Abstract: In this paper, a permafrost cross-section at the northern slope of the Bayan Har Mountains in the source region of the Yellow River is studied. Based on the field observations, herein, the data has been collected from various sources including atmospheric precipitation, soil moisture, and supra-permafrost waterflow. According to the variations of the gathered data, the seasonal variability of soil hydrological processes in active layers is statistically investigated. In addition, the influence of freeze-thaw action on the hydrological process in an activity layer is numerically simulated by HYDRUS-1D software package. The obtained results are summarized in the following:① There is a close relationship between the supra-permafrost water flow and soil-water-heat at the slope scale. Using the variation of soil temperature in an active layer, the soil moisture and the supra-permafrost water flow are divided into four different phases based on the freeze-thaw action, including the frozen stability, the rapid thawing, the thawing stability, and the rapid frozen. ② Rainfall infiltration is regarded as the main driving force of soil hydrological processes in an active layer on the slope scale, as well as the freeze-thaw action in an active layer in which both are taken into account as major factors, imposing limitations. Due to the effect of freeze-thaw process in active layers, the precipitation in the freeze period decreases. In addition, due to the soil freezing, the soil water storage capacity reduces. Moreover, the soil water infiltration stops as well as the slope lateral flow diminish. Therefore, the soil moisture and the supra-permafrost water flow are regarded in a downward trend. Furthermore, the precipitation in the thaw period and the soil water storage capacity, due to the thawing of the soil, will eventually increases. It should be mentioned that the soil water infiltration and slope lateral flow increase; consequently, the soil moisture and the supra-permafrost water flow are taken into account in an upward trend. ③ The thickness of an active layer on the upslope is higher than that one on the downslope because of the effect of terrain slope, leading to changing the freeze-thaw action on the upslope which its rate is higher than that one on the downslope. Additionally, the variation of the soil moisture and the supra-permafrost water flow on the upslope is higher than that one on the downslope. Consequently, the soil moisture content on the upslope is lower than that one on the downslope, while the supra-permafrost water flow on the downslope is relatively stable.
Abstract: Remote sensing of snow information in arid regions of Central Asia can provide data support for the allocation and utilization of water resources in transboundary rivers and play an important role in the ecological security of major national strategies. In this paper, data fusion method was used to merge MOD10A2 and MYD10A2 data for cloud removal and extraction of snow cover. Snow cover data from meteorological stations were used to evaluate the snow recognition accuracy after cloud removal. Information of snow cover percentage (SCP) and snow day (SCD) was extracted and analyzed. Temporal and spatial variation of SCP under different elevation zones was analyzed by using digital elevation model (DEM). The results showed that:① The fusion of MOD10A2 and MYD10A2 data can effectively remove cloud and improves the accuracy of snow information extraction. ② During a year, the maximum SCP ranged from 55.7% to 77.4% and the minimum ranged from 1.6% to 2.9%. There was a clear regional difference in the rate of the decline of SCP during the snowmelt period, and the overall SCP showed a slowly increasing trend. ③ The overall SCD showed a slight downward trend, 32.2% region showed a downward trend, 30.7% region showed an upward trend, 36.9% of the region remained stable. ④ Under the altitude of 1 000 m, the annual variation of SCP during the year is U-shaped and the annual variation is significant. In the regions of 1 000-4 000 m, the variation of seasons is V-shaped during the year of SCP, and the annual variation shows a steady fluctuation; permanent snow, temporal and spatial variation of SCP are not obvious.
Abstract: Urban hydrological models are widely used in urban water management. Compared with a hydrological-hydrodynamic model, urban hydrological models always show some limitations for estimating inundated area rapidly and therefore need to be enhanced. In this research, an enhanced inundation model which considers the feedback of water from lower depression element was developed and coupled to the SWMM model to simulate inundated areas in the Tiantang River basin in Beijing. A comparison with the results from a 2-D hydrodynamics model obtained in previous study showed that the enhanced model can quickly and accurately estimate the depth of inundation. The design standard of flood discharge capacity in the Tiantang River basin is lower than 20-year return period, and high-flood-risk areas are concentrated in downstream sections of the river and around the confluence of Tianting River and the Tianying and Yongbao channels. Flood risk in these downstream areas is also likely to increase with the development of new airports in the Tiantang River basin. This research proposes a new method to estimate urban inundation.
Abstract: In order to address the issue that the water resources carrying capacity varies with the change of the relationship between carrying ability, carrying pressure and regulation ability of water resources accordingly, this article analyzed three systems relating to water resources carrying capacity (i. e., carrying ability system, carrying pressure system and regulation ability system), and further, established an index system for evaluation, which is based on the analysis of the theory, characteristics and influencing factors of water resources carrying capacity. In addition, this article developed the water resources carrying capacity evaluation model from the view of carrying standard. This model also considered water availability under different guarantee rates of utilization of water resources and different loading levels of carrying objects simultaneously. The population and the size of economy that water resources could support under different water availability and carrying standard in Shaanxi Province were calculated by the application of this model. The results could provide theoretical reference for reasonable allocation of water resources in Shaanxi Province. The practical application showed that the water resources carrying capacity evaluation model is simple and easy to use under different carrying standards, and it has good application effects as well.
