Ice-covered Conditions Research Articles

Prediction Method for Mechanical Characteristic Parameters of Weak Components of 110 kV Transmission Tower under Ice-Covered Condition Based on Finite Element Simulation and Machine Learning

Icing on transmission lines may cause damage to tower components and even lead to structural failure. Aiming at the lack of research on predicting mechanical characteristic parameters of weak components of transmission towers, and the cumbersome steps of building a finite element model (FEM), the study of prediction for mechanical characteristic parameters of weak components of towers based on a finite element simulation and machine learning is proposed. Firstly, a 110 kV transmission tower in a heavily iced area is taken as an example to establish its FEM. The locations of the weak components are analyzed, and the accuracy of FEM is verified. Secondly, meteorological and terrain parameters are considered as input parameters of the prediction model. The axial stresses and nodal displacements of four weak components are selected as output parameters. The FEM of the 110 kV transmission tower is used to obtain input and output datasets. Thirdly, five machine learning algorithms are considered to establish the prediction models for mechanical characteristic parameters of weak components, and the optimal prediction model is obtained. Finally, the accuracy of the prediction method is verified through an actual tower collapse case. The results show that ACO-BPNN is the optimal model that can accurately and quickly predict the mechanical characteristic parameters of the weak components of the transmission tower. This study can provide an early warning for the failure prediction of transmission towers in heavily iced areas, thus providing an important reference for their safe operation and maintenance.

Refined Simulation Study of Hydrodynamic Properties and Flow Field Characteristics around Tandem Bridge Piers under Ice-Cover Conditions

Ice cover is a common phenomenon in rivers in cold regions during the winter freeze-up period, leading to the formation of unsteady bypass structures around underwater piers. To reveal the variation law of the flow field around a pier under ice, a numerical calculation method is proposed to obtain the spatial and temporal characteristics of the fluid flow environment around the pier. The verification of flow conditions and convergence showed that the numerical model constructed in this study is reliable and can meet research requirements. The simulation results showed that the ice-cover condition considerably impacted the extent of a scour hole, and in the horizontal plane Z of −0.02 m, the lateral influence of the scour hole was approximately 2.6 times the diameter of the pier, which was approximately 42% wider than that of a scour hole under open-flow conditions; in the area on the side of the pier, there was a peak in longitudinal section y/D of −0.6, and the relative turbulence intensity was 0.4 and 0.51 under open-flow and ice-cover conditions, respectively, indicating that ice cover made the peak more significant in the area.

Metatranscriptomic analysis reveals dissimilarity in viral community activity between an ice-free and ice-covered winter in Lake Erie.

Winter is a relatively under-studied season in freshwater ecology. The paucity of wintertime surveys has led to a lack of knowledge regarding microbial community activity during the winter in Lake Erie, a North American Great Lake. Viruses shape microbial communities and regulate biogeochemical cycles by acting as top-down controls, yet very few efforts have been made to examine active virus populations during the winter in Lake Erie. Furthermore, climate change-driven declines in seasonal ice cover have been shown to influence microbial community structure, but no studies have compared viral community activity between different ice cover conditions. We surveyed surface water metatranscriptomes for viral hallmark genes as a proxy for active virus populations and compared activity metrics between ice-covered and ice-free conditions from two sampled winters. Transcriptionally active viral communities were detected in both winters, spanning diverse phylogenetic clades of putative bacteriophage (Caudoviricetes), giant viruses (Nucleocytoviricota, or NCLDV), and RNA viruses (Orthornavirae). However, viral community activity metrics revealed pronounced differences between the ice-covered and ice-free winters. Viral community composition was distinct between winters and viral hallmark gene richness was reduced in the ice-covered relative to the ice-free conditions. In addition, the observed differences in viral communities correlated with microbial community activity metrics. Overall, these findings contribute to our understanding of the viral populations that are active during the winter in Lake Erie and suggest that viral community activity may be associated with ice cover extent.IMPORTANCEAs seasonal ice cover is projected to become increasingly rare on large temperate lakes, there is a need to understand how microbial communities might respond to changing ice conditions. Although it is widely recognized that viruses impact microbial community structure and function, there is little known regarding wintertime viral activity or the relationship between viral activity and ice cover extent. Our metatranscriptomic analyses indicated that viruses were transcriptionally active in the winter surface waters of Lake Erie. These findings also expanded the known diversity of viral lineages in the Great Lakes. Notably, viral community activity metrics were significantly different between the two sampled winters. The pronounced differences we observed in active viral communities between the ice-covered and ice-free samples merit further research regarding how viral communities will function in future, potentially ice-free, freshwater systems.

