Abstract:Under the circumstances that equal intensity point source is discharged off-bank in rivers of medium width with the consideration of the reflection of both banks, a calculation method of pollutant mixing zone was derived from the analytical solutions of the simplified two-dimensional advection-diffusion equation. The form of the boundary shape curves and the non-dimensional equation of the pollutant mixing zone were obtained. Using the methods of iterative calculation and trial calculation, pollutants mixing zones of river bank and off-bank were identified. The relationship between the geometric characteristic parameters(coordinates), the area and area coefficient of the zone, and the relative off-bank distance were found. As a result, the relative off-bank distance a′was proposed as a classification criterion of discharge types. The classification criteria for river bank, off-bank and river center discharge types are as follows: (1)for 0≤a′≤a₁′, the outfall can be simplified as the type of river bank(near-bank)discharge; (2)for a₁′<a′<a₂′, it is named as the type of off-bank discharge; (3)for a₂′≤a′≤0. 5, the outfall can be simplified as the type of river center discharge, and the expressions of a₁′and a₂′ have been put forward to represent the classification lines of the river bank and off-bank discharge, off-bank and river center discharge respectively. By regression analysis, an empirical formula of the main characteristic parameters for off-bank discharge in pollutant mixing zone in rivers of medium width is proposed, which provides the basis for the optimization of outfall locations and for the calculation of pollutant mixing zone.

Abstract:The governance strategies and regulation measures for the Yellow River have always been discussed for generations. In recent years, some researchers suggested controlling the wandering reach with the counterpart spur dikes in the Lower Yellow River to increase the sediment transport capacity. To study the effects of the counterpart spur dikes, three different kinds of runoff and sediment series were selected. The erosion and deposition situation in the Lower Yellow River was simulated by a 1-D numerical model. The results indicate that the sediment transport capacity of the wandering reach can be increased under the remediation of counterpart spur dikes. More than a half of the extra sediment from the wandering reach is transported to the downstream reach of Lijin station. The rest deposits between Gaocun and Lijin station, especially in the reach from Gaocun to Aishan station. The erosion and deposition situation between Aishan and Lijin station varies little before and after the construction of counterpart spur dikes.

Abstract:Based upon the theory of hydrodynamics, river mechanics, thermodynamics, river-ice hydraulics and mechanics of solids etc. , a mathematic model of the river-ice processes for the Yidan reach is constructed. 30-year long-term series comprehensive field observation data, including geomorphy, meteorology, hydrology, thermo-dynamics and ice regime, are used to simulate the water transfer process of the Yidan River during freezing period. The results show that steady ice cover can be formed by juxtaposition on the Yidan River, which achieves the goal of water transfer beneath the ice cover. In addition, the design discharge of the Yidan River water transfer project can be guaranteed during freezing period.

Abstract:Heihe River is a typical meandering river located in the Zoige Basin, which is an important tributary of the Yellow River source. Many oxbow lakes developed along Heihe River due to natural cutoffs, which record the cutoff frequencies and old channel morphologies. By processing the remote sensing images of SPOT(1990 and 2000)and Google Earth(2000-2014), 216 oxbow lakes in the mainstream and three tributaries(i. e. , Gequ, Maiqu, and Haqu Rivers)along the river channel were identified and the morphological parameters of the meander belts were further defined and analyzed. The results show that the width of the meander belt along the channel increases with a trend of “quick-slow-quick” and moreover most of the oxbow lakes developed in the middle reach. Due to the impact of sediment deposition in the lower reach, the formation time of Ω-shape oxbow lakes is much less than that of U-shape and C-shape oxbow lakes in the middle and upper reaches. Only two cutoffs occurred during 1990-2013 and a Ω-shape and U-shape oxbow lake gradually formed, indicating that the formation rate of oxbow lakes in the Zoige basin is slow.

Abstract:The variation of the hydrological conditions of Dongting Lake and its influenceafter the operation of the Three Gorges Reservoir was studied in the present paper. Based on the actual measured hydrological and topographic data, the variations of Dongting Lake were analyzed, including the change of sediment at the three inlets, the relationship between water levels at Chenglingji and the shrinking of lake area, the uncertainty of water source of the three inlets river network. Under the regulation of the Three Gorges Reservoir and the cascade reservoirs in the upstream, clear water discharge and the smooth of runoff process result in flood accumulation in Chenglingji. The water resources of the three inlets has also been damaged. In the future, only Songzi estuary can maintain constant runoff to avoid river blanking. The deepwater region of the west, south and east Dongting Lake will transform into rivers. To alleviate the impact of these changes and adapt to the flood control near Chenglingji, improving and regional optimizing of the flood control engineering systems in the lake area should be implemented. Dredging in the downstream can improve water environment at the three inlets area. The water level in the outlet of Chenglingji can be adjusted so that to protect the water condition of Dongting Lake and to ensure the ecological security of the wet land.

