indicate the existence of a geomorphological disequilibrium of its relief. This result was observed in the transition from the medium to the low basin and in the base levels of the Chapecó and Chapecozinho rivers. Such disequilibrium is shown by convex and irregular longitudinal profiles, knickpoints, sub-basins with high values of asymmetry and hypsometric integral (HI), as well as a low correlation between slope and channel gradients for the sub-basins analysed. This context is consistent with the neotectonic hypothesis of a regional uplift that provide energy to the system to reactivate faults, tilt blocks, and deepened the incision of the river network, leading to the creation of new knickpoints and a transient river network. From the results and analysis, we can conclude that the largest knickzones and waterfalls in the study area can be considered markers associated with quaternary tectonic forcings, although many of these geomorphological features may have originated simply by joints and fractures in the rocks.
•A fluvial incision deepening observed in the lower Chapecó River Basin (CRB) was highlighted by a local relief and demonstrates an active morphogenesis.•The Chapecó River Falls is on an NW-SE fault and may be an brittle faulting associated with a tectonic forcing.•Rapids and small knickpoints may simply occur due to the rock fracturing.•Cenozoic landscape evolution of the CRB supports the action of factors probably associated with uplift (upward blocks).
In the piedmont of uplifting mountains, alluvial fan rivers undergo significant aggradation-degradation processes, which are usually attributed to climate change. An ongoing debate is whether this ...process requests the participation of glaciation. To address this debate, we need the knowledge of the quantitative relationship between the ratio of water to sediment flux (qw/qs) with the aggradation/degradation process. This study examined the aggradation and degradation processes in three alluvial rivers at the piedmont of the Qilian Shan (Shan referes to Mountain) and simulated the river processes by a one-dimensional numerical model based on the transport-limited principle. Along the studied piedmont rivers, field measurements show a magnitude of 120–200 m degradation and aggradation in the Late Pleistocene. Through simulation analysis, we explored how factors like the ratio of water to sediment flux (qw/qs), channel width, and sediment grain size influence river processes and longitudinal profiles, and found distinct morphologies in different processes, where aggradation is characterized by concave-up profiles, while degradation is characterized by convex-down profiles. Additionally, the water flux is inversely proportional to the time required for the river to reach a new equilibrium profile. The simulated degradation amplitude aligns closely with the measured data in the Qilian Shan, indicating that precipitation during the Last Glacial Maximum in the region amounted to approximately ∼32% of the Holocene precipitation. This supports the notion that changes in water flux or precipitation alone can induce significant piedmont deepening without the necessity of glaciation.
•Built a model to quantify the link between water-sediment fluxes and river processes.•Simulated Qilian Shan piedmont river incision: ∼32% LGM precipitation vs. Holocene.•Precipitation alone can create deep canyons without requiring glaciation.
•Investigated influence of slight cyber-attacks on longitudinal safety of connected and automated vehicles (CAVs).•Utilized an empirical CAV model to describe vehicle dynamics and rear-end collision ...risk index (RCRI) to evaluate safety.•Conducted extensive simulations to test impacts of slight cyber-attacks on one CAV, multi CAVs as well as different periods.
Connected and automated vehicle (CAV) has been a remarkable focal point in recent years, since it is recognized as a potential method to reduce traffic congestion, emission and accident. However, the connectivity function makes CAVs vulnerable to cyber-attacks. An intuitive method to defend cyber-attacks on CAVs is that if the error between expected and measured behaviors exceeds a predetermined threshold, a security scheme should be activated. This study investigates another type of cyber-attack, denoted as slight attacks, in which the communicated data of CAVs are randomly deviated from the actual ones and deviations do not exceed the threshold. The primary objective is to evaluate the influence of slight cyber-attacks on longitudinal safety of CAVs. An empirical CAV model is first utilized to describe vehicle dynamics and generate trajectory data. A rear-end collision risk index (RCRI) derived from safe stopping distance is used to establish relation between longitudinal safety and trajectory data. Two attacked factors, communicated positions and speeds from preceding vehicles are tested. Extensive simulations are conducted and parameters are also tested via sensitivity analysis. Results indicate that (1) when one CAV is under slight cyber-attacks, it is more dangerous if communicated positions are attacked than speeds; (2) when multi CAVs are under attacked, it is possible that a situation with more vehicles under attack at a low severity may be more dangerous than that with fewer vehicles but under attack at a high severity; (3) the impact of slight cyber-attacks on deceleration period is more serious compared to acceleration period. The findings of this study provide useful suggestion for defending cyber-attacks on CAVs and improving longitudinal safety in the future.
The use of sensors fixed to in-service trains has the potential to provide real-time track condition monitoring to inform maintenance planning. An Irish Rail intercity train was instrumented for a ...period of 1 month so that a numerical method developed to find track longitudinal profile from measured vehicle inertial responses could be experimentally tested. A bogie-mounted accelerometer and gyrometer measured vertical acceleration and angular velocity as the train made regular service operations between Dublin and Belfast on the island of Ireland. Cross entropy optimisation is used to find a track longitudinal profile that generates a numerical inertial response that best fits the measured response. Tolerance limits are used to inject variance where required to ensure a good match between measured and modelled signals. A section of track with known track settlement history is selected as a case study. A level survey was undertaken during the measurement campaign to characterise the longitudinal profile through the test section. Bandpass filters are used to compare inferred profiles and the surveyed profile. Good agreement is found between the two profiles although improvements in accuracy and reproducibility are required before conformance with current standards is achieved.
Objectives
. The theory and methods of spline approximation of plane curves given by a sequence of points are currently undergoing rapid development. Despite fundamental differences between used ...splines and those considered in the theory and its applications, results published earlier demonstrate the possibility of using spline approximation when designing routes of linear structures. The main difference here consists in the impossibility of assuming in advance the number of spline elements when designing the routes. Here, in contrast to widely use polynomial splines, the repeating element is the link “segment of a straight line + arc of a circle” or “segment of a straight line + arc of a clothoid + arc of a circle + arc of a clothoid.” Previously, a two-stage scheme consisting of a determination of the number of elements of the desired spline and subsequent optimization of its parameters was proposed. Although an algorithm for solving the problem in relation to the design of a longitudinal profile has been implemented and published, this is not suitable for designing a route plan, since, unlike a profile, a route plan is generally a multivalued function. The present paper aims to generalize the algorithm for the case of spline approximation of multivalued functions making allowance for the design features of the routes of linear structures.
Methods
. At the first stage, a novel mathematical model is developed to apply the dynamic programming method taking into account the constraints on the desired spline parameters. At the second stage, nonlinear programming is used. In this case, it is possible to analytically calculate the derivatives of the objective function with respect to the spline parameters in the absence of its analytical expression through these parameters.
Results
. An algorithm developed for approximating multivalued functions given by a discrete series of points using a spline consisting of arcs of circles conjugated by line segments for solving the first stage of the problem is presented. An additional nonlinear programming algorithm was also used to optimize the parameters of the resulting spline as an initial approximation. However, in the present paper, the first stage is considered only, since the complex algorithm of the second stage and its justification require separate consideration.
Conclusions
. The presented two-stage spline approximation scheme with an unknown number of spline elements is also suitable for approximating multivalued functions given by a sequence of points on a plane, in particular, for designing a route plan for linear structures.
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