Abstract: Based on the one- and two-dimensional coupled hydrodynamics model of the Yangtze River and Dongting Lake,the hydrological processes of the Dongting Lake area before and after the impoundment of the Three Gorges Reservoir were simulated. Quantitative analysis was carried out for the response relationship between the impoundment of the Three Gorges Reservoir and the outflowing water volume of Dongting Lake. The results indicate that the inflowing water volume of Dongting Lake from the three outlets along Jingjiang was reduced due to the impoundment of the Three Gorges Reservoir during the water storagerefill period. This also changed the variation speed of the Dongting lake storage capacity. Compared to the original conditions,the outflowing water volume of Dongting Lake was significantly reduced from September to October in each typical year,with greater reduction in October than in September,while the change in November was not distinct. The water volume change of the three outlets along Jingjiang from September to October was the dominant factor for the outflowing water volume variation of Dongting Lake,with the change of the lake storage capacity being the dominant factor in November. Through multiple regression analysis,the response relationship between the impoundment of the Three Gorges Reservoir,the outflowing water volume of the Dongting Lake,and the change of lake storage capacity was constructed. Under the conditions of constant lake storage capacity,the reduction of the outflowing water volume of Dongting Lake was about 23% of the impoundment of the Three Gorges Reservoir.
Abstract: In view of the significant impacts that polar ice has on the climate of the mid-low latitudes,this paper mainly analyses the effects and possible mechanism of Arctic sea ice on the precipitation in the main flood season of the Yangtze River basin by statistical methods such as Singular Value Decomposition. The precipitation data is collected from 116 rainfall stations in the Yangtze River basin and the sea ice data is provided by the United States National Snow and Ice Data Center (NSIDC),both periods are 1979-2017. The results show as follows:In winter and spring,when ice area in the Barents Sea and Okhotsk Sea was more than the average and that in the Beaufort Sea was less than the average,then summer precipitation in upper and middle reaches of the Yangtze River,the upper reaches of the Hanjiang River and the Yalong River increased;When winter-spring ice area in the northern part of the Arctic Archipelago,Chukchi Sea and Laptev Sea was much,summer precipitation in the Dongting Lake and Poyang Lake was much too,but it was less in the upper reaches of the Jialing River and Hanjiang River; and vice versa. The possible mechanism is that the sea ice variation in key regions in winter and spring stimulates atmospheric energy fluctuation by affecting turbulent heat flux. This fluctuation propagates to East Asia in the form of atmospheric wave trains and affects the summer atmospheric circulation and water vapor transport in East Asia,thus indirectly affecting precipitation of the Yangtze River basin in the main flood season. Based on the multivariate regression method,four prediction models of precipitation in the main flood season are built by taking the sea ice area in key region as predictors. The models have obvious fluctuation on quantitative precipitation prediction,but it has a relatively good effect on precipitation trend prediction.
Abstract: The Yellow River Water Allocation Scheme ("Scheme 1987") provides an important foundation for basin-scale water resources management. The Scheme 1987 has been in place for more than 30 years,during which time both the natural environment and the socioeconomics in the Yellow River basin have changed dramatically. Thus there is an urgent need to assess the adaptability of Scheme 1987 in changing environments. We have developed a dynamic differential equation and comprehensive evaluation model to assess water allocation scheme adaptability using power system principles. We have constructed an index system consisting of 20 metrics of sensibility,stability,resistance,and resilience and used our method to assess Scheme 1987 between 1999 and 2017. The Hodrick-Prescott (HP) filter has been used to reveal the adaptability trend. The results show that Scheme 1987 adapted well to the changing environment,with highly adaptable years accounting for more than 63.2% of the 19-year period. Adaptability increased early,peaking in 2005,and then decreased. The scheme began showing an inability to adapt since 2014. We have identified the major factors influencing the adaptability of Scheme 1987 and suggested some adjustments for basin-scale water resources management.
Abstract: This study developed an intuitive and reliable urban flood-risk zoning map for scientific decision-making by departments related to urban flood control and drainage. The Donghaochong (DHC) basin of Guangzhou city was the study area. A 1 D-2 D coupled urban flood simulation model was constructed based on InfoWorks ICM to obtain disaster-causing factor data by simulating the flood process under the rainstorm return periods of 1 a,5 a,and 50 a. This study also investigated the surveyed areas of hazard-inducing environment,hazard-bearing body,and hazard prevention and mitigation capacity. Risk assessment of flood disasters was carried out in combination with the analytic hierarchy process (AHP),assessment grade,and threshold value division. The results revealed that the urban flood simulation model had good accuracy and reliability in the 1 D drainage system and the 2 D ground submergence simulation,thus ensuring the reliability of the disaster-causing factor data. Also,the risk-zoning map adequately reflected the risk distribution within the basin;moreover,as the return period increased,medium-high risk zones and high risk zones increased significantly,requiring flood prevention and drainage.
