BGC Engineering (Canada)

Debris flows are one of the most common geomorphic processes in mountainous areas, and can form a great threat to local communities and infrastructure. Traditionally, mitigation efforts have focused on engineering solutions such as check dams or debris basins. Recently, focus has started to shift towards more nature-based solutions such as forest buffer zones, which require an understanding of interactions between debris flows and trees for their design. Some research into debris flow-forest interactions has been done using field data, aerial imagery or simplified physical experiments, however, quantitative knowledge of tree removal by debris flows is still lacking. This study aims to assess tree survival and removal by debris flows, and to identify controlling debris flow and vegetation properties.We use multi-temporal, high resolution airborne laser scanning (ALS) data covering multiple debris-flow events over four different forested debris-flow fans in the Squamish-Lillooet region in British Columbia, Canada, to track sediment deposition and tree removal. Tree survival patterns are linked to tree and debris-flow characteristics (tree size, location and proximity to the next tree, and deposition and erosion depth, respectively) to gain insight into the interaction between debris flows and forests.Preliminary results show that smaller trees have a higher chance of being removed by a debris flow, and that the chance of tree survival increases with distance from the fan apex and with higher tree density. Next steps include numerical simulations of debris-flow velocities to quantify the relationship between debris-flow impact forces and tree removal or survival. The results of this study will help identify optimal characteristics for resilient debris-flow forest buffer zones.

<strong class="journal-contentHeaderColor">Abstract.</strong> Karst springs in alpine catchments are important for maintaining groundwater-dependent ecosystems in fragile environments and for sustaining baseflow in mountain rivers. Despite its importance, rugged and inaccessible terrains pose major challenges in hydrogeological studies of alpine karst. This study developed a practical approach for characterizing an alpine karst system in the Canadian Rocky Mountains that had no previous information aside from the location of the spring outlet. Using geological maps, satellite images, simple water balance, water sampling and analysis, and dye tracer tests, it was possible to estimate the extent of the spring catchment and infer the hydrogeological characteristics of the karst system. Of particular importance was the information obtained from the fluctuations of spring discharge and electrical conductivity in response to diurnal snowmelt cycles. Synthesis of the diverse data set indicates that the karst system has a large volume of groundwater stored in the fractured rock matrix that buffers the interannual variability of precipitation and sustains steady baseflow throughout the year. The karst system consists of fractured rock matrix, saturated conduits acting like pipes, unsaturated conduits acting like open channels, and many pools delaying the propagation of transport and hydraulic signals through the conduit network. The approach developed in this study will be applicable to other alpine karst systems in snow-dominated catchments in rugged and inaccessible terrains.

Advances in distributed fiber optic sensing technologies are enabling new methods to monitor changes in tailings dam performance. Distributed acoustic sensing (DAS), a distributed fiber optic sensing technology relying on Rayleigh light backscattering, can provide continuous spatial and temporal coverage along the length of a fiber optic cable extending tens of kilometers. In 2019, nearly six kilometers of fiber optic cable were installed at ∼1 m depth along an active upstream tailings dam in northern Canada. DAS seismic data were acquired at 400 Hz over a four-month period, from April to August 2021. We applied coda wave interferometry to a 120 m cable segment to obtain relative changes in seismic velocities (dv/v). Such coda waves are typically dominated by Rayleigh surface waves and dv/v can be used as a proxy for shear wave velocity changes. The dv/v estimates decrease by up to ∼1.9% over an initial two-month period of spring thaw and rainfall. Subsequently, dv/v recover by ∼1%, and generally show an inverse correlation with tailings pond levels up until the end of data acquisition. This correlation is supported by a known power-law relationship between shear wave velocity and effective stress. Rayleigh surface wave sensitivity kernels incorporating nearby seismic cone penetration testing data are used to estimate the approximate depths of dv/v sensitivity at ∼10 m. Despite active construction causing noise contamination, we obtain stable cross-correlation waveforms with as little as one hour of data per day. Overall, our results demonstrate how DAS can be used to augment geotechnical monitoring networks by providing in situ estimates of dv/v to inform changes in tailings dam performance over time.

