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Large, sediment-laden floods in mountainous terrain can have disastrous consequences and play important roles in landscape evolution. These events often unfold as a series of interconnected processes, but understanding of such “hazard cascades” has been hampered by lack of quantitative data on sediment movement. Here, we use a time series of high-resolution satellite imagery to quantify erosion and aggradation during the 2021 Melamchi Khola Floods in the Himalaya of central Nepal, providing a unique sediment budget for such an event. Our analysis reveals massive headwater erosion via remobilization of Gorkha landslides, gullying, debris-flows, and incision of glacial deposits. Unlike many other high mountain floods, the widely distributed erosion suggests this event was not primarily driven by a single source, e.g., glacial lake or landslide dam failure. High sediment supply caused aggradation in a high-elevation, low-relief glacial valley and triggered catastrophic incision into associated ancient fills. As this material was transported downstream, it caused further riverbed incision that in turn resulted in failures of surrounding hillslopes. Further downstream, as river steepness diminished, the main channel in the lower basin was widened by 3-5-fold and aggraded by ~ 5–20 m. However, deposition in the Melamchi Khola was not enough to accommodate the vast amount of flood material, and over 70% was delivered from the Melamchi Khola to the downstream Indrawati basin. Our sediment budget provides rare insight into the chain of events involved in a massive flood and helps shed light on how such floods can magnify hazard and reshape the fluvial landscape.

Small Island Developing States (SIDS) are acknowledged as particularly vulnerable to extreme climate events; however, the realities for transport infrastructure and bridges are still poorly studied. Assessing bridges in this context can be challenging due to data scarcity, a lack of local standards, and uncertainty due to climate change. While bridges are designed to connect transport networks, they also carry energy, water, and communication networks, making them critical cascading failure points worthy of special attention in terms of risk assessment and resilience measures. We explore what resilience actually means for the design and management of SIDS bridge infrastructure by applying a post disaster forensics and systems approach that is not reliant on complex methods or large amounts of data. To demonstrate the practicality of our approach, we apply it to the island of Dominica, which is regularly impacted by both tropical storms and hurricanes. Our results document the extreme conditions for infrastructure and nearby settlements and the complex interrelated physical processes that occur during these events. We reflect on the implications for design approaches for bridges under these conditions and detail specific recommendations on how the resilience of existing and new bridges can be enhanced through practical measures that are achievable, even within the constraints experienced by those managing bridge infrastructure in SIDS contexts. This work adds to the growing number of studies exploring forensic disaster investigation and systems thinking, but is the first to explore bridge resilience in SIDS.

To evaluate ground deformation resulting from large (~10 m) coseismic strike-slip displacements, we focus on deformation of the Kekerengu fault during the November 2016 Mw 7.8 Kaikōura earthquake in New Zealand. Combining post-earthquake field observations with analysis of high-resolution aerial photography and topographic models, we describe the structural geology and geomorphology of the rupture zone. During the earthquake, fissured pressure bulges (“mole tracks”) initiated at stepovers between synthetic Riedel (R) faults. As slip accumulated, near-surface “rafts” of cohesive clay-rich sediment, bounded by R faults and capped by grassy turf, rotated about a vertical axis and were internally shortened, thus amplifying the bulges. The bulges are flanked by low-angle contractional faults that emplace the shortened mass of detached sediment outward over less-deformed ground. As slip accrued, turf rafts fragmented into blocks bounded by short secondary fractures striking at a high angle to the main fault trace that we interpret to have originated as antithetic Riedel (R′) faults. Eventually these blocks were dispersed into strongly sheared earth and variably rotated. Along the fault, clockwise rotation of these turf rafts within the rupture zone averaged ~20°–30°, accommodating a finite shear strain of 1.0–1.5 and a distributed strike slip of ~3–4 m. On strike-slip parts of the fault, internal shortening of the rafts averaged 1–2 m parallel to the R faults and ~1 m perpendicular to the main fault trace. Driven by distortional rotation, this contraction of the rafts exceeds the magnitude of fault heave. Turf rafts on slightly transtensional segments of the fault were also bulged and shortened—relationships that can be explained by a kinematic model involving “deformable slats.” In a paleoseismic trench cut perpendicular the fault, one would observe fissures, low-angle thrusts, and steeply dipping strike-slip faults—some cross-cutting one another—yet all may have formed during a single earthquake featuring a large strike-slip displacement.

