Abstract: Based on field data from the Hulu Watershed in the Qilian Mountains of China, five types of experiential parameters of alpine hydrology are calibrated: ① wind-induced factors of gauge-measured precipitation; ② threshold air temperature (day and half-hourly) for classifying snowfall, rainfall and mixed snow and rainfall; ③ relevant parameters for alpine shrub interception; ④ threshold temperature of completely frozen soil and ⑤ critical air temperature (daily and half-hourly) for snow melting. If the vegetation zone moves upward due to global warming, then the ratio of evapotranspiration/precipitation will increase while the runoff coefficient should decrease in the alpine watersheds of China. Current precipitation data does not match accurate simulations of alpine hydrology in China, and the interception model should be improved and simple methods developed to describe glacier and snow melting. Long-term hydrological simulations should consider snow drifting, permafrost evolvement and glacier flow. Further research on subpermafrost water, snow sublimation and glacier flow concentration in the alpine regions of China is urgently needed.
Abstract: In order to cope with the increasingly serious global drought issue, this treatise investigates the relatively complete evaluation and analysis model on the regional meteorological drought. It proposes a three-step evaluation and analysis method, which includes the regional meteorological drought identification, the drought characteristic value calculation and the multivariable analysis on drought characteristics. Taking Weihe River basin as a case study example, the treatise first carries out a rectangular drought evaluation-unit division on the research area, selecting reconnaissance drought index as an evaluation indicator to identify drought conditions in each unit at different time periods in the research area. The result is almost in accordance with the historical record on the years of drought. Then the treatise uses statistical methods such as the distribution fitting, the correlation coefficient, the copulas function to carry out characteristic analysis on the regional drought characteristic values (the drought duration, the drought area, the drought severity and the drought frequency), drawing a series of analytic and comparative results on the univariate, the bivariate and the multivariate characteristics. Based on the distribution function calculation and construction on different distribution functions, the treatise comes to the occurrence conditional probability and recurrence interval of droughts in Weihe Basin, forming a relatively complete evaluation and analysis model on the regional meteorological drought.
Abstract: In order to perform a detailed investigation of the characteristics of temporal and spatial isotopic variation in the Dongting Lake region and to understand the interrelations of different water bodies in the same area, samples of surface water and groundwater were taken in April and August 2012, respectively. The hydrogen and oxygen isotopic compositions of all the samples were analysed and by combining them with isotopic data obtained from precipitation in Changsha from 1988 to 1992, published by the global network of isotopes in precipitation (GNIP), we find that this region is influenced by different monsoons throughout the year. Consequently, the isotopic compositions of precipitation and surface water demonstrate significant seasonal differences: Enriched in April and depleted in August. Additionally, the isotopic composition of surface water displays great spatial variation. The slopes of the surface water lines in April and August are all smaller than that of the local meteoric water line, which indicates the existence of evaporation of surface water. Even though the original source of both surface water and groundwater is precipitation, groundwater exhibits little seasonal variation compared with surface water, because groundwater recharge by surface water is a long-term process.
Abstract: The relationship between surface water and groundwater is an important content of the research on the water cycle and water resource management. The methods of field water sampling and laboratory analysis were combined with the stable isotopes (δD, δ18O) and hydrochemistry to study the relationship between surface water and groundwater in the second Songhua River basin. The spatial difference of stable isotopes in the surface water and groundwater was obvious. The water samples in the upstream were isotopically depleted, but isotopically enriched in the downstream. The evolution of water type ranged from the Na-HCO3 type in the Changbai Mountain area to the Ca-Mg-HCO3 type. However, the evolution of water type was Ca(Mg)-Cl(SO4) impacted by human activities. The two-component method was used to calculate the quantitative relationship between surface water and groundwater. The deep groundwater was recharged from the river and shallow groundwater, and the contribution of shallow groundwater was about 50%. The contribution of the shallow groundwater discharged to the river was about 20% in the plain area. The results could provide the theoretical basis for the comprehensive utilization of surface water and groundwater, and the sustainable utilization of water resources.
Abstract: As the largest freshwater lakes in China, the Poyang and Dongting Lakes enter a complicate coupling with the middle reach of Yangtze River, which plays a significant role in flood control and eco-environment protection. Based on the field flow-sediment and topography data, the leading factors to the characteristics of sediment erosion and deposition in both Lakes have been studied, of which the Three Gorges Reservoir is highlighted. The results indicate that the rate of siltation in both Lakes shows visibly slowdown to occasional erosion in the recent decade. The decrease of sedimentation rate in Dongting Lake is basically induced by the reduction of incoming sediment due to the operation of Three Gorges Reservoir, while the erosion dominated in Hukou reach of Poyang Lake is mainly caused by excessive sand mining rather than the Three Gorges Reservoir which still remains uncertain.