Jacob Gens, the head of the Vilnius Ghetto Police Force, and eventually the entire Ghetto during the Holocaust, was murdered on 14 September 1943 by the head of the Vilnius Gestapo. Historical documents and Holocaust survivor testimonies indicate that he was killed at a site that became known as the Rasu Street Prison, and not the Gestapo Headquarters, as it is widely believed. In 2016, research was completed at the Rasu Street Prison site using ground penetrating radar (GPR) and electrical resistivity tomography (ERT) to locate subsurface reflection patterns that possibly indicate the location of where Jacob Gens is buried. Intersecting GPR and ERT reflection patterns were discovered and a plan was put in place to excavate that location. The excavation revealed the presence of human remains at 1.45 m below the surface. A skull and upper torso were exposed, and two teeth were collected for DNA and radiocarbon analysis. The DNA from the tooth was compared to Jacob Gens’ daughter’s DNA, and this comparison yielded a negative result, so the human remains were not those of Jacob Gens. The radiocarbon analysis provided a date between 1685 and 1735. In 1705, a plot of land was donated to the Visitation Monastery, which used this plot, and which coincides with the location of the Rasu Street Prison, as a cemetery for the poor. In 1709 and 1710, a plague epidemic was prevalent in Vilnius, as was turmoil and famine associated with the Great Northern War (1700 to 1721). Based on these discoveries, rather than finding the remains of Jacob Gens, it is likely that we found human remains that are part of a forgotten 18th century cemetery associated with the Visitation Monastery.

In 2023 and 2024 and in partnership with Sage on Earth Consulting, BGC Engineering undertook a province-wide hazard exposure assessment for the provincial government of British Columbia, Canada. British Columbia spans approximately 940,000 square kilometers, stretching from the Pacific Ocean in the west to the Rocky Mountains in the east and from the Yukon border in the north to Washington State in the south. This expansive region faces a wide array of natural hazards, including flooding from mountain streams, tsunamis and shoreline erosion in coastal communities; earthquakes; landslides; debris flows; wildfires; drought; extreme heat and, increasingly, cascading hazards intensified by climate change. The goal of this project was to design and implement a geospatial workflow for assessing exposure of valued assets to hazards, delivered to a government agency in a standardized format that facilitated future updates and public governance over data sharing. &amp;#160;To accomplish this, BGC designed a data model and analysis pipeline that had sufficient performance for the iterative processing of large multi-hazard and asset datasets and that could be packaged for government agency development of a data portal. Within the data model, hazards were defined as areas which exceed hazard-specific intensity thresholds and/or annual probability of occurrence; these binary hazard data were the primary input to the analysis pipeline for each hazard type. The list of assets to be included in the analysis was determined through a series of consultations with project stakeholders aimed at identifying which assets are most important and what data was available consistently for the entire province. The result of the analysis was a set of exposure metrics representing population counts, monetary values of property exposed to hazards, and the lengths of transportation and utility networks within hazard zones summarized using a uniform 1.5 km x 1.5 km grid. These metrics were delivered along with documentation of the data model, the data, and the codebase for the analysis pipeline.The resulting analysis revealed spatial patterns of hazard exposure and provided actionable insights to support provincial-scale risk management. This work represents a foundational step in risk assessment and mitigation planning. It offers a means of prioritizing local-scale risk assessments within a jurisdiction as vast as British Columbia, enabling focused resource allocation and informed decision-making. Collaboration was central to the project's success. In association with Sage on Earth Consulting , BGC engaged with multiple stakeholders to refine inputs and validate assumptions, and ensure the outputs were accessible and meaningful. The results are designed for government-managed web access to both data inputs and analysis outputs, promoting transparency and usability for diverse audiences.This provincial hazard exposure assessment highlights the importance of integrating data, &amp;#160;geospatial analysis, stakeholder collaboration, and practical tools to address the complex challenges posed by natural hazards in British Columbia. The findings not only advance the understanding of hazard exposure but also lay the groundwork for more detailed, localized risk assessments and targeted mitigation efforts.&amp;#160;

