Abstract: This study assessed the performances of the traditional temperature-index snowmelt runoff model (SRM) and an SRM model with a finer zonation based on aspect and slope (SRM+AS model) in a data-scarce mountain watershed in the Urumqi River Basin, in Northwest China. The proposed SRM+AS model was used to estimate the melt rate with the degree-day factor (DDF) through the division of watershed elevation zones based on aspect and slope. The simulation results of the SRM+AS model were compared with those of the traditional SRM model to identify the improvements of the SRM+AS model’s performance with consideration of topographic features of the watershed. The results show that the performance of the SRM+AS model has improved slightly compared to that of the SRM model. The coefficients of determination increased from 0.73, 0.69, and 0.79 with the SRM model to 0.76, 0.76, and 0.81 with the SRM+AS model during the simulation and validation periods in 2005, 2006, and 2007, respectively. The proposed SRM+AS model that considers aspect and slope can improve the accuracy of snowmelt runoff simulation compared to the traditional SRM model in mountain watersheds in arid regions by proper parameterization, careful input data selection, and data preparation.
Abstract: Experiments using electrical resistivity tomography (ERT) have shown promising results in reducing the uncertainty of solute plume characteristics related to estimates based on the analysis of local point measurements only. To explore the similarities and differences between two cross-borehole ERT inversion approaches for characterizing salt tracer plumes, namely the classical smoothness-constrained inversion and a geostatistically based approach, we performed two-dimensional synthetic experiments. Simplifying assumptions about the solute transport model and the electrical forward and inverse model allowed us to study the sensitivity of the ERT inversion approaches towards a variety of basic conditions, including the number of boreholes, measurement schemes, contrast between the plume and background electrical conductivity, use of a priori knowledge, and point conditioning. The results show that geostatistically based and smoothness-constrained inversions of electrical resistance data yield plume characteristics of similar quality, which can be further improved when point measurements are incorporated and advantageous measurement schemes are chosen. As expected, an increased number of boreholes included in the ERT measurement layout can highly improve the quality of inferred plume characteristics, while in this case the benefits of point conditioning and advantageous measurement schemes diminish. Both ERT inversion approaches are similarly sensitive to the noise level of the data and the contrast between the solute plume and background electrical conductivity, and robust with regard to biased input parameters, such as mean concentration, variance, and correlation length of the plume. Although sophisticated inversion schemes have recently become available, in which flow and transport as well as electrical forward models are coupled, these schemes effectively rely on a relatively simple geometrical parameterization of the hydrogeological model. Therefore, we believe that standard uncoupled ERT inverse approaches, like the ones discussed and assessed in this paper, will continue to be important to the imaging and characterization of solute plumes in many real-world applications.
Abstract: Minimizing parameter uncertainty is crucial in the application of hydrologic models. Isotopic information in various hydrologic components of the water cycle can expand our knowledge of the dynamics of water flow in the system, provide additional information for parameter estimation, and improve parameter identifiability. This study combined the Philip infiltration model with an isotopic mixing model using an isotopic mass balance approach for estimating parameters in the Philip infiltration model. Two approaches to parameter estimation were compared: (a) using isotopic information to determine the soil water transmission and then hydrologic information to estimate the soil sorptivity, and (b) using hydrologic information to determine the soil water transmission and the soil sorptivity. Results of parameter estimation were verified through a rainfall infiltration experiment in a laboratory under rainfall with constant isotopic compositions and uniform initial soil water content conditions. Experimental results showed that approach (a), using isotopic and hydrologic information, estimated the soil water transmission in the Philip infiltration model in a manner that matched measured values well. The results of parameter estimation of approach (a) were better than those of approach (b). It was also found that the analytical precision of hydrogen and oxygen stable isotopes had a significant effect on parameter estimation using isotopic information.
Abstract: As mass transport mechanisms, the spreading and mixing (dilution) processes of miscible contaminated compounds are fundamental to understanding reactive transport behaviors and transverse dispersion. In this study, the spreading and dilution processes of a miscible contaminated compound in a three-dimensional self-affine rough fracture were simulated with the coupled lattice Boltzmann method (LBM). Moment analysis and the Shannon entropy (dilution index) were employed to analyze the spreading and mixing processes, respectively. The corresponding results showed that the spreading process was anisotropic due to the heterogeneous aperture distribution. A compound was transported faster in a large aperture region than in a small aperture region due to the occurrence of preferential flow. Both the spreading and mixing processes were highly dependent on the fluid flow velocity and molecular diffusion. The calculated results of the dilution index showed that increasing the fluid flow velocity and molecular diffusion coefficient led to a higher increasing rate of the dilution index.
