Abstract: The runoff and sediment regimes in the Yellow River Basin have been undergone significantly changes in recent years. This study analyzes the changes in runoff and sediment regimes during the period 1997-2006 using the combined approach of hydrological methods, soil and water conservation methods and mathematical modeling. The hydrological and sediment data measured at stations on the main stream and tributaries of the middle and upper reaches of Yellow River are used in the study. The mechanism of changes in runoff and sediment is analysed. Projections of future changes in runoff and sediment regimes are also provided. Results show that in comparison to the long-term average runoff from the source area of Yellow River, a reduction of 43.90 billion m3 in the annual runoff has been found in recent years (1997-2005). Among which, precipitation and other natural factors can account for 92.26% of the reduction and the remaining is due to the effect of human activities. The observed value of Yellow River annual runoff during the same period has decreased 112.1 billion m3 compared to that before 1970. Human activities are responsible for 76.50% of the decrease and the rest is due to the reduction of precipitation. At the same time, the observed annual sediment load has been reduced by 11.80 million tons, 49.75% of which is due to the result of human activities such as the integrated control measures on soil and water loss and the remaining portion of the reduction can attribute to the reduction of precipitation. The impacts of human activities and precipitation reduction on the changes in runoff and sediment regimes vary significantly over space. For example, the effect of human activities on runoff reductions is much greater than that of precipitation reduction in the area along the middle reach of Yellow River. While for the reduction of sediment load, the human activities contribute nearly as much as precipitation does. Despite the fact that significant changes have been found in runoff and sediment regimes, the quantitative relationships generally remain unchanged between runoff and sediment load and between precipitation, floods and sediment load in most areas of Yellow River tributary basins. For example, the hyperconcentrated flow occurs during heavy storm events. There are few exceptions on the relationships between precipitation, floods and sediment load in individual tributary basins, which are often accompanied by a significant reduction in runoff and sediment yields. A slight downward trend is projected for both runoff amount and sediment load in the coming decades until 2050 with occasional occurrences of plentiful runoff and heavy sediment load.
Abstract: The Huang-Huai-Hai River basin is one of the important agro-ecological zones and major grain producing areas in China. The spatial distribution and temporal variations of drought and flood affected areas are analyzed using the daily precipitation time series for 1961-2010, the national 1:250 000-scale digital elevation model (DEM) model, and a 1:200 000-scale land use dataset. Precipitation data is collected from 204 meteorological stations distributed in the Huang-Huai-Hai River basin and its surrounding areas. The data is used to calculate the China-Z Index for measuring drought severity. The calculated China-Z Index is further corrected using an underlying surface correction procedure and is analyzed using the Set Pair Analysis (SPA) meteorological diagnostics routines. Maps of drought and flood prone areas are obtained and the regions with alternating dry-wet conditions are identified. The result shows that drought and flood are most likely to occur during summer and autumn seasons. There is a clear upward trend in the drought affected areas in autumn. Both Yellow River basin and Haihe River basin are prone to drought, while the Huaihe River basin often experiences both drought and flood disasters. The regions with alternating dry-wet conditions are gathered around the middle and upper reaches of Huaihe River.
Abstract: In order to understand the current status of atmospheric moisture content and to analyze the spatial and temporal variations in the distribution of precipitable water over China, the Japan Meteorological Agency reanalysis data set is used to map distributions of annual and seasonal moisture content for 1979-2010. The obtained maps are compared to those based on sounding data, and necessary corrections to the maps are made accordingly. The study uses China river basins as units for the trend analysis of moisture content. The result shows that there is a little interannual variation in the annual moisture content in each of the China river basins, as revealed by small values of the coefficient of variation (CV<0.1) for each basin separately. The higher values of CV>0.06 are found in river basins of Northwest China. Significant upward trends in annual precipitable water have been detected in river basins of Beijiang, Tarim, Hexizoulang and Alashan, Qaidam and Changtang. The opposite is true for river basins of Southeast and Inner Mongolia. No significant trend in moisture content has been found in the rest of China river basins.
