Abstract: The reconstruction of river paleodischarge can determine the quantitative hydrologic and climatic characteristics of the drainage basin. Three paleochannel cross-sections of the Yangtze River at Nanjing section are restored by borehole data. Based on 14C and ESR (Electron Spin Resonance) ages and analysis of sedimentary facies, the paleochannel between the -50--90 m existed in the last glacial maximum (LGM). According to the sediment sizes, the right sediment incipient formulae calculate the average vertical velocity at different depths. Then, the average vertical velocity multiplies by the corresponding area to get the unit paloedischarge. Finally, adding all of the unit paleodischarge reconstructs the paleodischarge in the LGM. The paloedischarge in the LGM is about 10 000-12 000 m3/s that is equal to the present January average annual discharge. Longitudinal gradient in the LGM is about 4×10-4-5×10-4 and is the same with the present upper Yangtze River at Pingshan-Yibin section.
Abstract: Under the influence of climate changes, the hydrologic system has the characteristics of multiple time scales. The bank-full discharge, as a function of inflow conditions, also has the characteristics of multiple time scales. This phenomenon was studied based on the observed data of bank-full discharge, flow discharge and sediment concentration at hydrologic stations in the lower Yellow River from 1950-2007. The main time scales of these data series were obtained, and the relationship between bank-full discharge and inflow conditions under the same time scale was analyzed using the method of continuous wavelet analysis. Results show that the bank-full discharge of selected stations in the lower Yellow River have main time scales of 5-6 years and 19-20 years. In addition, the multiple time scales phenomenon at selected stations in the upper Yellow River and lower Wei River was also analyzed. A phase difference between bank-full discharge and sediment concentration was founded, with its value being different at different river reaches. Moreover, it was founded that the delayed time decreases as the annual sediment concentration increase. The phenomenon of multiple time scales of inflow condition and bank-full discharge in the Yellow River investigated in this paper is helpful for the study of multiple time scales existing in fluvial processes.
Abstract: Soil moisture (SM) is one of the key factors for plant growth and eco-environment reconstruction on the Loess Plateau of China. To ascertain the spatial variability of SM in deep soil layers at a regional scale, 234 sampling sites were located with a GPS receiver, and 12 198 soil samples were collected with a soil auger before the rainy season in 2008. The distribution and variation characteristics of SM were evaluated by using classic statistical and geostatistical methods. Results showed that ① SM decreased gradually from southeast to northwest in the horizontal direction, while in vertical direction, SM decreased from 0 to 90cm and then increased from 90 to 500 cm soil depth. ② Land use had a significant impact on the amount and profile distribution of SM. ③ The coefficients of variation and nugget ratios of SM at different depths in 0-500 cm profile demonstrated a decreasing-increasing trend, and these indices showed a good consistency in expressing the variation of SM. Understanding this information is beneficial to the management/mediation of soil and water processes, and to the restoration of eco-environment on the Loess Plateau.
Abstract: In order to improve the accuracy of real-time flood forecasting, the unit hydrograph was introduced to the real-time flood forecast updating system. The error feedback updating model tracing the source of information was established. In this paper, the details of the model structure and principles were described, and the ideal model was set to test the efficiency of the updating system. The correct results of different error ranges were compared. The results indicated that the efficiency of the updating system was improved, and the proposed method with simple structure, clear physical concept, and the forecast lead period is not lost. Conclusively, the proposed method could be widely applied in real-time flood forecast updating.
Abstract: There is currently stochastic, fuzzy and gray information in the complex flood disaster system. Furthermore, the theoretical analysis frame is based on general entropy and intelligence integration methodology for flood disaster risk management. The model (AIRM-POME) named attribute interval recognition model based on the principle of maximum entropy is proposed for flood disaster risk analysis. Then, the analytic hierarchy process is combined with trapezoidal fuzzy numbers to calculate the weights of criteria, and the average coefficient is applied to transform the attribute interval measure into an integrative attribute measure. In addition, the flood hazard grades and flood vulnerability grades can be obtained by using the assurance criterion and feature value equation. Finally, on the basis of the natural disasters risk expression recommended by the United Nations, risk grade for each unit can be achieved, respectively. AIRM-POME is employed for flood disaster risk analysis in Jingjiang flood diversion district, and the results demonstrate that the model is reasonable and has the advantage of illustrating very well the uncertainties. Thus, the model has bright prospects of application for comprehensive risk assessment of other natural disasters.
