Lake Bathymetry Research Articles

Reconstructing Tibetan Plateau lake bathymetry using ICESat-2 photon-counting laser altimetry

Lake bathymetry is important for quantifying and characterizing underwater morphology and its geophysical state, which is critical for hydrological and ecological studies. Due primarily to the harsh environment of the Tibetan Plateau, there is a severe lack of lake bathymetry measurements, limiting the accurate estimation of total lake volumes and their evolutions. Here, we propose a novel lake bathymetry reconstruction by combining ICESat-2/ATLAS (Advanced Topography Laser Altimetry System) data with a numerical model. An improved grid-based photon noise removal method is used to address the photon signal buried in the background noise during the local daytime. The developed model was validated for seven lakes on the Tibetan Plateau and showed good agreement between simulated and measured lake volumes, with an average absolute percentage error of 8.0 % for maximum water depth and 19.7 % for lake volume simulations. The model was then utilized to estimate the water volume of other lakes by combining it with the self-affine theory. The lake depths obtained from ICESat-2/ATLAS show good agreement (RMSE = 0.69 m; rRMSE = 10.3 %) with available in-situ measurements for lakes with depths <16.5 m, demonstrating the potential of ICESat-2/ATLAS for improved reconstruction of the bathymetry of clear water inland lakes. Our study reveals for the first time, that the Tibetan Plateau has an estimated total lake water volume of 1043.69 ± 341.31 km3 for 33,477 lakes (>0.01 km2) in 2022. Over 70 % (∼734.8 km3) of the lake water storage is concentrated in the Inner Plateau, with the Yellow River basin accounting for 10.9 % (∼113.9 km3), followed by the Indus River basin with 7.2 % (∼75.1 km3). Our study provides a robust method for estimating total lake volumes where in-situ measurements are scarce and can be extended to other clear water lakes, thus contributing to more accurate global assessments and towards comprehensive quantification of Earth's surface water resources distribution.

Risk assessment of a glacial lake with abruptly slowing expansion, Jiongpu, Southeastern Tibet

The expansion of potentially hazardous glacial lakes is a symptom of global warming during this interglacial period. A pertinent example is the Jiongpu glacial lake in southeastern Tibet, the area of which has expanded approximately fivefold in the last half-century. However, recently, the glacier tongue has retreated to a high steep slope, and the rate of retreat of the glacier and expansion of the lake have temporarily slowed. The risk of a glacier tongue landslide after glacier detachment and subsequent glacial lake outburst flood (GLOF) needs to be assessed. In this study, we employed a combination of unmanned aerial vehicle (UAV), sonar, geological radar, remote sensing, field investigation, sampling, drilling, and dating techniques to determine the critical parameters of potential GLOFs, including glacier tongue geometry, lake bathymetry, and moraine dam geometry and composition. Utilizing empirical models and multiphase flow models, we identified the most hazardous triggers and simulated the processes of a glacier tongue landslide into the lake, moraine dam overtopping by a displacement wave, and subsequent flood evolution. The results showed that the most hazardous trigger in volume is a glacier tongue landslide, accounting for 58.29 % of all triggers associated with potential GLOFs. Lapped by the largest glacier tongue landslide impulse wave, the moraine dam would not fail because the minimum safety factor is approximately 1.66 ± 0.7 according to empirical methods and geological slope simulation. However, overtopping would occur, resulting in a peak discharge of approximately 9740 ± 4137 m3/s at the moraine dam based on r.avaflow calculations. The flood would reach the densely populated Jinling township and inundate approximately 46 ± 4.55 % of the houses according to HEC-RAS. Reducing the water level of the glacial lake represents an effective strategy for mitigating potential losses. This concise, physics-based method effectively assesses GLOF triggers and processes and can be applied to risk assessments of other expanding glacial lakes.

