Bernard Laval

Professor

Relevant Degree Programs

 

Great Supervisor Week Mentions

Each year graduate students are encouraged to give kudos to their supervisors through social media and our website as part of #GreatSupervisorWeek. Below are students who mentioned this supervisor since the initiative was started in 2017.

 

Bernard is a great supervisor because he always has time for his students. He pushes us to do things on our own but is there when we need him. He understands that we have lives outside of school and is very supportive. He provides opportunities to grow and develop as researchers.

Also, I am lucky enough that I get to work with him in the field for my research. Few students get their supervisors in the field. I get mine to hike a mountain and carry my gear every two weeks :)

Kelly Graves (2019)

 

Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - May 2019)
Ice-ocean interactions in Milne Fiord (2016)

Widespread break up of ice shelves, glacier tongues, and the loss of ice-dammed epishelf lakes on the northern coast of Ellesmere Island has motivated a need to understand fjord dynamics, yet the oceanography of fjords here is not well studied. Here, we present ocean profiling and mooring data collected from 2011 to 2015 in Milne Fiord, the last ice shelf-epishelf lake-glacier tongue fjord in the Arctic.The data reveal that seasonal and interannual variations of fjord water properties and circulation are strongly impacted by the presence of the Milne Ice Shelf. The ice shelf forms a floating dam that traps surface runoff resulting in strong stratification and an elevated fjord heat content. Water exchange below the ice shelf is restricted to a narrow basal channel, prolonging the export of fjord-modified water, including subglacial runoff, by several months. In contrast, intermediate waters that penetrate to the Milne Glacier grounding line are freely exchanged and respond to offshore variations, with implications for submarine melting.Unexpectedly, the depth of the halocline between the epishelf lake and seawater, often used to infer the thickness of the ice shelf, varied by several meters each year. This variability resulted from rapid inflow of surface runoff during summer followed by slow drainage under the ice shelf over winter, which is well modelled as hydraulically-controlled flow through a channel. A mixing event also abruptly changed the depth of the halocline by 1.5 m in less than 24 hours, indicating caution must be used when inferring ice shelf mass balance from halocline depth.Submarine melt rates, estimated by two independent approaches, are strongly dependent on the vertical distribution of heat in the fjord. Spatial variation of ice thickness resulted in a heterogeneous distribution of melt. The highest estimated melt rate (4 m/a) occurred where the glacier was in contact with warm AtlanticWater at the grounding line, and enhanced near-surface melting is driven by the elevated heat content of the upper water column. Estimated melt rates are limited by weak currents ( 1 cm/s) in the fjord imposed by the presence of the ice shelf.

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Modal decomposition of the baroclinic response to wind in elongated lakes (2012)

The baroclinic response to wind is examined in narrow elongated lakes. The main objective is to link the excitation and modulation of baroclinic modes to lake bathymetry and stratification, temporal and spatial characteristics of wind forcing, and damping. Three lake bathymetries are examined which represent 1) variable-depth single basins with straight thalweg, 2) two-basin lakes with straight thalweg, and 3) two-basin lakes with arms at which the thalweg bends sharply. The bathymetries are examined using idealized lake forms as well as data from two Canadian lakes. Modal analysis and a three-dimensional hydrodynamic numerical model are used to analyze the baroclinic response. Also, a modal-based forced model is developed to simulate the decoupled modal responses to wind and provide a direct link between lake and forcing characteristics and modal composition of the response.This study shows that coupling between wind-forcing spatial structure and bathymetry determines which modes are excited, while wind-forcing temporal patterns modulate the magnitude of excited modes. It is found that, when wind is near-uniform, the first horizontal mode, H1, dominates the response regardless of bathymetry, because the near-uniform wind couples with the spatial distribution of layer flow for H1. In sub-basins separated by geometric constrictions (sills and contractions) or sharp bends in the thalweg relative to wind direction, the wind induces local metalimnetic tilts that are superimposed on the domain-wide H1 tilt. The sub-basin tilts are attributable to higher horizontal modes which are equivalent to the H1 modes of the decoupled sub-basins.Furthermore, this study demonstrates the following: 1) interbasin exchange due to H1 shifts from two to more layers due to interaction of vertical modes, 2) geometric constrictions result in strong damping of H1 which causes high forcing-response coherence and broadens the resonance bandwidth, and 3) along-thalweg depth variability in single basins increases the number of excited modes and localizes the interface shear for asymmetric basins and causes the opposite effects for symmetric basins. The findings of this study contribute to understanding the baroclinic response to wind in lakes of complex bathymetry.

