Abstract: China has been frequently hit by extreme floods and droughts due to its unique geographical features and climatic conditions. The inherently low precipitation in North China makes the conflict between water supply and demand increasingly prominent in the region. Under a changing environment, the observed runoff in northern major rivers has been declining over the last few decades. On the other hand, the rapid socio-economic development in the region has resulted in a substantial increase of water consumption. These two factors have further aggravated the water supply-demand conflict. The attribution analysis of runoff variability reveals that intensive human activities have a major influence on the reduction of runoff in northern major rivers, which include the land-use change, the industrial and agricultural developments, and other socio-economic activities. Implementing the most stringent water resources management policy and enhancing the construction of water saving society would be the fundamental way out of the water shortage problem in North China.
Abstract: To quantify the effect of topography and snowmelt on hydrologic simulation, the (Soil and Water Assessment Tool (SWAT) model is employed for the hydrological simulation in the Yellow River's source region for the period 1960—1990. The topographical effect is determined through the partitioning of subbasins into elevation bands. While, the snowmelt effect is simulated using a snowmelt module. A series of simulations is conducted. The result shows that a satisfactory result of model simulations can be obtained when the snowmelt module applied alone or jointly with the consideration of elevation bands. The model will have a better performance if the topography effect is considered, indicating that topography plays a dominant role in water balance simulations. The model temperature is more sensitive to the partitioning of subbasins than precipitation. A reduced temperature value will lead to the reduction of evapotranspiration from subbasins, and hence increases the water yield of subbasins. Groundwater will get the most yield increase and followed by surface water and lateral flow. The influence of topography and snowmelt is likely to change to the source of groundwater recharges. An excellent simulation result can be obtained through calibrating model groundwater parameters that consider the effect of topography and snowmelt. The study provides valuable information for other hydrologic simulation in mountainous watersheds.
Abstract: The effect of frost degradation on runoff variability in cold regions has become a hot issue under a changing climate. However, most existing researches on the subject have focused on exploring the relationship between permafrost degradation and runoff. In this study, the relationship between frost degradation and runoff and its variability over the last 30 years are investigated. The study uses the frozen depth data from the Manzhouli meteorological station for the period 1974—2006 and the monthly runoff data from four hydrological stations on the Hailaer River basin for the period 1974—2008. The result shows that the winter discharge has increased 13%-20% at the Hailaer, Bahou, and Honghuaerji three hydrologic stations, and no significant change is found at the fourth one (Yakeshi). The discharge ratio of February to November (Q2/Q11) has increased significantly, while the maximum frozen depth at the Manzhouli meteorological station has decreased about 50cm for the same time period. These results imply that the winter recession curve has shown a slowing trend mainly due to the effect of frost degradation under climate warming. The hydrologic impact of frost degradation would be explainable by the following three aspects. First, the degradation of frozen ground will lead to the increases in aquifer thicknesses, surface water infiltration amounts, and groundwater storages. Subsequently, the groundwater increment will increase the winter discharge. Second, the circulation of groundwater is moving much more slowly than the surface water does. The enlarged groundwater reservoir will lead to a longer river runoff recession. Third, the response of frost degradation to climate warming is a slow process and its effect on runoff variability is also a gradual one.
Abstract: In Xinjiang, snow constitutes a major water resource important to crop production, ranching, water supply, and other user needs. The snow water equivalent is estimated and its spatial-temporal distribution is analyzed using the MODIS (Moderate Resolution Imaging Spectroradiometer) EOS (Earth Observing System) remote sensing data collected during 2004—2010, and a 50-year dataset of snow depths and densities from 89 meteorological stations in Xinjiang. The result shows that the maximum value of annual snow water equivalent in Xinjiang during 2004—2010 was about 36.883 billion m3, which occurred in the winter of 2009—2010; while the minimum value was only 9.391 billion m3, which occurred in the winter of 2006—2007. The difference between maximum and minimum is about four times, and the difference in the earliest and latest dates for the peak occurrence can be 50 days long. Snow water resources in Xinjiang is mainly distributed in four regions, which are South Xinjiang, eastern Xinjiang, Yili and Bozhou, northeast of North Xinjiang. The time of peak occurrence of snow water equivalent varies from region to region around Xinjiang. The peak value of snow water equivalent is the sum of peak values in the four regions. The snow water equivalent has fluctuated dramatically in past 50 years in Xinjiang. An upward trend with a slope of 0.083 2 in the snow water equivalent variation has been detected, which indicates that the snow water resource in Xinjiang has increased annually. A gradually increased fluctuation range indicates there may be years with less snow water resources.