Abstract:In order to investigate the influence of guide vane parameters on the hydraulic characteristics of a mixed-flow pump, using a model pump with a specific speed of 438 as a study object under the condition that other parameters remain constant, the hydraulic characteristics of mixed-flow pumps in four schemes of different numbers of guide vane blades and in seven schemes of different sweep angles of guide vane blades were numerically simulated using the computational fluid dynamics method based on model test verification. The results show that the number of guide vane blades has a significant effect on the external characteristics of the mixed-flow pump. Different optimal numbers of guide vane blades exist for different discharges: the number of guide vane blades should be appropriately increased under low discharge conditions, and it should be appropriately reduced under large discharge conditions. The sweep angle significantly influences the hydraulic characteristics in the large discharge area. Different optimal sweep angles exist for different discharges. The optimal sweep angle changes from -16° to +24° with the increase of discharge, and the influence of the sweep angle within the computational range on the efficiency reaches 5. 5% when the discharge is 510L/s.

Abstract:There is still no research reports on the hydraulic characteristics and discharge capacities of Z-shape weirs. To study the hydraulic characteristics of Z-shape weirs, six schemes of weir shapes and twelve groups of different flow discharges were carried out by model tests, and the experimental data was analyzed. The results show that, the discharge capacity of Z-shape weirsis proved to be stronger than that of linear-type weirs. Furthermore, the ratio of flow discharge of Z-shape weirs to that of linear-shape weirs(in the same channel)increases with the larger ratio of the crest length to the channel width. In addition, the flow discharge of Z-shape weirs can be calculated by the general weir formulas, and the integrated discharge coefficient is related to the water height on the crest(H), the height of weir(P), the crest length, the width of the front and back weir. The discharge coefficient has a positive relation with the ratio of crest length to channel width and the ratio of the front weir width to the back weir width while it had an inverse relation with H/P. A novel experimental formula is established in the consideration of H/P, the ratio of the crest length to the channel width and the ratio of the front weir width to the back weir width, which can estimate the discharge coefficient of Z-shape weirs.

Abstract:The longitudinal dispersion coefficient is usually computed directlyby empirical formulas or indirectly through introducing empirical formulas during the solution tovelocity distributions, which cannot fully reflect the physical mechanisms of dispersion. Based on the one-dimensional governing equation of river dynamics, a method to calculate longitudinal dispersion coefficient involving a power series solution to velocity distributionwas proposed. This formulation has been extended to the applications in 104 natural rivers with simplified rectanglecross-sections. The computed values are in the same order of magnitudes with the measured ones, indicating acceptable results.

Abstract:The long-term safe operation of a dam can be influenced by the ageing of anti-seepage curtains under its foundation. Based on a synthetic analysis method, basic ageing patterns and some indexes of identification are presented. Three kinds of patterns, including a relatively stable pattern, a slow-weakening pattern and a weakening in stage pattern were classified in terms of the relative anti-seepage efficiency. Each pattern has its unique anti-seepage efficiency during the analysis time. Three types of indexes can be used to identify the ageing. The first type is the micro dynamic elements of seepage, including Ca²⁺, TDS, pH, inorganic and organic matters, which can be used to reveal the ageing mechanisms. The second one is the macro dynamic elements, including the uplift pressure and flow rate, which can be used to identify the ageing degrees and the basic aging patterns. The third type is the numerical analysis indexes, including the saturation index and ratios of the different seepage sources, which can be used to quantify the ageing process. Evaluation systems for the aging behavior of anti-seepage curtains under a concrete-dam foundation can be constructed based on the 3 types of identification indexes.

Abstract:Water conservancy modernization(WCM)forms an important part of the national modernization. To make the evaluation of WCM be more scientific and reasonable, an evaluation index system consisting of seven sub systems and twenty seven indices is established, including flood control and waterlogged reduction, water resources guarantee, water environment and ecological protection, rural water project guarantee, urban drainage and supply, water management service and water conservancy development guarantee. A cloud model(CM), which has both fuzziness and randomness is used for the evaluation. The CM determines the comprehensive evaluation index weight by using backward and forward cloud generator, and calculates the rank by condition cloudgenerator. The paper uses set pair analysis as a comparative analysis(SPA). A case study is put forward with XinyiCity of Jiangsu province. The results show that, the evaluation values are 85. 53(CM)and 84. 56(SPA)in 2015 and the level of WCM in Xinyi City is basic modernization, consistent with the actual situation. In 2020, the evaluation values are 93. 71(CM)and 91. 38(SPA), both can achieve the level of comprehensive modernization, consistent with the 13^th Five-Year Plan. The effectiveness and applicability of the CM is verified.