Abstract: In order to improve rainfall-runoff simulations in urban area and enhance the details of digitalized urban area with complicated land-surface characteristics,this study selected the core district of Yizhuang Economic Development Zone in Beijing as the study area,and the methodology of sub-catchment division,generalization of drainage pipe networks,and identification of outfall drainage wells was proposed for large-scale urban regions larger than 10 km2 with complicated land-surface characteristics,in which local geographical properties,regional waterlogging characteristics,and critical information such as digital elevation model,drainage pipeline networks,and land-use types were considered. This study provides technical support for the researches on rainfall-runoff simulation and disaster warning in urban areas where pipeline-flow observations are sparse in China.
Abstract: As the (Yangtze) River-(Dongting) Lake relationship changed and human activities increased,the water system pattern and connectivity in the Dongting Lake area have been also changed a lot,which exacerbated the deterioration of water environment and water ecology. Carrying out the researches on water system patterns and connectivity are important for the comprehensive improvement and ecological restoration of water systems of the Dongting Lake. Based on the network connectivity analysis method in landscape ecology,we created an evaluation index of water system pattern and connectivity including river frequency,river network density,circle degree of water system (α),node connection rate (β),and network connectivity (γ). Here,we analyze the current water system pattern and connectivity of the Dongting Lake Area compared to a planned water system,and we propose an optimized planning scheme for the studied water system. Our results demonstrate that the water system pattern and connectivity of the total area of the Dongting Lake are acceptable,but that there are large differences among sub-areas. The pattern and connectivity of the existing water system in the tail-stream area of the Xiangjiang and Zishui Rivers are at an acceptable level but are poor in the Song and Li Rivers area and the northern region of the Dongting Lake. The planned project will improve the water system connectivity efficiently in the Song-Li Rivers area,but not in the northern region. In the northern region,according to our optimized planning scheme,three indices (α,β,γ) increased by 13.2%,6.9% and 4.7%,respectively,compared to the existing water system,and our optimized planning scheme yielded an improvement of the proposed plan by 26%,9.4%,and 9.4%,respectively.
Abstract: The industrial water use environmental Kuznets curve (EKC) and its formation mechanism can not only indicate the relationship between industrial water use and economic development,but also provide important information for industrial water use management. The cubic model,quadratic model,and Locally Weighted Scatterplot Smoothing (LOWESS) were used to identify this relationship in Shandong Province. To quantitatively analyze the formation mechanism of the industrial water use EKC,the contributions to the change in industrial water use by the three drivers,including water use efficiency (WUE),industrial structure and economic scale,was calculated by the logarithmic mean divisia index (LMDI) method;while the long-term change characteristics of industrial WUE was analyze by the four-parameter logistic curve. Results indicate that the industrial water use in Shandong Province during 1980-2016 first increased,then declined,and finally increased again;further,there is an N-shaped EKC,in addition to the inverted U-shaped one. After the WUE is greatly improved and industrial water use continuously reduced,the WUE will gradually approach its limit. Thus,the rate of improvement of water use efficiency slows down and the water saving effect is greatly reduced. When the increase in water use caused by the expansion of the economic scale cannot be offset,the industrial water use will increase again instead of decline,and the shape of the curve changes from an inverted U-shaped to N-shaped. The existence of an N-shaped curve indicates that the industrial water use may increase again instead of an automatic continuous decline. To reduce industrial water use,it is necessary to make full use of the water-saving potential,continuously improve water use efficiency,and adapt the industrial structure to promote water saving.
Abstract: Water use efficiency (WUE) is an important indicator of evaluating irrigation efficiency. However,errors associated with WUE in evaluating irrigation efficiency of regions with different climate have been neglected. Based on the concept of Potential Water Use Efficiency (PWUE) and meteorological data,this study fills this gap by calculating the PWUE of wheat,maize,and rice of China in 2014 as well as evaluating the effect of climate difference on WUE. We put forward and examine concepts and calculation method of Relative Water Use Efficiency (RWUE) and Theoretical Agricultural Water Saving Potential (TAWSP).Our results show that standard deviations of PWUE of main grain crops are between 0.49 and 1.01 kg/m3,and the spatial variance of PWUE of most crops was larger than their actual WUE. The average RWUE of main crops is 50.7% and their TAWSP are between 884.8 and 4 064.5 m3/hm2. More importantly,the index of WUE and traditional agricultural water saving potential may overestimate or underestimate the water use efficiency and water saving potential of crops. In addition,we find that the impact of climate difference should not be neglected in comparing WUE in different regions. The indexes of RWUE and TAWSP are more reasonable as they can take into account the regional climate difference.