Abstract: Sandbar clogging occurred frequently at the confluence between hyper-concentrated flood flows from tributaries and the main stream in the Upper Yellow River, with consequence of severe flooding disasters. The properties of hyper-concentrated flood flow in tributaries and the characteristics of sandbar clogging at the confluences between tributary and main stream were analyzed based on field data for sandbar clogging events in the Upper Yellow River. Effects of key factors, such as discharge ratio (tributary discharge to that of main stream) and water amount and sediment load of hyper-concentrated floods, on the sandbar clogging were investigated. A general discriminant formulation for sandbar clogging at confluences was proposed based on the momentum principle. By taking account into the characteristics of flood and sediment transport in the main stream and tributaries, two criteria for sandbar clogging were further derived from the general discriminant formulation, one expressed by relationship between discharge ratio and water amount of tributary flood and another expressed by water amount and sediment load of tributary flood. Therefore, the occurrence of sandbar clogging can be predicted using discharge ratio, water amount and sediment load of tributary flood. This is of critical importance for preventing disasters caused by sandbar clogging at confluences that is associated with hyper-concentrated flood flows during rainstorm events in the Upper Yellow River.
Abstract: The influence of land use types on soil infiltration is one of the hot research topics in soil hydrology. In this research, four typical land use types in the Fengqiu region were chosen to systematically study the intensity, structure and main sources of the spatial variability of soil infiltration under different land use conditions. The result shows that the frequent cultivation can reduce soil heterogeneities, and thus weaken the spatial variability of soil structures. Compared to traditional tillage practices, soil properties exhibit high degree of apparent spatial structure in no-till and honeysuckle fields. The infiltration characteristic in forest soils, which received the least disturbance, varies most and exhibits a smallest range of variability among the four land use types. The soil bulk density, soil organic matter content and initial soil moisture are the major sources of variation for the spatial variability of soil infiltration. The initial soil moisture is the sole source of variation in the honeysuckle field. On the forest soil, the soil organic matter content and initial soil moisture are the major sources of variation. No significant variation sources are found on the no-till field. In some cases, the temperature of water could be an important factor to distort the spatial variability of soil infiltration.
Abstract: This study shows in detail how the classical time fractional advection-dispersion equation (TFADE) can be generalized using the concept of tempering. The generalized TFADE model is then approximated by a new spatiotemporal splitting method, which is computationally more efficient than the classical Eulerian solver due to the logic tempering of the time nonlocal dependence in solute transport. Numerical experiments show that the generalized TFADE model captures a broad range of non-Fickian diffusion, where the tempering parameter λ (which is the inverse of the characteristic time), fractional index γ, and mobile/immobile capacity coefficient β can control the nuance of transport behavior. The model also efficiently distinguishes the mobile phase from the total phase for solute transport through heterogeneous media, which is critical for practical applications.
Abstract: When modeling the flood routing process in diversion areas with numerical models, the phenomena of scour and collapse at the diversion gate is very serious, which requires the model can adjust the boundary and move the calculation grids accordingly. The traditional constant calculation grid is not suitable to solve the problem of the dynamic change at the calculation boundary, so, in this paper, with the method of dynamic grids, combined with the collapse mechanism of cohesive riverbank in soil mechanics, a two-dimensional (2-D) dike failure plane numerical model with movable grids is established. The model is based on the comparison of calculated and measured data. The model is validated on the Datangwei flood detention basin. The result shows that during the erosion of dike burst flow, the landslip failure to the dike occurs, the flood discharge near the dam burst increases rapidly, which closes to actual experiences. It also shows that with the combination calculation method of the movable grid and collapse mechanism of the cohesive soil river-bank in Soil mechanics, the model simulates reasonably well the broadening process at the diversion gate.