Following the Cephalonia, Greece, 2014 earthquake sequence (Mw=6.1 and Mw=6.0), liquefaction of gravelly earthfill materials at the ports of Lixouri and Argostoli resulted in the manifestat...

Developing a reliable, cost-effective liquefaction triggering procedure for characterizing the liquefaction potential of gravelly soils based on in situ penetration testing has always been ...

On May 19, 2020, after several days of heavy precipitation, two earth dams failed (Edenville and Sanford) and two other dams were damaged (Secord and Smallwood), north of the town of Midland, MI. The failures resulted in about $100M in damages and the evacuation of about 11,000 people during the COVID-19 pandemic. In response to this destructive event, the Geo-Institute Embankment, Dams, and Slopes Technical Committee organized a team with the main objective of capturing perishable data. The Edenville Dam site was of interest because the slope failure was captured on video and occurred prior to the dam being overtopped. Based on our observations, investigation and analyses, two failure mechanisms were considered likely for Edenville Dam: (1) static liquefaction (similar to 2019 failure of Brumadinho Dam in Brazil);and (2) slope instability, where the slide debris which was contractive in nature, expelled pore water in the form of water jets and flowed as it became liquefied along the toe of the dam. © 2021 American Society of Civil Engineers (ASCE). All rights reserved.

The implementation of unmanned aerial vehicles (UAVs) in civil engineering has primarily focused on remote sensing using optical cameras, light detection and ranging (LiDAR), and communicat...

Extreme events, such as earthquakes, hurricanes, or major storms, typically cause thousands of landslides in mountainous topography over the course of minutes to hours. In the last few years alone, we’ve witnessed more than 25,000 landslides during the 2015 Mw 7.8 Gorkha earthquake in Nepal, and more than 20,000 in the 2016 Mw 7.8 Kaikoura earthquake in New Zealand. The 2018 Mw 6.6 Hokkaido earthquake in Japan demonstrated the lethal combination of a rainy season followed by an earthquake, which led to significant parts of the landscape being scarred and stripped bare by adjacent landslides despite relatively flat topography.

In 2017, hurricane Maria caused unprecedented damage and fatalities on the Caribbean island of Dominica. In order to ‘build back better’ and to learn from the processes causing the damage, it is important to quickly document, evaluate and map changes, both in Dominica and in other high-risk countries. This paper presents an innovative and relatively low-cost and rapid workflow for accurately quantifying geomorphological changes in the aftermath of a natural disaster. We used unmanned aerial vehicle (UAV) surveys to collect aerial imagery from 44 hurricane-affected key sites on Dominica. We processed the imagery using structure from motion (SfM) as well as a purpose-built Python script for automated processing, enabling rapid data turnaround. We also compared the data to an earlier UAV survey undertaken shortly before hurricane Maria and established ways to co-register the imagery, in order to provide accurate change detection data sets. Consequently, our approach has had to differ considerably from the previous studies that have assessed the accuracy of UAV-derived data in relatively undisturbed settings. This study therefore provides an original contribution to UAV-based research, outlining a robust aerial methodology that is potentially of great value to post-disaster damage surveys and geomorphological change analysis. Our findings can be used (1) to utilise UAV in post-disaster change assessments; (2) to establish ground control points that enable before-and-after change analysis; and (3) to provide baseline data reference points in areas that might undergo future change. We recommend that countries which are at high risk from natural disasters develop capacity for low-cost UAV surveys, building teams that can create pre-disaster baseline surveys, respond within a few hours of a local disaster event and provide aerial photography of use for the damage assessments carried out by local and incoming disaster response teams.