Abstract: In recent years, the number of extreme weather events rose greatly, especially larger flood disasters, happening more frequently and impacting more seriously. Based on numerous concepts of vulnerability, urban vulnerability was clarified, and an evaluation index system of urban flood disaster vulnerability was constructed. As one of methods of multiple attribute decision making, Technique for order preference by similarity to ideal solution (TOPSIS) could not compare the dots on the mid-perpendicular of positive ideal solution and negative ideal solution. Kullback-Leibler distance was used to calculate the similarity degree between the evaluation object and positive ideal solution. And then, this KL-TOPSIS model was made use to evaluate the Harbin's flood disaster vulnerability from 2005 to 2009 dynamically with the conclusion that it first increased and then dropped. Through the horizontal comparison, it was found that Harbin's flood disaster vulnerability was less than contemporary Shenyang, Wuhan and Shanghai.
Abstract: Around 80% of population in Taiwan has concentrated in urban areas, which increase loading in water supply, and weakens water supply systems. Rapid urbanization also increases runoff volumes and therefore intensifies the risk of flooding. For this, this study explored the hydraulic mechanism and volume analysis of the integrated rainwater retention-detention system for multi-purpose application, i.e., water supply, emergency water supply, and flood mitigation. Using green building design method and rainfall-runoff modeling, a method for multi-purpose evaluation for option analysis was established. The rainwater harvesting systems, infiltration gutters and ecological pound of one primary school in New Taipei City were investigated as case study. Results show that using system volume from 55 to 185 m3 the integrated system can achieve 26.5%-100% runoff volume and 15%-100% peak flow reduction with 5%-7.5% water supply rate and emergency water supply for 3 to 19 days. Therefore, the resulting plane can effectively reduce the size of tank volumes in the multi-purpose urban storm water retention and utilization.
Abstract: Based on both the NCEP/NCAR reanalysis data and the observed rainfall data, the results show that summer precipitation conversion rate of the whole layer over the Yellow River basin is relatively low. This considers that there should be a certain pressure level which has the most favorable conditions of water vapor transportation, lifting condensation and vertical motion during the entire layer. Thus, this pressure level is defined as the layer of effective precipitation conversion rate (referred to as the effective layer), and the ratio of precipitation to the effective layer's precipitable water is called the effective precipitation conversion rate. Through analyzing the average factors such as vertical velocity and water vapor in every subarea, the summer effective layers of the upper, middle and lower reaches are identified as ground -500 hPa, 600-400 hPa and 850-600 hPa, respectively. It's proven that the evolutional trends of summer mean water budget and precipitation conversion rate in the whole layer and in effective layer are consistent, peak and valley corresponding, and the values of precipitation conversion rate of the effective level are greater than that of the whole layer during the whole 49 years. The summer effective precipitation conversion rate reaches the highest over the Tibetan Plateau and the eastern part of the middle Yellow River but the lowest over the northeast side of Tibetan Plateau separately. Its distribution forms are similar in drought/flood years and multi-year mean, while the values in flood years are significantly higher than those in drought years.
Abstract: This paper systematically studies the hydraulic factor and sediment transportation character in the reservoir area after the impoundment of the Three Gorges Reservoir, the influencing factor to the sediment diversion ratio of the TGP. The conclusion indicated that there are three important influencing factors to the sediment diversion ratio, one is the riverbed character of the reservoir area, the other is the flow and sediment condition, and the third is the water level before dam. From June 2003 to December 2010, the sediment diversion ratio is 26.1%. The sediment discharging centers from May to October each year, during which the sediment diversion ratio is about 29.0%, especially during the flood peak time, the velocity is large, and the flow has a strong sediment transportation ability, the sediment diversion ratio is high, when the inflow discharge is larger than 30000m3/s, the highest sediment diversion ratio is 81.0%. Further more, with the rise up of the water level before dam, the sediment diversion ratio decreased, especially the capacity of coarse particle, to some extent, it affects the sediment diversion ratio, the sediment transport ability decreases with the decreasing of the flow velocity, accordingly, the sediment diversion ratio of the coarse particle decreases more evident than the total load with the decreasing of the flow velocity.
Abstract: Sediment deposition is a big problem that affects the lifespan of reservoirs in heavily sediment-laden rivers. Furthermore, venting turbidity currents is an important measure to reduce the sedimentation in reservoirs, especially at the initial operation stage of the Xiaolangdi Reservoir. The occurrence of plunge point means the formation of turbidity current, and the research into the prediction of turbidity current formation can help to better understand its motion laws in reservoirs. Qualitative descriptions and quantitative calculation methods for the prediction of turbidity current formation are summarized firstly in this paper, with the shortcomings and application conditions of these methods also being given. The momentum equation for the motion of turbidity current is then deduced, and the effects of non-uniform vertical distributions of sediment concentration and velocity on the formation of plunge point are investigated. Finally, a new formula for predicting the formation of turbidity currents is proposed herein, and its predictive accuracy is validated by lots of flume and field measurements. Validated results indicate that the proposed formula can be used to predict the formation of turbidity currents in the Xiaolangdi Reservoir.
