Abstract: Ground ice is a distinguishing characteristic of permafrost soil.As permafrost profoundly influences the hydrology, ecology and engineering design in cold regions, it is important to accurately estimate the underground ice reserves of permafrost.Thus, this study investigated landforms and their genetic types in the source area of the Yellow River.The lithologic composition and water content were analyzed using field data from 105 boreholes.The underground ice reserves at depths of 3.0-10.0 m were estimated in the source area of the Yellow River.This research also focused on the spatial distribution of shallow underground ice.The results show that ① the total amount of ice reserves at depths between 3.0 and 10.0 m was approximately (49.62±17.95) km3 and the ice reserve per unit was (0.293±0.107) m3; ② in the horizontal direction, high ice contents were associated with lacustrine-marshland plain and periglacial hill landforms, while low ice contents correlated with erosional platform and alluvial-proluvial plain landforms; and ③ in the vertical direction, high ice contents were observed close to the upper limits of permafrost and gradually decreased with depth.
Abstract: The northern Loess Plateau is characterized by dense gullies and fragmented topography. The status of soil water shortage in this region is complicated under the combined effects of topography and vegetation. In this research, we designed 15 observational sites on 3 dividing waterlines in the gully area of Liudaogou catchment in Shenmu country. Based on long-term observation with neutron probe, we studied the spatial-temporal distribution of deep soil moisture as well as the characteristics of dried soil layer. The specific results were showed as follow:① Soil moisture was in deficit in 0-3 m soil layers in the growing season, then it was recharged above 1.2 m depth. Soil moisture under 1.2 m depth did not recover and soil water deficit was serious in 2.6-6.4 m soil layers. ② The profile distribution of soil water content and relevant depths of extreme values as well as the occurred range of dried soil layers were inconsistent among different observational points. Moreover, the profile distribution of dried soil layers along the dividing waterline was discontinuous. ③ The thickness of dried soil layers varied within the range of 0.4-8 m, the average formed depth of dried soil layer and mean soil moisture within the dried soil layer were 2.03 m and 9.03%, respectively. The former had negative linear correlations with the latter two quantitative indices. Compared with the average status of the Loess Plateau, dried soil layers in the gully area was more prominent. These results were expected to provide help for comprehensively evaluating the function and status of soil water reservoir in gully area.
Abstract: Aiming to investigate the influence of design storm pattern on urban flood inundation, this work applies a numerical model to simulate the hydrological and hydrodynamic processes and analyze urban flood inundation patterns in Xi'an New Area, Shaanxi Province, China. Design hyetographs with different position coefficients for the storm peak and return period are considered. By comparing the simulation results in terms of water depth and inundation extent, it is found that the lower position coefficients of storm peak with the return period less than 20 a may cause more total inundation, but opposite conclusion may be drawn for the storms with the return period greater than 20 a. Apart from the return period of 2 a, the storms with a higher position coefficient of storm peak will result in more total inundation, but the more serious Ⅳ-level inundation is reduced. With a lower position coefficient of storm peak and longer return period, the lag between the times to the peak inundation and to the storm peak becomes bigger. This work demonstrates quantitatively the effects of design storm pattern on urban flood inundation. The research may help make more informed decisions on urban flood management.
Abstract: In order to further improve the practicality of moment analysis theory on the study of the transport characteristics of wetted pattern under tow-dimensional infiltration of furrow irrigation, the effects of initial soil water content, water depth, bottom width and slope parameter on the spatial moment character parameters of soil wetted pattern under free infiltration were studied quantitatively by combination of numerical simulation and theoretical analysis method. The function relationship between the spatial moment character parameters of soil wetted pattern and the main influence factors was established. The results showed that the mass center of vertical soil moisture distribution is greatly influenced by initial water content, water depth and bottom width. The average dispersion of the horizontal wetted front is mainly influenced by initial water content, water depth, bottom width and slope parameter, while the average dispersion of the vertical soil wetted front has higher sensitivity to initial water content and water depth. Then, the reliability of the model was further verified through several different soil textures. The results showed that the values of spatial moment character parameters estimated by the proposed model at different infiltration times agree well with calculated values based on the simulation results by the HYDRUS software. The mean absolute values of the relative error of all combinations were lower than 8.5%, and there was no significant difference, which indicated the proposed model can be used to estimate the spatial moment character parameters of soil wetted pattern under furrow irrigation with a high reliability. The results can provide theoretical basis and technical support for the design and management of furrow irrigation.