Abstract: A series of dredging and hydrologic data in situ measurement are collected to study temporal-spatial variation characteristics of siltation, and the dependency relationship of siltation on riverine discharge, tidal range and local suspended sediment concentration in the 12.5 m Deepwater Navigational Channel (DNC) in the Yangtze Estuary.The results show that: ① the quantity of siltation in DNC is much greater in flood season than that in dry season; ② the sedimentation during storms is very serious; ③ the deposited sediments mainly distribute in the South Channel—Yuanyuansha Channel and the middle reach of the North Passage; ④ the grain size of the dredged sediment in the upper reach is greater than that in the lower reach; ⑤ the quantity of siltation in the South Channel—Yuanyuansha Channel is no sensitive to the riverine discharge, but it deposits more during spring-tide and less during neap-tide; ⑥ the central position of the siltation in the North Passage varies with the intensity of discharge, when the discharge becomes small, it move up-estuary, and vice versa; the quantity of siltation in the North Passage will get greater in flood season than in dry season; ⑦ the resuspension of the deposited sediments near the estuarine turbidity maxium area is the main contribution to the siltation in the dredged navigational channel.
Abstract: To investigate the cause of an abrupt change in the morpho-dynamic processes of a shoal reach downstream of the Three Georges Dam, the mechanisms of fluvial processes pre and post the dam closure were compared for the recurrent shoaling in the Lujiahe reach. The impacts of multi-factors including the incoming flow and sediment regime and the channel adjustment were identified using the hydrological and topography data measured after dam construction. These results indicate that the degree of bed erosion caused by sediment deficit is more intensive in the flood flow path in a multi-branched channel, which leads to a reduction in the critical discharge for the bed scour in the main flow path during dry seasons. Furthermore, with the operation of the Three Georges Reservoir at a pool level of 175m, the recession rate of the dam released flow is more rapid and the suspended sediment load is mostly discharged during flood periods. All these changes tend to accelerate the deposition in a shoal reach during a flood season, instead of causing the channel erosion during a post-flood period. The integrated effects of all these factors lead to an abrupt change in the channel evolution of the shoaling reach since 2008. Therefore, it is concluded that recurrent shoaling may exist for a long period in the Lujiahe reach, and more attention should be paid to the similar shoals in multi-branched reaches in the middle and lower Yangtze River.
Abstract: Step-pool system is a typical bed micro-morphology in high gradient (>3%) mountain rivers, which creates extremely high turbulence intensity and thus dissipates most of the flow energy. An artificial step-pool system was constructed in the Wenxia River downstream of the Wenxia Reservoir and experiments were conducted to study the characteristics of turbulence in step-pool system. The velocity and turbulence intensity were measured with the three dimensional acoustic doppler velocimeter (Vectrino) made by the Nortek Cooperation. The sampling frequency of the instrument was 200 Hz. The fluctuating velocity was measured at 3 cross sections at upstream of the step, on the step, in the pool and along the thalweg. The flow discharge was controlled stable during the measurement at 10 L／s, 50 L／s, 100 L／s, 150 L／s, 290 L／s and 420 L／s. The results showed that the flow around the step-pool was very three dimensional. At the cross-sections upstream of and on the step, turbulence intensity was small and the mean velocity was high. In the pool, however, the mean velocity was greatly reduced and turbulence intensity became extremely high. The relative turbulence intensity, defined as the ratio of the turbulence intensity over the mean velocity, was around 0.1 at upstream of the step, and increased to 8.0 in the pool. Most of the flow energy transformed from mechanical energy to the tubulence energy as water flowed from upstream of the step to the pool. The Reynolds stress was calculated with the fluctuating velocity components and the results showed that the Reynolds stress in the pool was about 50 times higher than that on the step. Following increasing flow discharge from 10 L／s to 420 L／s the energy dissipation ratio reduced from 91% to 64%.
Abstract: This paper investigates flow structures around a bridge pier with a slot by experimental data obtained with PIV (Particle Image Velocimetry). Dynamic structures of the flows are examined on the central vertical flow plane and horizontal planes at different heights. It is found that the presence of the slot reduces the rise of water surface in front of the pier and subcutaneously changes wake vortex structures behind the pier. The flows around the pier with a slot exhibit strongly three dimensional characteristics. The maximum relative width of the low velocity region beside the pier and that at the wake region located at z／h=0.45 vary approximately linearly with the value of w／b, w being width of the slot and b being width of pier. On the horizontal plane at z／h=0.75, the relative length of vortex pair behind the pier with a slot(w／b=0.5)is 70% of that in case of the traditional pier, whereas, on the plane z／h=0.15, it increases slightly. In addition, the relative width of the vortex pair remains as 1 all the time.