Abstract: Measurement of open-channel-flow in a bend was made by using particle image velocimetry to get instantaneous two-dimensional velocity data based on which the mean, three-dimensional flow fields were reconstructed. The results show the main flow deviates to the convex bank upon entering the bend, then quickly shifts to the concave bank due to centrifugal force and remains near the concave bank until the end of the bend. Velocity gradient near the bed and location of the maximum velocity of the streamwise mean velocity profiles at each transverse location keep changing along the bend due to the action of concave bank lockup and secondary flow. Distance between bend entrance and the section in which the maximum depth-averaged streamwise velocity approach the concave bank increases with the curvature of the bend flume. There exist three-vortex structure in each section near the bend entrance affected by the secondary flow in the upstream straight flume, but this quickly decay into two-vortex structures in other sections. Both the strength of the major secondary flow and the location of its core changes along the bend.
Abstract: The transport and distribution of Dense Non-Aqueous Phase Liquid (DNAPL) in subsurface media are affected by many factors, which include DNAPL physical and chemical properties, soil properties, and leakage conditions, etc. The structure of multiphase flow can be more complex due to the effects of porous media heterogeneity. In this study, the Monte Carlo method is applied to a synthetic case in an effort to investigate the effect of the spatial variability of permeability on the fate and transport of DNAPL contaminant plumes. Numerical results show that the lower the leakage rate, the higher the heterogonous effects are on DNAPL migration in the case of fixed total leakage flux. Since the transport of DNAPL is affected by the gravity, for both centroid of the plume (first moment) and the distribution of the plume (second moment), the variability in the vertical direction is found to be greater than that in the horizontal direction.
Abstract: An operator-splitting algorithm for the two-dimensional convection-dispersion equation is developed. The governing equations are split into two successive initial value problems, which include a pure convection problem and a pure dispersion problem. For any arbitrary triangle calculation grids, suitable algorithms will be applied to resolve the problems at each grid point according operator characteristics. In the case of the convection problem, the method of characteristics can be applied. While for the dispersion problem, a semi-implicit finite element method will be employed. The issue concerning interpolation in convection problem will be discussed in detail, and a cubic interpolation method will be proposed to reduce the numerical damping effect. To overcome the numerical oscillation problem in high-order interpolation, it is required to keep the continuity of function and its partial derivatives. The testing results show that the numerical simulations of this study agree well with analytical solutions. The proposed operator-splitting algorithm can significantly reduce the numerical damping effect and overcome the numerical oscillation problem in high-order interpolation when solving pure convective transport problems.
Abstract: Understanding of flow characteristics of multiple tandem jets is essential to the study on the mechanism of diffusion and ionic transport in the jets. In this study, a particle image velocimetry technique is used to measure the hydrodynamics of multiple tandem jets in cross flow with 1, 2, 4 nozzles. The experimental results show that the entrainment on the front face of the first jet in a nozzle group is apparently stronger than that of a single jet. The region between two jets can be divided into two parts. The flow in the upstream part of the region is entrained into the front jet, while the flow in the downstream part will be entrained into the rear jet. The cross flow velocities in front of the rear jets are apparently smaller than that of the first jet. There exists an effective cross flow velocity that makes the rear jet bends.
Abstract: For the cascade hydropower plant development it is important to conduct a risk analysis on the cascade system of construction diversion, which is composed of two adjacent hydropower stations undergoing synchronous construction. Based on the risk assessment theory, and considering the hydrologic and hydraulic uncertainties, an integrated risk analysis model is developed. The risk calculations for different combinations of flood events can thus be carried out using the integrated risk analysis model and the Monte-Carlo method to couple with major risk factors. Aiming at the condition of floods encounter, the flooding process designed for the construction period of the downstream diversion system can be obtained by introducing an initial time difference stochastic factor into the risk calculation. The result from an engineering case study shows that the proposed risk analysis model and the derived risk calculations are reliable and effective, which provide an important basis for the adoption of the diversion construction standard and the optimization of diversion construction planning under the condition of cascade hydropower plant development along a river reach.