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Horizontal and temporal variability of transport processes in lakes (2011)

This work examines the three dimensional nature of three important physical transport processes in lakes: (1) convection generated from a negative surface buoyancy flux; (2) transport resulting from rotational adjustment; and, (3) underflow fate during episodic wind stirring. Vertical and horizontal temperature gradients were characterized using a combination of traditional (moorings and vertical profilers) and novel techniques (an Autonomous Underwater Vehicle) at two sites; Pavilion Lake, British Columbia, Canada and Lake Thingvallavatn, Iceland. The former site is a relatively small (5 km²), temperate lake, with comparatively low snow cover that allows solar radiation to be the dominant energy flux to the system during late winter months. Analysis of water temperature distribution in surface waters during summer and winter enabled convective patterns resulting from a negative surface buoyancy flux to be inferred. In addition to previously studied physical transport phenomena, this work has revealed the existence of a cyclonic eddy under winter ice cover in Pavilion Lake, consistent with the internal Rossby radius of deformation, extending down to ~ 14 m below the ice surface and rotating with an azimuthal speed of ~ 3 cm s⁻¹ (as predicted by equations of cyclogeostrophic flow). Horizontal temperature transects beneath the eddy revealed temperature fluctuations associated with 1 – 2 m vertical displacements in the region 5 m directly below the eddy and are thought to be an undocumented source of mass transport. The latter field site was an embayment of a larger (88 km²) subarctic lake with a groundwater inflow that propagates through the embayment as a negatively buoyant underflow. Surface wind shear events entrain the underflow into the overlying lake water. This entrainment alters the characteristics and the ultimate fate of the underflow in the lake. Calculated entrainment of the underflow and entrainment calculated from the bulk Richardson number are in close agreement. Measurements made during these studies not only elucidated details of the three dimensional nature of known transport mechanisms but also revealed previously undiscovered modes of mass transport associated with wintertime lake hydrodynamics.

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Master's Student Supervision (2010 - 2018)
Climate change impacts on a eutrophying lake : Cultus Lake, British Columbia, Canada (2017)

This study characterizes the thermal dynamics of Cultus Lake, British Columbia, Canada, and assesses the impacts of climate change on critical habitat for species-at-risk Sockeye Salmon (Onchorynchus nerka) and Cultus Lake Pygmy Sculpin (Cottus aleuticus). Historical field data spanning 1920s–1930s, 2001–2003, and 2009–2016 were analyzed and a one-dimensional hydrodynamic model (General Lake Model) was calibrated using field data collected in 2016, and validated using field data from 2001–2003 and 2009–2016. The thermal structure of the lake was simulated to 2100 using outputs from the downscaled Canadian Regional Climate Model (CanRCM4) for two climate change scenarios (RCP4.5, moderate emissions scenario; and RCP8.5, extreme emissions scenario). Historically (1923–2016), the total lake heat content increased at a rate of 0.80 MJ m⁻² a⁻¹ and is projected to warm by 2.0 MJ m⁻² a⁻¹ (4.2 MJ m⁻² a⁻¹) for RCP4.5 (RCP8.5). Historically, the Schmidt stability increased by 2.2 J m⁻² a⁻¹ and is projected to increase by 2.6 J m⁻² a⁻¹ (6.5 J m⁻² a⁻¹) for RCP 4.5 (RCP8.5). The duration of stratification has historically been increasing at a rate of 0.18 d a⁻¹ and is projected to increase by 0.18 d a⁻¹ (0.50 d a⁻¹) for RCP4.5 (RCP8.5). The onset of stratification is now two weeks earlier than the 1920s–1930s and currently occurs around 23 March while the breakup date has not changed and occurs around 15 December. However, it is predicted that there will be no change in the date of onset of stratification while breakup will be delayed to 12 January (25 January) for RCP4.5 (RCP8.5). Lake surface temperature and outflow temperature is most important for salmon survival in August through November corresponding with the salmon run. Historical change in mean monthly temperature ranged from 0 °C a⁻¹ in November to a maximum of 0.016 °C a⁻¹ in August. This is predicted to increase to 0.016 °C a⁻¹ (0.046 °C a⁻¹) in November and 0.031 °C a⁻¹ (0.069 °C a⁻¹) in August for RCP4.5 (RCP8.5). Projections indicate fundamental changes to the thermal characteristics of Cultus Lake, which may further degrade water quality, particularly in conjunction with ongoing eutrophication, eliciting fundamental changes in the structural and functional attributes of critical habitat for species-at-risk.

