Abstract: Digital elevation models (DEMs) are widely used to define the flow direction in distributed hydrological models for simulation of streamflow. In recent decades, numerous methods for flow direction determination have been applied successfully to mountainous regions. Nevertheless, some problems still exist when those methods are used for flat or gently sloped areas. The present study reviews the conventional methods of determining flow direction for such landscapes and analyzes the problems of these methods. Two different methods of determining flow direction are discussed and were applied to the Xitiaoxi Catchment, located in the Taihu Basin in southern China, which has both mountainous and flat terrain. Both the agree method and the shortest path method use drainage networks derived from a remote sensing image to determine the correct location of the stream. The results indicate that the agree method provides a better fit with the DEM for the hilly region than the shortest path method. For the flat region where the flow has been diverted and rerouted by land managers, both methods require observation of the drainage network to determine the flow direction. In order to clarify the applicability of the two methods, both are employed in catchment hydrological models conceptually based on the Xinanjiang model and implemented with PCRaster. The simulation results show that both methods can be successfully applied in hydrological modeling. There are no evident differences in the modeled discharge when using the two methods at different spatial scales.
Abstract: Based on ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) remote sensing data, bare soil evaporation was estimated with the Penman-Monteith model, the Priestley-Taylor model, and the aerodynamics model. Evaporation estimated by each of the three models was compared with actual evaporation, and error sources of the three models were analyzed. The mean absolute relative error was 9% for the Penman-Monteith model, 14% for the Priestley-Taylor model, and 32% for the aerodynamics model; the Penman-Monteith model was the best of these three models for estimating bare soil evaporation. The error source of the Penman-Monteith model is the neglect of the advection estimation. The error source of the Priestley-Taylor model is the simplification of the component of aerodynamics as 0.72 times the net radiation. The error source of the aerodynamics model is the difference of vapor pressure and neglect of the radiometric component. The spatial distribution of bare soil evaporation is evident, and its main factors are soil water content and elevation
Abstract: This study evaluated the application of the European flood forecasting operational real time system (EFFORTS) to the Yellow River. An automatic data pre-processing program was developed to provide real-time hydrometeorological data. Various GIS layers were collected and developed to meet the demands of the distributed hydrological model in the EFFORTS. The model parameters were calibrated and validated based on more than ten years of historical hydrometeorological data from the study area. The San-Hua Basin (from the Sanmenxia Reservoir to the Huayuankou Hydrological Station), the most geographically important area of the Yellow River, was chosen as the study area. The analysis indicates that the EFFORTS enhances the work efficiency, extends the flood forecasting lead time, and attains an acceptable level of forecasting accuracy in the San-Hua Basin, with a mean deterministic coefficient at Huayuankou Station, the basin outlet, of 0.90 in calibration and 0.96 in validation. The analysis also shows that the simulation accuracy is better for the southern part than for the northern part of the San-Hua Basin. This implies that, along with the characteristics of the basin and the mechanisms of runoff generation of the hydrological model, the hydrometeorological data play an important role in simulation of hydrological behavior.
Abstract: In order to monitor water quality in the Yangtze Estuary, water samples were collected and field observation of current and velocity stratification was carried out using a shipboard acoustic Doppler current profiler (ADCP). Results of two representative variables, the temporal and spatial variation of new point source sewage discharge as manifested by chemical oxygen demand (COD) and the initial water quality distribution as manifested by dissolved oxygen (DO), were obtained by application of the Environmental Fluid Dynamics Code (EFDC) with solutions for hydrodynamics during tides. The numerical results were compared with field data, and the field data provided verification of numerical application: this numerical model is an effective tool for water quality simulation. For point source discharge, COD concentration was simulated with an initial value in the river of zero. The simulated increments and distribution of COD in the water show acceptable agreement with field data. The concentration of DO is much higher in the North Branch than in the South Branch due to consumption of oxygen in the South Branch resulting from discharge of sewage from Shanghai. The DO concentration is greater in the surface layer than in the bottom layer. The DO concentration is low in areas with a depth of less than 20 m, and high in areas between the 20-m and 30-m isobaths. It is concluded that the numerical model is valuable in simulation of water quality in the case of specific point source pollutant discharge. The EFDC model is also of satisfactory accuracy in water quality simulation of the Yangtze Estuary.
Abstract: Sand ripples are common bedforms. The formation of sand ripples is related to flow conditions; different flow conditions cause different ripple geometries. The main aim of this study was to assess the relationship between flow intensity and two-dimensional ripple geometry characteristics. The experiments were carried out in a laboratory flume with natural sand whose bulk density was 2 650 kg/m3 and median diameter was 0.41 mm. The Froude number (Fr), a flow intensity parameter, varied from 0.16 to 0.53, entirely within the subcritical range. Two-dimensional sand ripple geometry was measured and processed via statistical methods. The probability distributions of ripple length and height were obtained with different flow conditions. Through dimensionless analysis, the relationship between the flow intensity parameter (grain size Reynolds number ) and the sand ripple geometry characteristic length ( ) and height ( ) was analyzed, and two formulas were obtained: and , which are consistent with previous research results.