Mixing behaviour and sources of Ag, Pd, and other trace elements in the Estuary and Gulf of St. Lawrence under winter conditions

The marine chemistry of platinum group elements is poorly documented despite robust evidence of their widespread emissions and deposition around the globe. Here, we report the concentrations and discuss the geochemical behaviours of Ag, Pd and other trace and ultra-trace elements in the Estuary and Gulf of St. Lawrence (EGSL). We highlight the contrasting mixing behaviours of these elements, i.e., conservative (Cd, Re) vs. non-conservative (Ag, Pd), in samples collected during the winter and under ice-covered conditions. We ascribe the contrasting geochemical behaviour of these elements to their differential affinity for reactive surfaces carried into the estuary from the frozen watersheds. We also report an increase of the concentrations of Ag (up to 40 pmol L−1), Pd (up to 10 pmol L−1) and Pt (up to 0.4 pmol L−1) in the bottom and oxygen-depleted waters of the Gulf of St. Lawrence (GSL). A strong correlation between dissolved Pt concentrations and the stable carbon isotopic composition of the dissolved inorganic carbon (δ13C-DIC) suggests that the increased mobility of Pt may result from the aerobic mineralization of organic carbon or the oxidation of Pt-bearing organic complexes. Molar Pt/Pd ratios in the three water masses that compose the water column in the EGSL highlight a potential influence of anthropogenic sources near urban centers. The signature of continental end-members will be required to confirm the impacts of road traffic on the estuarine geochemistry of these elements.

Rough ice cover modified hyporheic exchange: A numerical study on the mechanical effect propagating from the ice-water interface to the sediment–water interface

Many rivers are subject to ice-covered flow conditions in cold climate regions or during the winter months. The presence of ice cover can change stream flow hydrodynamics and thus affect the hyporheic exchange involved in many biogeochemical processes in aquatic environments. Among the various features of ice cover, its underside roughness is a main factor modifying the surface–subsurface flow hydrodynamics. To date, there has been little research on how ice cover affects the hyporheic exchange, even less on the effect of the ice cover roughness. This leaves open questions on the mechanical changes initiated at the ice-water interface and transferred to the water–sediment interface. In this study, a coupled surface–subsurface computational approach was used to model conjunctively the channel flow over dune bed and the underlying porous flow under different ice cover conditions. The results show that ice cover can enhance the hyporheic flux and reduce the hyporheic zone depth when compared to open channel flow at equivalent discharge. As the river flow depth increases to 4 times the height of the dune, the effect of the ice cover on the hyporheic flow becomes negligible. Within this effective range, the hyporheic flux via the channel water depth follows a power-law function. Ice cover roughness greatly augments the exchange rate while compresses the exchange space, therefore reduces flow residence time in the hyporheic zone. Based on the modeling results, prediction models were proposed for evaluating the impacts of ice cover roughness on the hyporheic exchange flux and depth. Our study indicates that hyporheic flow exchange is significantly impacted by the roughness of the ice cover which in turn the hyporheic exchange is likely to affect the river ice processes as well as the water quality and ecological functions throughout the river corridors.

Iceberg danger in the seas of the Russian Federation Arctic Zone under modern climate change conditions

