Abstract: In order to optimize the operation mode of reservoir groups in the Middle and Lower of the Yellow River, and to give full play to the advantages and potential of the water-sediment joint regulation of reservoir groups and river channel, taking the reservoir groups and river channel in the Middle and Lower of the Yellow River as the research objects, the method of joint dynamic regulation of reservoir groups and river channel was studied, and the mutual feedback index, mutual feedback model, regulation principle and application of joint dynamic regulation of reservoir groups and river channel were constructed. In this way, we developed a water-sediment joint regulation simulation model of reservoir groups and river channel, and analyzed regulation effects of the current project in the Middle and Lower of the Yellow River. The results show that under the scenario of 800 million to 300 million tons of incoming sediment of the Yellow River in the future, the water-sediment joint dynamic regulation of reservoir groups and river channel comprehensively takes into account the reduction of siltation in the reservoir and the river course, and can extend the sediment retention period of the reservoir by 4 to 9 years. In a relatively long period of time, the coordination degree of the water-sediment relationship entering the downstream has been improved. The total siltation of the downstream river channel is less, and the minimum bank-full discharge of the river channel has increased by 200—250 m3/s.
Abstract: The exploration of variation trend of ground water resources is basic work to identify groundwater environmental problems and strengthen groundwater resource management. Based on the data of previous evaluation results of water resource survey and water conservancy statistical yearbook from local water conservancy departments, the change of groundwater resources from 1956 to 2016 and its influencing factors were analyzed. In addition, the causes of groundwater resource variation were investigated. The results showed that the amount of groundwater resources declined from 1956 to 2016 in the Xinjiang plain area. The dynamic variation of groundwater recharge was featured with stable natural recharge. Moreover, the surface water conversed recharge had a dramatically shrunk. Analysis from the structure of groundwater recharge showed that the significant decrease in canal seepage resulted in the decrease in groundwater resources, the increase in river seepage offset the decrease of groundwater resources. The increase in irrigation water consumption in plain area, which was led by the expansion of irrigation area, resulted in the decrease in groundwater resources. The impact of human activities on groundwater resources is greater than that of climate change.
Abstract: China has a very large number of reservoirs, and the operation of high-density reservoir networks impacts the terrestrial water cycle and the land-atmosphere moisture and energy exchange, which brings challenges to the understanding of hydrological processes and the hydrologic simulation and forecasting. In this regard, this study focuses on the Poyang Lake basin (PLB) and over 1000 reservoirs in the basin, and developed a reservoir network scheme in terms of the reservoir water balance, reservoir release rules, and routing methods with the sectioned two-dimensional diffusion wave equation. The scheme was then fully coupled to the land surface-hydrological model CLHMS through surface water, subsurface water, evapotranspiration and energy balance. Results indicate that the scheme can well capture the reservoir operation, and can enhance the accuracy of streamflow simulation; the reservoirs in the PLB can decrease the runoff by 3.7%—6.0% in the wet season, increase the runoff by 5.9%—12.6% in the dry season, and decrease the multi-year average runoff by 0.6%—1.5% for the Gan, Fu and Xin River. Spatially, reservoirs have a more prominent regulating effect on the streamflow in the middle and northern part of the basin. The newly modified land surface-hydrologic model in this study can provide an analyzing tool and model basis for multidisciplinary research of atmosphere, hydrology and water resources, thereby supporting the sustainable use of water resources in areas under changing environment.
Abstract: There are some problems in the current mathematical model of the optimal operation of reservoir floods, such as continuous adjustments of the discharge gate and sudden change in discharge between time periods. In response to these problems, the model of the optimal operation of reservoir flood control is divided into the instantaneous outflow model and the constant outflow model. In a basic flood control system consisting of a reservoir and a flood control station, with a constant outflow rate considered the decision variable, a compensative reservoir flood control regulation is developed through the confluence curve of the Yangtze Water Resources Commission; this system can meet the requirements of refinement and safety. Compared with the instantaneous outflow model, the results of the constant outflow model show that the flood storage capacity decreased by 0.05%—0.18%, while the maximum discharge shows the behavior of both increasing and decreasing, indicating that the constant outflow model is not inferior to the instantaneous outflow model. At the same time, the results reveal that the regulation of secondary compensation reduces the flood control storage capacity by 10.6% compared with that obtained with the equal-storage operation model; this result provides a new method for determining the flood control storage capacity of a reservoir.
