Abstract:The magnitude and variation of the sediment loads transported by rivers are of important significance to the functioning of river system, and changes in sediment loads of rivers are driven by numerous factors. In this paper, key drivers of changes in sediment loads of rivers in China are analyzed by reviewing recent publications of studies on changes in sediment loads. It can be concluded that nearly all of the major rivers in China exhibit an apparent decline in annual sediment loads except for the Songhua River, which presents no clear tendency of changes in runoff and sediment loads. The total annual sediment loads of major rivers transported to the coasts in China decreased from 2. 03 billion t/a during the period of 1955 to 1968 to 0. 50 billion t/a during the period of 1997 to 2010. The primary drivers of changes in the sediment loads of rivers are dam construction, soil and water conservation measure, catchment disturbance, sand mining and climate change. Case studies for rivers in China show the following: construction of a large number of reservoirs in the Yangtze River basin is the primary driver of the reduction of the sediment load of the Yangtze River; soil and water conservation measure is one of the key drivers of the sharp decline in the sediment load of the Yellow River; the catchment disturbance explains why the reduction of the sediment load of ChiangSaen Station was much lower than that of Gajiu Station on the Lancang-Mekong River; the decreasing sediment load resulting from the growth of agricultural production may be the main driver of the sediment reduction of the Huaihe River; the decrease in the sediment load of the Pearl River was influenced by sand mining activities; and climate change in the Haihe River Basin is one of the key drivers of the great reduction of the sediment load of the Haihe River.

Abstract:Based on meteorological data generated by Kriging spatial interpolation, International Geosphere-Biosphere Program(IGBP)land cover data, and Normalized Difference Vegetation Index data observed by the Advanced Very High Resolution Radiometer(AVHRR NDVI), the potential evapotranspiration(PET)in the Hanjiang River Basin during the period from 2000 to 2006 was estimated with the Shuttleworth-Wallace(S-W)model. The results show that the spatial distribution of PET over the basin is significantly non-uniform, with annual PET values ranging from 496. 6 to 1 741. 8 mm/a and an annual standard deviation of 165. 9 mm/a. The non-uniform distribution of PET is mainly caused by local climate and vegetation types. PET changes seasonally with climate and the growth of vegetation. Input data with low resolution may homogenize the PET results to a certain extent in the same coverage. The density of the meteorological stations will affect the estimated results of PET. The density of meteorological data from Kriging spatial interpolation is much higher than that of the Climatic Research Unit(CRU)data. The spatial distribution and seasonal change of PET calculated using the Kriging interpolation data and CRU data were compared, and the results show that the PET data calculated using the Kriging interpolation data are more accurate than those using the CRU data.

Abstract:In order to investigate the effects of linear shear flow on characteristics of flow past a square cylinder, a numerical model for shear flow past a square cylinder was established by introducing the convective outflow boundary condition into the characteristic-based operator-splitting finite element method. The reliability of the numerical model was verified through simulation of the uniform flow past a square cylinder. The numerical results show that the shear parameter k has a significant effect on the two rows of vortices in the wake of flow past the square cylinder, and a larger k value inhibits the vortex shedding from the cylinder. When k≥0. 4, the formation region of vortices behind the cylinder becomes a triangular zone. As the value of k increases, the stagnation point shifts towards the lateral separation point. When k≥0. 3, the location of the stagnation point remains unchanged. The significant change in the mean drag coefficient occurs in the range 0. 2 ≤k≤0. 25. When k≥0. 2, the mean lift coefficient is negative.

Abstract:The wave-damping performance of a single perforated and inclined plate was explored through physical model tests under two-dimensional regular waves. In the tests, the plate is installed with angles of 15° and -15°, and porosity ratios of 0%, 10%, 20%, and 30%, respectively. The variation of the reflection, transmission, and energy dissipation coefficients with the relative width(the ratio of plate width to wave length)are also presented. The results demonstrate that an inclined plate with an angle of 15° can dissipate more energy than that with an angle of -15°. The relative width and the porosity ratio both influence the wave-damping performance.

Abstract:To explore resistance characteristics and calculation methods of resistance parameters in uniform steady open channel flow with a suspended flexible curtain group(SFCG), 92 sets of flume experiments were carried out with different curtain spacing, curtain heights, and flow conditions. The hydraulic gradients along the flume were obtained through curve fittings of water surfaces, and the drag coefficient Manning roughness and Darcy-Weisbach friction factor were studied. It is shown that the mutual interference among the SFCG would almost disappear under the critical curtain spacing. The SFCG significantly exhausts flow energy and increases resistance, and the drag coefficient hardly changes in different turbulent flow conditions with the range from 1. 60 to 2. 05. The Manning roughness is mainly related to the relative height and arrangement density of SFCG, and a modified calculation method for Manning roughness is proposed. In addition, the Darcy-Weisbach friction factor can be obtained from a fitting formula depending on relative height, distribution density of SFCG, and Reynolds number.