Seven municipal solid waste (MSW) specimens with variable initial waste compositions were biodegraded in large (d = 300 mm, h = 600 mm) laboratory landfill simulators under leachate-recirculation-enhanced anaerobic biodegradation conditions to investigate changes in the biochemical and physical characteristics of solid waste, leachate and biogas during biodegradation. The evolution with time of the monitored characteristics of the three phases was presented and the characteristics empirically correlated. The impact of the initial composition of waste on the biodegradation process was quantified. Although removal of soluble compounds in leachate, and methane (CH4) generation from waste was practically completed after around 300 days, changes in vertical strain, total unit weight and volumetric moisture content of waste continued in decreasing rates even after 1000 days. Methane generation potential (L0) of the waste was correlated to the percentage of biodegradable waste prior to degradation expressed by parameter B0. Maximum methane generation rate (rCH4,max) increased with increasing L0 and maximum soluble chemical oxygen demand in leachate. Final strain (or settlement) of waste due to anaerobic biodegradation (εB,f) increased with increasing B0 and L0. The compression ratio was found to vary during the process, although it is commonly assumed to be constant. The maximum long-term compression ratio increased with increasing εB,f and rCH4,max. The total unit weight at submerged and field capacity states and volumetric moisture content of waste were also dependent on the initial composition and compression (quantified by strain) of waste. The trends presented in this study contribute to the quantitative understanding of coupled processes during enhanced biodegradation of MSW of variable waste composition.

Understanding the factors that affect the monotonic and cyclic response of gravelly soils during earthquake events is critical to infrastructure design. In this study a large-size Cyclic Simple Shear (CSS) device was utilized to perform monotonic and cyclic shear tests on mixtures of either subrounded 9 mm Pea Gravel or angular 8 mm Crushed Limestone (CLS8) with subrounded Ottawa C109 sand. Tests were performed in constant volume conditions and shear wave velocity was measured for each specimen. Monotonic and cyclic test results at Dr = 47% show that there is an optimum mixture percentage that results in the greatest shear strength and resistance to liquefaction (40% Sand for Pea Gravel Mixtures and 60% Sand for CLS8 Mixtures). The effects of particle angularity, cyclic stress ratio, and initial vertical stress on monotonic and cyclic response of loose and dense gravel mixtures were investigated and are presented. Comparison of the results from the cyclic simple shear tests with existing liquefaction triggering charts suggests the need for improved charts for gravelly soil liquefaction evaluation.

Although large-size simple shear (SS) testing of municipal solid waste (MSW) may arguably provide a more realistic estimate of the shear strength (τ ) of MSW than the most commonly used direct shear (DS) testing, a systematic comparison between the shear responses of MSW obtained from the two testing methods is lacking. In this study, a large-size shear device was used to test identical MSW specimens sampled in USA in DS and SS. Eight DS tests and 11 SS tests were conducted at vertical effective stresses of 50–500 kPa. The stress–displacement response of MSW in SS testing was hyperbolic and a maximum shear stress was reached, whereas a maximum shear stress was not reached in most DS tests. The τ, effective friction angle (ϕ ′) and cohesion (c ′) of MSW were obtained from DS and SS tests by using a displacement failure criterion of 40 mm. τ in SS testing was found to be equal to or lower than τ in DS testing with ratios of τ between 73 and 101%. SS testing resulted in higher ϕ ′ but lower c ′ than DS testing. The shear strength parameters were lower than those obtained in previous studies from DS tests at 55 mm displacement.

We present field evidence and a kinematic study of a rock block mobilized in the Ponti area by a Mw = 6.5 earthquake near the island of Lefkada on 17 November 2015. A detailed survey was conducted using an unmanned aerial vehicle (UAV) with an ultrahigh definition (UHD) camera, which produced a high-resolution orthophoto and a digital terrain model (DTM). The sequence of impact marks from the rock trajectory on the ground surface was identified from the orthophoto and field verified. Earthquake characteristics were used to estimate the acceleration of the rock slope and the initial condition of the detached block. Using the impact points from the measured rockfall trajectory, an analytical reconstruction of the trajectory was undertaken, which led to insights on the coefficients of restitution (CORs). The measured trajectory was compared with modeled rockfall trajectories using recommended parameters. However, the actual trajectory could not be accurately predicted, revealing limitations of existing rockfall analysis software used in engineering practice.