Abstract: Land use (LU) change and large-scale exploration and utilization activities of water resources have resulted in apparent disturbance on the hydrologic circle in the Sanjiang Plain. To identify the water balance characteristics and problems, this paper, based on the hydrologic baseline model, which can reflect the continuous change of land use from 2000 to 2014 (dynamic LU scenario or actual scenario), established a hypothetical model and a predictive model to simulate the hydrologic processes under the 2000 LU (2000 static LU scenario) and the 2014 LU (2014 static LU scenario), respectively, by replacing the LU data of the baseline model, and then compared the simulated water balance in the three scenarios. The results showed that if active LU control measures were taken since 2000, meaning the LU kept constant since 2000, the dependence on external water resources would have been effectively reduced compared to the actual scenario. The groundwater overdraft problem could be largely alleviated, and the groundwater storage in plain areas could even increase by 308 million m3/a in the following 15 years. However, if the LU control measures were implemented after 2014, meaning the 2014 LU was used for the whole simulation period, it would cause the annual groundwater deficit in the plain areas to be as much as 1426 million m3. The water storage in the whole region would have turned from positive to negative, with an average annual deficit of 425 million m3. To achieve water balance at various levels in the Sanjiang Plain, it is imperative to carry out more active allocation of water resources and construction of relevant water projects while taking immediate measures to contain excessive growth of high-water-consuming LU types.
Abstract: The lack of flood disaster data in many cities has led to an insufficiency of effective means to quantify flood losses in these cities. To meet the increasingly severe risk management requirements of urban flooding, there is an urgent need of implementing a quantitative assessment method for quantifying the flood losses in cities lacking disaster data. The method of "factor variation-dynamic matching-objective-driven-scenario fitting" was proposed to construct the flood loss rate functions with lack of data. In this study, based on the idea of equiproportional substitution, a variance analogy factor was constructed using multiple reference objects and multiple characteristic indicators; a dynamic analogy method was established to form a transplantation sample matrix to minimize the coefficient of variation; the water depth-loss rate fitting sequence was determined to maximize the probability of beta distribution; multiple fitting scenarios were set, and the preferred flood loss rate function was selected with the criterion of maximizing the fitting correlation coefficient. Taking Zhengzhou City as an example, the flood loss rate functions of 4 land use types were simulated. The results demonstrated that the proposed method for establishing flood loss rate function in cities lacking data was feasible; the characteristic combination indexes showed dynamic variability and the fitting effect of multiple-function combinations was optimal.
Abstract: Bank erosion in the seasonally frozen river (SFR) is subject to the coupling effects between hydrodynamic forces and frost heave/freeze-thaw, and the mechanism is complex. Bank erosion plays an important role in channel evolutions of the SFR. Taking the downstream near dam section of the Dadingzishan Navigation and Hydropower Project in the mainstream of the Songhua River as an example, a bank erosion model coupling hydrodynamic forces and frost heave/freeze-thaw interaction was developed. Bank erosion and fluvial processes in this typical SFR were simulated by the numerical model. The results indicated that the lateral erosion at the bank toe was mainly controlled by hydraulic forces. The cracking depth of the riverbank increased due to the frost heave effect, and the mechanical strength of riverbank soil reduced because of the freezing and thawing process, which has great effects on the stability of riverbanks. The simulation results of bank erosion were in agreement with the measured data, which demonstrated that the numerical model could simulate the complex channel evolution processes caused by river bed scour as well as bank erosion. This study could provide technical support for the in-depth study of bank erosion and channel evolution in the SFR.