Abstract:An experimental study of local scour around a seaside single house and a group of houses by tsunami waves was carried out in a wave tank. The experimental results show that local scour occurs around the house, especially on the sea side due to a hydraulic drop generated by tsunami wave overtopping and the disturbed flow generated by tsunami waves passing through the house. The hydraulic drop is the main cause of local scour and disturbed flow is the secondary cause. For a single house, the empirical relationship between the relative maximum scour depth and relative overtopping height of the tsunami wave was established. For a group of houses, the empirical relationships between the maximum local scour depth and the tsunami wave height, house width, house height, the number of houses, and center spacing of houses were established. The internal relation between the maximum local scour depth and the incident wave height, house size and layout was determined.

Abstract:In order to explore the feasibility of simulating wave propagation and deformation on a steep reef with the Funwave-TVD wave model based on the second-order fully nonlinear Boussinesq equation, using feasibility validation with the data form experiments and published papers, the wave propagation and deformation process on the steel reef was simulated with the model, and the wave propagation characteristics on the reef were analyzed with different wave elements and water depths. The numerical results show that when the ratio of the wave height to the water depth exceeds a certain value, the wave breaks and the wave height decreases quickly. In deep water conditions, the average wave height on the steep reef decreases to a stable value when the wave moves away from the slope toe of the reef to a distance four times the incident wavelength or further.

Abstract:In order to present the actual situation of dam removal in the United States of America(USA)comprehensively and objectively, a reference search and a special survey were carried out. Based on a review of the background and status of dam removal activities, the causes for dam removal in the United States were analyzed, namely environmental, safety, and economic factors. The cases study shows that dam removal in the USA aims to eliminate the safety risk of aging dams, restore anadromous fish migration, and save non-cost-effective expenditure. Dam decommissioning is an important stage in dam lifecycle management. Dam removal in the USA does not operate with the belief that dam construction is unnecessary. Currently, hydropower remains the largest renewable energy source in the USA. The concepts and experience of dam decommissioning in the USA can provide references for reservoir demotion and retirement management in China.

Abstract:In order to improve water-cooling efficiency for massive concrete, to achieve precise control and transparent management, and to prevent and control concrete cracks, an intelligent water-cooling control system was developed. After three years of field trials of practical engineering and applicability research, key technology for stable and reliable operation under complex conditions in mass concrete construction of hydropower projects was created, and eventually the system was applied to the highest hyperbolic arch dam in the world, the Jinping-I Arm Dam. The results show that the system can realize standardization, refinement, and intelligentization of temperature control during the construction period of mass concrete, and greatly improve the efficiency of temperature control of mass concrete.

Abstract:The inner compass of the acoustic Doppler current profiler(ADCP)hydrological monitoring system with steel buoys is affected by a ship’s magnetism, which leads to deviation of the measured flow direction. Based on data measured at Xuliujing Hydrological Station during the spring tide and middle tide from 2009 to 2011, the effects of steel buoys on the flow measurement accuracy of an ADCP flow measurement system and the calculation results of discharge and tidal volume were investigated under the conditions when the angle perpendicular to the cross-section was used as the flow direction(without flow direction correction)and when the measured mean flow direction of the verticals on the cross-section was used as the flow direction(with flow direction correction). The results show that, compared with the data measured with the vessel-mounted ADCP, the discharge and tidal volume of flood tides and ebb tides and the sum of tidal volume show small errors and high precision, whether the flow direction is corrected or not. It is concluded that the flow direction of the ADCP system with steel buoys can be uncorrected in the calculation of discharge and tidal volume.

Abstract:Using a navigation-obstructing section downstream the Xiangjiaba Dam of Changjiang River as a research object, a two-dimensional unsteady fractal mathematical model that can meet the requirement for maintaining a minimum water depth was established for statistical analysis of the channel width, and the fractal dimension of the river channel’s transverse section was calculated, demonstrating one-order fractal dimension characteristics. The results show that the fractal dimension of the channel width has a close relationship with the water depth, the topography of river reach, and the shape of transverse section, demonstrating a general increasing trend of the fractal dimension of the channel width with the increasing water depth for a shoal and a general decreasing trend of the fractal dimension of the transverse section with the increasing flow velocity. Comparison of the fractal dimension of different shoals in the same river reach shows that the fractal dimension is relatively small for a transverse section with smooth topography under the same flow rate from upstream.

