Abstract: Using the software DigitalHydro V1.0, the hillsploe Péclet (Pe) number is derived for the Hemuqiao catchment in the source area of the Tai Lake basin together with the hillslope unit and the profile/plan curvature. The 1:10 000 elevation contour lines and 90 samples of soil depths are used for the derivation of these hillslope parameters. The hillsploe Pe number is a dimensionless similarity factor. Its physical meaning is analyzed through the construction of correlation functions involving four selected geomorphic parameters e.g. the length, the soil depth, the convergence ratio and the slope of a hillslope. The correlation between the ratio of hillslope length and soil depth (L/D) and the hillsploe Pe number is also studied. The result shows that Pe value of different hillslope types in the catchment generally varies from 200 to 2 000, and there is a strong linear relationship between L/D and Pe with the high value of R2=0.94. The slope of the linear trend line is 0.95, indicating that the ratio of L/D has a strong positive impact on Pe. The analysis of hillslope contour and profile curvature reveals that the advective component will overwhelm the diffusive component when the shape of hillslope changes from convergent to divergent plan shape and from concave to convex profile shape.
Abstract: A gully node is the intersection of gully or river networks, which reflects the geomorphological structure and hydrological characteristic of the gully area. Effective extraction and analysis of gully nodes are essential to understand the spatial structure, morphology, and hydrological characteristic of a catchment. An algorithm based on high resolution digital elevation model (DEM) data is proposed for extracting gully nodes together with the classification method. The algorithm and method are tested in an experimental area on the Loess Plateau of North Shaanxi Province. The numbers of gully nodes of different order gullies and the flow accumulation value associated with each gully node are obtained. The relationship between the numbers of gully nodes in any given order class and the sum of corresponding flow accumulation values is obtained using a mathematical model. The variations in the spatial distribution of flow accumulation values in different geomorphological regions are studied using the arithmetic progression classification method. Finally, the spatial regularity of geomorphological features is preliminary discussed.
Abstract: The SWAT (Soil and Water Assessment Tools) is a physically based semi-distributed hydrological model. The basic computational unit in the SWAT is the hydrological response unit (HRU) that is usually determined by land uses, soil types, and slope and aspect of an area. Each HRU is assumed to have a homogeneous hydrological response. HRUs obtained with the traditional approaches for delineation of hydrologic response units are often spatially discontinuous and it is difficult to locate them in a catchment. The interaction among HRUs cannot be precisely described and analyzed. In this study, the land use and soil type data from a typical watershed in the Taihu Lake region are processed using the geographic information system (GIS) tools. A new approach for spatial discretization of hydrologic response units is proposed and applied to the processed data. As the result, the location of each HRU in the watershed can be accurately identified. Accordingly, different values of the surface runoff lag time in the SWAT can be applied. The improved version of SWAT is tested on the Xitiaoxi watershed of the Taihu Lake basin. The result shows that a notable improvement is achieved in the hydrological simulation compared to the original SWAT simulation for both model calibration and validation periods. The Nash-Sutcliffe model efficiency coefficients have been improved from 0.64 to 0.67 for calibration and from 0.70 to 0.76 for validation, respectively. The improved SWAT model can better reflect the runoff lag process and achieve a better simulation result. The new approach for spatial discretization of hydrologic response units is an effective solution for the model optimization, and can provide better estimates to the spatial data analysis at finer scales.
Abstract: In order to improve the flow concentration accuracy of the Xinanjiang model and to reduce the influence of personal experiences on the model calibration, a new rainfall-runoff model called XBK (XAJ-BP-KNN) is developed, coupling the Xinanjiang runoff generation model with the improved version of the back propagation (BP) flow concentration model. The latter uses the BP neural network algorithm to simulate the nonlinear relationship of the flow concentration process. The flow calculated by Xinanjiang runoff model and antecedent flow are used as the XBK inputs to a BP simulation network. The flow inputs are routed by the BP concentration model to the outlet of the network, which forms the hydrograph at the outlet of the BP simulation network. XBK uses the similarity theory and the K-nearest neighbor algorithm for pattern recognition in an effort to correct the simulation error due to the absence of the observed initial flow data. XBK parameters are optimized globally using the combined method of the shuffled complex evolution (SCE-UA) algorithm and the genetic early stopping Levenberg-Marquardt (LM) algorithm. The XBK model is applied to the Chengcun watershed. Compared to the original version of the Xinanjiang model, the result shows that a better model simulation can be achieved with XBK. XBK is easy to apply, and the combined global optimization algorithm is able to identify optimal parameter values.