The aim of the research was to study the relationship between the intensity of iceberg formation in the Russian Arctic including the number of icebergs calving annually from outlet glaciers and surface air temperature anomalies. The research was carried out on the basis of satellite monitoring using non-commercial, freely distributed satellite information from optical-electronic satellites Landsat-8 (spatial resolution 15 m) and Sentinel-2 (spatial resolution 10 m) and the radar satellite Sentinel-1 (pixel size 20×40 m). To achieve the aim, an iceberg detection technique was used based on statistical criteria for searching for gradient zones in the analysis of two-dimensional fields of satellite images. Based on the analysis of satellite data of the visible spectral range of the Landsat-8 and Sentinel-2 satellites and Sentinel-1 radar data the maximum spatial dimensions of icebergs formed by the outlet glaciers of Severnaya Zemlya, Franz Josef Land (ZFI) and Novaya Zemlya in 2012–2022 were estimated. Satellite monitoring of the Severnaya Zemlya region was carried out using visible range images in the spring season (March–May), characterized by the best observation conditions in terms of cloudiness, natural light, and monitoring of icebergs most of which are located in fast ice at this time. Monitoring of the ZFI area was carried out using radar data in the period August-September, corresponding to the minimal ice cover conditions. Satellite monitoring of the Novaya Zemlya region was carried out using visible images in the summer season. In total, about 500 satellite images were analyzed. The discusses the dependence of the intensity of the iceberg formation process on the ice shelf and outlet glaciers with a floating edge on the surface air temperature and the maximum thickness of fast ice. It is shown that the abnormally warm weather that set in 2020 during the period of ice melting led to a sharp intensification of the process of glacier melting in the Russian Arctic and the formation of almost 8,000 icebergs near Severnaya Zemlya, more than 6,600 icebergs near ZFI and over 1,000 icebergs near the western coast of Novaya Zemlya. For all the areas of the Russian Arctic studied in the period 2012–2022 an increase was noted in the maximum observed sizes of icebergs calving from glaciers. The largest iceberg, whose length was 5 km, broke off in 2020 from the Matusevich ice shelf.

Characteristics of turbulent flow around bridge abutments in the presence of vegetation in channel bed under ice-covered flow conditions

During winter, ice cover frequently forms on the water surface of rivers with vegetated channel beds in cold regions. The investigation of the impacts of both ice cover and channel bed vegetation on flow structures around bridge abutments is essential for engineers to gain a comprehensive understanding of the complex interactions occurring in such a situation. In the present study, the flow structure around a rectangular bridge abutment in the presence of vegetation under ice-covered conditions has been studied. Considering different vegetation densities by arranging vegetation elements in square and staggered configurations, this study incorporates the influence of ice covers with different roughness, namely smooth and rough ice cover. Key turbulence parameters, including turbulence intensity, Reynolds shear stress (RSS), and turbulent kinetic energy (TKE), are also examined based on laboratory experiments. Results show that the shape of velocity profiles for flow over a vegetated channel bed changes from an S-shaped curve under an open flow condition to a convex shape under ice-covered conditions. The effects of an ice cover and vegetation on the flow around the bridge abutment create unpredictable turbulence intensity patterns. Under a rough-covered flow condition, there appears a larger area with negative Reynolds shear stress (RSS) downstream of the abutment. Turbulent kinetic energy (TKE) under ice-covered conditions has substantially lower magnitudes than in open flow conditions.

Evaporation and sublimation measurement and modeling of an alpine saline lake influenced by freeze–thaw on the Qinghai–Tibet Plateau

Abstract. Saline lakes on the Qinghai–Tibet Plateau (QTP) affect the regional climate and water cycle through water loss (E, evaporation under ice-free conditions and sublimation under ice-covered conditions). Due to the observational difficulty over lakes, E and its underlying driving forces are seldom studied when targeting saline lakes on the QTP, particularly during ice-covered periods (ICP). In this study, the E of Qinghai Lake (QHL) and its influencing factors during ice-free periods (IFP) and ICP were first quantified based on 6 years of observations. Subsequently, three models were calibrated and compared in simulating E during the IFP and ICP from 2003 to 2017. The annual E sum of QHL is 768.58±28.73 mm, and the E sum during the ICP reaches 175.22±45.98 mm, accounting for 23 % of the annual E sum. E is mainly controlled by the wind speed, vapor pressure difference, and air pressure during the IFP but is driven by the net radiation, the difference between the air and lake surface temperatures, the wind speed, and the ice coverage during the ICP. The mass transfer model simulates lake E well during the IFP, and the model based on energy achieves a good simulation during the ICP. Moreover, wind speed weakening resulted in an 7.56 % decrease in E during the ICP of 2003–2017. Our results highlight the importance of E in ICP, provide new insights into saline lake E in alpine regions, and can be used as a reference to further improve hydrological models of alpine lakes.