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Mitigating impacts of temperature-oxygen squeeze in a mesotrophic-eutrophic lake : Wood Lake, BC, Canada (2017)

Warm surface waters and hypoxic hypolimnion during summer stratification in eutrophic lakes, known as a temperature-oxygen squeeze, can limit available habitat for aquatic species. This study of Wood Lake, a calcareous eutrophic lake situated in the semi-arid Okanagan Valley of BC, Canada, was motivated by a decline in kokanee return spawners following a severe temperature-oxygen squeeze in 2011. Field data collected in 2015/2016, combined with DYRESM, a one-dimensional physical simulation model, was employed to investigate the factors influencing the thermal aspect of the temperature-oxygen squeeze. A relatively early and weak spring freshet in 2015 was followed by severely restricted inflows due to upstream diversions and coincident with relatively warm regional air temperatures from May through July. These factors triggered a marling event in Wood Lake and also resulted in the early onset of high epilimnetic temperatures and hypoxic hypolimnion (>20°C and
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The free oscillatory response of fjord-type multi-armed lakes (2017)

This study examines the structure and frequency of free seiche modes in fjord-type multi-armed lakes in order to generalize features of the response of those lakes. The effect of multiple arms on seiches within a lake is not easy to predict. To do so, this study develops a simplified analytical model (SAM) based on idealized lake geometries. In addition, a characterization of surface (barotropic) modes is compared for two ``Y-shaped'' lakes: Quesnel Lake in Canada, and Lake Como in Italy. Lake Como and Quesnel Lake are studied through a combination of field observations and modelling, both numerically using a Finite Element Method (FEM) scheme and using SAM.SAM demonstrates that multi-armed lakes are subject to two classifications of behaviour: a full-lake response, in which all arms are active; and a decoupled response, in which seiching is constrained to only two arms of the lake. A geometric parameter in each arm, which represents the travel time of a progressive shallow-water wave in that arm, determines the range of behaviours expressed: each lake will either experience only a whole-lake response or it will exhibit alternating whole-lake and decoupled modes.The behaviour predicted by SAM is consistent with modes observed and predicted in both Quesnel Lake and Lake Como. Modal periods are identified from observed water level measurements using spectral analysis. FEM predicted periods agree with observations. SAM correctly reproduces the periods of the lowest frequency modes in both lakes when a constant depth is used for each arm. Mode-shapes predicted by SAM qualitatively match those given by the FEM model. While all modes of Quesnel Lake are whole- lake modes, some of the modes in Lake Como exhibit a decoupled response. The results given here also support generalization of the fundamental mode as being inherently the same structure as Merian-type modes in simple elongated lakes.While the study focusses on barotropic modes, SAM can be similarly applied to internal (baroclinic) modes, and so the general behaviours observed here are appropriate for describing both the barotropic and baroclinic responses of multi-armed lakes.