Coseismic landslides pose immediate and prolonged hazards to mountainous communities, and provide a rare opportunity to study the effect of large earthquakes on erosion and sediment budgets. By mapping landslides using high-resolution satellite imagery, we find that the 25 April 2015 Mw7.8 Gorkha earthquake and aftershock sequence produced at least 25,000 landslides throughout the steep Himalayan Mountains in central Nepal. Despite early reports claiming lower than expected landslide activity, our results show that the total number, area, and volume of landslides associated with the Gorkha event are consistent with expectations, when compared to prior landslide-triggering earthquakes around the world. The extent of landsliding mimics the extent of fault rupture along the east-west trace of the Main Himalayan Thrust and increases eastward following the progression of rupture. In this event, maximum modeled Peak Ground Acceleration (PGA) and the steepest topographic slopes of the High Himalaya are not spatially coincident, so it is not surprising that landslide density correlates neither with PGA nor steepest slopes on their own. Instead, we find that the highest landslide density is located at the confluence of steep slopes, high mean annual precipitation, and proximity to the deepest part of the fault rupture from which 0.5–2 Hz seismic energy originated. We suggest that landslide density was determined by a combination of earthquake source characteristics, slope distributions, and the influence of precipitation on rock strength via weathering and changes in vegetation cover. Determining the relative contribution of each factor will require further modeling and better constrained seismic parameters, both of which are likely to be developed in the coming few years as post-event studies evolve. Landslide mobility, in terms of the ratio of runout distance to fall height, is comparable to small volume landslides in other settings, and landslide volume-runout scaling is consistent with compilations of data on larger slope failures. In general, the size ratios of landslide source area to full landslide area are smaller than global averages, and hillslope length seems to largely control runout distance, which we propose reflects a topographic control on landslide mobility in this setting. We find that landslide size dictates runout distance and that more than half of the landslide debris was deposited in direct connection with stream channels. Connectivity, which is defined as the spatial proximity of landslides to fluvial channels, is greatest for larger landslides in the high-relief part of the High Himalaya. Although these failures are less abundant than those at lower elevations, they may have a disproportionate impact on sediment dynamics and cascading hazards, such as landslide reactivation by monsoon rainfall and landslide dams that lead to outburst floods. The overall high fluvial connectivity of coseismic landsliding in the Gorkha event suggests coupling between the earthquake cycle and sediment/geochemical budgets of fluvial systems in the Himalaya., Geomorphology, 301, ISSN:0169-555x, ISSN:1872-695X

Thousands of landslides occurred during the April 2015 Gorkha earthquake in Nepal. Previous work using satellite imagery mapped nearly 25,000 coseismic landslides. In this study, the satellite-based mapping was analyzed in three areas where field deployment was also conducted—the Budhi Gandaki, Trishuli, and Indrawati river valleys—to better characterize the landslides. Unmanned aerial vehicles (UAVs) were deployed to map the three-dimensional (3-D) geometry of failed slopes using photogrammetry, as well as to characterize rock structure and strength. The majority of landslides were rock slides along the ridges and the steeper portions of the basins primarily involving the weathered rock zone. Additional landslides included rock falls and soil failures. Satellite imagery analysis indicated that landsliding was concentrated north of the physiographic transition, in steep areas, and in close proximity to the major rivers. The Trishuli area experienced the lowest landslide density in terms of number of landslides compared to the Budhi Gandaki and Indrawati areas, although all three areas had similar density in terms of total landslide area and other landslide statistics.