Fluctuations of ice in a lake due to the impact of the North Atlantic Oscillation (1960/61–2009/10) – a case study of Łebsko Lake

The paper represents an attempt to understand the impacts produced by the North Atlantic Oscillation on the ice cover regime of the largest coastal lake in Poland situated in the northern part of the country. The purpose of the study was to estimate the impact of the North Atlantic Oscillation on selected ice cover parameters. The study also attempts to examine other factors that may affect its significant impact on observed changes in the climate. Water temperature data are used to assess temperature conditions in aqueous ecosystems as well as determine the heat absorption capacity of these systems. This allows one to then determine cooling rates in the event of ice cover formation. The data analysis provided in the paper focuses on selected characteristics of ice cover conditions (i.e. dependent variables) including the number of days with ice and maximum ice thickness in relation to NAO index changes (i.e. independent variables) for the reference period 1960/61–2009/10. In addition, the paper divides the studied period into 10-year subperiods in order to capture the weakest and strongest phases of NAO and assess the extent to which they affect the duration of ice cover. A large increase in the mean air temperature (1.8°C) occurred in the years 1960–2010. Trendline analysis indicates that the number of days with ice cover declined by about 60 days and the maximum thickness of ice cover decreased by about 10 cm. Oceanographic research employs satellite image data in order to accurately assess human impact. Therefore, ice cover forecasts generated for consecutive winter seasons may become an important tool in this type of assessment.

STATE OF POPULATIONS AND BREEDING BIOLOGY OF THE HORNED PUFFIN (<i>FRATERCULA CORNICULATA</i> ALCIDAE, CHARADRIIFORMES) IN THE NORTHERN PART OF THE SEA OF OKHOTSK

The breeding biology of the Horned Puffin, Fratercula corniculata, was studied in 1989–2019 on Talan Island, Tauiskaya Bay, Sea of Okhotsk. Even though the estimates of the population size of the Horned Puffin made in the early 1990s and 2007–2008 (90–100 and 75–112 thousand individuals, respectively) failed to reveal its dynamics due to different study methods applied, data on the nesting density in these periods indicated its increase by more than 30%. In subsequent years, higher bird densities were recorded on the surface of model screes. Taking into account these data, the maximum numbers of horned puffins on the island could reach 166 thousand individuals. Depending on ice cover conditions, the dates of the onset of egg laying varied between June 6 in 1990 and June 17–18 in 1987, 1999 and 2001, the average long-term date being June 11. Chicks in different years started hatching between July 17 to 29, the average long-term being July 22. The weight of hatchlings varied from 35 to 53 g (mean 47.2). The average weight of monthly chicks in 1999–2006 ranged from 145 to 329 g, in some individuals from 80 to 410 g. The average age of the young birds captured on the ground was 44.7 days. The first individuals were recorded in different years at the end of August (August 27–30) and at the beginning of September (September 2). According to indirect estimates, fledglings left nest burrows between September 10 and 20, to end in late September to early October. The average weight of fledglings heading to the sea in 1987, 1988, 1989 and 1991 was 349, 338, 347 and 318 g, respectively. The wing length varied from 153 to 156 mm. The reproductive success of horned puffins varied from 10.3 to 90.5% (on average 56.4%), the hatching success from 19.8 to 95.2% (on average 75.5%), the fledging success from 26.7 to 100% (on average 74.6%). In the long-term aspect, the breeding success was most often quite high, with the exception of 2001, 2009–2012 and 2014–2015, when this indicator was lower than the long-term average. Among terrestrial mammals, red foxes cause the main threat to adult horned puffins living on the island, as well as to their clutches and chicks descending to the sea, but foxes fail not render a significant impact on the state of the horned puffin population. Due to their small numbers, these predators control only a certain parts of the island, while horned puffins are dispersed almost throughout its territory, where in most cases they are safe from fox predation. Voles act as utilizers of already abandoned eggs. Slaty-backed gulls and ravens do not attack adult horned puffins, but willingly eat adult birds found dead, as well as dead or still alive chicks during their descent to the sea. Adult birds are also taken, albeit rarely, by Steller’s sea eagles.

Current frequency variation trends of dangerous winds in the Eastern sector of the Russian Arctic

The article aim is to identify mean values and change trends in the frequency of winds that pose a danger to navigation on shipping routes of the Laptev and East Siberian Seas which became evident in 2010–2021 period. In the period under review the winds were considered dangerous if their average hourly speed over the water surface at 10 m altitude exceeded 15 m/s. The factual material is based on information from the ERA5 global reanalysis. The research methodology involves the use of standard methods of mathematical statistics. A comparative analysis of the last two 12-year periods (1998–2009 and 2010–2021) has shown that the climate changes that happened in 2010–2021 significantly affected the wind regime of the studied region, which had consequences for shipping. In August, a significant decrease in the frequency of dangerous winds was recorded in the region, which generally contributed to the improvement of navigation safety by reducing storm risks. Opposite trends manifested themselves from September to December, which led to increased storm surge and a rise in the likelihood of ships icing, especially on the high-latitude paths of the Northern Sea Route and approaches to the Long Strait. The decrease in the frequency of winds, revealed in January and April, contributed to the preservation of a stable ice cover and stable difficult navigation conditions in these months. The persistence of the identified trends in interannual changes in the wind regime in the region under consideration in the future is not guaranteed. Therefore, the development of the existing network of Arctic weather stations remains an urgent problem for shipping.