Abstract: Better understanding of the temporal and spatial evolution of river networks in plain polders of the Taihu basin is essential for the management planning and development in the region.Using geographic information system (GIS) and remote sensing (RS) technologies, the evolution of river networks in the Fenhu town and other typical polders in the region is explored for the period 1994—2009.Results show that there exists a distinctive variation in lower-order streams within polders, while little change occurs in higher-order streams.The spatial variations of river networks among the 6 typical polders are significantly different from each other.In times of rapid urbanization, a river network could be improved should the rivers in polders be well managed and controlled, and vice versa.Based on the evolution of river networks and the rate of urbanization in each polder, a river network has four evolutionary modes, which are the active conduction mode, the passive transformation mode, the restoration and recovery mode, and the priority protection mode. Main reasons for the revolution are mankind's activities such as river network protection, enhancement and destroy, so there is no specific relationship between the urbanization and the evolution of river networks within polders.
Abstract: The use of an annularaerator placing in the vertical shaft of flood discharge tunnel is a new engineering idea, and is different from the traditional ones.In order to better understand this new type of technology, the ventilation and aeration characteristics of the annular aerator are studied based on the prototype and modeling experiments carried out in the gyrating discharge tunnel of the Gongboxia Hydropower Project.The results show that the ventilation is caused by the pressure difference of air vents.The relationship between the ventilation and relative cavity length follows the linear distribution.The aeration effect on the annular aerator is obvious.The jet is striking water in the shaft, and then a large-scale aerated vortex is generated with bubbles thereby contributing to the aeration forming.The aeration concentration presents a power distribution in the vertical shaft.The ventilation and aeration scale effects of models are both obvious.Therefore, the use of an annular aerator is necessary to set in the vertical shaft of gyrating discharge tunnel while satisfying the structural designs demands, which can improve the flow pattern and increase the energy dissipation significantly.
Abstract: Gravel dunes are the typical form of bed load motion and one of the research focuses in river dynamics, which determines the bed resistance, the bed geometry and the bed load transport rate in alluvial rivers. Most previous studies focused on the fine sediment in the middle and lower reach of rivers or in estuaries and coast areas where the grain diameter is less than 1mm. Thus, further research should be done to determine whether gravel dunes (D>2 mm) exist in mountain rivers and how to estimate the critical condition. On the basis of field surveys at Jiuduizi and Shaojibei sites in the upper reach of the Yangtze River, it is apparent that the natural form of gravel dunes does exit in mountain rivers. A series flume experiments were carried out with nature sediment (D50=1.8 mm, 5.3 mm) and coal (D50=4.8 mm) and stable uniform flow conditions, to simulate the formation of gravel dunes. A formula of critical condition for gravel dunes is proposed, which is expressed in terms of the dimensionless flow power w*, R/D and the slope S according to the energy slope, the average water depth, the discharge and other parameters of the flume experiment. The discriminate coefficient of gravel dunes GDcr is also proposed to determinate whether dunes exist on gravel transport belt. The study can provide a reference for the regulation of channel activity, flood defense preparations and bed load transport predictions.
Abstract: The fracture toughness of sea ice is an important parameter to analyze ice load on offshore structures, and also affects the sea ice dynamics, such as sea ice breakage, rafting and ridging, etc. In this study, sea ice samples were collected in the Liaodong Bay of Bohai Sea in the winter of 2011—2012.The values of sea ice fracture toughness KIC were tested under different ice temperatures, salinities and loading rates with bending tests of three loading points. The results show that the brine volume (as a function of sea ice temperature and salinity), and the loading rate have obvious influences on the value of KIC. The value of KIC decreases with either increasing ice temperature or loading rate. It has a negative exponential relation with the square root of brine volume. The results of this study will be a reference to study the fracture process of sea ice cover under ultimate conditions, and can also be applied to analyze ice load on offshore structures.
