Tiejie Cheng’s research while affiliated with Hefei University of Technology and other places

River ice formation during the winter period is a common phenomenon for most rivers in the northern hemisphere. The combined effect of hydraulic, thermodynamic, and geometric boundary conditions results in a highly complex system when compared to open channel conditions, particularly in regard to ice cover and ice jams. These differences have a considerable impact on the evolution of river morphology, sediment transport, and the stability of hydraulic structures. The presence of ice cover and ice jam results in an increase in river channel roughness, which in turn changes the velocity and shear stress distribution in the riverbed. The present review summarizes the current state-of-the-art research on river ice, including field observation, experimental study, and numerical simulation. Finally, the review concludes with an overview of the current state of research in the field, accompanied by an analysis of the challenges that remain and suggestions for future research directions.

In winter, the water transfer channel of the Middle Route of South-to-North Water Transfer Project (MR-StNWTP) in China always encounters ice problems. The preciously simulation and prediction of water temperature is essential for analyzing the ice condition, which is important for the safety control of the water transfer channel in winter. Due to the difference of specific heat between water and air, when the air temperature rises and falls dramatically, the range of change of water temperature is relatively small and has a lag, which often affects the accuracy of simulation and prediction of water temperature based on air temperature. In the present study, a new approach for simulating and predicting water temperature in water transfer channels in winter has been proposed. By coupling the neural network theory to equations describing water temperature, a model has been developed for predicting water temperature. The temperature data of prototype observations in winter are preprocessed through the wavelet decomposition and noise reduction. Then, the wavelet soft threshold denoising method is used to eliminate the fluctuation of certain temperature data of prototype observations, and the corresponding water temperature is calculated afterward. Compared to calculation results using both general neural network and multiple regression approaches, the calculation results using the proposed model agree well with those of prototype measurements and can effectively improve the accuracy of prediction of water temperature.

Flow structure and channel bed deformation caused by double piers in a tandem arrangement under ice-covered flow conditions in a bent channel is more complicated than those around a single pier in a straight channel. Based on experiments in an S-shaped flume, the scouring phenomenon at double piers in a tandem arrangement under an ice cover has been conducted by varying pier spacing distance, bend apex cross section (BACS), and hydraulic parameters. Results show that, under identical hydraulic conditions, the variation trend of the scour depth in the vicinity of double piers in a tandem arrangement in a bent channel is similar to that in a straight channel. The deepest depth of scour holes at the upstream BACS is more than that at piers at the downstream BACS. At each BACS, the effect resulting from the interaction of double piers gradually decreases with the pier spacing distance. Different from the characteristics of local scour at double piers in a tandem arrangement in the straight flume, when the ratio of pier spacing distance to pier diameter (L/D) is more than 15, the horseshoe vortex generated by the front pier has negligible impact on the rear pier, and the maximum depth of scour hole at the rear pier scour hole is about 90% that of the front pier. Also, when L/D is higher than 15, the influence of the rear pier on the front one is negligible, and the scour hole depth at the front pier remains the same. However, this phenomenon occurs when the straight flume’s L/D is greater than 17.

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.

Ice jam, a unique hydrological phenomenon of rivers in cold regions, is a major cause of ice flooding. There are many different kinds of damage that can result from ice jams: e.g., blockage of the water flow, rising water levels that can flood farmland and dwellings, damage to hydraulic structures, and interruptions to shipping. The formation of an ice jam is influenced by various factors associated with different fields of study. The accumulation of an ice jam is thus a complex process worth investigating. However, previous studies seldom take account of ice discharge factors. This study carries out 29 tests on the accumulation of an ice jam, and discovers four kinds of phenomena: inlet ice that fails to submerge (case 1); thickening ice from upstream to downstream (case 2); thickening ice from downstream to upstream (case 3); and failure to form an ice jam (case 4). Two typical examples are used to detail cases 2 and 3. The authors suggest differentiating between the two cases using the longitudinal boundary line running through the point of the Froude number (Fr) = 0.119. Furthermore, the authors analyze the phenomena that make it difficult for an ice jam to form and suggest using the critical discriminant line to distinguish between cases 3 and 4. Combined with the longitudinal boundary line, a partition result diagram of the different accumulation features of ice jams is presented to differentiate between the four modes of accumulation of ice jams.

Ice jam is a unique hydrological phenomenon in rivers in cold regions. The appearance of an ice jam in a river results in an increase in the wetted perimeter of the flow cross-section, and thus an increase in flow resistance as well as water level. It may cause ice flooding sometimes. Similar to the “sand wave” phenomenon in riverbed, it has been observed in laboratory experiments that the waved-shape accumulation of ice particles (termed as “ice wave”) under an ice jam occurred. In this study, an Equation for describing the relationship between the approaching flow Froude number (Fr) and the ratio of ice jam thickness to flow depth (t/H) has been proposed. Taking the inflection point value of the equation under different flow depths, a characteristic curve has been developed to judge whether ice waves under an ice jam occurs. When the flow Froude number in front of an ice jam is below the value at the inflection point of the curve, the ice jam can maintain a mechanical stability within the ice jam thickness in a range from the lower limiting value to the upper limiting value, which were close to the ice wave trough thickness and the ice wave crest thickness, respectively. An Equation for calculating the ice wavelength has been derived and verified by using results of laboratory experiments. The relationship between the migration speed of ice wave and the ratio of ice discharge to water flow rate (Qi/Q) has been also analyzed. At last, case studies have been conducted with respect to ice accumulation in the St. Lawrence River, the Beauharnois Canal and the La Grande River. Results of case studies show that the shoving and ice dam have been dominated by mechanical factors, which would be accompanied by the ice wave phenomenon during the ice jam accumulation process. Results of case studies about ice accumulation in natural rivers also show that the relative thickness of an ice jam (t/H) of 0.4 is the criterion for assessing whether an ice jam in a river belongs to an ice dam.

