Coastal road asset management: Dealing with uncertainty using quantitative erosion monitoring and modelling

The A183 is an essential transportation link in the northeast UK that joins coastal areas from South Shields to Sunderland. The route runs through the hinterland of Marsden Bay and concerns have been raised about the proximity of the road to the eroding cliff line. The Shoreline Management Plan (Lane and Guthrie, 2007) sets out the overarching management policy in the area and, based on the analyses of historic map data, uses projected coastal cliff retreat rates of 0.1 – 0.2 m a-1, although more recent investigations have suggested the rates may be nearer 0.04 – 0.1 m a-1. Quantitative data on the true rates and nature of cliff erosion are scarce and asset management decisions typically use the higher rate of 0.2 m a-1 when considering the potential impact on road operations and lifespan in order to account for uncertainty and future sea-level rise; which is additionally used to accelerate the predicted rates of retreat. Consequently, an enhanced high order estimate of cliff erosion rates has restricted the serviceability of the A183 to within 20 – 50 years, and there are three areas (pinch points) of particular concern where the close proximity of the cliff line threatens the safe operation of the road. This approach and the data it uses suggest that significant and potentially costly decisions may soon be required to ensure the viability of this vital transport corridor. Set against the context of assumed high cliff erosion rates, and further predicted increases to this metric, this work presents the results of a re-evaluation of existing map and aerial imagery data that highlights the typically high uncertainty associated with historic map data. The errors often exceed the changes being detected in rock cliffs, producing contradictory results and variability in processing and interpretation that restricts the reliability of the data used in current policy decisions. Using a significance-based analysis, questions are raised about how appropriate it is to reduce a three-dimensional recession process down to a single linear retreat. To provide a more appropriate and accurate assessment of the erosion occurring here we present the results of a monitoring approach of the Marsden Bay site using three-dimensional survey analyses to improve understanding of cliff failures at the site and ultimately to aid policy decisions

Concordance of EDI-based prevalence rates of health disorders with administrative data in two Canadian provinces

Introduction Population level data provide unprecedented opportunities to explore low-frequency health disorders, yet few suitable sources exist for young children. Early Development Instrument (EDI) data on child development in kindergarten in publically-funded schools in Canada include information on children’s health disorders that may be used as a source for prevalence estimates. Objectives and Approach We aimed to examine the concordance of EDI-based prevalence rates of health disorders with administrative data in two Canadian provinces by linking data at various levels. In Manitoba, individual EDI data were linked with health and educational data containing information on diagnosis prior to kindergarten for six health disorders: Autism Spectrum Disorder (ASD), Fetal Alcohol Spectrum Disorder (FASD), Attention Deficit and Hyperactivity Disorder (ADHD), Cerebral Palsy (CP), Anxiety, and Asthma. In Ontario, the prevalence rate of ASD based on the EDI was compared to the prevalence rate obtained from regional ASD service providers, matched on area geocodes. Results In Manitoba, the total number of children with one of the six diagnoses in the linked database was 10,181. EDI data from 2011 and 2013 demonstrated concordance rates ranging from 0% (Anxiety) to 37% (ASD) between EDI and pre-kindergarten individual administrative data for the prevalence of the health disorders. In Ontario, interrater reliability was established with 2010-2012 EDI data in 12 regions (total number of children with ASD based on the EDI =1,329) to examine consistency among the two data sources. Results showed a “fair” concordance rate for the two sources of ASD prevalence information (Kappa = 0.329; p < 0.001), with rates varying from 0.85% to 1.05%. Linkages with subsequent cohorts of children are ongoing and will be examined for consistency with current results. Conclusion/Implications While the results are somewhat lower than expected, they established feasibility of linkages in 2 provinces and will be repeated in others, potentially with a broader time-frame (up to 1-2 years post-kindergarten). This will further inform successful utilization of existing data sources to monitor the prevalence of children’s health disorders

Interannual surface evolution of an Antarctic blue-ice moraine using multi-temporal DEMs