Abstract: Characterization of spatial variability of hydrogeologic properties is the key to simulate and predict the fate and transport of contaminants in the subsurface. In this study, we present a sequential data assimilation framework to estimate the heterogeneous saturated hydraulic conductivity fields through the assimilation of Electrical Resistivity Tomography (ERT)-monitored data and groundwater flow/transport observation data. This framework is integrated Ensemble Kalman Filter (EnKF), groundwater flow/transport models and effective medium resistivity model. To test the performance of the framework, synthetic cases of contaminant transport are reconstructed. We compare the performance of the coupled and uncoupled methods. The factors to control the performance of coupled and uncoupled methods are also discussed in a number of different scenarios. Results showed that both methods can effectively estimate the spatial distribution of hydraulic conductivity via time-lapse ERT-monitored data. The coupled method performs better than the uncoupled one when the prior statistics are close to real field. Meanwhile, the uncoupled method is more robust when the prior statistics is biased. The accuracy of estimated heterogeneous parameter field could be improved when integrating of multiple type observations including ERT-monitored data and a few observations of groundwater flow/transport model (i. e., concentration). As the uncoupled method requires a small computational effort compared to the coupled one, it is suggested to use the uncoupled method as a preliminary inversion before refining the results with a fully coupled method. We conclude that integrating multiple types of observations is recommended to improve the ability to delineate subsurface heterogeneity.
Abstract: Numerical simulations are an important tool for quantitative research on the volume and quality of groundwater. To reveal the cause of an abnormal waterhead phenomenon using the finite element method, a three-dimensional inhomogeneous model is applied as a case study. The Lumped Mass method is an alternative approach for computing storage changes, which can be used to ameliorate abnormal waterheads. In this paper, the Lumped Mass method is applied to an abnormal waterhead phenomenon by analyzing the local conservation. It is observed that the advection fluxes in the control domain of a vertex refer to the hydraulic gradients in that slice and in adjacent slices. As water starts to be pumped, the potential of the well vertex decreases rapidly. This leads to a positive flux flowing into the control domain of an adjacent vertex in an adjacent slice. The storage change of the control domain in this adjacent vertex is positive, and so the potential increases. Hence, the computation of advection fluxes in the finite element method is the cause of the abnormal waterhead phenomenon.
Abstract: Sediment deposition is one of the key issues during the processes of reservoir construction and operation. On the basis of the observed sedimentation patterns in the dam area of Three Gorges Reservoir (TGR), a schematic diagram of fine-grained particles sedimentation in the dam area was proposed. Critical slope was used to judge the incipient motion of the fine-grained deposits. It was assumed that the mass transport processes of fine-grained deposits were dominated by the shallow flow equations. A numerical method of gravity-driven motion of fine-grained deposits was developed and combining with a 3-D flow and sediment transport model. Then, the sedimentation patterns of fine-grained particles in the dam area of the TGR were simulated by the developed method. The simulated results agreed well with the measured data. Sediment deposits in the dam area are mostly found at the bottom of the main channel, which have reshaped the river bed with a flat surface that is nearly horizontal. In contrast, very little fine sediment deposits can be found on the bank slopes of the channel. The developed method can be applied to improve our understanding of fine sediment transport mechanisms in large reservoirs.
Abstract: To further realize the correlation between rainfall and the starting mechanism of the slope debris flow in the source area of Yindongzi gully, a typical model was selected after a detailed fieldwork and engineering investigation. The rainfall intensity and gradient were set as control variables using 20 large artificial rainfall physical model tests under four gradients and five rainfall intensity conditions to research the instability mechanism and failure patterns of the slope debris flow. The experimental results revealed the starting and failure model of the source of the loose slope and the response relationship of the surface deformation and the underground physical mechanical parameters. Then, a traditional I-D (rainfall intensity-duration) early warning model was established. Next, reliable warning parameters (i. e. gradient and moisture content) were extracted and the exponential model and means of the mathematical regression analysis were used to determine the IGD and IGM multi-parameter forecast model, while the traditional model was effectively modified for dependability and practical utility.