Abstract: The threshold of peak-over-threshold (POT) flood series has changed for many rivers in the world. Improper selection of threshold will affect the rationality of frequency analysis. The changing rule and influence of the threshold selection for POT flood series under the changing environment in Wujiang River was analyzed using historical flood data. The research results indicate that watershed vegetation and runoff coefficient varied significantly in 1991.After the environment was changed, the threshold increased significantly, and the occurrence number of flood exceeding a certain magnitude also increased. The POT model can flexibly capture the information on changes of flood magnitude and frequency of occurrence. The threshold values, which changed before and after environment, were selected to calculate designed flood peak. The difference degree of designed flood peak for different threshold is up to 19.21% at Pingshi and more than 8.12% at Lishi station when the return period is greater than 200a. High threshold in the selection after the environment was changed can effectively improve the fitting degree of distribution to higher flood flow and improve the accuracy of design flood under the changing environment.
Abstract: In order to coordinate the role of reservoirs in water resources development and river ecosystem protection, a scheme for designing ecological storages were presented and applied on Danjiangkou reservoir. Tennant Method was used to calculate reference values of ecological flow in Xiangyang and Xiantao, two control sections downstream of Danjiangkou reservoir. Then an optimization model for ecological storage were established based on an integrated consideration of the reservoir's multi-function, including flood control, ecological water demand, water supply, water transfer, power generation and navigation. Finally, solutions were obtained by integrating Adaptive Genetic Algorithm (AGA) with scheduling simulation technology under the background of four operation rules respectively. Results indicated that the operation charts with ecological storages could meet the demand of ecological flow in the control sections with a superior comprehensive benefit. In addition, optimize-simulate technology was approved to be a viable approach for the ecological storage design.
Abstract: An experiment of the dissolved oxygen transport and diffusion with water and air mixture in plug discharge is established, in order to study the undersaturated dissolved oxygen behavior of water and air mixture plug discharge and illustrate the influence of air volume fraction, inlet dissolved oxygen concentration, Reynolds number and geometry size on dissolved oxygen concentration. Velocity, pressure and dissolved oxygen concentration are measured, respectively. A three-dimensional mathematical model of dissolved oxygen transport and diffusion is established to compute water and air mixture flow, and, it is validated by the experimental data. It is used to compute the dissolved oxygen distribution with different inlet air volume fraction, dissolved oxygen concentration, Reynolds number, length, and diameter of the plug section. The results show that the increment of dissolved oxygen concentration increases with increasing air volume fraction, and, increasing difference between inlet dissolved oxygen concentration and saturation dissolved oxygen concentration, respectively. It also increases with decreasing Reynolds number. Finally, it increases with increasing length of plug section, and increases with decreasing diameter of plug section.
Abstract: Determining the cycle of riverine sulfate, affected by natural weathering and anthropogenic activities, is necessary for surface water management. Mainstream and tributaries of Yellow River from Xiaolangdi Reservoir, including Qinhe River and Yiluo River, were selected. River water samples were collected during different seasons, and dual isotopes of dissolved sulfate were measured, together with hydrochemical compositions of surface water and isotopic compositions of potential sources. Based on these, sources of dissolved sulfate in Yellow River and its tributaries with the mixing ratios of different sources in Qinhe River could be identified. The results indicate that: ① dissolved sulfate in Yellow River mainly derived from Quaternary loess, and the mean sulfate content was 2.23 mmol/L, with the mean δ34SSO4and δ18OSO4values of +8.9‰ and +10.4‰, respectively; ② during flood season, 24% of dissolved sulfate in Qinhe River derived from rain water, 61 percent of dissolved sulfate derived from soil, and 15 percent of dissolved sulfate derived from gypsum dissolution. During temperate season, the mixing ratios of rain water, soil and gypsum were 39%, 36% and 25%, respectively. The mean sulfate concentration was 2.44 mmol/L, and mean δ34SSO4and δ18OSO4values were +9.8‰ and +9.7‰, respectively; and, ③ dissolved sulfate in Luohe River more derived from sewage water and that in Yihe River was mainly controlled by soil and fertilizer. The mean sulfate concentration in Yiluo River was 1.27 mmol/L, and mean δ34SSO4and δ18OSO4values were +10.4‰ and +6.5‰, respectively. Dissolved sulfate in local river water was mainly controlled by natural weathering processes, such as dissolution of evaporites minerals and soil sulfate. At the same time, it should not be ignored that anthropogenic activities had altered the hydrochemical composition of the water Yiluo River, which should be paid more attention by local surface water managers.
