Abstract: Water resources assessment impacted by climate change is very important to water resources planning and management. This issue is becoming more urgent as evidences of intensifying climate change are growing. In the current research of climate change impact, climate natural fluctuation (variability) has seldom been studied separately. It keeps attributing all changes (runoff, e.g.) to climate change, which may lead to wrong understanding of climate change impact assessment. Since without long enough historical series, impacts of climate variability have been always avoided deliberately. Aiming at this issue, this study proposed a type of simulation methodology, which could analyze the effect of climate natural variability by means of reproducing long series based on the baseline period resampling. The wide used time horizon (1961-1990) was selected as baseline period. Based on Latin Hypercube Sampling (LHS) technique, a block sampling approach was proposed for climate variability simulation. TOPMODEL (TOPography based hydrological MODEL) as a hydrological model was employed, while GLUE (Generalized Likelihood Uncertainty Estimation) for hydrological model parameters calibration and uncertainty, and climate variability uncertainty was estimated. The results show that changes from climate variability has a comparable magnitude with that from climate change, which highlights the importance to separate impacts of climate variability from the total variation in assessing climate change, instead of attributing all changes to climate change solely.
Abstract: Based on the methodology of sampling natural variability in calibration period (baseline period) and the analysis of runoff variation probability affected by climate natural variability of Part I, this part focuses on the runoff change and attribution analysis in future climate of two future periods (2021-2051, 2061-2091). Allowing for seven future climate projections in total of three GCMs (CSIRO, NCAR, MPI) and three emission scenarios (A1B, A2, B1), based on the same hydrological model, study case and the calibrated parameters from the part I, the impact of future climate change on water resources was estimated in terms of separating the contribution from climate natural variability. Delta change approach was employed for removing the systematic errors of GCM. These tow parts research mainly demonstrated how to identify the effect of climate natural fluctuation in climate change impact assessment, to derive the impact assessment in a more objective manner. The results show relatively the contribution of climate natural variability could vary in the foreseeable and far future. For the future period from 2021 to 2051, the impact of climate natural variability may play a major part. While for the period from 2061 to 2091, climate change attributed to greenhouse gases may dominate the changing process.
Abstract: The neotectonic activity can have a profound influence on the development of drainage networks and the morphological evolution of fluvial systems in the Yarlung Tsangpo River on the Qinghai-Tibet plateau. Combining field surveys with a Digital Elevation Model (DEM) and the Google Earth 3D map technology, the drainage network pattern and the fluvial morphology of the Yarlung Tsangpo basin are analyzed in this study. The fluvial deposits of the main channel and tributaries in the basin are measured using the EH4 electromagnetic imaging system. The results show that the drainage network in the Yarlung Tsangpo River exhibits a trellis-dendritic drainage pattern. This is mainly due to the north-south contraction and the east-west trending extension in the plateau resulting from the neotectonic activity. The alternating wide and narrow fluvial landscapes could be the result of the uneven uplift of the Qinghai-Tibet Plateau. The braided and anastomosing rivers are usually found in wide river valleys. While a single, entrenched, relatively straight channel often develops in the narrow V-style valley, and many knickpoints occur along the longitudinal profile of rivers. The mechanism behind the knickpoint development is that the fluvial deposits of narrow channels increase at a faster rate than that of wide channels. The presence of knickpoints will lead to enhanced overall sedimentation rates, which forms a wide U-style valley with a deposition depth of over 800 meters. It is estimated that the total amount of sediment deposited on the Yarlung Tsangpo basin on an the order of magnitude of 0.9 trillion cubic meters.
Abstract: The 3 D virtual simulation technology has changed the way to traditional sense of the world and provided a friendly and high degree of immersion for experts and scholars. It is introduced together with the scientific visualization technology into the sediment research to propose the overall framework of the 3 D visualization system of sediment erosion and deposition based on virtual reality technology. The system realizes the virtual representation of the real watershed, 4 D temporal and spatial changes of large-scale river erosion and deposition process in virtual environment and visual analysis of cross-section form change. Several techniques, including the river boundary identification, automatically adaptive modeling of river channel evolution, seamlessly nested modeling between dynamic river and the surrounding watershed scene, Levels of Detail (LOD) of river channel and seamlessly tiling of LOD patches, display mode and control mode for temporal and spatial visualization, interacting with dynamic river channel, extracting the section based on local interpolation, et al., used in the system are proposed and studied. These techniques are proved to be practicability and feasibility with the Three Gorges Project as an example.