A Lake Biogeochemistry Model for Global Methane Emissions: Model Development, Site‐Level Validation, and Global Applicability

AbstractLakes are important sentinels of climate change and may contribute over 30% of natural methane (CH4) emissions; however, no earth system model (ESM) has represented lake CH4 dynamics. To fill this gap, we refined a process‐based lake biogeochemical model to simulate global lake CH4 emissions, including representation of lake bathymetry, oxic methane production (OMP), the effect of water level on ebullition, new non‐linear CH4 oxidation kinetics, and the coupling of sediment carbon pools with in‐lake primary production and terrigenous carbon loadings. We compiled a lake CH4 data set for model validation. The model shows promising performance in capturing the seasonal and inter‐annual variabilities of CH4 emissions at 10 representative lakes for different lake types and the variations in mean annual CH4 emissions among 106 lakes across the globe. The model reproduces the variations of the observed surface CH4 diffusion and ebullition along the gradients of lake latitude, depth, and surface area. The results suggest that OMP could play an important role in surface CH4 diffusion, and its relative importance is higher in less productive and/or deeper lakes. The model performance is improved for capturing CH4 outgassing events in non‐floodplain lakes and the seasonal variability of CH4 ebullition in floodplain lakes by representing the effect of water level on ebullition. The model can be integrated into ESMs to constrain global lake CH4 emissions and climate‐CH4 feedback.

Validation of remote sensing derived ice-thickness with in-situ Lake Bathymetry in the recently vacated area of gepang-gath glacier, Lahaul Himalaya, India

ABSTRACT Field observations provide authenticity in remote sensing studies when it comes to glacierized areas where weather conditions and terrain are not accessible. This study is an attempt to validate the relation between the Randolph Glacier Inventory (RGI) ice thickness and DEM through a field survey in the recently vacated area occupied by the moraine-dammed proglacial lake of the rapidly retreating Gepang-Gath glacier in the Lahaul Himalaya. We used Randolph Glacier Inventory (RGI) version-6 data of ice thickness for Gepang-Gath glacier with SRTM digital elevation model (DEM) of the year 2000 and Sentinel-1 Synthetic Aperture Radar (SAR) interferometry-based DEM of the year 2020 to calculate the lake depth. This relation is validated with ground-based investigation and lake bathymetry data collected using a kayak and metallic nob tied with rope and measuring tape in June 2021 where the maximum depth of the lake is 48 m. The SRTM-DEM profile and ice thickness data suggested that the Gepang-Gath glacial lake will expand ~2 km with a maximum depth of ± 10 m measured near the snout. As this lake is potentially vulnerable, this type of study will help measure lake depth using snout height and vice-versa with the help of DEM data to avoid hazards in feeding glaciers retreating.

An Ice Loss Evaluation of Lake-Terminating Glaciers Based on Lake Bathymetry—A Case Study of the Jiongpu Glacier

Lake-terminating glaciers are among the most severely retreating glacier types in high mountain areas. However, the characteristic of being covered by glacial lakes after retreat makes it hard to estimate their actual ice loss in recent years, as does the contribution of different parts in ice loss, which leads to significant obstacles not only in evaluating solid water resources but understanding inter-relationships between glacial ice and glacial lakes. This study presents a detailed investigation of Jiongpu Co, one of the biggest glacial lakes in the Tibetan Plateau, including its bathymetry and area evolution. The ice loss in the last two decades was analyzed using a multisource DEM dataset. The main results showed that from 1976 to 2021, Jiongpu Co had expanded from 1.19 ± 0.09 km2 to 5.34 ± 0.07 km2. The volume of Jiongpu Co showed a surprising increment from 0.09 ± 0.004 Gt to 0.66 ± 0.03 Gt from 1976 to 2021, leading to a subaqueous equivalent ice loss of 0.32 ± 0.01 Gt water from 2000 to 2020 and resulting in an underestimated ice loss of 0.06 Gt, 19% compared with previous evaluations. The total ice loss of the Jiongpu glacier was 1.52 ± 0.37 Gt from 2000 to 2020, and more than 1/3 ice loss was related to lake expansion (0.32 ± 0.01 Gt underwater, 0.19 ± 0.02 Gt above water). This study makes a further contribution to the understanding of ice loss in the complicated system of lake-terminating glaciers.