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Three-dimensional numerical simulations of subaerial landslide generated waves (2015)

This research aims to advance the continuing effort of general purpose computational fluid dynamics model validation of subaerial landslide generated wave (SLGW) simulations. Specifically, using the open source program weakly compressible Smooth Particle Hydrodynamics model, DualSPHysics, three-dimensional simulations are quantitatively compared against a combination of physical model data and traditional general-purpose computational fluid dynamics, Flow-3D™, data.Many simulations were conducted to determine the effect of both numerical parametrization and numerical scheme prescriptions on SLGW accuracy. A systematic approach was taken to parse out insignificant physical processes using Flow-3D™ - specifically surface tension - and to determine the optimal numerical scheme settings that yield the most accurate results for both Flow-3D™ and DualSPHysics.From this research, it is found that DualSPHysics is able to accurately simulate both wave generation and wave propagation, but tends to over-predict the maximum wave run-up by about 70%. In contrast, Flow-3D™ was able to accurately simulate wave propagation, but under predicted wave generation by about 25% and over predicted the maximum wave run-up by about 40%.The question as to why both DualSPHysics and Flow-3D™ both over predict the maximum wave run-up during a SLGW simulation is still open. However, it is speculated that this due to a lack of either energy dissipation through air entrainment or eigenfrequency consideration’s.

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Under-ice circulation in an Arctic lake : observations from two field seasons in Lake Kilpisjärvi, Finland (2015)

High spatial resolution CTD profiles and Acoustic Doppler Current Profiler velocity measurements show significant rotational basin-wide, under-ice circulation in May of 2013 and 2014 at Lake Kilpisjärvi, Finland (69°01'N, 20°49'E), a seasonally ice-covered, Arctic lake with negligible through-flow.In 2013, a high-pressure horizontal density anomaly with vertically paired rotating circulations was observed. The estimated maximum cyclonic and anti-cyclonic azimuthal velocities magnitudes were 0.03 and 0.02 m s-¹. The Rossby radius (Rri), horizontal length scale at which rotational effects become as important as pressure effects, was estimated to be ∼ 160 m and the Rossby number(R⃘⃘⃘⃘⃘ ), the ratio of the centripetal acceleration to the Coriolis acceleration, ∼ 0.2. It is hypothesized that this circulation was driven by heat flux at the shorelines from warm incoming streams causing a density flow down the slopes to the centre of the lake where the flow converged. This flow was balanced with a shoreward flow beneath the ice. These flows were modified by the earth's rotation, which resulted in the rotational circulation observed.In 2014, a cyclonic, low-pressure horizontal density anomaly was observed near the centre of the lake and was vertically paired with a weak anti-cyclonic anomaly in the top 10 m (mean depth of the lake is 19.5 m). The estimated azimuthal velocities had maximum cyclonic and anti-cyclonic magnitudes of 0.006 and 0.003 m s-¹. The anomaly was estimated to have Rri ∼ 240 m, with R⃘⃘ ∼ 0.12. It is hypothesized that this circulation was driven by sediment release of heat to the overlying water causing a tilt in the isopycnals near the shores of the lake that caused an inward pressure force that was balanced by the Coriolis force and, to a lesser extent, the centripetal acceleration force.The 2013 observations were made immediately prior to ice-off, and the 2014 observations were 12 days prior to ice-off. This time difference allowed for significantly different ice and snow conditions, and the addition of warm inflows, which forced the circulation closer to the ice-off date. These observations add to the growing understanding of the relationship between thermal distribution and circulation under ice.

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Optical benthic imagery survey in a lacustrine basin using an autonomous underwater vehicle (2011)

Photographs are needed to map and characterize fine-scale benthic features and underwater habitats. Acoustic imaging methods lack sufficient resolution, colour and the ability to define many low reflectance features. Other optical methods such as LiDAR also lack spectral information important in the identification of biological features. Historically, photographs of benthic surfaces are collected over small areas or single line transects. Here techniques are developed and optimized to perform an extensive optical benthic survey remotely with an Autonomous Underwater Vehicle (AUV) over the area of a lacustrine basin. The technique was applied to surveys at Pavilion and Kelly Lake, B.C., and Lake Tahoe, CA, USA. The major challenges associated with the photographic surveys included overcoming AUV performance and stability issues associated with steep bathymetry, through-water light attenuation, limited light availability, and camera system limitations. Photographic imaging with a small AUV and CCD camera was optimized for the lacustrine environment, through manipulation of the non-optimal hardware. Benthic features were identified and mapped in Pavilion Lake, revealing profundal zonation patterns of previously unexplored epipelic flora.

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