Multi-temporal and fine resolution topographic data products are increasingly used to quantify surface elevation change in glacial environments. In this study, we employ 3D digital elevation model (DEM) differencing to quantify the topographic evolution of a blue-ice moraine complex in front of Patriot Hills, Heritage Range, Antarctica. Terrestrial laser scanning (TLS) was used to acquire multiple topographic datasets of the moraine surface at the beginning and end of the austral summer season in 2012/2013 and during a resurvey field campaign in 2014. A complementary topographic dataset was acquired at the end of season 1 through the application of Structure-from-Motion with multi-view stereo (SfM-MVS) photogrammetry to a set of aerial photographs acquired from an unmanned aerial vehicle (UAV).Three-dimensional cloud-to-cloud differencing was undertaken using the Multiscale Model to Model Cloud Comparison (M3C2) algorithm. DEM differencing revealed net uplift and lateral movement of the moraine crests within season 1 (mean uplift ~0.10 m), and surface lowering of a similar magnitude in some inter-moraine depressions and close to the current ice margin, although we are unable to validate the latter. Our results indicate net uplift across the site between seasons 1 and 2 (mean 0.07 m). This research demonstrates that it is possible to detect dynamic surface topographical change across glacial moraines over short (annual to intra-annual) timescales through the acquisition and differencing of fine-resolution topographic datasets. Such data offer new opportunities to understand the process linkages between surface ablation, ice flow, and debris supply within moraine ice

Decoding Complex Erosion Responses for the Mitigation of Coastal Rockfall Hazards Using Repeat Terrestrial LiDAR

A key factor limiting our understanding of rock slope behavior and associated geohazards is the interaction between internal and external system controls on the nature, rates, and timing of rockfall activity. We use high-resolution, monthly terrestrial light detection and ranging (LiDAR) surveys over a 2 year monitoring period to quantify rockfall patterns across a 0.6 km-long (15.3 &times; 103 m2) section of a limestone rock cliff on the northeast coast of England, where uncertainty in rates of change threaten the effective planning and operational management of a key coastal cliff top road. Internal system controls, such as cliff material characteristics and foreshore geometry, dictate rockfall characteristics and background patterns of activity and demonstrate that layer-specific analyses of rockfall inventories and sequencing patterns are essential to better understand the timing and nature of rockfall risks. The influence of external environmental controls, notably storm activity, is also evaluated, and increased storminess corresponds to detectable rises in both total and mean rockfall volume and the volumetric contribution of large (&gt;10 m3) rockfalls at the cliff top during these periods. Transient convergence of the cumulative magnitude&ndash;frequency power law scaling exponent (ɑ) during high magnitude events signals a uniform erosion response across the wider cliff system that applies to all lithologies. The tracking of rockfall distribution metrics from repeat terrestrial LiDAR in this way demonstrably improves the ability to identify, monitor, and forecast short-term variations in rockfall hazards, and, as such, provides a powerful new approach for mitigating the threats and impacts of coastal erosion

Reconstructing the Chongbaxia Tsho glacial lake outburst flood in the Eastern Himalaya: Evolution, process and impacts