First Results on Lake Bathymetry of Panch-Pokhari Complex, Langtang Region, Central Nepal

The Panch-Pokhari complex, a group of five lakes, is one of the high-altitude wetlands of Nepal that has received very less attention. While these lakes hold significant religious importance, they are less known from a morpho-ecological perspective. The objective of this study is to develop a bathymetry model of the lakes through afield survey and geospatial analysis. This study generated new insights into the limnological and morphometric features of the five lakes through detailed mapping and profiling. The bathymetric analyses revealed diverse basin morphometry among the lakes, with Lake 1 being the largest, in term of its depth of 12.1 m and water volume of 208,352 m3. In contrast, Lake 5 was the smallest and the shallowest with a depth of 1.4 m and volume of 1,921 m3. This study establishes a new baseline to advance scientific understanding of the Panch-Pokhari complex. Further, integrated research combining limnological, ecological, and social aspects is recommended to support evidence-based planning for the conservation of these vital Himalayan wetlands.

Long-term Satellite-derived Bathymetry of Arctic Supraglacial Lake from ICESat-2 and Sentinel-2

Abstract. The polar ice sheets serve as natural thermostats, regulating Earth’s temperatures. The Greenland Ice Sheet (GrIS), the second-largest ice sheet, is a critical indicator of climate change and global warming. Estimating the volume of supraglacial lakes on the GrIS, which is directly linked to the extent of melting in the Arctic ice sheet, requires information on both lake area and water depth. Conventional bathymetric methods (i.e., airborne bathymetric LiDAR, shipborne echo-sounder) are commonly used for accurate water depth measurement. However, polar supraglacial lakes face challenging conditions, leading to uncertainties in their spatial and temporal distribution. To overcome the limitations, this study combines Sentinel-2 and ICESat-2 (Ice, Cloud, and Land Elevation Satellite-2) to estimate bathymetry and detect changes in lake volume on the GrIS from 2019 to 2023. Firstly, Sentinel-2 images were pre-processed, and ICESat-2 single-photon LiDAR points were extracted using the DBSCAN (Density-Based Spatial Clustering of Applications with Noise) method, followed by the bathymetric corrections as the training data. Subsequently, three bathymetry models (i.e., log-linear, log-ratio, and BP (Back Propagation) neural network) were constructed using Sentinel-2 images and ICESat-2 data. Lastly, the highresolution ArcticDEM (Arctic Digital Elevation Model) was used as the validation data to assess the satellite-derived bathymetry accuracy. In this study, the log-ratio model yielded the best results with the R2, RMSE, and MAE of 0.92, 0.79 m (lower than 10% of the maximum depth), and 0.62 m. The results demonstrate the feasibility of the integrated active and passive remote sensing approach for bathymetry in Arctic supraglacial lakes.

Mapping inundated bathymetry for estimating lake water storage changes from SRTM DEM: A global investigation

Lake water budgets are sensitive to climate change and human activities and have been undergoing rapid changes worldwide over the past few decades. Satellite altimeters greatly promote the large-scale monitoring of lake level and storage variations. However, limited spatiotemporal coverage of the existing individual altimeters prevents long-term and spatially seamless observations on global lakes. These limitations are partially surmounted by the gridded digital elevation model (DEM) data, which can facilitate spatially contiguous measurements of lake bathymetry exposed at the low-level period. The high-resolution SRTM DEM has been widely used for estimating lake level variations due to its early collection time and reliable data quality, while how many lakes worldwide and to what extent of the newly inundated areas can be monitored based on SRTM DEM remains unexplored. Here, we conduct a quasi-global investigation of SRTM DEM regarding its capability of mapping inundated-area bathymetry and estimating lake storage variations. After generating a global-scale lake inventory (122,444 lakes below 60°N, >1 km2) representing the maximum water inundation extents between 1984 and 2020, the feasibility of mapping lake inundated-area bathymetry was evaluated by comparing the maximum inundated area with the waterbody extent derived from SRTM DEM and analyzing the characteristics of interannual and seasonal variability of each lake. Results show that the maximum exposed lake bathymetries from the SRTM DEM data cover an area of 372,986 km2, accounting for 15.95% of the maximum water area of our investigated lakes. Climate-driven lake expansions or human-induced reservoir impoundments after 2000 (the SRTM mission period) are the main contributors to the higher availability of SRTM DEM-based bathymetry mapping on the Tibetan Plateau, India, eastern China, and Amazon Plains. As the newly launched Surface Water and Ocean Topography (SWOT) mission is anticipated to monitor lake water budget variation at an unprecedented resolution, this study provides a base map for supplementing inundated bathymetry information. The joint use of SRTM and SWOT-based observations will extend the time and space extents of lake-level measurements, thereby enhancing our understanding of lake dynamics at a longer timescale.