Abstract: The self-adjustment of an alluvial channel is a complicated process with various factors influencing the stability and transformation of channel patterns. Although the formation of alluvial channels has been extensively studied, the problem of the alluvial channel stability still remains to be systematically resolved. This paper presents a cusp catastrophe model for alluvial channel stability. The model enables the discrimination and the prediction of the equilibrium state for channel patterns. Equations of equilibrium state of alluvial channel patterns and the transformation of channel patterns are established based on the cusp model of catastrophe theory and choosing appropriate state variables. The result shows that the model predictions in about 100 natural rivers are consistent with field observations. The proposed cusp catastrophe model is applicable to the study of natural river regimes and to assisting the decision making in river engineering.
Abstract: Analyzing the probability of synchronous asynchronous encounter of multiple hydrologic regions can be reduced to the problem of estimating multivariate probability distribution functions. However, the problem can become more complicated when more hydrologic regions and variables are involved. This study presents a simple and effective method for solving high-dimensional (n≥3) copula-based multivariate probability distribution functions. The latter is used to analyze the joint probability and the conditional probability of annual runoff in the Yangtze River, Huaihe River, and Yellow River. The result shows a high-dimensional (n≥3) copula-based multivariate probability distribution function can be easily constructed for the three rivers using the methodology. For a given set of hydrological variables, it is possible that several candidate copulas fit the variable reasonably well. The goodness-of-fit test can be applied to identify the best copula. The probability of synchronous asynchronous encounter of multiple hydrologic regions can thus be analyzed based on the best copula. Comparing to the method for converting a multi-dimensional space into a one-dimensional one, the three-dimensional Frank copula is simple, excellent goodness of fit, unbiased, and effective.
Abstract: Due to the lack of studies on numerical modeling of the rainfall-runoff process combined with snowmelt runoff in China, a distributed rainfall-runoff model with a snowmelt module is developed based on geographical information systems (GIS) techniques. The kinematic wave theory and the energy budget method are used in the model development. The model is tested using streamflow data. Results of numerical experiments indicate that the model can generate large simulation errors without the full implementation of the snowmelt module. In contrast, the new model can help to reduce the simulation error to the permissible range (within <3%). The study demonstrates the necessity of having such a snowmelt module in rainfall-runoff modeling. The new model provides a means to study the rainfall-runoff process in snowmelt-dominated regions.
Abstract: Pedotransfer functions are commonly used to predict soil hydraulic characteristics. However, the analysis of prediction uncertainty is often ignored by researchers. In an attempt to reduce the prediction uncertainty and to improve the applicability of pedotransfer functions, two existing pedotransfer functions are used to predict the spatial distribution of soil saturated hydraulic conductivity in the Pingdu city of Shandong Province. The two functions are the Vereeckens pedotransfer function and the database of HYdraulic PRoperties of European Soils (HYPRES). The Latin hypercube sampling method is applied to estimate the uncertainty in predicting soil saturated hydraulic conductivity. Results show that there are two major sources of uncertainty, which are: (1) the uncertainty in the spatial interpolation of basic soil properties using Kriging;and (2) the uncertainty associated with the use of pedotransfer functions to predict soil saturated hydraulic functions. The Kriging error is the major source of uncertainty in predicting soil saturated hydraulic conductivity using the Vereeckens pedotransfer function. While, the prediction results are affected by both HYPRES and Kriging.
Abstract: Mathematical models have become important tools for establishing the relationship between relative permeability and saturation. In this study, a porous media model is construed to investigate the relative permeability-saturation relations. The model is applied to an artificial planar porous media consisting of standard sands. The particle size of sands ranges from 0.5 mm and 1 mm. The experiment uses pure water as the wetting phase and 93# gasoline the non-wetting phase, which forms a two-phase system in the artificial planar porous media. The gasoline contains Sudan Ⅲ. The relative permeability-saturation curves are measured and are compared to the ones simulated by two models. The two used models are the van Genuchten-Mualem (VGM) model and the Brooks-Corey/Burdine (BCB) model. The result shows that both VGM and BCB models can reasonably well simulate the relative permeability-saturation curves in porous media. The multiphase flow characteristic has an influence on the model performance. The BCB model has a better performance in porous media. In contrast, the VGM model is relatively easy to apply but with certain restrictions.
Abstract: A coupled one- and two-dimensional (1D and 2D) numerical model is used to simulate levee-breach flows. The model uses the Godunov method and can take full advantage of both 1D and 2D modules. The modules can enhance the computational efficiency and improve the simulation accuracy of the coupled model. The exchange of important hydraulic information among the two modules is achieved through the use of a weir flow equation. The approximate Riemann solver of Roe is used in the 2D module for flow computation, while the 1D module uses the HLL (Harten-Lax-van Leer) Riemann solver. Both solvers can ensure the spatial synchronization. The coupled model is tested against a classic data set. The model is also applied to simulate the 1998 levee-breach case occurred in the Songhuajiang River. An analysis is done on the use of Pangtoupao as a flood detention area for accommodating 200-year flood events. The result shows that the coupled model is able to simulate the flood wave propagation through the breaches. The Pangtoupao study provides the valuable information for the levee-breach flood management in the area.