Abstract: This study investigated the effects of water fluctuations induced by reservoir operations on hyporheic exchanges in an island in Manwan Reservoir of Langcan River. In-situ measurements of water level and temperature were conducted synchronously in the study area. The lateral hyporheic exchange flux was calculated, and the relationship between water temperature and water level was established. The dissolved oxygen and soluble carbon were also analysed along the hyporheic flow path. Results showed that periodic fluctuations of water level due to reservoir operations enhanced lateral hyporheic exchange in the island. The maximum variation of water level was 2.2 m, and the amount of water flowing in and out of the island reached 3 956 m3 during one filling-releasing cycle. The water exchange at the edge of the island was 4 to 5 times higher than that at the island centre. During water level rising, water temperature in island decreased and the temperature gradient was larger at the middle-bottom layer; while during water level falling, water temperature in island increased and the temperature gradient was larger in the upper-middle layer. The contents of dissolved oxygen, dissolved organic carbon and inorganic carbon decreased from 3.27 mg/L, 7.3 mg/L, 66.0 mg/L to 0.17 mg/L, 2.4 mg/L and 40.6 mg/L along the hyporheic flow path from reservoir to island, respectively. These results indicated that reservoir operations could enhance hyporheic exchange between reservoir and island, which imposed potential influences on the biogeochemical cycle of elements in the river.
Abstract: This study employs a three-dimensional hydrodynamic model to analyze the spatial and temporal characteristics of stream flows at spawning sites of Chinese Sturgeon. The overarching goal here is to identify the suitable flow conditions for the sturgeon's reproduction success. Such information will provide better design criteria for habitat management. The results showed that, while flow depth and velocity were determined by the water discharge, the intensity of vorticity was highly dependent upon the local geomorphological features. The velocity and vorticity exhibited much larger magnitudes and higher spatial variability at the location immediately downstream of the dam and between the spur dikes, as compared to other places. More specifically, the mean velocity and vorticity magnitudes there were reported as 2.4 m/s and 11 m2/s, respectively. Such an intense flow condition represented an appropriate spawning cue to the Chinese Sturgeon. Since the spawning activities usually took place near the water surface, this study distinguished the hydrodynamics of the flow within the upper layer from those in the intermediate and bottom layers. The mean velocity and horizontal vorticity manifested a similar distribution among the three different layers, except that the upper layer always had a larger intensity than the lower parts of the flow. The vertical vorticity, on the contrary, attained peak values in the intermediate layer exceeding the intensities observed in the upper and bottom layers. This result indicated the high spatial variability of hydrodynamics that could change with flow depth. Overall, the pertinent flow properties at the upper, intermediate, and the bottom layers may contribute to spawning success in different ways. It is reasonable to expect that the Chinese sturgeon will select the sites that are more likely to meet their special needs in the spawning processes.
Abstract: For pursuing an appropriate numerical method for free surface flow with large deformation, a vertical two dimensional corrected MPS numerical model for the simulation of the dam break flow was built based on the Moving Particle Semi-implicit (MPS) method. A new free surface detection method and a highly precise pressure gradient model were proposed to mitigate the issues of particle misrecognition and numerical energy dissipation in the original MPS method. Furthermore, the influence of the source term of pressure Poisson equation on the shocking pressure associated with the dam break flow was discussed by the comparison with the experimental results of Lobovský et al., and then a new form of source term was proposed. The calculated results show that the new free surface detection method and the highly precise pressure gradient model have remarkable effects on the decrease of particle misrecognition as well as numerical energy dissipation. Moreover, the comparisons of the numerical pressure calculation and the experimental result reveal the proposed source term of pressure Poisson equation is useful for the reduction of the numerical pressure fluctuation.
Abstract: Farm dikes constructed along the main channel in the Lower Yellow River can withstand small and median floods, and protect farmland and villages from flooding. Farm dike-break induced overbank floods not only cause water level changes in the main channel, but also lead to severe flood disasters on the floodplain. Numerical simulation is often employed to study dike-break floods, and previous results obtained from prototype and model measurements are very limited. In this study a sketched laboratory model was constructed to investigate the inundation process of farm dike-break induced overbank floods, and characteristics of water level changes along the main channel and over the floodplain were analyzed. Experiment results show that:① after the farm dike burst, the diffusion flood wave rapidly routed over the floodplain, which caused the surface-negative wave in the main channel and the surface-positive wave on the floodplain. Water levels in the main channel decreased first, and then kept stable, and then rose to another stable level, and the rates of water level change were different in the reaches upstream and downstream of the dike breach site. Water levels on the floodplain generally kept rising firstly and finally tended to be stable, with inverted slopes of water surface in local regions; ② arrival times of wavefront routing in overbank floods were mainly associated with the terrain and the distance from the site of dike breach, and the measured wavefront had a distribution of symmetric elliptic shape firstly and then a asymmetric distribution. Hydraulic jumps occurred in the process of dike-break induced overbank floods, and the position of hydraulic jump gradually approached the dike breach site from a farther distance; and ③ the breached discharge was directly related to the difference in water levels on both sides of breach. The breached discharge decreased first, and then remained stable, finally decreased to zero. Experimental results can provide the basis experimental data not only for the research into overbank floods due to farm dike-break, but also for validation of mathematical models.