Ice problems in channels for water transfer in cold regions seriously affect the capacity and efficiency of water conveyance. Sometimes, ice problems such as ice jams in water transfer channels create risk during winter periods. Recently, water temperature and environmental factors at various cross-sections along the main channel of the middle route of the South-to-North Water Transfer Project in China have been measured. Based on these temperature data, the heat balance state of this water transfer channel has been investigated. A principal component analysis (PCA) method has been used to analyze the complex factors influencing the observed variations of the water temperature, by reducing eigenvector dimension and then extracting the principal component as the input feature. Based on the support vector machine (SVM) theory, a new approach for judging the heat loss or heat gain of flowing water in a channel during winter periods has been developed. The Gaussian radial basis is used as the kernel function in this new approach. Then, parameters have been optimized by means of various methods. Through the supervised machine learning process toward the observed water temperature data, it is found that the air–water temperature difference and thermal conditions are the key factors affecting the heat loss or heat absorption of water body. Results using the proposed method agree well with those of measurements. The changes of water temperature are well predicted using the proposed method together with the state of water heat balance.

The interaction between the evolution of an ice jam and the local scour at bridge piers becomes much more complicated due to the evolution of both the channel bed and ice jam. Thus, research work regarding this topic has been hardly conducted. In the present study, experiments under different flow conditions with three different pier shapes were carried out. Through laboratory experiments, the development of scour holes around bridge piers under open flow, ice-covered, and ice-jammed flow conditions was compared. The results show that under the same hydraulic condition and with the same ice discharge rate (Qi/Q), the development of an initial ice jam with a local scour around bridge piers along the entire flume takes a relatively short time. However, it takes a longer time for an ice jam to achieve an equilibrium state. With the presence of a local scour at bridge piers, after an ice jam reaches an equilibrium state, the ice jam thickness, water level, and water depth for flow are relatively larger compared to that without a local scour at the pier. The equilibrium ice jam thickness around the pier is negatively correlated with the initial flow Froude number. When the development of an initial ice jam is dominated by a mechanical thickening process, the rate of the development of a scour hole around a pier is faster. On the other hand, when the development of an initial ice jam is dominated by a hydraulic thickening process, the development of a scour hole around a pier can be treated as a scour process under an ice-covered flow condition. An equation was developed to determine the scour depth around a pier under an ice-jammed flow condition by considering related factors such as the flow Froude number, ice jam thickness, and ice discharge rate. The results of this research can provide a reference for bridge design and safety protection, as well as the interaction mechanism of local scour and ice jam evolution.

Compared to the scour around a single pier, the local scour process around tandem double piers is much more complicated. Based on laboratory experiments in a flume, we conducted the scour process around tandem double piers under an ice-covered flow condition. The results showed that when the pier spacing ratio L/D = 2 (where L = the pier spacing distance, and D = the pier diameter), the rear pier (the downstream one) will intensify the horseshoe vortex process behind the front pier, and the scour depth around the front pier will increase by about 10%. As the pier spacing ratio L/D increases, the scour depth around the front pier will gradually decrease. When the pier spacing ratio L/D = 5, sediment scoured around the front pier begins to deposit between these two piers. To initiate a deposition dune between piers, the pier spacing distance under an ice-covered condition is about 20% more than that under an open flow condition. The results also showed that the existence of the rear pier will lead to an increase in the length of the scour hole but a decrease in the depth of the scour hole around the front pier. The local scour around the front pier interacts with the local scour of the rear pier. The maximum scour depth of the scour hole around the rear pier increases first, then decreases and increases again afterward. When the pier spacing ratio L/D = 9, the scour depth around the rear pier is the least. With an increase in the pier spacing ratio, the influence of the local scour around the front pier on the local scour around the rear pier gradually decreases. When the pier spacing ratio L/D is more than 17, the scour around the front pier has hardly any influence on that around the rear pier. The scour depth around the rear pier is about 90% of that around the front pier.

The formation, development and melt of ice in pumped storage reservoirs in cold climate are studied by numerical simulation. Based on the theory of ice hydrodynamics and the MFC module of Visual C++ 6.0, a mathematical model of ice regime of pumped storage power station in the form of dialog box was established, which includes the hydraulic calculation module, the temperature diffusion module and the ice sheet thermal fluctuation module. The model was applied in Pushihe pumped storage power stations and the results showed that the simulation results were in good agreement with the prototype observation results. The research results can provide effective technical reference for the selection of anti-ice operation mode and the reserve of frozen storage capacity of pumped storage power station in cold area in winter.