Bridge pressure flow scour at clear water threshold condition is studied theoretically and experimentally. The flume experiments reveal that the measured scour profiles under a bridge are more or less 2-dimensional; all the measured scour profiles can be described by two similarity equations, where the horizontal distance is scaled by the deck width while the local scour by the maximum scour depth; the maximum scour position is located just under the bridge about 15% deck width from the downstream deck edge; the scour begins at about one deck width upstream the bridge while the deposition occurs at about 2.5 deck widths downstream the bridge; and the maximum scour depth decreases with increasing sediment size, but increases with deck inundation. The theoretical analysis shows that: bridge scour can be divided into three cases, i.e. downstream unsubmerged, partially submerged, and totally submerged. For downstream unsubmerged flows, the maximum bridge scour depth is an open-channel problem where the conventional methods in terms of critical velocity or bed shear stress can be applied; for partially and totally submerged flows, the equilibrium maximum scour depth can be described by a scour and an inundation similarity number, which has been confirmed by experiments with two decks and two sediment sizes. For application, a design and field evaluation procedure with examples is presented, including the maximum scour depth and scour profile.
Residence time is an important indicator for river environmental management. In this paper, a 3D hydrodynamic model has been successfully applied to Little Manatee River to characterize the mixing and transport process and residence time. The model employs horizontal curvilinear orthogonal grids to represent the complex river system that consists of branches and bayous. The model has been satisfactorily calibrated and verified by using two continuous data sets. The data sets consist of hourly observations of all forcing boundaries, including freshwater inputs, tides, winds, salinity and temperatures at bay boundary, and air temperatures for model simulations. The data sets also consist of hourly observations of water levels, salinity, and temperature at several river stations. The calibrated and verified hydrodynamic model was used to predict residence time in the Little Manatee River. Under the minimum flow of 0.312 m3/s, the pulse residence time (PRT) is 108 days. Model simulations were also conducted for 17 flow scenarios. Empirical regression equations have been satisfactorily derived to correlate PRT to freshwater inflow. Correlation coefficient R 2 is 0.982 for PRT.
Applying stiffness migration method, a 3D finite element mechanical model is established to simulate the excavation and advance processes. By using 3D nonlinear finite element method, the tunnel boring machine (TBM) excavation process is dynamically simulated to analyze the stress and strain field status of surrounding rock and segment. The maximum tensile stress of segment ring caused by tunnel construction mainly lies in arch bottom and presents zonal distribution. The stress increases slightly and limitedly in the course of excavation. The maximum and minimum displacements of segment, manifesting as zonal distribution, distribute in arch bottom and vault respectively. The displacements slightly increase with the advance of TBM and gradually tend to stability.
Among the numerous inland river basins in the arid northwest China, Shiyang River basin is known for its most serious water shortage that constrains its social and economic developments and for some of the worst ecological and environmental deterioration in China. The research on the value of water resources used for ecosystem is the basis for reasonable allocation of water resources between users of ecosystem and economic system. In this paper the concept of dynamic value for the ecosystem services is proposed. A modified coefficient for the ecosystem service value per unit area is proposed according to the cover degrees of biomes combined with expert consultation. Based on the developmental stage coefficient and scarcity of ecological resources, a dynamic evaluation method is proposed. The theoretical formula and simple calculation formula of the sharing benefits coefficient and benefits per unit ecological water utilization are proposed. The result shows that the benefit of unit ecological water utilization in the lower reach was greater than that in the upper reach in the Shiyang River basin.
According to the results of the water and sediment regulations of the Yellow River in year 2002–2007, the effect of erosion and deposition on the lower reaches, the amount and distribution of erosion and deposition in the river mouth area, the adjustment of river regime, the effect of river regulation projects and changes of flowing capacity of the channel are analyzed. It is revealed that the water and sediment regulation is efficient to reduce deposition and improve the flowing capacity and the conditions of sediment transport.
In this paper, the criteria set related to the priority preorders of water resources projects is introduced. A fuzzy multiple criteria group decision-making model is established, which incorporates quantitative analysis, judgments, experience and preferences of decision-makers. The model is used in practice to determine the priority preorders of five water resources projects, and the results show that the best choice can supply more new employment, domestic water and irrigation water, and has better quality.