A conceptual model for glacial lake bathymetric distribution

Abstract. The formation and expansion of glacial lakes worldwide due to global warming and glacier retreat have been well documented in the past few decades. Thousands of glacial lake outburst floods (GLOFs) originating from moraine-dammed and ice-dammed lakes were reported, causing devastating impacts on downstream lives and properties. Detailed glacial lake bathymetry surveys are essential for accurate GLOF simulation and risk assessment. However, these bathymetry surveys are still scarce as glacial lakes located in remote and high-altitude environments hamper a comprehensive investigation. We developed a conceptual model for glacial lake bathymetric distribution using a semi-automatic simulation procedure. The basic idea is that the statistical glacial lake volume–area curves conform to a power-law relationship indicating that the idealized geometric shape of the glacial lake basin should be hemispheres or cones. First, by reviewing the evolution of various types of glacial lakes, we identified nine standard conceptual models to describe the shapes of lake basins. Second, we defined a general conceptual model to depict the continuum transitions between different standard conceptual models for those specific glacial lakes that lie between two standard conceptual models. Third, we nested the optimal conceptual model in the actual glacial lake basin to construct the water depth contours and interpolate the glacial lake bathymetric distribution. We applied the conceptual model to simulate six typical glacial lakes in the Third Pole with in situ bathymetric surveys to verify the algorithm's applicability. The results show a high consistency in the point-to-point comparisons of the measured and simulated water depths, with a total volume difference of approximately ±10 %. The conceptual model has significant implications for understanding glacial lake evolution and modeling GLOFs in the future.

Bathymetric modelling for long-term monitoring of water dynamics of Ramsar-listed lakes using inundation frequency and photon-counting LiDAR data

Accurate information on lake bathymetry and water dynamics is crucial for comprehending the intricate ecological processes in wetland ecosystems, which in turn can inform effective conservation and management strategies. However, obtaining such information can be challenging, particularly in remote areas with limited data. This study presents a way to leverage inundation frequency and ICESat-2 photon-counting LiDAR data to develop bathymetric models for Ramsar-listed lakes in a semi-arid region of Australia. Based on developed bathymetric models, monthly time series of water areas, levels and volumes were derived, providing a long-term view of the water dynamics of the two lakes from1987-2021. This is the first time that such detailed bathymetry and long-term water dynamics have been established for Ramsar-listed lakes in Australia's Outback. The findings of this study provide the most up-to-date information on the long-term trends of the Ramsar-listed lakes in the region and highlight the lakes’ prolonged dry spells when drought conditions prevailed through much of the 2000s and the 2010s as denoted by rainfall deficiencies and high evaporation. The outcome of this study serves as a valuable baseline for understanding the historical and ongoing status of these Ramsar-listed lakes in a warming and drying climate and contributes to the development of strategic plans to fulfill international obligations for wetland protection under the Ramsar Convention.

Cascading hazards from two recent glacial lake outburst floods in the Nyainqêntanglha range, Tibetan Plateau