Abstract: Statistical downscaling is widely used to make up the shortcomings of General Circulation Model (GCM) in simulating regional climate change. A statistical downscaling model with GCM precipitation is developed for the Yangtze-Huaihe region. Using the NCEP/NCAR re-analysis data and the observed precipitation of 1960-2009 at 52 meteorological stations in the region, a model linking 10 large-scale atmospheric variables (predictors) to the local precipitation amount is proposed. A combined approach of Principal Component Analysis (PCA) and Support Vector Machine (SVM) is used for training the model to establish a statistical relationship between the 10 predictors and the local precipitation amount for the Yangtze-Huaihe region. The results show that the model can significantly reduce the precipitation error compared to that of using GCM simulations directly, and the monthly and annual variations in precipitation can be better described. The model is then applied to the HadCM3 simulation of the SRES A2 scenario for three time periods 2020-2039, 2050-2069 and 2080-2099. Both seasonal and annual variations in the projected future precipitation for the Yangtze-Huaihe region are analyzed. Compared to the baseline (1960-1999) period, a relatively small increase in precipitation could be expected to the climate change during the period 2020-2099. Among which, the highest increase in the precipitation rate of 3.6 mm/a could be in the period 2080-2099. The seasonal precipitation changes are different from each other during the three time periods.
Abstract: Purple soils with variable rock fragment cover are widespread and the effect of rock fragment cover on hydrological processes is important. We quantitatively study the effect of rock fragment cover on infiltration, surface runoff and subsurface runoff through in-situ artificial rainfall experiments. The experimental plots (1 m×2 m and 23°slope) with different rock fragment covers (0%, 11%, 20%, 33% and 42%)were exposed to three rainfall intensities ((53.9±2.8) mm/h, (90.8±6.1) mm/h and (134.3±14.9) mm/h). The results show that the hydrological differences in these experiments are significant and a positive relationship is found between the steady infiltration rate/coefficient and the rock fragment coverage. For the three experimental rainfall intensities, the coefficients of steady infiltration rate range respectively from 47.7% to 86.59% for the intensity of (53.9±2.8) mm/h, from 30.61% to 82.83% for the intensity of (90.8±6.1) mm/h, and from 17.76% to 77.44% for the intensity of (134.3±14.9) mm/h. The steady infiltration rate can be 1.95 to 4.94 times higher on the experimental plot with the most rock fragment cover of 42% compared to that with the least one of 0%. The surface rock fragment cover can retard surface runoff and reduce surface runoff generation. The larger the rock fragment cover, the longer the time for surface runoff generation. The surface runoff rate/ coefficient decreases with the increase of rock fragment coverage. The relationship between the relative surface runoff coefficient and the rock fragment coverage could be expressed by an exponential decay function. Surface rock fragment cover can enhance the generation of subsurface runoff and thus increase the amount of subsurface runoff. The larger the rock fragment cover, the shorter the time for surface runoff generation. Both flow rate of subsurface runoff and subsurface runoff coefficient are proportional to the rock fragment coverage. The relationship between the relative subsurface runoff coefficient and the rock fragment coverage could be expressed by an exponentially increasing function.
Abstract: Based on the bed form control factor theory and the existing flume experimental data, the correspondence between values taken by the control factor and different bed form configurations is analyzed. A bed form parameters including the particle Froude number and the relative depth (ratio of depth to median diameter of sediment particle) are proposed. In addition, a computational method on the basis of simplified control factor m, and its scope of application are introduced. The adaptability of the relationship between bed form control factor and the bed form parameter is discussed. With the relationship and the characteristics of bed form movement observed in the lower reach of Yellow River, a method to discriminate bed forms is established. The study suggests that the flow resistance characteristics in upper and lower flow regimes can be described by the control factor m, and the relationship between the control factor m and the bed form parameter exists not only in the laboratory flume experiments but also in the natural river systems. The preliminarily test of the established method to discriminate various bed form phases is done using the field observations. The result shows that the method is able to discriminate bed forms in different flow regimes in the lower reach of Yellow River.
Abstract: The analytical solution for advection-diffusion equations exists in different forms depending on the solution conditions. The river width class is an important parameter for choosing a solution for calculating the pollutant diffusion rate in rivers due to pollution discharge. However, it would be difficult to implement such a guiding principle in practical applications due to lack of specific criteria for classification of river width. In accordance with the level of river pollutions affected by boundary reflectivity and the result of the consideration of simplified conditions for analytical solutions of advection-diffusion equations, we propose a river width as wide, medium, and narrow three categories. The criteria for classification of river width and the corresponding method of classification are presented. The mathematical expressions for the identification of the three categories are also deduced. The influence of boundary reflection is usually negligible for 2-D river flow and the mixing length in a well-mixed cross section is less or equal to the river width. These conditions are used to solve the advection-diffusion equations for the three categories. The critical dividing line is obtained for separating the wide category from medium and narrow ones. While, the similar line for separating the medium category from the narrow ones is also derived. Finally, it is important to point out that the classified wide, medium, and narrow three categories are relative to each other. Different results could be obtained in the different hydraulic elements, diffusion coefficients, sewage strengths and allowable pollutant concentrations in the same river.