Abstract: The groundwater flow with entrapped air was termed as quasi-saturated flow. The entrapped air in quasi-saturated flow of aquifer had a significant influence on hydraulic conductivity of porous media. In this paper,the relation between entrapped air saturation and hydraulic conductivity was studied by the column experiments with respect to four medium,silt,fine sand,medium sand and coarse sand,respectively. The results illustrated that the entrapped air saturation in a quasi-saturated aquifer was related to the particle size of the medium,and the entrapped air saturation in the fine-grained media was greater than that in the coarse-grained. Within a saturation range of 0-15% of entrapped air saturation,the hydraulic conductivity decreased by 32.82%-56.38% compared with that at entrapped saturation,and the hydraulic conductivity can be expressed as a negative linear correlation with entrapped air saturation. The results also showed that the variation of the quasi-saturated hydraulic conductivity could be generalized as the entrapped air occupied the original effective poresand resulted in a decrease in the original effective porosity and hence in hydraulic conductivity. According to this air entrapment theory,the Kozeny-Carman equation could accurately exhibit the variation of the hydraulic conductivity with entrapped air saturation in the quasi-saturated aquifer,and furthermore,the results illustrated the hydraulic conductivity formula based on the Hagen-Poiseuille equation was not suitable for quasi-saturated hydraulic conductivity. In Addition,the experimental results also showed it was necessary to remove entrapped air in laboratory measurement of hydraulic conductivity.
Abstract: As the serving time of low-head dams prolonged,security,economy and ecology issues of these dams have become increasingly prominent. For small dams with little repair values,forced retirement or demotion would be the best management measure. After removal of the dam,large amounts of sediment in the reservoir will be released,which leads to the change of river morphology hence affecting aquatic habitats. To predict the evolution characteristics of river channel in different time scales,Xihe dam in Wujiang drainage system was chosen as an example. By establishing two-dimensional sedimentation model,riverbed evolution in different time scales after dam removal was simulated and studied. The results showed that:in the short term after dam removal,the upstream of the dam experienced a strong scour,and sedimentation appeared in the front part of the reservoir delta;in contrast,the riverbed changes in the downstream of the dam was not obvious,only a small amount of sediment deposition occurred near the estuary and downstream of the dam;as for the long-term evolution after dam removal,both the upper and lower reach experienced different degrees of scour. After 2 years of dam removal,the morphology of downstream riverbed tended to be stable,while the evolution of the upstream transformed from scour to alternating deposition and erosion,and the riverbed morphology was under constantly adjusting. Results of our study can provide important basis for further river channel managements,aquatic habitat restorations after removal of sick dams and small hydropowers.
Abstract: To improve the basic theoretical research of overland flow,this researcher used a fixed-bed flume test and ultrasonic sensor measurement technology to study the hydrodynamic characteristics of laminar flow and roll waves on the slope surface. Glycerol solution was used as test fluid and combined tests were performed under four levels of roughness,five slope gradients and 13 single-width flow conditions. The results show that the flow index fluctuates around the theoretical value of 0.33 for Reynolds numbers ranging from 8 to 160. It first increases and then decreases as the roughness increases. The roughness is around 0.10 mm. The peak is reached,and the drag coefficient is significantly affected by the slope and roughness,which can be expressed as the relationship between slope,roughness and Reynolds number;as the Reynolds number increases,the roll wave velocity and the peak value increase in the form of a power function. There is no readily visible change in the magnitude of the rolling cycle;the increase in the slope causes the layer to lose stability and the critical single-width flow gradually decreases. The increase of the roughness causes the critical Froude number to decrease. The research results can provide theoretical basis for the development of hydraulics and hillside hydrology.