Glacial lake outburst floods (GLOFs) are a major natural hazard in high mountain regions and have caused significant loss and damage. In the past decade, two lakes (Ranzeria Co in 2013 and Jiweng Co in 2020) burst out within a single river basin in the Nyainqêntanglha range of the Tibetan Plateau. These GLOFs destroyed local infrastructure and vegetation, and eroded river banks. In this study, field measurements, satellite remote sensing, and hydrodynamic modelling were used to reveal the causes, mechanisms, and flow dynamics of both events. Field surveys in 2020 and 2022 including lake bathymetry, lake shorelines, high-resolution aerial photographs, geomorphological data, and downstream damage provided evidence to analyze the triggers and mechanisms involved in both cases. The results show that Ranzeria Co expanded by 123% in area between 1976 and 2012, and contracted by 53% in 2013 due to the outburst. The area of Jiweng Co grew by 54% from 1976 to 2020, and shrank by 57% after the dam breach. Lake levels decreased by 20.2 ± 0.3 m in 2013 for Ranzeria Co and by 25.8 ± 0.3 m in 2020 for Jiweng Co, corresponding to water volume losses of about 7.9 × 106 (68%) and 1.1 × 107 m3 (87%), respectively. Using the hydrodynamic model HEC-RAS, it was found that the GLOFs reached peak discharges of about 7,500 m3/s with an average velocity of 8.8 m/s at Ranzeria Co, and 5,100 m3/s with 3.7 m/s at Jiweng Co. The Ranzeria Co outburst involved a cascade of processes, including the collapse of the parent glacier, a displacement wave in the lake, and the overtopping of the moraine dam. The processes of the Jiweng Co outburst flood were more complex, including an unstable lateral moraine, landslides entering the lake, rising water level, dam erosion, and finally dam failure. The study provides important insights into the mechanisms of two GLOFs, which are key to assessing and managing the hazards of critical glacial lakes in the Tibetan Plateau and its surroundings.

Predicting lake bathymetry from the topography of the surrounding terrain using deep learning

AbstractLake morphometric features like surface area, volume, mean, and maximum depth are important predictors of many physical, biological, and ecological processes. Lake bathymetric maps that present the lake basin contours are thus an integral part of limnological investigations. Accurate but cumbersome traditional bathymetric surveys measure the depth using a lead line or echosounder. Recently, airborne bathymetric mapping using imagery or laser scanning has been attempted in shallow freshwater and coastal habitats. However, these methods depend on the ability of light to penetrate the water column, which can be problematic in eutrophic lakes and shallow lakes. To alleviate these issues, we developed and tested a deep learning model (based on the U‐net) using data from 153 lakes in Denmark to predict bathymetry using the topography of the surrounding terrain. The deep learning model performed much better (pixel‐wise mean absolute error: validation set = 1.75 and test set = 2.15 m) than baseline interpolation approaches (validation set = 3.12 m). In addition, the deep learning model generated more realistic bathymetry maps that did not suffer from interpolation artifacts. We find that the model performance improves slightly with increasing model size (number of trainable parameters) and the extent of the surrounding terrain. In addition, our pretraining procedure improved performance and reduced the time for model convergence. Because the model only relies on digital elevation data which are widely available, it can be fine‐tuned and used to predict lake bathymetry in other geographical regions.

Tracing groundwater discharge into a coal mining subsidence lake in eastern China: Observations from water stable (δD and δ18O) and radon (222Rn) isotopes

Many coal mining subsidence lakes have formed in eastern China due to underground coal mining. Lacustrine groundwater discharge (LGD) is of great importance to the hydrological cycle and the eco-environment of lakes. However, LGD in coal mining area is rarely reported. In the study, we quantified groundwater discharge into a Huainan coal mining subsidence lake (China) using water stable (D and 18O) and radioactive (222Rn) isotopes. 222Rn and 18O mass balance models were used to independently estimate LGD. The lake water was sampled based on the horizontal and vertical profile sampling. The isotope depth profiles were weighted according to the lake bathymetry to obtain a representative isotope inventory by geographic information system (GIS) analysis. The LGD rates estimated from two models were comparable, and the values were 18 mm d−1 for the 18O and 14 ± 8 mm d−1 for the 222Rn. Compared with the LGD of Ammelshainer See lake (Germany), a subsidence lake formed by coal mining, the LGD in the study was larger, which may be related to the different hydrological conditions in different areas. By integrating the LGD rates from these two models, this study quantitatively analyzed the role of groundwater in maintaining the water balance in subsidence lakes, which is of great significance to water resources assessment and sustainable utilization of coal mining subsidence lakes in eastern China.