Abstract: Hillslope debris flows are the major geological hazards in East China. It is very important to predict these dangerous phenomena. Three groups of conditions related to topography, geology and hydrology have influence on the triggering of these hillslope debris flows. We isolated and analyzed the influence of the topography on the triggering of hillslope debris flows in catchments with almost identical hydrological and geological conditions and propose a new so called T-condition as a topographical indicator which is a combination of slope angle, upslope contributing area and cross-section and free-face of a (potential) hillslope debris flow. The T-condition can be used to define threshold values for possible hillslope debris flow development. Higher T-condition values are related to higher probabilities of debris flow events. An R-condition is used as a rainfall indicator, which is a combination of the antecedent one hour rainfall, the antecedent cumulative rainfall and the annual rainfall. Higher R-condition values are generally related to higher probabilities of hillslope debris flow events. The prediction condition P, which is the combination of T and R, gives a final indication of debris flow probability and it can be used to define threshold values for the hillslope debris flows.
Abstract: Vegetation in open channels has a significant influence on the characteristics of bed load movement. To date, studies of incipient motion of sediment in open channels with submerged vegetation have been restricted by limitations in statistical approaches and measuring equipment. Researchers have also neglected incipient motion of sediment in the presence of vegetation when deriving semi-empirical equations for the rates of bed load transport, and have generally considered it the same as that without vegetation, which is clearly inconsistent with, and does not represent, the actual conditions. In this study, we therefore studied the vegetation and sandy bed in a natural river to determine the characteristics of incipient motion of sediment within rigid vegetation on a movable bed. From the spatially averaged velocity, we then described the incipient motion of sediment under the water-vegetation interface. We found that there were three phases of incipient motion of sediment, namely static, partially in motion, and entirely in motion. We defined the incipient motion of sediment from the conditions for the third process. We derived a semi-empirical equation for the sediment incipient velocity in the presence of submerged vegetation from our experimental results, and found that, of the factors explored, the vegetation factor Fv had most influence on the incipient motion velocity of sediment with vegetation. For a given vegetation density, the average depth of the scour holes around the vegetation elements were linearly related with the spatially averaged velocity of the flow under the water-vegetation interface. These results demonstrate that our method gave reasonable estimates of the spatially averaged velocity for incipient motion of sediment.
Abstract: In order to calculate the flood risk in flood diversion zones under the condition of the operation of a diversion project, a mechanics-based based model of flood risk in flood diversion zones is proposed. The 2-D hydrodynamic module is used to simulate the processes of flood inundation in a flood diversion zone. A mechanics-based formula for the incipient velocity of a human body for toppling instability, the empirical formulas for flood loss of buildings and crops are adopted to evaluate the flood risks to flooded objects. Then the 2-D hydrodynamic module was verified against the two physical experimental data of flood flows, with a favourable agreement being obtained between the predicted and measured data. Finally, the proposed model was used to predict the flood inundation process and assesse the flood risks to people and property during the operation of the Jingjiang flood diversion zone. The results show the average loss rates of human body, building, rice and cotton would be 80%, 59%, 63% and 72% at 140 h. A mechanics-based method is adopted in the proposed model for flood risk analysis, which is better than empirical methods based on water depths in evaluating flood risk. It would be helpful for flood risk management and providing a reference to the operation standards in flood diversion zones, and could be applied to risk analysis of extreme floods such as flows of dam-break and landslide dam break.