Numerical Modeling of Local Scour in the Vicinity of Bridge Abutments When Covered with Ice

The occurrence of bridge collapse is frequently attributed to the prevalent erosion in the vicinity of bridge abutments. Accurate determination of the maximum scour depth in the vicinity of bridge abutments is imperative to ensure a secure and reliable bridge design. The phenomenon of local scour at bridge abutments can exhibit significant variations when compared to open-flow conditions, primarily due to the additional obstacle posed by the presence of ice cover. Research has demonstrated that the erosion of bridge abutments is more pronounced in the presence of ice. The vertical velocity distribution has a direct impact on both the bed shear stress and the resulting scour geometry in ice-covered conditions. This study aims to analyze the effects of flow through open channels and covered flow conditions on the local scour process around semi-circular and square bridge abutments using FLOW-3D V 11.2 software. The utilization of the volume of fluid (VOF) approach is employed for monitoring the free surface, while the Reynolds averaged Navier-Stokes (RANS) equations and the RNG k turbulence model are employed for simulating the flow field in the vicinity of bridge abutments. The sediment transport equations formulated by Meyer-Peter and Müller were employed for the purpose of simulating the movement of sediment particles. The numerical simulation results are compared with the experimental results. The result shows that the presence of ice cover and its roughness can increase the maximum scour depth both in numerical and experimental studies. The results also indicate that the maximum scour depth is located at the upstream section of the bridge abutments. These findings demonstrate the ability of the numerical model to predict the occurrence of local scour in the vicinity of bridge abutments under conditions of ice presence.

Local Scour around Side-by-Side Double Piers in Channel Bends under Ice-Covered Conditions—An Experimental Study

The pier scour process is normally intensified in the presence of an ice cover, which poses risks to the longevity and safety of bridges. In the present study, the impact of the densimetric Froude number, locations, and pier spacing of side-by-side piers on the local scour depth under ice-covered flow conditions were investigated based on clear water scour experiments in an S-shaped laboratory flume. The results demonstrated that the local scour at piers along the convex bank was more substantial than that along the concave bank when other factors stayed identical. The densimetric Froude number clearly has more impact on local scour at piers along the convex bank than that along the concave bank. Different from the mechanism of the pier scour in a straight channel, the scour depth around a pier along the convex bank in the S-shaped flume increases as the distance between two piers (or pier spacing) increases, while it decreases around the piers along the concave bank. Similar scour patterns were observed when the side-by-side piers were installed at different bend apex cross-sections. The maximum local scour depths at piers along the convex bank measured at different bend apex cross-sections were relatively unchanged when other influencing factors were held constant. However, the maximum scour depth around piers along the concave bank decreased as the bends increased toward downstream.

Suspended-sediment transport related to ice-cover conditions during cold and warm winters, Toudaoguai stretch of the Yellow River, Inner Mongolia, China

The presence of winter ice in cold regions changes the water level, flow rate, velocity distribution, and other parameters of the river, which in turn affects the sediment concentration and channel evolution. Based on data obtained from Toudaoguai Hydrological Station from 1959 to 2021, this study examines the characteristics of the ice regime during cold and warm winters and the water and sediment transport processes along the Yellow River in Inner Mongolia in the context of climate change. The Mann–Kendall test and trend analysis were applied to define the years of temperature mutations and their trends, and the temperature mutation point was determined to be the 1987/1988 season. The study considers the effect of climate change on the combination of hydrological and hydraulic conditions. Therefore, trends in suspended sediment transport, ice type formation, water discharge, and storage in different ice flood seasons (November 1 to March 31, from 1998 to 2021) were attained. Based on the cumulative negative air temperature, winters were categorized into three types, warm, normal, and cold (52.2%, 17.4%, and 30.4%, respectively). Strong and weak grades further divide cold and warm winters, and statistical analyses were used to examine the characteristics of ice, water discharge, channel storage, and sediment transport. The duration of open water, freeze-up, ice cover, and breakup periods were calculated, and the relationship between the suspended sediment transport rate and discharge rate in these various ice periods was defined. The obtained relations show that the suspended sediment rate during the ice cover and first drift was smaller than that during the open water and post-breakup conditions. For the ice cover period, the sediment transport rate was on average approximately four times smaller than the freeze-up condition and six times smaller than the open water condition. The reduced sediment transport rate in the freeze-up period can be attributed to the weakened vertical turbulent mixing and increased flow resistance.