Abstract: Sediment discharge in the Jingjiang reach has sharply reduced since the Three Gorges Project operation, and the channel has been scoured by the clear water in order to recover the sediment transport capacity. However, the recovery rate of nonuniform suspended sediment was different with the different bed material compositions along the Middle Yangtze River. Therefore, the equation of settling distance of nonuniform sediment is derived, based on the theories of Markov stochastic process and sediment motion. Then, according to the definition of saturation recovery coefficient (α) based on the diffusion theory of suspended sediment, the formula of grouped saturation recovery coefficient (αi) is modified using the equation of settling distance; However, it ignores the effect of bed material composition (BMC) on suspended sediment recovery. For the actual process of sediment transport in the Jingjiang reach, a formula of αi is then proposed with the effect of the BMC being considered. These results show that: ① The value range of αi in this study was 0.12—0.27 at Shashi and Jianli when the influence of the BMC was not taken into account, but it became to the range of 0.000 3—0.171 8 and 0.003 5—0.157 9 respectively when considering the BMC effect; ② Among αi of different sediment groups, the relationship of αif for fine sediment > αim for medium sediment > αic for coarse sediment existed when the BMC effect was not considered, but the relationship of αif < αim < αic existed when considering the influence of BMC; and the recovery rate of suspended sediment at Shashi was higher than that at Jianli except for the recession period; ③ The variations of αi at Shashi and Jianli were sensitive to different groups during different periods, in which αi during the flood period was higher than the value during other periods. Through comparation and analysis, the proposed formula in this study can predict the value of αi for the Middle Yangtze River well, and it also providing a basis for further research on the recovery mechanism of suspended sediment in the reach downstream of the Three Gorges Dam.
Abstract: The hyporheic zone is a region where surface and subsurface water mix in rivers. It is an important area for the exchange of mass and energy and an essential habitat for aquatic organisms. However, the deposition of colloidal particles in the hyporheic zone can modify the hydrodynamics and ecological environment of the river system. Through recirculating flume experiments and numerical simulations, this paper aims to investigate the transport of colloidal particles between stream and streambed, and clarify the pattern of colloidal particles' deposition in the hyporheic zone as well as the influence of different factors over particles' deposition. The results show that the colloidal particles in the overlying water will gradually retain in the streambed and accumulate in the shallow layer. The horizontal distribution of the retained particles tends to be higher on the stoss-side and lower on the lee-side. Hyporheic exchange, settlement of particles and retention of streambed are 3 most important factors in the deposition of colloids in the hyporheic zone. This paper can be helpful for understanding ecological and environmental functions of colloidal particles in hyporheic zone, and it can provide theoretical support for environmental and ecological restoration and health management of rivers.
Abstract: The main objective of this study is to investigate the morphological response and variability in the wavelength, height, steepness of bed forms developed over a quasi-uniform, coarse-sand bed under unsteady flows, with zero sediment feed condition specified at the upstream boundary. A series of smooth, bell-shaped hydrographs are generated within a titling flume, each defined parametrically by their shape (η), unsteadiness (ΓHG) and total water work (Wk). By contrast, the bed forms generated in the sediment bed are quantified through their wavelength (λ), height (D) and steepness (ψ). Experimental results indicate that different categories of bed forms, such as dunes, alternate bars, or transitional structures, developed on the bed surface over the hydrograph duration. A close examination of relative importance of three hydrograph's parameters (i.e. η, ΓHG and Wk) on bed-form dimensional descriptors (i.e. λ, D, ψ) reveals that the flow unsteadiness and total water work appear to be the primary and second-order control on bed-form category developed and their overall magnitude, whereas the hydrograph shape (η) appears to have a minimal impact. Based on this knowledge, a constitutive model to describe the effect of unsteady flow hydrographs on the bed-form categories and magnitude is developed from the results in the present study.
Abstract: River connectivity, a fundamental property of river ecosystem, is affected by human activities as well as seasonal differences. A one-dimensional river network mathematical model was established to evaluate the impact of riverbed evolution and fluvial-tidal dynamics change on river connectivity during flood season in the lower reaches of Dongjiang River from Boluo to Shilong and Dongjiang River Delta (DRD) from 1999 to 2009. The results show that the loopiness of the study area was low, the linking sharing index was high and node connection rate was greater than 1, which indicated a relatively high topological connectivity. Noticed that the topological connectivity did not change with the uneven riverbed downcutting and fluvial-tidal variation. However, the dynamic connectivity has changed significantly with the uneven riverbed downcutting and fluvial-tidal variation. Due to the riverbed downcutting, fluvial dynamics decreased and tidal dynamics increased, with the decrease in the water conveyance capacity and dynamic connectivity of the study area. The results obtained from this study provides scientific supports for the research on water security such as flood control, water conservancy project planning and water ecological environment in the DRD.