Abstract: A finite volume model based on structured grids is proposed for numerical simulation of dam-break flow over complex terrains with irregular boundaries in the study. In the proposed model, HLLC's approximate Riemann solution is used to compute the flow flux based on the two-dimensional shallow-water equations with conservation. The spatial and temporal precisions of the model are increased to the second-order precision by the MUSCL-Hancock method. Slope source terms and friction source terms are discretized in order to guarantee the model's stability. A robust procedure is introduced to efficiently and accurately simulate the movement of wet/dry fronts and water flow characteristics of complex terrains with irregular boundaries. Finally, flume experiments, physical models and actual case computation are used to verify the proposed model. Numerical results of dam-break flow from different test examples are highly consistent with observations and numerical results obtained by existing models, indicating that the proposed model has the higher stability and precision for a wide range of applications.
Abstract: Nature-like fishways not only satisfies the migration needs of different fishes, but also increases the diversity of fish habitats in river channels. It is the hot research area, to which researchers pay much attention recently. For the complexity of the structure, the variability of cross section type, and the difficulty of roughness calculation at bottom and side slope, there is no accepted and perfected method to study the flow condition of nature-like fishways at present. This paper takes nature-like fishway of Xin'gan hydro-junction as research object. An integral physical model test with scale of 1:12 is established to explore the feasibility of flow conditions in fishway scheme. The results show that the research methods of technical fishways can be used to control the parameters of nature-like fishways such as bottom slope, bottom width, pool length, deviation rate, permeability, and so on. Then the integral physical model test with validation and optimization can be applied to guide the design of nature-like fishways. Compared to technical fishways, the velocity difference in nature-like fishways route is obviously influenced by size error of cross section and construction material. Especially, in the curved section of fishways, the deviation rate is affected by the curve, and the velocity is easy to be higher or lower than the one in the straight route. The research may offer a sound basis for engineering design, and also provide a frame of reference to study the nature-like fishways.
Abstract: It showed a very complex hydrodynamic process in tidal rivers. For making reasonable fine emergency plan, the scope, time and extent of pollution damage influence of sudden water pollution incident had been analyzed by EFDC model under different hydrological conditions in Shenzhen Estuary. It had put forward a method for accurately analyzing the dominant hydrodynamic factors in sudden water pollution incident in estuary. On this basis, the dominant hydrodynamic factors of pollutant transport and diffusion had been identified out by the spectrum analysis method based on Fourier transform, and UNIANOVA was used to corroborate the result. It suggested that the tidal hydrodynamic process was the main driving factors in Shenzhen River; but variation of pollutant concentration at each monitor cross-sections was closely associated with land runoff in sudden water pollution incident. It showed that runoff was the dominant hydrodynamic factor of pollutant transport for sudden water pollution incident in the tidal river.
Abstract: An experimental study was carried out on the round jet flow at different inclination angles in wave environment by using particle image velocity measurement and plane laser induced fluorescence techniques, comparing and analyzing the impact of discharge angles on instantaneous flow pattern, mean velocity field and mean concentration field of jet flow. The experimental result shows that changes in discharge angle have significant impacts on flow pattern, velocity distribution and mixing range of jet flow in wave environment. When the jet flow moves in the wave direction, the velocity profile of jet dominant region presents bimodal distribution, and the mixing range increases with the increase of discharge angle and then decreases when initial concentrations of 20%, 30%, 40% and 50% are reached. When the jet flow moves in the reverse wave direction, the jet flow velocity profile presents bimodal distribution which is not obvious, and the corresponding mixing range decreases with the increase of discharge angle. Under the combined action of wave traction and jet flow entrainment, the dilution effect of reverse jet flow is generally better than forward jet flow at the same angle between vertical line.