Abstract: Spectra, salinity, total suspended solids and colored dissolved organic matter are sampled at 44 locations in the Pearl River estuary on December 18, 19 and 21, 2006. The samples are analyzed. Based on the experimental results, the relationship between the absorption coefficient of chromophoric dissolved organic matter (CDOM; g400) and the remote sensing reflectance is obtained. In the Modaomen waterway, the result shows that there is a strong positive linear relationship between the in-situ reflectance ratio (R704/R513) and g400 (R2=0.7, P<0.001); and in the Humen waterway, a negative linear relationship between the in-situ reflectance ratio (R703/R488) and g400 (R2=0.58, P<0.001) is found. Additionally, the absorption coefficient of CDOM and the salinity in the two waterways are studied, and the two parameters are highly correlated (R2>0.67). Finally, using the result of this study, a novel method is developed to monitor the surface salinity distribution in estuarine waters. The new method is validated using the simulated Medium Resolution Imaging Spectrometer Instrument (MERIS) data with satisfactory results. The study demonstrates that the salinity variation in the Pearl River estuary (ERMS<0.308%) can be monitored by remote sensing techniques (e.g., MERIS).
Abstract: The estuarine reach of Qiantang River provides 85% fresh water supply to Hangzhou city. However, the estuarine water quality is threatened by salt water intrusion during spring tides of dry seasons. It is thus important to analyze the temporal-spatial variation of salt water intrusion and to develop a two-dimensional (2D) numerical model for the estuarine reach of Qiantang River. In this study, the temporal-spatial variation of salt water intrusion is analyzed using observed chloride profiles collected during spring tides. A 2D numerical model for coupled fluid flow with salinity transport is developed accordingly. The governing equations of the model are solved by an explicit finite-volume method with good conservation performance. The influence of river runoff and tidal current on salt water intrusion in the estuarine reach of Qiantang River is studied using the 2D numerical model. The result shows that both river runoff and tidal current have great influence on salt water intrusion in the estuarine reach. Countermeasures such as increasing discharge from the upstream Xin'an reservoir can effectively restrain the salt water intrusion and thus to reducing the chloride concentration and the over-standard time in estuarine waters. As a result, good water quality at the intakes can be maintained at the level of safe water supply.
Abstract: Assessing the influence of reservoirs on downstream water temperature constitutes an important part of environmental impact study for hydropower development. A set of evaluation indicator system is established from the perspective of downstream water temperature fluctuation. The latter is the result of reservoir-induced temperature changes in downstream waters. The evaluation indicators include the baseline deviation, the phase shift and the extreme change. Each indicator is defined and the corresponding formula is provided. An evaluation method using the indictors is proposed for assessing the influence of reservoirs on downstream water temperature. The cascade reservoirs on the upstream of Yellow River are selected for a case study in an effort to test the proposed evaluation indicator system and the evaluation method. A spatial and temporal evaluation of the influence of reservoirs on downstream water temperature is conducted. The result shows that the evaluation indicator system and the evaluation method are able to adequately reveal the seasonal change of water temperature, as well as its time lagging and flattening resulting from reservoir operations. The main characteristics of water temperature variation can also be determined by the system and the method. Furthermore, through analyzing various indicators at different river reaches, the cumulative influence of cascade reservoirs on downstream water temperature can be revealed. The evaluation indicator system and evaluation method provide a general methodology, and can be applied to other river systems to study the influence of reservoirs on downstream water temperature.
Abstract: Global Climate Models (GCMs) are the primary tools for understanding how the global climate might change in the future. However, the relatively low spatial resolution of GCMs outputs is unsatisfactory for the local-scale climate impact assessments. Compared to dynamic downscaling, the statistical downscaling approach is widely used to bridge this gap. In this review paper, recent advances in three fundamental statistical downscaling approaches (regression methods, weather type approaches and stochastic weather generators) were presented firstly. Furthermore, uncertainties in statistical downscaling were discussed. The developments and applications of statistical downscaling in China were then summarized. The review study concludes that the comparisons and combinations of statistical downscaling and dynamic downscaling approaches, downscaling of extreme events and uncertainty analysis in statistical downscaling will become the mainstream of future related studies.
Abstract: It is of great significance to study the hydrodynamic behaviors of jet flow in coastal waters, which can enrich the basic theories of jet flow for coastal dynamics and provide the design guidance for sewage disposal in coastal zones. In this paper, the research progresses of jet flow under various coastal dynamic conditions, including currents, waves and co-existing currents and waves are extensively reviewed. Comments on the necessity and feasibility for the further research on jet flow under the combined wave and current conditions are provided. An integrated approach with the combination of experimental study by the particle image velocimetry and the laser-induced fluorescence measurements and numerical study by the large eddy simulation is proposed to address this issue.