Abstract: The stable isotopes characteritics of hydrogen and oxygen in precipitation is an important aspect of the regional isotope hydrologic cycle. The variations of δD and δ18O values in event-based precipitation samples are analyzed. The samples were collected from three stations (No.1, Zongkong, Houxia) in the upper Urumqi River basin from May 2006 to August 2007. The δ18O in event-based precipitation exhibits an extremely wide range and a distinct seasonal variation with enriched values in summer and depleted values in winter. The slopes and intercepts of the local meteoric water lines (LMWLs) along the Urumqi River Basin are No.1>Zongkong>Houxia>Urumqi the nearest Global Network of Isotopes in Precipitation (GNIP) station. The δ18O and δD values in event-based precipitation and the mean air temperature show a significant positive correlation, and a better linear relation exists between δ18O and air temperature than that of δD. Seasonal variations can be observed in d-excess of precipitation. The results of air-mass back trajectories of each precipitation event with the HYbrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model indicate a dominant effect of westerly air masses in summer and the integrated influence of westerly and polar air masses in winter for the study area.
Abstract: The rocky mountain areas in Northern China are confronted with water resources scarceness due to the sustainable development and utilization of the precious resources. To effectively utilize limited water resources, the isotope techniques are widely used to study the movement of water in hydrological cycle. The study was conducted at the Jiufeng low mountain region of West Beijing. We identify the transforming relationships among those water sources in Jiufeng through analyzing the isotopic variations of precipitation, soil water and spring water. Results show that the water line in rainy season in Jiufeng is significantly different from the local meteoric water line in Beijing, both slope and intercept of the water line in rainy season are smaller than that of the local meteoric water line, along with the rain, the characteristics of D and 18O have scheduled changes and rainfall effect, and the scheduled changes in precipitation also affect the soil water isotopic characteristics. The isotopic compositions of soil water are relatively concentrated in the study region. Both slope and intercept of evaporation line equation are smaller than that of the local meteoric water line and the rainy seasonal water line. The soil in Quercus Variabilis Mixed Forest is not sensitive to small precipitation events. The soil water movement in Platycladus Oriatalis plots is faster than that in Quercus Variabilis Mixed Forest, which can account for the affection of forest types and soil characteristics to the conversion between different water sources. The isotopic composition of spring water is relatively stable, and they mainly distribute on the bottom right of the local meteoric water line, near the intersection point with the rainy seasonal water line. There have different isotope variations among different water sources. The largest variation is in rain water and the least is in spring water. The values of hydrogen and oxygen isotopes in different water sources decrease with the water cycle path from precipitation to soil water, and then to ground water.
Abstract: The deficit in soil moisture or soil moisture storage capacity for a particular point is estimated based on the van Genuchten soil water characteristic curve model. The deficit is then used together with the relationship between the depth to groundwater table and the TOPMODEL topographic index in the development of a watershed storage capacity model taking into account the effect of soil properties and topography. Based on statistical analysis of the storage capacity of each grid point, the watershed storage capacity curve can be obtained. The watershed-scale capacity curve is used to replace the calibrated storage capacity curve of the traditional Xin'anjiang model. The Ziluosha sub-basin of Huaihe River basin is chosen as a test site to validate the new model and to study the influence of terrain and soil types on the watershed storage capacity. Results show that the new model can better simulate the event-based flood hydrograph compared to that obtained with the traditional Xin'anjiang model. The use of an explicit formula for the storage capacity in the new model reduces the number of user calibrated parameters in the traditional Xin'anjiang model, which provides a new tool for hydrological simulation in ungauged basins.