Abstract: Accurate prediction of maximum scour depth at groin heads has always been the key concern for the design of spur dikes. The simulation of flow and sediment transport processes around spur dikes in tidal rivers often involves the application of three-dimensional hydrodynamic models. In this study, a three-dimensional (3D) turbulence model is developed to simulate the sediment transport around spur dikes in tidal rivers. Using the 3D model, the local scour processes around spur dikes are simulated under both tidal current flow and unidirectional steady flow conditions. The result shows that both local scour processes and resulting scour patterns under the two conditions are significantly different from each other. It is thus important to correctly identify the flow conditions for the design and construction of spur dikes.
Abstract: In order to understand the hydrodynamic characteristics of overland flow on hillslopes, based on the theories in fluid mechanics and sediment transport mechanics, variations in hydraulic parameters of overland flow are studied experimentally for 5 artificial rainfall intensities and 5 slope gradients. The results show that the Reynolds numbers of shallow flow are found to be less than 580 under all 5 artificial rainfall conditions, and the corresponding flow regimes are all unstable laminar flow. The flow type varies with the rainfall intensities and the slope gradients. For gentle slopes and low rainfall intensities, the bed forms are at the low-energy condition and in the transition state. Sand ripples appear on the bed surface and the flow is sub-critical in general. In contrast, for steep slopes and high rainfall intensities, the transition from sand ripples to sand dunes occurs on the bed surface and the flow is supercritical in general. A formula is derived to estimate the shallow flow resistance and tested using the experimental data. The result shows that the formula gives negligible error in resistance calculations. The formula can thus be used as a reference to the establishment of prediction models for the soil erosion simulation on hillslopes.
Abstract: Due to separated flow and free shear flow, the turbulent properties at river channel confluences are much different from that in common channels. By comparing experimental data with numerical simulations, the significance of additional resistances resulting from separated flow and free shear flow is illustrated in this study. Because of the two-dimensional (2D) assumption, the vertical velocity variation is not considered in 2D models, which can result in large errors for high flow rate ratios. In contrast, the assumption is generally valid for low flow rate ratios. Thus, the proper treatment of additional resistances in numerical simulation of confluence flow is vital to the success of solving engineering problems.
Abstract: Compared to the unpervious slab, the pervious slab can improve the stability of protective structures through the reduction of hydrodynamic stresses. In order to better understand this new type of protective structures, an experimental study of the fluctuating pressure on pervious slab is carried out in a stilling basin under jet flow from tail-flaring piers. The fluctuating pressure is imposed on both sides of the pervious slab. Measurements are made on the variation of fluctuating pressure along the longitudinal direction, the density distribution of fluctuating pressure, the time-space relationship between the top and the bottom of the pervious slab, the integral scale, and the power spectral density. The experimental results and the subsequent discussion on the decompression mechanism of pervious slabs provide valuable references for the design of pervious slabs.
Abstract: The vertical profile of critical shear stress is determined using both experimental data and in-situ measurements. A tuning fork densimeter is employed to measure the vertical density distributions of mud on the Lianyungang muddy shoals in Jiangsu Province of China. Laboratorial experiments are conducted to study the incipient motion of sediment collected from the sea area where the vertical density of mud is measured. Both annular flume and long straight flume are used in the experiments under gradually increasing flow velocity. The result shows that there is a logarithmic relationship between the mud density and the water depth as revealed by the field survey. Laboratorial experiments indicate that the critical shear stress needed to initiate sediment movement ranges from 0.1 to 1.0 Pa for the density of 1 050~1 400kg/m3 mud, and the critical shear stress increases exponentially with the densification of the mud layer. As the result, a formula is established to describe the relationship between the critical shear stress and the water depth. The formula could be useful to simulate the incipient motion of sediment particles in a muddy environment.
Abstract: The mechanism of incipient motion of sediment transport can be very complicated. In this study, the major wave-induced forces acting on sand particles on sea beds are discussed;and a comparison is made between the seepage forces and the uplift and effective weight forces. An experimental study is conducted in a flume to investigate the effect of wave-induced porewater pressure gradients on incipient sediment motion. The result shows the direction of seepage forces varies with wave height changes. There exist phase differences between the seepage forces and the uplift and effective weight forces. For different sand particles, there exist certain time periods during which the seepage force can be much larger than the uplift force. For fine sediment deposition with low permeability coefficient values, the seepage force can always be much larger than the uplift and effective weight forces. The experimental results show that the wave-induced seepage force plays an important role on the incipient motion of fine sediment. The wave-induced seepage force should be properly considered when analyzing the incipient motion of fine sediment especially under the influence of long nonlinear waves.