Abstract: A modification of Green-Ampt model is proposed based on the stratification hypothesis, which dynamically divided the soil column is into saturated layer, transient layer and dry layer. The model uses the concept of an equivalent hydraulic conductivity in the saturated layer, and employs a new method to estimate the Green Ampt wetting front suction. The Richards equation is used to simulate the soil water movement through all three layers, and to study the properties of soil layers including the thickness, the soil water content, and the hydraulic conductivity. The results show that the ratio of the transient layer to the saturated layer decreases linearly as the soil profile becomes wetter. Moreover, the ponding depth and the profile of initial soil water content influence the interception and the slope of the linear relationship. However, the saturated hydraulic conductivity is found to have no measureable influence on the relationship. The soil water content in the transition layer follows an elliptical distribution, and the hydraulic conductivity decreases linearly with the increase of the soil depth in the layer. The infiltration process can be better simulated by the modified Green-Ampt model.
Abstract: Precision farming and decision-making in environmental protection will require a better understanding of the spatial distributions of soil moisture and nutrients. In this study, the block effect due to soil variability is defined and a Radial Basis Function (RBF) artificial neural network (ANN) with Block Effect (BE) is proposed to improve the accuracy of spatial interpolation of soil moisture and nutrients. The new RBFANNBE method is evaluated using soil moistures and organic matters observed from an experimental site in the north Yangzhou region of Jiangsu Province. Two sets of data samples are used in the RBFANNBE training process. The RBFANNBE performance is compared to the conventional RBFANN method and the ordinary Kriging (OK) method using the mean square errors (Mse) and the goodness of prediction fit (G). The results show that RBFANNBE reduce Mse by 19.0%-62.2% and improve G by 8.9%-28.8% compared to the OK method. In comparison with RBFANN, a 10.0%-48.8% reduction in Mse and a 3.4%-22.0% improvement in G are obtained by RBFANNBE, respectively. The new RBFANNBE method has better generalization capabilities over the RBFANN and OK methods. Thus, RBFANNBE is a promising method for studying the spatial distribution of soil properties.
Abstract: Incomplete data poses a challenge in river water quality risk analysis. Using the priori distribution of water quality indices and existing water quality data, a water quality model is established to dynamically simulate the concentrations of pollutants in the water. The statistical characteristics of the model parameters and super-parameters are estimated simultaneously using the Bayesian theory and the Gibbs sampling method. If the incomplete data are assumed to be missing completely at random, the proposed sampling method can provide large number of samples to the model parameter estimation. The substandard water risk analysis can thus be conducted by the model water quality. The result of a case study shows that the model is able to perform risk analysis of the river water quality with incomplete data, which provides a new approach to the risk analysis of water pollution.
Abstract: A monthly eco-hydrological model is developed to simulate the process of nutrient loading on the Xitiaoxi catchment of southeastern China. The environmental modeling language PCRaster is used in the model development. The eco-hydrological model combines a monthly water balance model with the export coefficient model (MECM) for estimating total nitrogen (TN) and total phosphorus (TP) loads. The spatial-temporal distribution of nutrients loads on the catchment is analyzed. The result shows that the monthly streamflows at both Hengtangcun and Fanjiancun stations are well simulated by the eco-hydrological model as revealed by high values of Nash-Sutcliffe coefficients (R2> 0.8). The simulated TN loads vary from 1670 to 2035 t/a during 2002-2005, which are within the reasonable ranges. For the period 1999-2007, the TP load simulation is from 102 to 164 t/a, which are consistent with the observed values of Hengtangcun station. The spatial distribution of simulated nutrients loads indicates that the dominant sources of pollutions are from rice/wheat or rice/rapeseed lands. The results demonstrate the applicability of MECM in identifying sources of pollutions for water resources and fertilization managements on large-sized catchments.
Abstract: The Laolonggou sea area in Caofeidian of Bohai Bay is a typical offshore barrier-lagoon coastal district with a mouth bar at the inlet region. The formation and the back-silting problem of the bar are studied using the data analysis technique and a 2-D mathematical model for sediment transport under the condition of co-action of waves and tidal currents. The back silting data collected during August-December 2008 is used to validate the 2D model simulation. The model simulates the formation of the mouth bar with regard to the observed waves condition in 2006-2007, tidal currents, sediment, and seabed evolution in Laolonggou sea area. The result shows that the difference in flood and ebb stream paths and the divergent ebb flow are two major factors for forming the bar. The back silting in the channel-mouth bar is further predicted for normal hydrological conditions and sudden siltation due to typhoon. Wave-induced sediment suspension is mainly responsible for the back-silting problem of the Laolonggou mouth bar.