Abstract: Kelvin-Helmholtz (KH) vortices, which exist in submerged vegetated open channels, have direct impacts on the energy exchange and mass transport in the flow. In laboratory experiments carried out in a flume whose bed is covered with rigid model vegetation, we use Particle Image Velocimetry (PIV) to measure the instantaneous velocity and vortex fields and examine the characteristic geometry of KH vortices, including their positions and heights. Meanwhile, the frequency of KH vortices is analyzed using the wavelet transform method and the velocity time series obtained with 3-D Acoustic Doppler Velocimetry (ADV). The influence of submergence on the position, height and frequency of the KH vortex is explored as well. Experimental results indicate that the upper and lower boundaries of the KH vortex are in agreement with those of the mixing layer which can be computed according to energy distribution. The upper boundary is about 0.7—0.8 times the water depth, while the lower boundary fluctuates around a value dependent on vegetation density. The frequency of KH vortices is between 0.14—0.20 Hz in the present experiments. With the increase of submergence, the upper boundary of the KH vortex moves upward, the lower boundary does not change much, while the height and frequency increase.
Abstract: High density saltwater discharge occurs frequently and exhibits complex hydrodynamic characteristics during seawater desalination. To study the hydrodynamic characteristics of saltwater jet under wave action, a three-dimensional computational fluid dynamics mathematical model of negative buoyant jet with vertical round was developed under regular waves. The model was validated via comparison with the experimental data. The comparison indicated good agreement between the model and experimental data. The diffusion characteristics of negative buoyant jet, the three-dimensional time average velocity, and the instantaneous concentration characteristics were analyzed. The results indicated that the wave height and period contribute slightly to the decay index of the dimensionless average vertical velocity in the jet axis. However, they affect the decay coefficient. An increase in wave height or wave period leads to an increase in velocity half-width, the decay coefficient of dimensionless average vertical velocity on the jet axis decreases. Hence, it contributes to jet diffusion in ambient water. Additionally, the wave to jet momentum ratio is used to conduct the equations of the dimensionless average velocity decay coefficient and the half-width of mean characteristic velocity, which can provide some reference for practical engineering applications of the negative buoyant jet.
Abstract: Rapid urbanization has significantly changed the spatial feature of the urban underlying surface, which can have significant impact on runoff processes. This study summarizes the research advances on the impact of the spatial features of the urban underlying surface on the surface runoff process. Herein, two types of spatial characteristics—impervious surface and microtopography—were investigated, by combing the spatial features of the urban underlying surface and its characterization methods. Moreover, spatial features of urban underlying surface are discussed from the perspectives of the variation of impervious rate and spatial distribution of impervious surface, as well as numerical simulations and physical experiments. In addition, the key points of research on the impact of the spatial features of the urban underlying surface on the surface runoff process in the future are highlighted. Overall, this study mainly includes the analysis of influence mechanism, the identification and sensitivity analysis of main control spatial features parameters, and the adaptive response to urban hydrological effects, thereby providing scientific reference for the analysis of urban hydrological effects, and the prevention and control of urban flood disasters under rapid urbanization.
Abstract: The understanding of the incipient motion of cohesive sediment is a great challenge in the research of sediment incipient motion. It is recognized that cohesive forces are critical in determining the characteristics of cohesive sediment incipient motion. Based on the analysis of current research, cohesive forces are summarized in two main categories (containing six types) according to the formation mechanism, and the formation mechanism and influencing factors of the typical electric double layer force and EPS cohesive force are explored. The impact of cohesive forces on cohesive sediment incipient motion is examined in terms of two aspects, i.e. sediment stability and incipient motion modes. Based on the discussion above, it is concluded that current studies generally focus on one certain cohesive force and seldom take the interaction and comprehensive effect between cohesive forces into consideration, lacking systematicness. Moreover, most of the current research achievements based on measured data are empirical and short of quantitative relationship derived from mechanism level, suffering from a theoretical deficiency. It is suggested that the various cohesive forces should be considered comprehensively in line with the specific sedimentary environment. What's more, the formation mechanism research of cohesive forces should be concerned fundamentally, and the quantification research of cohesive forces needs more attention.