Glacial lake outburst floods (GLOF) are one of the most destructive natural disasters. Understanding GLOF evolution, and their impacts, plays a fundamental role in GLOF hazard assessment and risk management. Reconstructing historical GLOFs is an important exercise because detailed case studies of such glacial hazards are rare, which hinders the capacity of glacial hazard practitioners to learn from these events. In this study, we reconstruct a historical GLOF from moraine-dammed Chongbaxia Tsho (89.745°E, 28.211°N) in the Eastern Himalaya, which is a unique case study because the outburst flood cascaded into two further lakes downstream. We employ a combination of i) multi-source and multi-temporal satellite imagery, ii) field investigation (including an unmanned aerial vehicle survey), iii) numerical dam breach and hydrodynamic modelling and, iv) qualitative and quantitative cryospheric and meteorological analysis, to investigate the evolution of the GLOF hazard, simulate moraine dam failure and GLOF propagation, and explore the role that long- and short-term climate trends played in providing the conditioning factors for the outburst. Chongbaxia Tsho expanded rapidly between 1987 until 2001 in response to glacier recession most likely caused by a regional warming trend of +0.37 °C per decade. Based on satellite image analysis we refine the outburst date to be 6 August 2001, instead of 6 August 2000, as previously reported, and attribute an ice avalanche into the glacial lake originating from the receding parent glacier as the most likely trigger for moraine dam failure. Through DEM differencing and lake level decrease, we estimate that a total water volume of 27.1 ± 1.6 × 106 m3 was released from the lake during the event, and using dam breach modelling we estimate that the peak discharge at the breach was >6600 m3 s−1. The GLOF flowed through downstream Chongbamang Tsho and Chongbayong Tsho, both of which served to attenuate the GLOF and reduce downstream losses; the latter stored an estimated 96% of the flood volume. Precipitation totals in the weeks preceding the GLOF exceeded the historical mean by up to 40%, and may have contributed to instability of the parent glacier, and generation of an ice avalanche with enough impact energy to cause lake water to overtop the moraine dam and initiate breach development. A future GLOF from Chongbaxia Tsho cannot be ruled out, but more field data, including detailed lake bathymetry, and information pertaining to the sedimentological and geotechnical characteristics of the moraine dam, are required for a more robust parameterization of a predictive GLOF model and quantification of the hazard posed by a future GLOF

Seasonal Dynamics of a Temperate Tibetan Glacier Revealed by High-Resolution UAV Photogrammetry and In Situ Measurements

The seasonal dynamic changes of Tibetan glaciers have seen little prior investigation, despite the increase in geodetic studies of multi-year changes. This study compares seasonal glacier dynamics (&ldquo;cold&rdquo; and &ldquo;warm&rdquo; seasons) in the ablation zone of Parlung No. 4 Glacier, a temperate glacier in the monsoon-influenced southeastern Tibetan Plateau, by using repeat unpiloted aerial vehicle (UAV) surveys combined with Structure-from-Motion (SfM) photogrammetry and ground stake measurements. Our results showed that the surveyed ablation zone had a mean change of &minus;2.7 m of ice surface elevation during the period of September 2018 to October 2019 but is characterized by significant seasonal cyclic variations with ice surface elevation lifting (+2.0 m) in the cold season (September 2018 to June 2019) but lowering (&minus;4.7 m) in the warm season (June 2019 to October 2019). Over an annual timescale, surface lowering was greatly suppressed by the resupply of ice from the glacier&rsquo;s accumulation area&mdash;the annual emergence velocity compensates for about 55 of surface ablation in our study area. Cold season emergence velocities (3.0 &plusmn; 1.2 m) were ~5-times larger than those observed in the warm season (0.6 &plusmn; 1.0 m). Distinct spring precipitation patterns may contribute to these distinct seasonal signals. Such seasonal dynamic conditions are possibly critical for different glacier responses to climate change in this region of the Tibetan Plateau, and perhaps further afield

Glacial lake outburst floods threaten millions globally

Glacial lake outburst floods (GLOFs) represent a major hazard and can result in significant loss of life. Globally, since 1990, the number and size of glacial lakes has grown rapidly along with downstream population, while socio-economic vulnerability has decreased. Nevertheless, contemporary exposure and vulnerability to GLOFs at the global scale has never been quantified. Here we show that 15 million people globally are exposed to impacts from potential GLOFs. Populations in High Mountains Asia (HMA) are the most exposed and on average live closest to glacial lakes with ~1 million people living within 10 km of a glacial lake. More than half of the globally exposed population are found in just four countries: India, Pakistan, Peru, and China. While HMA has the highest potential for GLOF impacts, we highlight the Andes as a region of concern, with similar potential for GLOF impacts to HMA but comparatively few published research studies