Ground motion modification is extensively used in practice to modify a seed acceleration time history in intensity and frequency content until its acceleration response spectrum matches a target spectrum. However, the decision to accept or reject a modified motion commonly relies on a subjective process where the time histories of the modified motion are visually compared to those of the seed motion. Various metrics were used to quantify the similarity between the modified time histories and their scaled counterparts for hundreds of modified ground motions from three different earthquake scenarios. Of the metrics considered, the inverse modified RMSE metric for time histories ( imRMSE t) was found most appropriate as it resulted in the least amount of dispersion in the goodness-of-fit values with respect to spectral mismatch. The imRMSE t was then found to be correlated to qualitative rankings assigned to the modified time histories through a visual assessment. The correlation between the quantitative imRMSE t values and qualitative rankings is used to establish threshold values to screen modified velocity and displacement time histories that are likely acceptable or likely unacceptable.

Research on the cities of the Classical Greek world has traditionally focused on mapping the organisation of urban space and studying major civic or religious buildings. More recently, newer techniques such as field survey and geophysical survey have facilitated exploration of the extent and character of larger areas within urban settlements, raising questions about economic processes. At the same time, detailed analysis of residential buildings has also supported a change of emphasis towards understanding some of the functional and social aspects of the built environment as well as purely formal ones. This article argues for the advantages of analysing Greek cities using a multidisciplinary, multi-scalar framework which encompasses all of these various approaches and adds to them other analytical techniques (particularly micro-archaeology). We suggest that this strategy can lead towards a more holistic view of a city, not only as a physical place, but also as a dynamic community, revealing its origins, development and patterns of social and economic activity. Our argument is made with reference to the research design, methodology and results of the first three seasons of fieldwork at the city of Olynthos, carried out by the Olynthos Project.

In-situ and laboratory tests were performed on lime sludge generated from a drinking water-softening process and disposed of in a sedimentation lagoon. The sludge consists predominantly of calcite. It is poorly graded, low-plasticity silt with in-situ w c around 70%, γ t around 15 kN/m3 and e between 1·5 and 2·5. The optimum w c for standard and modified Proctor compaction is 30% and the maximum γ d values are 12 and 13·5 kN/m3 respectively. The C c and C r for undisturbed sludge specimens are 0·54–0·68 and 0·021–0·046. C v and k decrease with increasing vertical stress. The disposed sludge is sensitive and the in-situ S u,max varies with depth. Stratification of the sludge is evident by the varying values of in-situ S u,max, S u,r and S t with depth and V s profiles. Potential engineering reuse options for the sludge are buffer for acidic soil and low-permeability fill for landfills and brownfields, as well as engineering fill. The properties of lime sludge are different from those of coagulation sludge, primarily due to their different chemical compositions. Coagulation sludge has the physical characteristics of high-plasticity clay. Consequently, lime sludge shows comparatively higher γ d, lower C c and C r and higher C v than coagulation sludge.

Unmanned aerial vehicles (UAV), or drones, have become popular tools for practitioners and researchers alike. Recent years have seen a significant increase in UAV uses for many applications...

Highways consist of many large structures requiring vigilant inspection and maintenance. While significant research attention has been focused on the health management of bridges, comparatively less attention has been paid to other highway structures including retaining walls. In the United States, there has been a recent emphasis on extending the use of risk management methods to the extremely large national inventory of retaining wall structures. In this paper, a long-term wireless monitoring system is developed as a cost-efficient approach to collecting data and information required for risk assessment of retaining wall structures. The study focuses on two reinforced concrete (RC) retaining walls to highlight the monitoring system design and to illustrate how measurement data offers insight to wall performance. The first wall is a caisson supported retaining wall along the M-10 freeway in Detroit, MI; the second is a classical reinforced concrete cantilever wall along I-696 in Southfield, MI. The wireless monitoring system installed on each wall system uses a cellular-based wireless sensor node termed Urbano that is solar powered and customized to measure wall tilt using inclinometers, wall strain using strain gages, and wall temperature using thermistors. The monitoring systems have been valuable in assessing the behavior of the M-10 and I-696 wall systems for a broader risk management framework. The monitoring results reveal both wall systems are operating as designed with limited tilt and strain responses to normal environmental factors including moisture and temperature.