Assessing the Parameterization of RADARSAT-2 Dual-polarized ScanSAR Scenes on the Accuracy of a Convolutional Neural Network for Sea Ice Classification: Case Study over Coronation Gulf, Canada

Arctic amplification has many impacts on sea-ice extent, thickness, and flux. It becomes critical to monitor sea-ice conditions at finer spatio-temporal resolution. We used a simple convolutional neural network (CNN) on the RADARSAT-2 dual-polarized ScanSAR wide archive available over Coronation Gulf, Canada, to assess which SAR parameter improves model performances to classify sea ice from water on a large volume of data covering 11 years of ice and surface water conditions. An overall accuracy of 90.1% was achieved on 989 scenes of 100% ice cover or ice-free conditions. An accuracy of 86.3% was achieved on the last year of data (134 scenes) which was kept out of the training process to test the model on an independent dataset. A better accuracy is obtained at lower incidence angles and the HH polarization provides the most information to classify ice from water. To achieve the best accuracy, the incidence angle and the noise equivalent sigma-nought had to be included as input to the model. A comparison done with the ASI passive microwave product shows similar errors in total sea ice concentration when using the Canadian Ice Service regional charts as reference. Nonetheless, errors from both datasets differ and the CNN outputs show greater potential to reduce masked areas, given the better spatial resolution, enabling data classification closer to land and identify features not captured by the ASI dataset.

Low-temperature heat transfer and stress analysis of LNG loading arm pipeline supports

The pipeline support is a complex component structure in liquefied natural gas (LNG) loading arm. In order to study the impact of ultra-low temperature conditions on the mechanical performance of pipeline brackets, the heat transfer analysis and thermal stress calculation of the pipeline support of the LNG loading arm are carried out under low-temperature conditions in this paper. Based on the principle of steady-state heat transfer, the finite element method is used to study the sensitivity of ambient temperature to heat transfer results of pipe support, the results show that the heat dissipated by the duct support is proportional to the temperature difference. The temperature field distribution of the pipe-bundle rib on the duct support under ice-free and ice-covered conditions is analyzed, and two different paths are selected to study the temperature distribution law of the structure, and the conclusion that the ice has the effect of cooling is drawn. Finally, based on the temperature field distribution results obtained by the heat transfer analysis, the low-temperature stress analysis of the pipe support is carried out. According to the thermal stress results, the corresponding improvement measures are proposed. It provides some guidance for the structural design of the loading arm.

The impacts of near-bed flow characteristics on river bed sediment transport under ice-covered conditions in 2016–2021

Global climate change has been projected to affect hydrology, the ice-covered flow period and river morphology (including changed sediment transport conditions) in northern high-latitude regions. To understand the impact of the expected shortening of the ice-covered period on bedload transport, one needs to understand the present sediment transport in these high-latitude rivers with annually occurring ice cover. Thus, the aims are (1) to define the impacts of ice cover on near-bed flow characteristics during hydrologically varying years, and (2) to analyse the impacts of these mid-winter flow characteristics on the bed sediment transport potential. The analyses are based on Acoustic Doppler Current Profiler (ADCP: 2016–21) and Acoustic Doppler Velocimeter (ADV: 2020–21) measurements performed in mid-winter ice-covered conditions of the sandy and small (circa 20 m wide) Pulmanki River in northern Finnish Lapland.Despite the ice-covered river conditions in winter, sediment transport occurs even during these harshest mid-winter conditions. The critical velocities and shear velocities of mid-winter conditions were exceeded in winters 2016–2021, and bedload transport occurred according to bedload measurements. Three different situations occurred regarding the bed sediment transport and near-bed velocity conditions: (1) high measured mid-winter discharges indicate high velocities throughout the meander bend; (2) low measured mid-winter discharges cause low near-bed velocities throughout the meander bend; (3) winters having intermediate discharges indicate near-bed velocities and sediment transport potential being higher at the upstream inlet and apex sections of the meander bend but clearly lower downstream of the apex. The confinement by the river ice cover, i.e. bottom-fast ice, explains the velocity variation. The near-bed velocities were the highest at the upstream inlet section of a symmetrical meander bend, where the measurement cross-sections were narrower and shallower. The velocities were the lowest downstream of the apex, where the channel changed from relatively narrow to wider and deeper.