Lake Atotonilco: A First Approach to Determining the Minimum Lake Level Necessary to Sustain Its Biodiversity

Lake Atotonilco is a shallow saline water body located in the central-west portion of Mexico. The lake is in the low plain of an endorheic watershed. It is shallow, with a large area of surrounding wetlands and serves as a refuge for dozens of native and migratory waterfowl. Its extremely flat morphometric features coupled with the precipitation and runoff regime from the watershed cause significant changes in the lake surface area and storage volume throughout the year. In recent years, the lake has behaved as an intermittent lake, remaining practically dry in June, and reaching its highest storage volume in October. An ecological water volume that the lake must maintain to support its biodiversity was estimated. This minimum lake storage volume can only be achieved if public policies are implemented to rationalize the use of water resources in the basin and to protect the few forest areas that remain in the watershed. Key Words: ecological minimum volume, endorheic watershed, lake bathymetry, playa lake.

A Quantification of Heat Storage Change-Based Evaporation Behavior in Middle–Large-Sized Lakes in the Inland of the Tibetan Plateau and Their Temporal and Spatial Variations

A large number of different-sized lakes exist in the inland area of the Tibetan Plateau (TP), which are examples of the important connection between the atmosphere and hydrosphere through the analysis of lake surface convergence and evaporation processes. The evaporation level changes that occur in middle–large-sized lakes (surface area &gt; 50 km2) in the area directly influence the regional mass and energy balance values, atmospheric boundary layer heat and humidity structures, and weather processes occurring in the lower-reach areas. The studies conducted in the literature at present, concerning lake evaporation processes, generally overlook the differences in lake heat storage behavior due to the reduced amount of data in the literature concerning lake bathymetry. According to the in situ bathymetric data obtained for 68 middle–large-sized lakes in the inner basin of the TP, in this study, we calculated their heat storage (G) change values by using the different vertical-depth water-temperature-change integral method, and we established a regression equation for the heat storage and lake surface net radiation values for 68 lakes. The evaporation rates of 134 middle–large-sized lakes larger than 50 km2 in the inland are of the TP were calculated by obtaining the G regression result and adopting it into the Penman model, as well as estimating the evaporation losses of theses 134 lakes from 2002 to 2018. The result shows that the annual average evaporation rate for these lakes is 927.39 mm/year, with an insignificant upward trend (0.10 mm/year). This method achieved good accuracy compared with the Bowen ratio method, which estimates the evaporation rate during the ice-free season, with a high correlation coefficient (R) value of 0.95 and least root mean square error (RMSE) value of 61 mm. The annual mean evaporation rate can be divided into the southern and northern lake groups along a 34°N line with a difference of 314.41 mm/year. The annual average evaporation volume of these lakes was 25.02 km3 and showed an upward trend of 0.35 km3/year. Among them, the annual average evaporation volume contribution ratio of level-1 lakes (50 km2 ≤ lake’s area &lt; 100 km2, 61 lakes) was 14.04%, showing an upward trend, and the contribution of level-3 lakes (lake’s area ≥ 500 km2, 10 lakes) was 41.50%, showing a downward trend. There were no obvious changes in the level-2 lakes (100 km2 ≤ lake’s area &lt; 500 km2, 63 lakes), which maintained at the same level in approximately 44.46%. Air temperature is the most important factor affecting the evaporation rate of lakes, while the lake surface area is the main factor affecting lake evaporation volume. Our study, considering the actual lake heat storage value, provides a useful reference for further improving lake water budget balance values and watershed hydrologic features in the inland closed lakes located in the TP.