Abstract:A hydrodynamic model integrated with river networks, ponler areas and the controlling of hydraulic structures was established. After validation and calibration with sufficient measured data and current situation investigation, this numerical model can successfully simulate the flood. Based on Web, GIS and database technology, the management system of dynamic flood risk maps coupledwith the hydrodynamic model was developed. Dynamic flood risk mapping can be produced after the employment of the hydrodynamic model, which can deal with multiple customized data, including precipitation, boundary conditions, parameters of hydraulic structuresand scheduling disciplines. Combined with online forecasting data, the management system can provide technical support and references for the application of flood risk maps on flood control and disaster relief, as well as flood management and forecasting in China.

Abstract:Pull out test of the anchors in the water diversion experimental project from Yangtze to Huaihe River in both expansive soil slopes and soft rock slopes was carried out on the basis of Technical Code for Engineering of Ground Anchorages and Shotcrete Support(GB 50086-2015)and Technical Specification of Shotcrete and Rock Bolt for Water Resource and Hydropower Project(SL 377-2007). The results show that the displacement of the rod measured by the GB method is larger than that of the SL method, with a displacement conversion coefficient of 0. 9~0. 95. The displacement of the rod in soft rock slopes is less than that in weak expansive soil slopes. During the anchor rodstests in soft rocks and weak expansive soils, both GB and SL method overestimate the elastic extension values and it is more reasonable to evaluate the rod quality through the time process of the displacement. There is a linear relationship between the axial force measured by the two methods and the conversion coefficient is around 0. 9~1. 05. The SL method is a more efficient approach for non-prestressed anchors and the test data obtained by both methods can be converted mutually, which has positive significance and economic value for the evaluation of engineering quality and construction progress.

Abstract:Determination of the drift distance of a riprap is critical for water riprap works. Most of researchers have focused on the drift distance of a single particle rock so far, and a systematic study on the drift distance of a rock group was rarely carried out. It remains to be verified whether the drift distance of a rock with an average mass can represent that of a rock group. In this paper, a series of experiments have been conducted to investigate the drift and diffusion of a rock group with different mass combinations under different water depths and flow velocities. Comparisons between the calculated drift distance of the rock with an average mass using the formula for a single particle rock and the average drift distance of the rock group from the experiments were curried out. The results show that the drift distanceof the rock with an average mass is close with that of the rock group if the water depth is less than 15m while the drift distance of the rock with an average mass is greater than that of the rock group if the water depth is around 30m. Furthermore, a formula for calculating the distribution area of a rock group riprap was derived through dimensional analysis. Reasonable agreement of the calculated results between the model experiment and field observations verified the reliability of the calculating formula.

Abstract:Global climate change is mainly manifested by the temperature increase due to the impact of human activities. In global environmental scale, it is the main cause of water resources crises, water pollution and ecological degradation issues that threaten river health and it has become a critical issue that must be solved for many countries around the world. By focusing on the background of changing environments, this paper discusses the progress and achievements in the studies on the evaluation of rivers’ health both domestic and abroad for the past few years. The reviewing aspects include the definition and the contents of river health, methods and applications of health evaluation. Under a certain social public value system at a specific time, river health can be definedas the ability to sustainably provide the neighboring populations with high environmental standards and the achievement of maximum added value from its exploitation with the prerequisite of maintaining the river’s own fundamental ecological requirements. Based on previous studies, the major problems of river health evaluation under changing conditions were highlighted. For example, the definition and connotation of river health are still under debate and the driving mechanism of river health variation remains unclear. Also, further improvement is required for the theory and methodology of river health evaluation and finally the practice of river health evaluation is delayed and the evaluation results cannot be applied in river management effectively. It is recommended to follow the trend of development for river health evaluation in changing environments, which mainly focuses on the studies of river health evaluation and regulation at watershed scales combined with multiple temporal scales. It is also proposed to conduct research on the evaluation indicator system and the evaluation standard of river health according to local conditions. Research on river health evaluation using technologies such as 3S, construction of a long-term and comprehensive river health monitoring network, defining the “reference points” for river health in a scientific manner and integrated research on river health evaluation and water resources regulation should be carried out.

Abstract:Research progresson the transport timescales of substances in estuaries and coastal areas in recent years was reviewed from three aspects, including the concepts, the research methods and the applications of transport timescales. The advantages and limitations of the current mathematical models for the computation of substance transport timescales, especially the progress of the constituent-oriented age and residence time(CART)theory are discussed emphatically in this paper. Aiming at the shortcomings of the current non-conservative substance transport timescales, it is pointed out that the interaction between adsorptive pollutants and suspended particles should be considered to describe the transport timescales completely. Strengthening the study on the transport timescales of non-conservative materials, sediments and adsorptive pollutants will help to reveal the transport characteristics of complex substances. The CART theory should be applied to calculate the transport timescales of non-conservative substances, sediments and the pollutant transport process that considers the interaction with sediments.