Thermal Sensitivity of High Mountain Lakes: The Role of Morphometry and Topography (The Tatra Mts., Poland)

This study presents the results of a 5-year monitoring program of ice cover, water temperature, and local meteorological conditions carried out in three reference lakes in the periglacial zone of the Polish Tatra Mountains. On the basis of this information, the relationships between the weighted mean water temperature of each of these lakes and the air temperature, wind speed, precipitation, and ice–snow cover in the summer, spring, and autumn seasons, as well as year-round, were described, and the roles of the morphometry of lakes and the topography of their catchments were determined. It was found that the sensitivity of the lakes to climate warming increased with a decrease in their area/depth and shade, and with an increase in altitude and the share of wind-blown snow in the formation of the ice–snow cover. An increase in the mean annual air temperature does not necessarily translate into the warming of lakes, but, paradoxically, may result in their cooling. The current climate may not be best reflected by the most sensitive lakes, but rather by the largest ones located in the subalpine zone.

Estimation of maximum scour depth around bridge piers under ice-covered conditions using data-driven methods

The scouring around bridge foundations is a significant concern in civil engineering. Several research has been conducted experimentally and numerically to study the maximum scour depth around the foundations of a bridge in open channel conditions. In cold regions, where ice forms on lakes, reservoirs, and rivers, the interaction between ice and hydraulic structures is further complicated. The flow distribution varies significantly leading to deeper and larger scouring around bridge foundations. The present study took advantage of the data-driven methods to investigate the impacts of ice conditions to maximum scour depth. In total, 96 datasets were extracted from previous studies. The M5 decision tree, Genetic Expression Programming (GEP), and Particle Swarm Optimization (PSO) were used in data analysis. The models were developed using the train-and-test approach to avoid over-training. The mentioned developed models were further compared with a previous empirical equation associated with the prediction of maximum scour depth around piers under ice conditions. Finally, a sensitivity analysis method was applied to evaluate the performance of the data-driven models. It was found that the approaching velocity and pier diameter play the most crucial role in determination of the maximum scour depth. The result is generally in agreement with those of previous experimental studies.

Impacts of sea ice on marine dynamics in western Laizhou Bay, Bohai Sea

The Bohai Sea is a region with wintertime sea ice development and high levels of human economic activity, where sea ice has a powerful destructive effect on maritime transportation and ocean engineering. In the Bohai Sea, sediment resuspension caused by waves and currents has not previously been systematically studied during periods of ice cover. In the winter of 2009–2010, severe ice conditions with a recurrence period of 30 years occurred. In this study, wave, residual water level (RWL), residual current (RC), and suspended sediment concentration (SSC) data were collected by two seabed-based observation stations (QD12 and QDG2) for one continuous year during both ice-covered and ice-free conditions. The data were systematically compared and analyzed. Generally, the results showed that sea ice coverage had a clear suppressing effect on the significant wave height (Hs) and RWL. Hs decreased by almost 50%, and RWL decreased by 0.19 m and 0.10 m during ice-covered conditions at two stations. Sea ice coverage had a suppressing effect on the sediment resuspension due to a reduction in wave induced shear stress. The reduction of sea level and SSC was mainly reflected in the decrease of fluctuation amplitude and overall magnitude, and the suppression effect was more obvious in conditions of strong wind. The RC velocity varied during periods of ice cover in Laizhou Bay. Sea ice enhanced RC velocity during the destruction period. The RC velocity increased dramatically at station QD12 probably due to the long length of the destruction period, but decreased slightly at station QDG2 possibly due to a shorter destruction period and the blocking of Weifang Port. The enhanced RC in the destruction period carrying broken ice caused significant damage to coastal engineering projects. The suppressing effects of sea ice on Hs, RWL, and sediment resuspension, and the strengthening effects on RC velocity were both closely related to the wind speed and direction. This study reveals the effects of sea ice on local hydrodynamics and sediments, providing important reference values for the generation and disappearance of sea ice in mid- and high-latitude bays under the background of dramatic global climate change.