Abstract: The influence of land surface schemes on precipitation simulation is examined through two multiyear simulations of the China's climate during the period from 2001 to 2005. The Regional Climate Model (RegCM Version 4.0) coupled to the Biosphere-Atmosphere Transfer Scheme (BATS) and the Community Land Model (CLM) respectively is used for the climate simulation. The precipitation simulations are compared to two precipitation datasets Climate Research Unit of University of East Anglia (CRU), and Global Precipitation Climatology Project (GPCP). The result shows that both spatial distribution and temporal variation of China's precipitation can be reasonably simulated by RegCM4.0 coupled to the two land surface schemes. However, the RegCM_BATS generally produces a positive bias in the simulated precipitation, while the opposite is true for the RegCM_CLM precipitation, indicating that precipitation simulation is sensitive to different land surface schemes. The largest positive bias is found in Northeast China for RegCM_BATS, and in the South of Yangtze River for RegCM_CLM, the RegCM_CLM precipitation has the biggest negative bias. The simulation bias is large in summer months, and small in winters. The precipitation differences between the two simulations decrease from Southeast to Northwest. Both RegCM_BATS and RegCM_CLM can well simulate the precipitation frequency for different intensities. RegCM_CLM generally overestimates low intensity precipitation and underestimates high intensity precipitation. The opposite is true for RegCM_BATS. Differences in the modeled evaporation and latent heat flux with the two land surface schemes are the major causes of the precipitation difference between the two simulations. The influence of evaporation on precipitation simulation is larger during the summer months than that of winter months. While, the water vapor advection has an insignificant influence on precipitation simulation.
Abstract: A common problem in hydrologic frequency analysis is that the sample size is often too small to adequately represent the statistical property of an entire population. Uncertainties can thus be introduced during the determination of design hydrologic characteristics. In this paper, a new method based on Bootstrap is used to estimate the influence of sample uncertainties on the design characteristics. Compared to conventional approaches, the new method provides not only point estimates and interval estimation for the design characteristics, but also a quantitative evaluation of uncertainties associated with hydrological frequency analysis. In addition, combing with the Bootstrap technique, three schemes are established for assessing the effectiveness of the new method when using different parameter estimation approaches. The schemes are the moment method, the weight function method and the linear-moment method. The Nantong annual rainfall data from 1970 to 2011 is used to validate the new method. The result shows that with the new method, the selection of different parameter estimation approaches will have an insignificant impact on the determination of design hydrologic characteristics. This is from the point of view of the expected value, 90% confidence intervals and the final design characteristics. The new method can also deal with the limitation of the B value.
Abstract: This paper analyses the contribution rate of sediment in bank collapse and river bed evolution and presents a study on the patterns of non-viscous bank collapse and the interaction between it and the riverbed erosion/deposition through a series of experiments carried out in a bend flume. The experimental results reveal that the destruction of bank in the process of flow washout is a repeated interaction of water scouring the foot of bank, bank collapse along with the deposition and transportation of landslide substances. The mode and velocity of collapse and bed deposition rate and sediment interblending are largely affected by flow velocity distribution, flow turbulence and secondary flow, water level and the riverbed boundary conditions. The faster the near-bank flow and the closer the mainstream to bank is, the more unstable the bank will become. The extent of bank collapse and bed sediment deposition, the bed accumulative deposition rate is proportional to near-bank velocity and water level, but contrary when it comes to stable bank slope. When water level is higher, landslide substances interblend more violently with riverbed, especially on the bends where the transverse sediment transport happens tempestuously. The result reveals the mechanism and patterns of bank collapse and river bed evolution, which could provide a theoretical basis for the planning and design of flood control projects.
Abstract: A two-dimensional hydrodynamic model is developed to simulate the dam-break flood wave propagation over complex topography. A structured grid and the finite volume method are used for the model development. A central upwind scheme is used to calculate the flux at the interface of computational meshes and the linear reconstruction of flow variables is adopted to achieve the second-order accuracy in space. The bed slope source term and friction term are respectively discretized using a central difference scheme and a semi-implicit method, which can ensure a well-balanced property and the stability of the model. The negative water depth is the key factor affecting the model stability when a dam-break flood simulation is performed on irregular terrains. The new model is able to avoid negative water depths when the Courant number remains less than 0.25. Therefore, the new model is more robust and stable compared to most existing models. The numerical result shows that the model is stable and robust, and has a wide range of application potentials.