Abstract: The attenuation process of transverse velocity in the straight outlet section downstream of a bend was investigated. An empirical equation of dimensionless attenuation length (DAL) was established via dimensional analysis. A series results of numerical experiments were adopted to calibrate this equation, as well as to analyze the impact of all factors and the distribution law of DAL. In addition, results were compared with theoretical predictions. The experiments show that Re and Fr have little effect on DAL. Horizontally, the DAL in concave-bank zone is the largest, followed by that in central zone, and the minimum value is in convex-bank zone. Whereas, vertically its value in near-bottom zone is the largest, followed by that in near-surface zone, and the minimum value is in central zone. The vertical distribution of DAL predicted by a typical theoretical equation is qualitatively in accordance with the experimental result. However, disregarding the impact of transverse slope caused its under-prediction near the bottom. Results show that considerations of the empirical equation in this paper are more comprehensive than those of the theoretical equations, and DAL varies horizontally and vertically. When using hydraulic model to investigate the attenuation process of transverse velocity, the similarity law of resistance should be followed, whereas the similarity law of Fr and Re can be neglected at specific conditions.
Abstract: Pre-aerator stepped spillways, where the aerator is placed prior to the primary step in the stepped spillway, can form a cavity chamber at the bottom to produce enough aeration concentration to avoid the cavitation erosion. To make a better understanding of the bottom aeration characteristics along the pre-aerator stepped spillways, laboratory experiments were carried out, in which aeration concentration distributions on the vertical and horizontal planes along the stepped spillway with different discharges and slopes were investigated. Ulteriorly, comparation of aeration characteristics was made between the pre-aerator stepped spillway and the transitional stepped spillway. It was showed that distribution of aeration concentration on the horizontal surfaces of the pre-aerator stepped spillway was similar to that on the vertical plane. Because of the pre-aerator, the aeration concentration is very high along the primary steps, decreases along the stepped spillways, and tends to the stability for a certain distance. With the increase of discharge per unit width and the decrease of the slope, the aeration concentration decreases. The results indicate that the pre-aerator can eliminate the clear water zone on the bottom of the primary steps, where the transitional steps cannot avoid. Therefore the pre-aerator stepped spillways can be widely used for larger discharges per unit width.
Abstract: A new two-dimensional numerical model is presented to simulate the flow in the vicinity of submerged spur-dikes, which employs a finite volume method based on structured triangular mesh, and considers water depth around dikes in continuity and momentum discrete equations. In this model, the spur-dikes are supposed as the dikes without thickness, and generalized as grid lines; the depth and velocity nodes are arranged in grid interface, and the water level nodes are arranged in grid center, which is different from the general staggered-grid nodes distribution. The model is first validated against the available observed data obtained from a flume experiment. It is then applied to simulate the flow with submerged spur-dikes in Dongliu waterway downstream the Yangtze River. The model predictions generally agreed with measured data including velocity and water depth, which demonstrates the capability of the model to simulate the flow in the field of submerged spur-dikes.
Abstract: Lihu subterranean river in South China was selected to study the contaminant transport behavior and self-purification capacity of a karst aquifer. The subterranean river was investigated through water sampling along the stream reach for one year. Analysis of inorganic ions and trace elements in different seasons and at different locations showed the major contaminants are NO2--N, NH4+-N, COD, As, Cd, and Hg, due to domestic waste, mining industrial waste, and fertilizer application in the recharge area. Along the course of the karst conduit, a self-purification process was observed because of significant decrease in some ions concentration. The mechanism of self-purification was caused by dilution and nitrification, which was determined by the suterranean river's structure and hydrogeological condition. By comparing the attenuation quantity and percentage of ions, it was found that ammonium had the highest, while chloridion had the lowest percentage. According to the attenuation rate, four types of attenuation character could be classified. Firstly, the ions decayed completely after they entered the karst aquifer, such as TFe, Zn, and Al; secondly, the ions had the highest attenuation rate when they traveled underground through the aquifer, such as K, Na, Mg, F, Cl, HPO4, and TP; thirdly, the concentration gradually decreased from upstream to downstream, which was represented by NH4+-N, CODCr, and BOD5; and finally, they had the highest attenuation rate when transformed from surface stream to underground stream, but secondary suspension of contaminants could happen in the cave, such as Mn, Ba, and Hg.