Abstract: To study the characteristics of mixing and stratification in the Modaomen Estuary, a three-dimensional numerical salinity model was established based on SCHISM and then calibrated against measured data. Combined with the theory of the water potential difference, the temporal and spatial variation characteristics of mixing and stratification in the dry season and stratification mechanism of a deep channel and shoal were studied. The results show that water stratification is the strongest during the neap tide and is the weakest during the medium tide. Saltwater from the sandbar to Guadingjiao is always highly stratified. Along-channel advection, along-channel depth-mean straining and vertical mixing are the main factors that influence the water stratification of the deep channel. While cross-channel advection, cross-channel depth-mean straining and vertical mixing are the main factors that influence the water stratification of the shoal. In addition, there is a relatively high dissipation of turbulent kinetic energy (TKE) at the surface and bottom of the water column and low TKE dissipation at the middle of it. There is an asymmetric flood/ebb tidal distribution, with the flood higher than the ebb.
Abstract: The inverted siphon is a commonly used hydraulic structure in water diversion projects.Therefore, research on the vertical flow velocity distribution in the upstream of the inverted siphon inlet is important to elucidating its hydraulic performance.The typical inverted siphon of the Tanghe River in the Middle Route of the South-to-North Water Diversion Project was taken as the research object.Generalized hydraulic model experiments were carried out, and measurements were performed to obtain the vertical velocity distribution in the upstream of the inverted siphon inlet under different combinations of water depth and flow discharge, using an acoustic doppler velocimeter.The experimental results demonstrated that owing to the influence of the inverted siphon inlet structure, the upstream vertical velocity distribution largely exhibited lower velocity at the top and higher velocity at the bottom.Moreover, for greater submergence and closer to the inverted siphon inlet, the aforementioned trend was more evident.Further, when the above vertical velocity distribution was represented using the open-channel logarithmic velocity distribution approach, its computing error exhibited a parabolic distribution.When the open-channel logarithmic velocity distribution formula was improved using exponential terms, a new modified formula was obtained, which can be employed to compute the vertical velocity distribution in the upstream of the inverted siphon inlet.
Abstract: In recent years, the problem of urban waterlogging has become more and more serious as the environment has changed through both climate change and urbanization. The fundamental assumption of stationarity in municipal engineering may be invalid because changing environments have changed the frequency and intensity of extreme rainfall in urban areas. For this reason, analysis of the impacts of changing environments on extreme urban rainfall and drainage infrastructure is important to urban water resources management, municipal engineering design, and disaster prevention and mitigation. The present study summarizes the advances in future projection of short-duration (sub-daily) rainfall and design criteria for urban drainage system and also reviews both the evolution of laws concerning urban short-duration rainfall and current research into studies of the impacts of changing environments on drainage infrastructure. We also explored the physical mechanism underlying the impact of changing environments on urban short-duration extreme rainfall. Besides, we summarize the methods for analyzing of impacts of changing environments on urban region and emphasized what type of future research is required:① strengthening physical mechanisms research focusing on impacts of climate change and urbanization on short-duration extreme rainfall; ② improving the capability of climate models to describe the interactions between urban land surface and local climate, and strengthen the applications of kilometer-scale convection-permitting models in urban areas; ③ strengthening the study of design criteria for urban drainage infrastructure in changing environments; and ④ comprehensively evaluating the impacts of changes in extreme rainfall and urbanization on urban drainage infrastructure including pipes' surcharges, pollution and water security.
Abstract: Using limited observation data of groundwater quality, models of groundwater pollution source identification can be used to estimate the locations, leakage rate, and the dominant processes of the pollution sources, which thus can provide a reference for formulating remedial schemes for groundwater pollution. Based on the principles and theories of pollutant movement and source identification, this paper presents an overview of existing mathematical methods, including direct methods (inverse particle tracing methods and regularization-based methods) and indirect methods (optimization-based and probability-based methods). The main problems in the application of these methods are ① the complexity of groundwater pollution source identification, ② groundwater organic contamination, and ③ the low efficiency of model calculation. Integrated research of soil-groundwater systems, instrumentation-based groundwater pollution monitoring, identification of NAPL pollutants, and GPU-based heterogeneous parallel computing will be the keys to groundwater pollution source identification in the future.