Abstract: Bed-load plays an important role in sediment transport in fluvial rivers. This paper presents a bed-load formula on the basis of kinetic theory. The pick-up rate of bed-load sediment in the formula is obtained by integrating the velocity distribution function derived by solving the Boltzmann equation of kinetic theory. During the integration, the effect of incipient probability is considered. The bed-load formula is derived by substituting the expression of the pick-up rate into the basic equation of bed-load transport developed by Einstein. Comparisons of the simulations with available experimental data for both weak and intensive sediment transport are presented. The relative errors range from 10% to 50%, which illustrates that the new formula can reasonably represent the statistical characteristics of the bed-load particles moving on the bed surface. Furthermore, the new formula has remarkably improved the result of Einstein equation for intensive sediment transport, and is very similar to the classical bed-load formulas, which proves the validity of the theoretical derivation of the formula.
Abstract: To efficiently solve the extended Boussinesq equations, a hybrid finite-difference and finite-volume scheme is developed. The one-dimensional governing equations are kept in conservation form. The flux term is discretized using the finite volume method, while the remaining terms are discretized using the finite difference method. A Godunov-type high resolution scheme, in conjunction with the Harten-Lax and van Leer (HLL) Riemann solver and the higher accuracy MUSCL (Monotone Upwind Schemes for Scalar Conservation Laws) method for variable reconstruction, is adopted to compute the interface flux. High order central difference formulas are used to discretize the remaining terms. The third order Runge-Kutta method with total variation diminishing (TVD) property is adopted for time marching. Numerical tests are conducted for model validation, and the computed results agree well with experimental data.
Abstract: Numerical solution of flow-transport equations usually has to handle complex surface topography, numerical damping effect and numerical oscillation. In order to solve these problems, a high-performance Godunov-type finite volume model is proposed. An approximate Harten-Lax-van Leer-Contact (HLLC) Riemann solver for the integration of transport convection terms is used in the model development to calculate the mass fluxes and transport fluxes. The model can capture shock waves, reduce the numerical damping effect and overcome the numerical oscillation problems. A weighted surface-depth gradient method and the Minmod limiter are used for water depth's reconstruction to improve the model accuracy. Moreover, the Hancock predictor-corrector method is adopted for time stepping. Numerical results show that the proposed model is highly accurate and stable, and can significantly reduce the numerical damping effect. Thus, the model is suitable for simulating the transport problems in complex water flow and has a wide range of application potentials.
Abstract: The flow fields of a vertical round jet in regular and random waves are measured by a 3-D Acoustic-Doppler Velocimeter. The phenomenon of "twin peaks" is found on the cross-sections of the jet vertical velocity in regular waves when close to the free surface, but it is less obvious on the cross-sections of the jet in random waves. Under the principle of equivalent wave energy and wave energy flux, the jet flow fields in regular and random waves are quantitatively compared. The results show that the jet centerline velocity exhibits a faster decay in regular waves than that in random waves, which could be directly related to the phenomenon of "twin peaks".