Abstract: The configuration of stepped channels in mountainous streams is influenced by the complex hydraulic characteristics,like the inflow,sediments and the larger slope river-bed. To further study its resistance mechanism,a new roughness height formula is derived and applied for the stepped channels by expanding the theory of roughness height of stepped channels configuration from the dimension of the hydraulic radius. The expression of Darcy-Weisbach form factor for the napping flow of the stepped channels is deduced. Thus the formula of total resistance factor is obtained from sources of resistance components. The results of the new formula shows that the error between the total flow resistance factor calculated from the three components and the actual field measured data is small based on the field data of different river sections. With the increase of Reynolds number and the size of step element,the resistance factor of sediment particles on the riverbed surface basically-stabilize at a certain. With the spill flow formed by the stepped riverbed configuration changing into the skimming flow,the resistance coefficient of the body gradually decreases,and the resistance factor of the flow generated by the larger loose boulder descends with the increase of Reynolds number.
Abstract: When a composite bank fails,slump blocks deposit at the toe of the bank. This alters the flow structure near the bank and affects the bank erosion processes. To investigate the effects of slump block at different locations on the flow structure near the outer bank,a generalized model of Shishou reach was conducted. Acoustic Doppler Velocimeters (ADV) was used to precisely measure the three-dimensional flow velocities. Experimental results show that the slump block upstream of the head-on scouring point shifts the region of maximum streamwise velocity away from the outer bank and reduces the averaged bed shear stress between the slump block and the bank toe. In contrast,the slump block downstream of the head-on scouring point makes the region of maximum streamwise velocity closer to the outer bank and increases the averaged bed shear stress between the slump block and the bank toe. This study enriches the understanding of composite bank erosion process,and helps to develop and improve the erosion model of composite bank.
Abstract: Numerical modelling of the bottom boundary layer (BBL) is an important tool for sediment transport analysis. In order to study the sediment movement in the wave-current BBL,an intra-wave process based 1DV model was established for silt-sand sediment concentration processes,considering the interactions among flow dynamics-sediment-bed forms. Some key approaches for silt-sand sediment are represented:the bed form module provides the type of bed form and related parameters;different approaches for sediment diffusivity over rippled beds and flat beds are employed;approaches for hindered settling velocity,reference concentration and critical shear stress for silt and sand are employed;the stratification effects and hindered settling are introduced to simulate interaction effects between flow dynamics and sediment concentration. A number of experimental datasets were collected to verify the model,and results showed that the model could properly simulate the sediment dynamics over different bed forms and in different combinations of wave-current conditions. Discussions are made on the simulation methods over different bed forms. The results showed that bed form is one of the important factors that impacts the sediment concentration profile,and it is not appropriate to simulate the concentration profile over a vortex rippled bed by only changing the roughness height and different approaches are suggested to be employed. This paper provides a tool for the study of the sediment transport in the wave-current BBL.
Abstract: This study investigated the wave forces on an incompletely submerged horizontal circular cylinder under large-amplitude wave action using a viscous fluid numerical wave tank model based on the finite volume method. By analysing the characteristics of the wave and slamming forces on the circular cylinder,the influences of wave amplitude and vertical position of the cylinder on the wave forces were investigated,and the relationships between the slamming forces and velocity were discussed. The slamming coefficients were based on a data fitting method. The results showed that the wave forces were significantly influenced by wave amplitude and vertical position of the cylinder. The mechanism can be explained by the features of the fluid motion in the wave field. Although the slamming forces were closely related to the slamming velocity,the influence of the vertical position of the cylinder on the minimum predicted slamming velocity for the situation,in which the slamming forces play a dominant role in the wave forces,were unremarkable. As the wave amplitude increases,the distribution of the slamming coefficients for different vertical positions of the cylinder changes from dispersed towards focused.
Abstract: The study of rip currents by intersecting waves is helpful to the comprehensive study of disaster mechanisms and risk assessment. To better understand the characteristics of rip currents controlled by hydrodynamic forcing and longshore topographical variability,an experimental study on rip currents by intersecting waves over barred beaches with rip channels is conducted. The investigation focuses on the distribution characteristics of rip currents resulting from intersecting waves and longshore topographical variability. Analytical results of velocity distribution measurements by acoustic Doppler velocimeters are presented for the distribution characteristics of rip currents on barred beaches with rip channel. The location and width of rip currents are controlled by rip channel and wave nodes,and the length of the rip currents depends on the wave height and coastal slope. The driving force of rip currents without rip channel is primarily determined by the alongshore pressure gradient of the wave setup caused by intersecting waves. By contrast,the driving force of rip currents with rip channel is determined by both the alongshore pressure gradient of the wave set-up and the radial stress gradient,and the relative magnitude of the two values depends on the wave period.