Abstract: In the case of sudden valve closure, water hammer creates the most powerful pressure and damage to pipeline systems. The best way to protect the pipeline system is to eliminate water hammer. The main reasons for water hammer occurrence are valve closure, high initial velocity, and static pressure. However, it is difficult to eliminate water hammer. Water hammer tends to occur when the valve is being closed. In this study, the pipe fracture caused by static water pressure, gradually increasing pressure, and suddenly increasing pressure were compared experimentally in a breaking PVC test pipe. The quasi-static zone, the dynamic zone, and the transition zone are defined through the results of those experiments, with consideration of the fracture patterns of test pipes and impulses. The maximum pressure results were used to design the pipeline even though it is in the dynamic zone.
Abstract: This study is the result of ongoing research for a European Union 7th Framework Program Project regarding energy converters for very low heads, and aims to analyze optimization of new cost-effective hydraulic turbine designs for possible implementation in water supply systems (WSSs) or in other pressurized water pipe infrastructures, such as irrigation, wastewater, or drainage systems. A new methodology is presented based on a theoretical, technical and economic analysis. Viability studies focused on small power values for different pipe systems were investigated. Detailed analyses of alternative typical volumetric energy converters were conducted on the basis of mathematical and physical fundamentals as well as computational fluid dynamics (CFD) associated with the interaction between the flow conditions and the system operation. Important constraints (e.g., size, stability, efficiency, and continuous steady flow conditions) can be identified and a search for alternative rotary volumetric converters is being conducted. As promising cost-effective solutions for the coming years, adapted rotor-dynamic turbomachines and non-conventional axial propeller devices were analyzed based on the basic principles of pumps operating as turbines, as well as through an extensive comparison between simulations and experimental tests.
Abstract: A study on the autogenous shrinkage (AS) of concrete from a mesocosmic perspective was carried out using numerical simulation technology. The temperature history and the autogenous relative humidity (ARH), two factors that have been shown to have occasional influence on this process in previous studies, were introduced into this study. According to these concepts, a program for simulation of the temperature field, humidity field, and stress field based on the equivalent age method and a fully automatic aggregate modeling tool were used. With the help of these programs, the study of a small concrete specimen provided some useful conclusions: the aggregate and the matrix show distinct distribution properties in the temperature field, humidity field, and stress field; the aggregate-matrix interface has a high possibility of becoming the location of the initial cracking caused by AS of concrete; the distribution of random aggregates is extremely important for mesoscopical analysis; and the temperature history is the main factor affecting the AS of concrete. On the whole, inherent mechanisms and cracking mechanisms of AS of concrete can be explained more reasonably and realistically only by considering the different characteristics of material phases and the effects of temperature and humidity.
Abstract: Hydraulic fracturing in the soil core of earth-rockfill dams is a common problem affecting the safety of the dams. Based on fracture tests, a new criterion for hydraulic fracturing in cohesive soil was suggested. Using this criterion, the mechanisms of hydraulic fracturing in cubic soil specimens were investigated. The results indicate that the propagation of the crack in a cubic specimen under water pressure occurs in a mixed mode I-II if the crack face is not perpendicular to any of the principal stresses, and the crack most likely to propagate is the one that is perpendicular to the minor principal stress and propagates in mode I.
Abstract: The electrochemical oxidation degradation processes for artificial and actual wastewater containing ammonia were carried out with a Ti/RuO2-Pt anode and a Ti plate cathode. We studied the effects of different current densities, space sizes between the two electrodes, and amounts of added NaCl on ammonia-containing wastewater treatment. It was shown that, after a 30-min treatment under the optimal conditions, which were a current density of 20 mA/cm2, a space size between the two electrodes of 1 cm, and an added amount of 0.5 g/L of NaCl, the COD concentration in municipal wastewater was 40 mg/L, a removal rate of 90%; and the NH3-N concentration was 7 mg/L, a removal rate of 88.3%. The effluent of municipal wastewater qualified for Class A of the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB18918-2002).
Abstract: The conditions for the positive operation of water conservancy projects are described in this paper. A scientific and effective evaluation index system was established based on frequency analysis, theoretical analysis, and expert consultation. This evaluation index system can be divided into six first-level indices: the degree to which facilities are intact and functionality standards are reached, the status of operation and management funds, the rationality and degree of advancement of the management team structure, the adaptability and rationality of the water conservancy project management system, the degree of automatization and informationization of the management techniques, and the conduciveness of the exterior environment. The weights for evaluation indices were obtained through the analytic hierarchy process method with consideration of the difference between public welfare and profit-oriented water conservancy projects. This study provides a scientific method for evaluating the positive operation of water conservancy projects.