Abstract: In recent years, submarine groundwater discharge (SGD) has been recognized as an important process in land-ocean interactions in the coastal zone (LOICZ). The subject has thus become the focus of intensive research. Geochemical tracers can be effective tools for estimating SGD in LOICZ. The objective of this study is to estimate SGD in the Wuyuan Bay using Radon-222 (222Rn) as naturally occurring tracer. The dynamic variation of SGD can thus be subsequently assessed. We continuously measure the seawater 222Rn and 226Ra activities, the near-sea surface air 222Rn, wind speed, sea water temperature and depth for two consecutive days. We also deploy an incubation device to measure the diffusive flux of 222Rn from sediments and the pore-water 222Rn activities. Based on the mass balance principle for the 222Rn flux, the measured seawater 222Rn are corrected for the decay product of parent 226Ra, the effects of tides, the losses to the atmosphere, the diffusive influxes from the sediments, and the mixing with offshore seawaters. The result shows a conservative estimate of 222Rn flux attributed to SGD is between 0 and 126.7 Bq/(m2 h), which can account for 54% 222Rn in seawater. Taking a SGD end-member as example, the calculated SGD input rates range from 0 to 29.3 cm/d with an average value of 9.3 cm/d. The end-member is made of the weighted average of groundwater and pore-water 222Rn activities. The fluctuation in the SGD input rate has a 12-h period, which matches well with the semi-diurnal tides in this region. The SGD input to the Wuyuan Bay could be as much as 1.86×105 m3/d if the estimation were made under the assumption that the average SGD input rate is applicable to the entire bay area. The input of terrestrially derived fresh groundwater in the Wuyuan Bay could be approximately 1.86×104 m3/d if the fresh groundwater were 10% of the total SGD input.
Abstract: This study conducts parametric uncertainty and sensitivity analysis of large shallow lake hydrodynamic models. The Environmental Fluid Dynamics Code (EFDC) model is applied to simulate the flow velocity and water level in Lake Taihu that is characterized by its shallowness and large surface area. The Latin hypercube sampling (LHS) method is used to sample values for five uncertain parameters in the EFDC model, which including the wind drag coefficient, the roughness height, the eddy viscosity coefficient, the turbulent diffusion coefficient, and the wind shelter. The results show that uncertainties of simulated hydrodynamics process exist due to the contributions of model parameter uncertainties. The extents and ranges of uncertainties in large lake hydrodynamic models (e.g., EFDC) are highly associated with the spatiotemporal distribution of winds, shorelines, lakes bottom topography, and geography around the lake. Among those parameters, the wind drag coefficient and the wind shelter play the most important role in the spatial distribution of modeled velocity and water level, especially in those semi-closure bays and the lake regions with complex topography in the lake. Vertically, the velocity in the surface layer is also largely influenced by the two wind parameters, followed by the velocity of bottom layer, and the middle velocity has a minimal impact. The roughness height also makes a contribution to the uncertainty of simulated hydrological process. However, the uncertainties of viscosity coefficient and turbulent diffusion coefficient have no clear effect on model simulations. Therefore, the wind drag coefficient, the wind shelter, and the roughness height should be paid much attention when calibrating a hydrodynamic model of larg shallow lakes. Additionally, LHS is a cost-effective sampling method to reduce the number of parameters needs to be calibrated and to improve the accuracy of numerical simulations.
Abstract: Both climate change and human activities have great effects on hydrological processes. How to estimate and separate the influences arose from these two driving factors has been the focus of attention in hydrologic science. In view of climate change and human activities, three aspects of the research have been concluded as following: the research progress of the hydrological impacts caused by the two driving factors respectively and comprehensively has been summarized;future climate scenarios and human activities have been introduced;the methods of decomposing the influences of climate change and human activity scenarios on hydrology both in the past and future have been illustrated, and the distributed hydrological models which are frequently-used have been listed as well. Finally, based on current research contents, the problem of overlap between climate scenarios and human activity scenarios, and also the lack of research on the hydrologic extreme events separately caused by climate change and human activities are summarized and discussed.
Abstract: Understanding of morphodynamic processes plays a significant role in the study of estuarine and coastal mudflats. This paper presents a review on the state-of-the-art knowledge about the morphodynamic process in estuaries and coastal mudflats. The review includes the morphodynamic mechanisms, the application of numerical modeling, and the role of remote sensing techniques. The review highlights areas for further study, which includes the field observation using advanced instruments, the combined effect of human activities and global warming on the morphodynamic of mudflats and the resulting disasters, the study of morphodynamic processes in the middle and lower reaches of mudflats, the cohesive sediment transport processes in mudflat areas with the interaction of various factors, and the international comparative analysis of mudflat morphodynamics.