Resolving Fine-Scale Surface Features on Polar Sea Ice: A First Assessment of UAS Photogrammetry Without Ground Control

Mapping landfast sea ice at a fine spatial scale is not only meaningful for geophysical study, but is also of benefit for providing information about human activities upon it. The combination of unmanned aerial systems (UAS) with structure from motion (SfM) methods have already revolutionized the current close-range Earth observation paradigm. To test their feasibility in characterizing the properties and dynamics of fast ice, three flights were carried out in the 2016–2017 austral summer during the 33rd Chinese National Antarctic Expedition (CHINARE), focusing on the area of the Prydz Bay in East Antarctica. Three-dimensional models and orthomosaics from three sorties were constructed from a total of 205 photos using Agisoft PhotoScan software. Logistical challenges presented by the terrain precluded the deployment of a dedicated ground control network; however, it was still possible to indirectly assess the performance of the photogrammetric products through an analysis of the statistics of the matching network, bundle adjustment, and Monte-Carlo simulation. Our results show that the matching networks are quite strong, given a sufficient number of feature points (mostly > 20,000) or valid matches (mostly > 1000). The largest contribution to the total error using our direct georeferencing approach is attributed to inaccuracies in the onboard position and orientation system (POS) records, especially in the vehicle height and yaw angle. On one hand, the 3D precision map reveals that planimetric precision is usually about one-third of the vertical estimate (typically 20 cm in the network centre). On the other hand, shape-only errors account for less than 5% for the X and Y dimensions and 20% for the Z dimension. To further illustrate the UAS’s capability, six representative surface features are selected and interpreted by sea ice experts. Finally, we offer pragmatic suggestions and guidelines for planning future UAS-SfM surveys without the use of ground control. The work represents a pioneering attempt to comprehensively assess UAS-SfM survey capability in fast ice environments, and could serve as a reference for future improvements

Using climate reanalysis data in conjunction with multi-temporal satellite thermal imagery to derive supraglacial debris thickness changes from energy balance modelling

Surface energy-balance models are commonly used in conjunction with satellite thermal imagery to estimate supraglacial debris thickness. Removing the need for local meteorological data in the debris thickness estimation workflow could improve the versatility and spatiotemporal application of debris thickness estimation. We evaluate the use of regional reanalysis data to derive debris thickness for two mountain glaciers using a surface energy-balance model. Results forced using ERA-5 agree with AWS-derived estimates to within 0.01 ± 0.05 m for Miage Glacier, Italy, and 0.01 ± 0.02 m for Khumbu Glacier, Nepal. ERA-5 data were then used to estimate spatiotemporal changes in debris thickness over a ~20-year period for Miage Glacier, Khumbu Glacier and Haut Glacier d'Arolla, Switzerland. We observe significant increases in debris thickness at the terminus for Haut Glacier d'Arolla and at the margins of the expanding debris cover at all glaciers. While simulated debris thickness was underestimated compared to point measurements in areas of thick debris, our approach can reconstruct glacier-scale debris thickness distribution and its temporal evolution over multiple decades. We find significant changes in debris thickness over areas of thin debris, areas susceptible to high ablation rates, where current knowledge of debris evolution is limited

Brief communication: An approximately 50 Mm3 ice-rock avalanche on 22 March 2021 in the Sedongpu valley, southeastern Tibetan Plateau

On 22 March 2021, a ~50 M m3 ice-rock avalanche occurred from 6500 m asl in the Sedongpu basin, southeastern Tibet. The avalanche transformed into a highly mobile flow which temporarily blocked the Yarlung Tsangpo river. The avalanche flow lasted ~5 minutes and produced substantial geomorphological reworking. This event, and previous ones from the basin, occurred concurrently with, or shortly after recorded positive air temperature anomalies. The occurrence of future large mass flows from the basin cannot be ruled out, and their impacts must be carefully considered given implications for sustainable hydropower and associated socioeconomic development in the region