Abstract: A 1 D wave breaking model is developed based on an existing set of second-order fully nonlinearity Boussinesq equations. The discretized equations are solved numerically on a staggered grid using a higher-order finite difference scheme. The non-reflective boundary condition for incident wave is achieved by deriving a standing wave solution of the equations and using a relaxation wave generation technique. The 1 D wave breaking model is used to solve the problem of water sloshing in a closed container. The shoaling of a solitary wave on a plane beach is simulated by the model in an effort to illustrate the importance of retaining full nonlinearity. The shoaling and breaking of regular waves on a sloping plane beach is studied numerically using the model. The result shows that there is a satisfactory agreement between the numerical simulation and the experimental data, which demonstrates the effectiveness of the 1 D wave breaking model.
Abstract: A process-based numerical model is developed to simulate the formation of a sandbar beach profile, which includes a set of sub-models for wave, undertow, sediment transport, and bed evolution. The model is validated to simulate the transformation of a gently sloping beach profile to a sandbar beach profile during 12 hours under random waves. The calculated wave height, undertow velocity, sediment transport rate and bed elevation agree well with the measured data. Additional numerical tests are performed to investigate the effects of the surface roller slope, the Schmidt number and the bed repose angle on the hydrodynamics and the resulting profile evolution. It is demonstrated that the present model can well represent the important physical mechanisms of the wave-induced sandbar formation.
Abstract: The aeration problem in spillway tunnels has attracted much attention in hydropower projects. A hydrodynamic model study of aeration devices is conducted for the 3# spillway tunnel of Xiluodu Power Station. The study uses a 3-D numerical model and a segmentation algorithm to simulate the flow field in the tunnel. The result shows that the simulation agrees well with the experimental data from a large-scale physical model test. The layout and design of spillway aeration devices, and the clearance between the water surface and the top of the tunnel are proven to be reasonably arranged for the 3# spillway tunnel according to the model simulations. The simulation proves the complicate nature of hydraulic regime in the ogee section. The emphasis should be on the design of the ogee section and its construction. The use of segmentation algorithms can improve the computational efficiency of high-speed flow simulation with presence of large velocity gradients.
Abstract: Based on the surface elevation profiles of sea ice in the Weddell Sea measured by a helicopter-borne laser altimeter during the Winter Weddell Outflow Study 2006, an optimal model is established with the relative deviations between the theoretical and measured ridge height (spacing) distributions as the performance index and the cutoff height as a control variable. An optimal cutoff height of 0.62 m is obtained and used to separate ridges from level ice surface. Analysis on the ridge distributions implies that the best fits to the observed sail height and spacing distributions are achieved by W'80 distribution and a lognormal distribution, respectively. All profiles are clustered into three regimes by the k-means algorithm based on the ridging intensity Ri (Ri ≤0.01, 0.01 <Ri ≤0.026 and Ri>0.026). The average sail height is 0.99m for the profiles of Ri ≤0.01, 1.12 m for 0.01 < Ri ≤0.026, and 1.17 m for Ri>0.026. While the average spacing are 232m, 54 m and 31 m respectively for the three different regimes. Effective thickness within the area covered by ridged ice, average thickness of ridged ice, sail cross-section, and the areal fraction of ridged ice are also calculated by the mathematical models, and the results indicate that these parameters increase with increase of the ice ridge intensity.
Abstract: Global climate change is having an impact on the water cycle. The spatial and temporal variation in water quantity and quality due to climate change has aroused great concerns among scientists and politicians all over the world. At present, most research activities concentrate on the assessment of climate change impacts on surface water quantity, and only few reports focuse on the water quality concern. Global climate change mainly includes changes in precipitation, temperature, radiation and wind speed. This paper reviews the research advances in the assessment of surface water quality due to the effects of rising temperatures and changing precipitation patterns, as well as the variation in wind-speed patterns, the radiation enhancement, and the changes in sunshine time. The paper demonstrates how changes in these climate parameters over time and space affect the surface water quality and environment. This is done through analyzing the direct and indirect influences of parameter variations on the water pollutant sources, migrations and transformations, as well as the rate of biochemical reactions and the ecological effect of pollution. And finally, research perspectives on the subject are provided from micro-, meso-and macro-point of view, respectively.
Abstract: The vertical velocity profile and bed-load transport in unsteady open-channel flow are major concerns of hydraulics and mechanics of sediment transport. In recent years, many researchers have come to do some serious explorations into the nature of the problems. Progresses on the subject are achieved and challenges for future research are pointed out. In this article we provide an overview of related research achievements including the experimental methodology, the vertical velocity profile and the bed shear stress in unsteady open-channel flow, the flow-sediment hysteresis effect and its reasoning, and the bed-load transport formula. Major deficiencies in current work are pointed out and future research suggestions of topics for focus issues are provided, which includes the study of the law of non-uniform sediment transport in unsteady flow with the advanced instruments.