Abstract: To explore the influence of sea level rise on the evolution of tidal flat and tidal creek system, adistorted physical model was established, taking a silt-muddy tidal flat-creek system in the central Jiangsu coastas the prototype. Based on the model, a variety of parameters were analyzed to illustrate the properties of the creek system changed with the sea level rise, such as duration of submergence, drainage density, cross section profile of the tidal channel, etc. Results indicate that the elongation increases more rapid than the elaboration at the initial stage of the creek system development, but both approach a dynamic equilibrium ultimately. Under the pressure of sea level rise, the inundation period increases hence the exposure duration of the tidal flats decreases, resulting in reduced shaping effects of the shift return flow on the creek bottom. Both mean unchannelled length and Hortonian drainage length show a decreasing trend, indicating a higher drainage ability of the creek system. In addition, the width/depth ratio follows an approximate lognormal distribution. The cross-section area and the width/depth ratio increase with sea level rise, as well as the distribution range of the width/depth ratio.
Abstract: In order to further understand the leading influential driving forces and their cooperative mechanism in saltwater intrusion of riverine estuaries in dry season, 3-D numerical simulation experiments were conducted in this study with a simplified estuary which was forced by sinusoidal tides of constant tidal ranges and main tidal constituents respectively at different runoff flow. The results indicate that in tidal saline equilibrium, with variation of relative strength of the runoff and tide, the shape and the location of salt water intrusion are automatically adjusted and end with balanced salt transportation. When the runoff rates are less than 3 000 m3/s and tidal ranges less than 2 m, there are obvious differences in the variability of maximum intrusion lengths with tides under different runoff flow. For weak mixing estuary, during the period time of spring and neap, the saline water presents fortnight non-equilibrium and their data points of tidal maximum intrusion length with respect to tidal range change clockwise like a loop around that of the equilibrium state. The density circulation induced by runoff and the tidal mixing collaborate and develop with interaction. The contrast of their intensity dominates the significant distinction of saline intrusion length in riverine estuaries.
Abstract: Water is a basic natural resource that plays an irreplaceable role in maintaining the integrity of the natural environment and promoting sustainable development. Socioeconomic growth and threats to water security have led to increasing attention to integrated water resources management (IWRM) in recent decades. China has introduced the most stringent water resources management system, the river chief system, and other water policies to explore and improve the institutional structure and mechanism of IWRM. This paper summarizes the general framework of IWRM, discusses its implementation status worldwide, and examines developing trends in its practice. The data show that:① with increasing awareness of the problems of fragmented water resources management, the concept of IWRM has gradually been accepted by the international community; ② by emphasizing the importance of integration in water resources management, IWRM promotes the optimization of enable environment, institutional roles, management measures, and reliable investments in water infrastructure to achieve balances among water efficiency, social equity, and environmental sustainability; ③ many countries have adopted the principles and framework of IWRM for policy making and institutional design, and have made substantial progress in water management practices; ④ international conceptions of IWRM and experiences with its implementation can provide inspiration and reference for the improvement of China's water resources management; ⑤ IWRM will be further promoted and implemented, and its application to the solution of specific water issues will be strengthened with diversified and dynamic characteristics. Despite the existing challenges, such as uncertainty and complexity of climate change and the water-socioeconomic nexus, the experience in IWRM and the improvement of water science will allow the further application of IWRM using a holistic, multidisciplinary, and sustainable approach to achieve sustainable development goals.
Abstract: Urbanization is an extensive and complicated human activity all over the world. Presently, it is a consensus that urbanization could exert certain impact on local precipitation. However, owning to the complexity of precipitation formation and distribution in different regions, as well as the limitation of metrological observation and numerical simulation models, there are different views on the physical mechanisms and driving factors about urbanization influencing rainfall. In addition, disputes continue on the phenomenon and traits of urban influencing rainfall. Hence, this paper reviews the main mechanisms of urban effects on rainfall. Then, observation analysis and numerical simulation of urbanization impact on precipitation are retrospected. For the former, main results are summarized and compared for studies both based on surface gauge observations and remote sensing data. For the latter, urbanization influence on precipitation are summarized both for single factor and compound factors. Finally, main problems requiring deep exploration in future are recommended from five aspects, i. e. the integrated observation of urban meteorology, the comprehensive detection of urbanization precipitation effects, the refined simulation of urbanization impact on precipitation and the adaptation and regulation measures. This paper is conducive to deepening the understanding of urbanization effect on precipitation. Additionally, it provides valuable references for the adaption and regulation of the negative change of precipitation caused by urbanization.