From the group movement of the bed load within the bottom layer, details of the nonlinear dynamic characteristics of bed load movement are discussed in this paper. Whether the sediment is initiated into motion corresponds to whether the constant term in the equation is equal to zero. If constant term is zero and no dispersive force is considered, the equation represents the traditional Shields initiation curve, and if constant term is zero without the dispersive force being considered, then a new Shields curve which is much lower than the traditional one is got. The fixed point of the equation corresponds to the equilibrium sediment transport of bed load. In the mutation analysis, we have found that the inflection point is the demarcation point of breaking. In theory, the breaking point corresponds to the dividing boundary line, across which the bed form changes from flat bed to sand ripple or sand dune. Compared with the experimental data of Chatou Hydraulic Lab in France, the conclusions are verified.
Based on the desilting research of one scheduling project in the southwest of China, the method of setting grid desilting gallery before the desilting tunnel is put forward to expand the scope of the scouring funnel before the dam and solve the problem of sediment deposition at the power station water intake. The experimental results show that, in the design of a grid desilting gallery, the width of the grid gallery should not be smaller than that of the desilting bottom intake, the size of the grid orifice should be in the range of 1.5,m–2.0,m along the flow direction, and the grid spacing should be 3–5 times the size of the grid orifice. The discharging ability of the desilting bottom intake will decrease after the grid desilting gallery is added. The average of the decrease rates is about 5%–10%. The scouring funnel draws in the longitudinal direction before the dam obviously after the construction of the grid desilting gallery.
Under forced ventilation, the dust diffusion of underground powerhouse construction is investigated using a 3D high Reynolds number k-ɛ model. The interfacial momentum transfers and the wall roughness in the wall function are considered. Ventilation in the third layer of underground powerhouse of Xiangjiaba hydropower station is used as a case. The geometric structure has a decisive effect on the airflow distribution. It is concluded that the dust concentration decreases gradually with the increase of the ventilation time. However, iso-concentration curves have the same tendency after 1 800 s. The dust concentration meets the ventilation and dust-prevention health standard after 2 300 s. The prediction by the present model is confirmed by the experimental measurement by Nakayama.
The water distribution system of one residential district in Tianjin is taken as an example to analyze the changes of water quality. Partial least squares (PLS) regression model, in which the turbidity and Fe are regarded as control objectives, is used to establish the statistical model. The experimental results indicate that the PLS regression model has good predicted results of water quality compared with the monitored data. The percentages of absolute relative error (below 15%, 20%, 30%) are 44.4%, 66.7%, 100% (turbidity) and 33.3%, 44.4%, 77.8% (Fe) on the 4th sampling point; 77.8%, 88.9%, 88.9% (turbidity) and 44.4%, 55.6%, 66.7% (Fe) on the 5th sampling point.
To prevent expanded polystyrene (EPS) beads from rising up to the surface in the molding process of EPS lightweight concrete, vibration with pressure was applied and the polyvinyl acetate (PVA) emulsion was adopted to improve its mechanical properties. The mechanical properties, thermal properties and durability of EPS lightweight concrete were tested. The microstructures of EPS lightweight concrete were observed by scanning electron microscope (SEM). Vibration with pressure reduces the number of small cracks. The 180 d compressive strength and flexural strength increase obviously as a large amount of PVA was added. The mixed amount of PVA has no obvious influence on the thermal performance when it is not more than 10% of the cement. Vibration with pressure and surface modification of EPS beads by PVA improve the combination of EPS beads with cement stone and the mechanical properties of EPS lightweight concrete.
Based on the laboratory experiments with the saltwater and freshwater replacing each other in the level sand column, taking the kaolin, illite, smectite, bivalent hydrargyrum ion (Hg2+) and phenol (C6H5OH) as examples, this paper studies the applications of water sensitivity in situ remediation in saltwater-freshwater transition zone. In the water sensitivity process, the release and migration of clay minerals can make the hydraulic conductivity (HC) decrease and pollutants remove. A new type of low penetrable or impenetrable purdah can be built by adding clay minerals into the sand media to replace the underground concrete impenetrable wall to prevent seawater intrusion, and a number of the heavy metals and organic pollutants in the sand media can be removed by in situ remediation. The results show that the content of kaolin and illite influences the water sensitivity process slightly, and HC of the sand columns descends from 0.011 cm/s to 0.001 4 cm/s and 0.001 2 cm/s respectively even if the content reaches 12% (weight ratio, sic passim). However, for smectite, HC descends sharply to about 1×10−8 cm/s when its content reaches 4%, and no water can flow through the sand columns beyond 5%. The particle release and migration processes can remove the Hg2+ and C6H5OH out of the sand columns efficiently, the removing rate of Hg2+ is 31.68% when the freshwater and saltwater are filtered through the sand columns polluted by Hg2+, while it is 67.55% when the water sensitivity occurs. With the same method, the removing rates of C6H5OH under the fluid flow and water sensitivity are 55.71% and 43.43% respectively.