Abstract: Existing physical habitat models could only be available and efficient for the rivers which have abundant monitoring data. To overcome this shortcoming, a new physical habitat simulation method by applying fuzzy logic inference was presented. Based on precise flow field simulation results, the proposed fuzzy habitat model linked these data to the expert knowledge base to compute habitat suitability indexes of each unit by using fuzzy logic reasoning. At last, the weighted usable area and highly suitable proportion of habitat at different river discharges were calculated to study the ecological water requirement. By using the proposed method, Chinese sturgeon spawning habitat on the downstream of the Gezhouba Dam was simulated. The results indicate that the suitable ecological flow range for Chinese sturgeon propagation is about 10 000-17 000 m3/s. The proposed method which is weak dependence on monitoring data by considering expert knowledge and experience is feasible and available. This research could be helpful to ecological protection and river management for the rivers which are lack of field-measured data, and could also provide a reference for the application of fuzzy mathematics in water ecology.
Abstract: Value of material production, water conservation, water quality purification, leisure tourism, culture/research/education, energy absorbed by transpiration, and habitat, as well as existing value, option value, and heritage value of West Lake in Hangzhou were evaluated by monetization. This analysis was based on market price method, shadow engineering method, cost of pollution prevention and control method, travel cost method, results reference method, benefits substitution method, contingent valuation method, The results shown that the total ecosystem services value of West Lake in Hangzhou was 73 576.247 million yuan/a, which was equal to 10.5% of gross national product in Hangzhou. The value of leisure tourism (73 157.602 million yuan/a) was the largest of the 10 evaluation indicators, accounting for 99.431% of the total ecosystem services value, followed by the value of absorbed by transpiration (138.642 million yuan/a), accounting for 0.188%. Ecosystem services function of West Lake in Hangzhou is mostly leisure tourism. The accounting of its economic value is beneficial to construct economic account of urban ecological, and can provide scientific reference for the sustainable development of the city.
Abstract: The Three Gorges Project, with maximum dam height of 181m, has been designed for water level storage. During the design and construction period of the dam: ① Distinctive geological exploration, a variety of stability calculation method of comparative analysis and comprehensive engineering measures have been applied to solve the left bank dam stability against deep sliding; ② Arranging multilayer outlets to satisfy flood discharge of large flow with multiple tasks, orifice reinforcement is based on FEM; ③ Aggregate secondary-cooling, individual water filling system and surface heat preservation are adopted for temperature control and crack prevention of the dam; ④ Rich slurry concrete permeability control and embedded cooling pipe are used in the construction of roller compacted concrete; and, ⑤ Closed pump drainage and no cover load consolidation grouting are used for foundation treatment. We put forward the relevant problems needed to be further studied on the aspects of longitudinal joint structural integrity of the high gravity dam, dam heel stress and stress control criterion of dam, seismic damage mechanism by intensive earthquake and anti-seismic measures, etc. by analysis of longitudinal joint opening variation and the change rule of the dam heel stress due to the water level variation.
Abstract: Driving mechanism of drought is the theoretical basis of understanding drought, both scientifically and for making effective drought-resisting policy. The forming processes of meteorological drought, hydrological drought and agricultural drought and the relationship among them are analyzed. A theoretical framework of the driving mechanism for drought evolution is established by adopting the "driving force-pressure-state-response" model. Key problems such as the principle factors of drought evolution, the driving mechanism of drought evolution, the methods of analyzing evolution rule and response of drought under changing environment are discussed.