Abstract: In order to accurately identify the contribution degrees of precipitation and groundwater exploitation to the groundwater flow field in shijiazhuang, interactive features between the average water level, central level and area of groundwater depression cone and the precipitation and groundwater exploitation are studied through the methods of Wavelet Transform (WT) and correlation analysis. The results indicate that: ① During the period of 1961—1973, the average water level shows a power-function declining trend with increasing precipitation; during the period of 1974—2010, every decline in precipitation by 100 mm results in a rise in drawdown of central level of groundwater depression cone by 7.35 m and a rise in drawdown of average groundwater level by 2.15 m. ② During the period of 1961—1973, every rise in groundwater exploitation by 0.1 billion cubic meters results in a decline in average groundwater level by 0.28 m, a rise of 11.74 km2 in area and a decline of 0.52 m in central level of groundwater depression cone; since 1974, every rise in cumulative amount of overexploitation by 0.1 billion cubic meters results in a rise of 1.52 km2 in area and a decline of 0.18 m in central level of groundwater depression cone. ③ Every rise in precipitation by 100 mm results in a decline in contribution degree of precipitation by 3.0% and a rise in contribution degree of human exploitation by 2.76%.
Abstract: Nash Instantaneous Unit Hydrograph (NIUH) is based on the assumption of zero initial conditions which is unable to represent river flood routing in real situation. The complete formula of NIUH for river flood routing which includes initial channel storage recession flow was deduced by the Laplace transform and mathematical induction. The physical meaning of each item of the complete formula was analyzed and discussed. It is demonstrated that outflow is composed of two portions: One is the recession of the initial channel storage, the other is the inflow routed through the channel. A real-time updating approach of the river flood routing was proposed based on the complete formula. The practicability and rationality of the formula were verified through the case study. The complete formula can be considered to be a more general case of the Nash river flood routing model. It is a development of the existed NIUH theory and can adequately improve the accuracy of the river flood routing.
Abstract: On the premise of not affecting the existed interest patterns in the context of flood control and water supply, the major scientific issue before us is how to improve the supply guarantee rate of ecological water for northern China water scarce regions, through improving reservoir operation rules and maximizing efficiency in the joint operation for multi-reservoir systems. A multi-reservoir ecological operation model is developed based on the subdivision of reservoir storage capacities. The model treats the river ecosystem as an independent water user, and formulates a scheduling scheme for partitioning multi-reservoir storage capacities for multiple water users. The effect of the scheduling scheme on the ecology and power generation benefits is considered through the establishment of a simulation module for the river basin water resources system. The module is used in combination with an objective function for the development of multi-reservoir ecological operation model. The purpose of the objective function is to maximize the supply guarantee rates while ensuring a balance as possible among all water users. The multi-reservoir ecological operation model is applied to the Luanhe River system of Haihe River basin. As the result of the application, the scheduling scheme is proposed for the joint operation of three reservoirs including Panjiakou, Daheiting and Taolinkou under the existed water supply conditions. The operational chart is provided on subdivision of reservoir storage capacities. The effect of the scheduling scheme is evaluated on the downstream ecological system and power generation benefits. The proposed model is proven to be effective by overall modeling results. Comparing to the current scheduling scheme, the new scheduling scheme can significantly increase the supply guarantee rate of ecological water from 46.9% to 93.8%, while not affecting the existed interest patterns in the context of flood control and water supply. The index for measuring eco-hydrological changes is also improved significantly.
Abstract: Drought warning is the major step and non-structural measure for disaster relief. However, it has not been worked with strong pertinence or practicality, due to the insufficiency of methodology studies. As a result, the role of drought warning has been fully exploited. In order to improve drought relief in China and taking the local situation into full consideration, the current situation and problem are reviewed based on explanation of concept of drought and reason of its formation. With completion of first hydrologic index system for drought warning in China and introduction of a new definition-waning level (flow) of hydrologic drought as well as methodologies for warning level determination, it creates a new methodology with hydrologic approach that fulfills the gap in drought warning related to river, lake or reservoir.
Abstract: The study aims to clarify the evolution of calculation methods of water environmental capacity of surface waters in China, and to discuss the development trend. Based on the systematic reviewing of previous relevant studies, the research history of water environmental capacity from the introduction of concept to current studies and then five calculation methods of water environmental capacity of surface waters in China were summarized as follows: Formula method, trial-and-error method, system optimization method (linear programming method and stochastic programming method), probabilistic dilution model method, and unascertained mathematical method. The basic theories, formation, and applications of the five calculation methods are analyzed. The scope of application, merits and drawbacks of each method are also commented. Taking into account of many factors including research trend, complexity of environmental issues and the demand for water resources management in China, it is suggested that the research in China should be focused on the development of the three methods: Probabilistic dilution model method, stochastic programming method and unascertained mathematical method.