Abstract: A five years (2000-2004) SeaWiFs satellite dataset is used to investigate the overall pattern of suspended sediments in the Bohai Sea Basin. The dataset consists of 354 charts of suspended sediment concentration (SSC) in surface water, which cannot be obtained by the conventional procedure through in-situ sampling. Results show that the 5-year mean seasonal cycle of SSC is constructed for the entire Bohai Sea Basin. The SSC exhibits a character of spatial distributions with higher values from inshore waters and lower values from offshore waters, except for those near Qinhuangdao Island. Furthermore, the SSC in the eastern part of Liaodong Bay is much higher than that of the western part. Highest concentrations occur during winter seasons and followed by spring and autumn seasons. The opposite is true during summers, except for estuary areas where the concentration remains higher during both summers and winters. The empirical orthogonal function decomposition (EOF) analysis is performed to reveal the spatial modes and the corresponding time coefficients in Bohai Sea. Results show that the first EOF mode indicates a basin-wide pattern of SSC in the Bohai Sea with an annual variation of 12-month period. The second mode reveals the influence of the Yellow River runoff on the SSC in the Bohai Sea with a dominant semi-annual (6 months) variation at the estuary of the Yellow River. The third mode indicates that there exists a clear difference in the variation of the SSC in different waters in Bohai Sea.
Abstract: To study the characteristics of total nitrogen (TN) during the period of lake ice freeze-up, vertical measurements of TN are made at ice thicknesses of 0 cm, 2.5 cm, 9.5 cm, 21 cm, 31 cm, 41cm, 50 cm and 59 cm. The regularity of TN migration in Wuliangsuhai Lake during ice growth process is examined. Results show that TN migrates from ice to water during the whole growth period of ice, which gives a rise of TN in under-ice water as the ice is getting thicker. TN of water is 2.85 times more than that of ice at an ice thickness of 59 cm. The rate of ice growth determines the flux of TN migration between ice and water. Within the ice layer, the TN migration mostly occurs during the initial stage of ice formation (0-21cm), and then TN is transformed into the steady nitrogen cell with bubbles in ice. The difference in measured and calculated TN in under-ice water indicates that TN still migrates from lake water to sediment during ice growth process. The study provides a reference for controlling eutrophication pollution during the period of lake ice freeze-up.
Abstract: For the safe operation of South-to-North Water Diversion Project, ice jam prevention of inverted siphon and other partial hydraulic structures is very important during the period of an icing event. The ice jam process at the entrance of inverted siphon is simulated by ice-hydrodynamics experiments under real ice conditions. The hydraulic conditions of ice jam prevention are obtained. Using the experimental data, the water diversion capacity and control regulations of inverted siphons for the Beijing-Shijiazhuang section of South-to-North Water Diversion Project are analyzed. This study provides a valuable reference for the safe operation of the project during the period of an icing event.
Abstract: Variations of Antarctic landfast sea ice are not only a direct indicator of Antarctic climate change at a local scale, but also an ideal parameter for climate model evaluation. Additionally, observational analysis of Antarctic landfast sea ice is useful for the assessment of inter-annual variability of the Antarctic sea ice. There have been increasing international efforts on the observation and research of the Antarctic landfast sea ice for the past few decades, which lead to a coordinated Antarctic landfast sea ice observation network. This paper provides a review of advances in the Antarctic landfast sea ice observations from the following perspectives, in-situ measurements of mass balance, ice core structure, surface radiation budget, the digital photography, and satellite remote sensing. Inter-annual variability of the Antarctic landfast sea ice on the different spatial scales is summarized. Also, the existing issues and the future research directions of the Antarctic landfast sea ice observation are discussed.
Abstract: Tsunami is one of the worst marine disasters. Coastal lowland areas can be seriously flooded as the result of high tsunami waves, which cause a significant threat to human life and property. High tsunami waves can move an extensive amount of coastal sediments and cause a significant change of beach profiles in flooded regions. This paper summarizes the status quo and advances in the study of tsunami waves from the perspective of beach profile evolution, sand grains sorting, scour around coastal structures and numerical simulation. In general, it has been a lack of experimental study and numerical simulation of tsunami impacts in a controllable manner. Specifically, it has been a lack of concern on sorting of sand grains by tsunami waves and insufficient understanding of the mechanism of scour around structures, as well as a lack of multi-scale numerical simulation. The experimental study in the giant wave flume, the development of multi-scale hybrid mathematical models and the improvement on the sediment transport computation theory should be the focus points in tsunami studies. This review study provides a useful reference for the future research.