The energy conversion potential of municipal solid waste (MSW) disposed of in landfills remains largely untapped because of the slow and variable rate of biogas generation, delayed and inefficient biogas collection, leakage of biogas, and landfill practices and infrastructure that are not geared toward energy recovery. A database consisting of methane (CH4) generation data, the major constituent of biogas, from 49 laboratory experiments and field monitoring data from 57 landfills was developed. Three CH4 generation parameters, i.e., waste decay rate (k), CH4 generation potential (L0), and time until maximum CH4 generation rate (tmax), were calculated for each dataset using U.S. EPA's Landfill Gas Emission Model (LandGEM). Factors influencing the derived parameters in laboratory experiments and landfills were investigated using multi-linear regression analysis. Total weight of waste (W) was correlated with biodegradation conditions through a ranked classification scheme. k increased with increasing percentage of readily biodegradable waste (Br0 (%)) and waste temperature, and reduced with increasing W, an indicator of less favorable biodegradation conditions. The values of k obtained in the laboratory were commonly significantly higher than those in landfills and those recommended by LandGEM. The mean value of L0 was 98 and 88L CH4/kg waste for laboratory and field studies, respectively, but was significantly affected by waste composition with ranges from 10 to 300L CH4/kg. tmax increased with increasing percentage of biodegradable waste (B0) and W. The values of tmax in landfills were higher than those in laboratory experiments or those based on LandGEM's recommended parameters. Enhancing biodegradation conditions in landfill cells has a greater impact on improving k and tmax than increasing B0. Optimizing the B0 and Br0 values of landfilled waste increases L0 and reduces tmax.

If you have been following the news, browsing the internet, or even gazing up in the sky, it is likely that you have seen an Unmanned Aerial Vehicle (UAV), also commonly known as Unmanned Aircraft ...

Estimation of landslide erosion rates and hazard prediction require a firm understanding of the physical controls on landslide size. In this study we seek to understand how the characteristics of different landscapes and forcing events influence the distribution of landslide size at a regional scale. We explore the parameter space of a mechanically-based landslide model through a series of simulations using digital elevation data. Consistent with previous studies, we find that large slope failures are infrequent due to the scarcity of large, steep hillslopes in typical mountainous topography. On the other hand, we find that the occurrence of small landslides is limited by the cohesive strength of hillslope material, which overcomes the weaker driving forces on short slopes. We test our model results with an empirical investigation of frequency-size distributions for eight real co-seismic landslide inventories. Although empirical data are noisy, we find a positive correlation between landslide size and hillslope relief, while the effects of PGA on landslide size are less pronounced. We conclude that landslide size distributions reflect the available distribution of hillslope geometries in a given landscape, and that external forcing (e.g., seismic ground motion) determines which subset of the hillslope distribution fails during a particular event. For a given landscape and forcing event, there is a particular length-scale over which landsliding is statistically favored, leading to the concept of characteristic landslide size distributions.

Landfill gas (LFG) is a product of the biodegradation of municipal solid waste (MSW) under anaerobic conditions. LFG primarily consists of methane (CH4) (40–60%) and carbon dioxide (CO2) (40–60%), both greenhouse gases. Methane has high energy potential that remains largely untapped as a national energy source. In order to recover LFG for energy generation purposes, a reliable estimate of gas generation at landfill sites is necessary. To that end, numerous LFG generation models have been developed with different assumptions made. In this study, three gas generation models – two first order decay (LandGEM and IPCC) and one sigmoidal model (Modified-Gompertz) are considered. The cumulative methane yield prediction of these models is fitted against three degradation experiments on well-characterized MSW specimens with significantly different waste composition ranging from “waste-rich” to “soil-rich”. The results indicate that the sigmoidal model better captures the evolution of methane yield compared to first order decay model and majority of the model parameters follow a systematic trend as a function of waste composition.