Bernard Laval

Thermobarically stratified Quesnel Lake shows relatively high rates of hypolimnetic mixing and transport over its winter (inverse) stratification period. A decade-long data set reveals annual winter trends of warming and cooling at 500 m depth, field measurements record increasing hypolimnetic oxygen levels between fall and summer, demonstrating regular ventilation. This research describes processes responsible for the ventilation of the deep hypolimnetic water of Quesnel Lake. Temperature records from moored instruments, and conductivity, temperature, and depth (CTD) profiles were processed to assess transport and mixing in the lake. Local weather stations, regional government data, and modelled data were used to calculate atmospheric forcing at the surface of the lake. These data were compared to find links between atmospheric events and deep-water behavior over the winter of 2006-2007. The results show that the deep water is ventilated by wintertime thermobaric instabilities induced by baroclinic seiche, and by a prolonged spring turnover. Turbulent mixing from seiche homogenizes the bottom water (within 0.02ºC) to a maximum height of ~400 m above the lake bottom. Deepening of the surface mixed layer is aided by the homogenized bottom layer to produce a full spring turnover. This study supports previous research on Quesnel Lake, demonstrating that wind forcing is an effective mixing and transport mechanism even in the deepest region of the lake.

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Cultus Lake, British Columbia is critical freshwater lake habitat for two species-at-risk, the Cultus Lake Sockeye Salmon (Oncorhynchus nerka, Cultus population) and Cultus Lake Pygmy Sculpin (Coastrange Sculpin, Cottus aleuticus, Cultus population). This lake ecosystem is degrading and threatened by epilimnetic warming and decreasing hypolimnetic dissolved oxygen concentrations, largely the result of the effects and interactions of ongoing lake eutrophication and climate change. Exploration of lake modeling and monitoring data (2009-2018) revealed a correlation between Cultus Lake, BC hypolimnetic temperatures and the volume of hypoxic (17ºC; -25% of lake volume currently; -30% (-34%) under RCP4.5 (RCP8.5) by 2100), and hypoxic hypolimnetic waters (
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In the four years that followed the 4 August 2014 tailings dam failure at Mount Polley Mine, British Columbia, Canada, water quality data indicated an ongoing sediment loading to Quesnel Lake and the Quesnel River. Within one day of the tailings dam failure, a flood of slurry entered the smaller, downstream basin of Quesnel Lake, called the West Basin. Previous studies had shown highly elevated turbidity in the West Basin through the first autumn and winter after the spill, and above background turbidity each autumn and spring from 2015 onwards. It remained unclear how long this seasonally elevated turbidity would last. In this thesis, we evalutate sediment transport in Quesnel Lake following the rapid inflow of a vast quantity of material. This thesis applies conservation of mass in two ways: first, using data collected between 10 September 2014 and 21 December 2018 to estimate suspended sediment mass and mass flows into and out of the West Basin; and second, using an analytical model. On 10 September, 37 days post-spill, an estimated 38000 $\pm$ 11000 Mg of solids remained suspended in the West Basin; this decreased to within background levels ($
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The last intact ice shelf in the Canadian Arctic is located at the mouth of Milne Fiord (82.6N, 81.0W), on Ellesmere Island, Nunavut. During melt season, the ice shelf acts as a dam preventing meltwater from flowing freely to the ocean. This results in a permanent layer of freshwater that "floats" on top of the seawater of the fjord. This layer of freshwater is called an epishelf lake. The winter data from a mooring installed in Milne Fiord epishelf lake (2011-2019) is analysed in the framework of a one dimensional model in order to study 1) mixing in the upper water column and 2) the evolution of a basal channel in the ice shelf. The results show that vertical mixing is surprisingly higher in the epishelf lake than in the seawater underneath. Estimation of the Richardson number using geostrophic balance indicates that enhanced mixing in the epishelf lake is associated with horizontal temperature gradients. Moreover, the analysis suggests that all of the freshwater reaching the ocean travels through a single basal channel in the ice shelf. The model did not detect significant variation in outflow characteristics over the eights years of study, implying that the basal channel area is in ice mass balance.

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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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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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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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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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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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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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