Abstract:With the aim of protecting expansive soil slope, four kinds of protective schemes were chosen for laboratory model tests, including geo-membrane covering, sand cushion bedding, sand layer covering, and replacement with cement-treated soil. Drying-wetting cycles were carried out for slopes with different protective methods. During the cycles, the deformation of expansion, the development of cracks, and the variation of moisture content were monitored and compared among these slope models. The effectiveness of each protective method and corresponding application problems were discussed. The results show that the method of replacement with cement-treated soil is the best of these four methods. Furthermore, for geo-membrane, attention should be paid to processing the joint between two pieces of geo-membrane. For the method of sand cushion bedding, the thickness of the sand cushion should be adjusted according to the climate conditions. The sand layer covering should be taken as a supplementary measure rather than being used independently. When the method of replacement with cement-treated soil is used, attentions should be paid to guaranteeing the thickness, controlling the degree of compaction, and doing careful maintenance work.

Abstract:In order to study the effects of root systems of herbs on unsaturated characteristics of the sandy soil, experiments were conducted to determine the soil-water characteristic indices of bare soil and vegetated soil around the root systems of three herbs(Cynodon dactylon, Festuca arundinace, and Vetiveria zizanioides)in the old course area of the Yellow River. Based on the soil-water characteristic curves fitted with the Brooks-Corey equation, functions of the pore radius change index and the unsaturated permeability coefficient were established. The results show that, compared with the bare soil, the air-entry value of the vegetated soil decreased, and the water-holding capacity increased. The average values of the soil pore radius of the vegetated sandy soil with Cynodon dactylon, Festuca arundinace, and Vetiveria zizanioides were 26 times, 12 times, and 59 times that of the bare soil, respectively. The permeability coefficients of the vegetated soil were two to three orders of magnitude higher than that of the bare soil with the same saturation within a range from 25% to 70%. The results show that the root systems of herbs formed aggregates in unsaturated sandy soil in the old course of the Yellow River.

Abstract:Based on the phenomenon of stress concentration induced by the soil arching effect and the variability of loads and soil parameters, a model for reliability analysis of stability evaluation of the pile-supported embankment was built, and the reliability index calculation method and flow chart were presented in this paper. Taking a typical pile-supported embankment of a highway as an example for stability analysis, the reinforced pile length for the embankment was designed with the safety factor method and reliability index method, respectively, and sensitivity analysis of the reliability index was conducted based on the variability of loads and soil parameters. The results show that the variability of loads and soil parameters has a large influence on the stability of the pile-supported embankment, and it is more reliable and reasonable to use the reliability index method to design the reinforced pile length. The results also indicate that the limit lateral resistance of the second-layer soil and the variability of additional loads on the embankment surface should be given close attention, and the internal friction angle of embankment filling and the ultimate resistance of the reinforced pile can be treated as constants.

Abstract:Alternating layers of sandstone and shale were established. According to the permeability values, the lithology of the sandstone layer was classified, and a multiple lithofacies model was built to investigate the heterogeneity. The distribution of CO₂ injected into deep saline aquifers composed of alternating layers was simulated using TOUGH2/ECO2N software, which was often used to simulate multi-component and multi-phase flow. The results show that CO₂ accumulated in the bottom of the low-permeability shale layer and showed a layered structure. CO₂ preferred to migrate in highly permeable rocks and was distributed dispersedly in the sandstone layer. The supercritical CO₂ dissolved in the formation water continuously, and the density of the salt water consisting of saturated CO₂ increased, leading to the gradual subsidence of the salt water. No significant stratification was found.

Abstract:In view of the ecological deterioration caused by massive concrete wastes and the lack of natural aggregate resources, an experimental study on mechanical properties of recycled concrete and the technique for their improvement was carried out for the Xicheng Canal three-class waterway regulation project through preparation of the recycled concrete with different strength grades and different recycled aggregate contents. The results show that the content of recycled aggregates has a weak effect on the mechanical properties of C35 concrete and concrete with even lower strength, but has a large influence on C40 concrete and concrete with even higher strength. With an increase of the recycled aggregate content, the mechanical properties of the recycled concrete degrade. The mechanical properties of the recycled concrete can be improved by rationally determining the recycled aggregate gradation, mixing in natural aggregates, strengthening the recycled aggregates, and optimizing the mix ratio. The application of the technique to the Xicheng Canal three-class waterway regulation project has achieved large economic benefits.