Role of Hydrology in Cyanobacterial Blooms in the Floodplain Lakes

River floodplains are sites of extremely high environmental and ecological value due to high biodiversity. Floodplain lakes (FPLs) are essential parts of complex floodplain ecosystems’ biological and hydro-chemical processes. Clear seasonal cycles, determined by the regime of the parent river and closely linked to climatic conditions, are observed in these lakes. Both the quantity and the quality of water are determined by the functional phases of a floodplain lake; limnophase, when the lake is isolated from the river, and potamophase (inundation), when the floodplain lake is overflowed by the river waters. These phases highly modify lake bathymetry, water balance, chemistry, and biology. Human pressure, mostly dam construction and land use changes, alter the frequency, duration, and intensity of natural cycles of inundation. The majority of large rivers in the Northern Hemisphere have been impacted by human activity. Floodplain lakes are also affected by continuous climate change, due to the alterations of the hydrological regimes. Cyanobacterial blooms in floodplain lakes are often characterized by high qualitative and quantitative annual and long-term variability. The main forces driving cyanobacterial blooms can be found in the flooding dynamics and intensity influencing hydraulic residence time and the concentration of biogenic compounds in lake water. Cyanotoxin production and seasonal dynamics in floodplain lakes have been rarely studied, particularly in connection with the hydrological regime. Moreover, the effects of cyanobacterial blooms and their toxicity to organisms inhabiting floodplain lakes, connected rivers, and floodplains are poorly understood. Therefore, knowledge of the processes controlling floodplain lakes’ ecological conditions is crucial to implementing water management and restoration practices, protecting those fragile and precious ecosystems from degradation and possible extension.

Measuring glacial lake bathymetry using uncrewed surface vehicles

Measuring glacial lake bathymetry using uncrewed surface vehicles

Evolution and bathymetry of glacial lake at the lowest elevation in Nepal Himalaya

Evolution and bathymetry of glacial lake at the lowest elevation in Nepal Himalaya

Floquet stability analyses of stratified oscillating boundary layers on adiabatic slopes

The presence of a no-slip, impermeable, adiabatic, sloped boundary in an otherwise quiescent, stably stratified, Boussinesq flow generates baroclinic vorticity within a diffusive boundary layer. Such conditions are typical of the oscillating boundary layers on adiabatic abyssal slopes, sloped lake bathymetry and sloped coastal bathymetry in the absence of high-wavenumber internal waves, mean flows, far-field turbulence on larger scales, and resonant tidal–bathymetric interaction. We investigate the linear stability of the oscillating flow within non-dimensional parameter space typical of the $M_2$ tide and hydraulically smooth, middle-latitude abyssal slopes through Floquet linear stability analysis. The flow dynamics depends on three non-dimensional variables: the Reynolds number for Stokes’ second problem, the Prandtl number, and a frequency ratio that accounts for the resonance conditions ( $C$ , criticality) of the buoyant restoring force and the tidal forcing. The Floquet analysis results suggest that oscillating laminar boundary layers on adiabatic abyssal slopes are increasingly unstable as Reynolds number, criticality parameter and/or spanwise disturbance wavenumber are increased. We also show that the two-dimensional Floquet linear instability necessarily generates three-dimensional baroclinic vorticity, which suggests that the evolution of the gravitational instabilities may be nonlinear as $t\rightarrow \infty$ .

A hydraulic modelling approach to study flood sediment deposition in floodplain lakes

AbstractAbandoned river channels on alluvial floodplains represent areas where sediments, organic matter, and pollutants preferentially accumulate during overbank flooding. Theoretical models describing sedimentation in floodplain lakes recognize the different stages in their evolution, where the threshold for hydrological connectivity increases in older lakes as a plug‐bar develops. Sedimentary archives collected from floodplain lakes are widely used to reconstruct ecological and hydrological dynamics in riverine settings, but how floodplain lake evolution influences flow velocities and sedimentation patterns on an event scale remains poorly understood. Here we combine sediment samples collected in and around a floodplain lake with hydraulic modelling simulations to examine inundation, flow velocity, and sedimentation patterns in a floodplain lake along the Trinity River at Liberty, Texas. We focus our analyses on an extreme flood event associated with the landfall of Hurricane Harvey in August 2017 and develop a series of alternative lake bathymetries to examine the influence of floodplain lake evolution on flow velocity patterns during the flood. We find that sediments deposited in the lake after the Hurricane Harvey flood become thinner and finer with distance from the tie‐channel in accordance with simulated flow velocities that drop with distance from the tie‐channel. Flow velocity simulations from model runs with alternative plug‐bar geometries and lake depths imply that sedimentation patterns will shift as the lake evolves and infills. The integration of sediment sampling and hydraulic model simulations provides a method to understand the processes that govern sedimentation in floodplain lakes during flood events that will improve interpretations of individual events in sedimentary archives from these contexts.