The 2019 windstorm in Nepal struck villages in the Bara and Parsa districts, central-south of Nepal, on March 31, 2019, causing widespread devastation. The storm, rated five (5) on the Enhanced Fujita Scale, cut a 33 km swath through central-southern Nepal. In total, 1,452 private houses were destroyed, while 1,373 others suffered partial damage. The tragic storm claimed 28 lives and left 1,155 individuals injured. The impact of this tragedy extended to nearly 3,000 families. Immediately after the storm, a comprehensive damage assessment framework was developed, and a field reconnaissance study was conducted to understand the damage distribution and building failure mechanisms under tornado wind loads. Common damage modes observed were roofing material damage, roof-to-wall connection failure, and brittle masonry wall failures in the affected areas. This paper presents the lessons learned from damage to the building infrastructure during the 2019 windstorm in Nepal. Examined buildings underscore the critical need for design alternatives and sustainable retrofits, emphasizing load path integration and strong roof-to-wall connection. Strengthening the building envelope can significantly enhance its resilience against storms and other disasters prominent in the region. This study highlights the importance of proactive measures to safeguard vulnerable communities against natural hazards and offers insights into resilient building construction technology.

Rockfall ditch effectiveness is a common component in risk calculations for cut slopes. Therefore, understanding ditch effectiveness deterioration is vital for forecasting changes in slope risk. However, studies analyzing changes in ditch behavior over time are limited. In this study, we propose a practical method for forecasting ditch effectiveness deterioration based on a conceptual model. The model assumes that ditch effectiveness is zero once a talus pile of rockfall debris has formed to its angle of repose. Using initial ditch effectiveness estimates, rockfall frequency estimates, and assuming linear deterioration of ditch effectiveness as a function of volume in the talus pile, ditch effectiveness can be forecasted. To evaluate the conceptual model, rockfall trajectory numerical models were developed for different cut slope and ditch geometries. Ditch-filling was simulated by approximating talus pile geometry as a triangle. The talus pile angle was increased incrementally until the angle of repose was reached, and ditch effectiveness was recorded as proportion of rockfall retained. Numerical modeling results can be approximated with our conceptual model for steeper cut slopes (∼4V:1H), while the conceptual model is conservative relative to modeling results for shallower cut slopes; we attribute this to the transition from bouncing- to rolling-dominated rockfall trajectories.

ABSTRACTTidally influenced groundwater systems in coastal environments represent important mixing zones of fresh groundwater and circulating seawater, manifesting as submarine groundwater discharge (SGD). Water circulation induced by tidal pumping enhances the exchange of chemicals between aquifers and coastal waters and thereby influences the biogeochemistry of coastal zones. Here, we report the results of an SGD field study conducted at a steep, mega‐tidal sand and gravel beach along the Canadian coast of the Bay of Fundy, a region with the world's highest tides (semi‐diurnal tidal ranges exceeding 10 m). Several physical and geochemical measurement techniques were employed to document the spatiotemporal SGD variability. SGD was directly sampled from seepage meters installed over multiple tidal cycles and two summer campaigns. SGD rates were estimated from tracer mass balances for radon (August 2020) and radium isotopes (July 2021) over multiple tidal cycles. Tidally averaged SGD estimates from seepage meters ranged from 12 to 87 cm d−1, with an average of 42 cm d−1, while radon tracing yielded a tidally averaged rate of 86 cm d−1. SGD estimates from radium tracing ranged from 23 to 43 cm d−1 along the shoreline and 6 to 71 cm d−1 offshore, depending on the estimated residence times. Radionuclide analyses of seepage meter waters suggest that the residence time of seawater circulation through the aquifer is less than 1 day. SGD measurements in mega‐tidal settings are rare, and the results suggest that the combination of the steep slopes, highly permeable sediments and high tidal range drive very high seepage rates for diffusive SGD. Salinity gradients in the intertidal zone demonstrate that SGD is primarily comprised of circulated seawater with negligible fresh groundwater. Although the freshwater proportion of SGD is relatively low, the large volumetric rates of total SGD can still contribute large amounts of terrestrially derived and remineralized nutrients to coastal waters.