Abstract: The impacts of channel morphology on the residues and ecological risks of 14 polychlorinated biphenyl (PCB) congeners in water and sediment were investigated in summer (July) and autumn (September) in the Chahe River, in Nanjing, China. The residual concentrations of tri-chlorobiphenyls (tri-CBs, PCB 18) and tetra-CBs (PCB 52) in water were obviously higher than those of penta-CBs to deca-CBs, and the average residual concentration of ∑PCBs (sum of 14 PCB congeners) in summer was about six times higher than in autumn. However, the residues in sediment did not change significantly. Redundancy analysis (RDA) indicated that channel morphology and the corresponding environmental indices had significant impacts on PCB residues and their composition profiles in water and sediment. The overflow weir and lake-type watercourse may remarkably reduce the residual concentration and ecological risks of PCBs in water. The highest reduction percentages of the residual concentration and ecological risks of PCBs induced by an overflow weir were 78% and 67%, respectively, and those induced by a lake-type watercourse were 36% and 70%, respectively. The residual ∑PCBs concentrations in watercourses with different channel morphologies were ranked in the following descending order: the natural ecological watercourse, vertical concrete watercourse, and vegetation-type riprap watercourse. However, those in sediment were ranked in the following descending order: the vertical concrete watercourse, vegetation-type riprap watercourse, and natural ecological watercourse.
Abstract: In this paper, we generally summarize the main issues in the operational period of water conservancy and hydropower projects in China over the past several decades. First, the adverse impacts of these projects since the technical guidelines were proposed in 2006 are analyzed. Then, combined with projects and experience from 2006 to 2014, the main issues from four aspects are summarized: (1) There exist many questions in the design and construction of fishways, which are useful for fish migration, and the migration effects are not as expected. (2) Temperature stratification impacting the downstream fish is the major impact of temperature, and alters the fish spawning in the reproduction season. (3) Ecological base flow has been one of the primary questions of the last 30 years in China, the greatest related difficulty being quantification of the amount and flow process necessary to satisfy fish life history. (4) Fish habitat protection and restoration are the most popular topics in recent years with the development of river ecosystem restoration. Fish habitat loss due to the impacts of dam construction and habitat fragmentation has become more and more serious. These four issues are now the main difficulties in water project management, and interact with each other to bear combined effects on river ecosystems. The issues of eco-hydraulic consideration in the design period are the key factors. Finally, the future priorities of research and practice of environmental protection for water conservancy and hydropower projects in China are proposed. The main purposes of this paper are to enhance the scientific research, monitoring, and assessment of operating effectiveness.
Abstract: Dam discharges over spillways are the main reason for the gas-supersaturated water generated in rivers. Local aquatic organisms, especially fish, readily develop gas bubble disease (GBD) in a river with total dissolved gas supersaturation (TDGS). Sometimes, fish will die after a specific exposure period, which harms the biological equilibrium. In this study, the influence of TDGS on silver carp was explored. Silver carp were exposed to gas-supersaturated water with TDGS levels of 140%, 135%, 130%, 125%, 120%, and 110% to test the impact of TDGS. Some silver carp died when the TDGS level was 120% or higher, and all the silver carp exposed to a TDGS level of 140% died within 10 hours. In comparison with the Chinese sucker, Prenant’s schizothoracin, and rock carp, silver carp seem less sensitive to TDGS. In addition, we tested the catalase (CAT) activity in the muscles and gills of silver carp after they were exposed to gas-supersaturated water with a TDGS level of 140%. The CAT activity changed with time; it increased first and then decreased until it was lower than the initial CAT activity. The results of this study can provide basic data for developing a standard for environmental evaluation.
Abstract: Local scour downstream of sluice gates in erosive beds is one of the main concerns of hydraulic engineers because it can cause considerable damage to the structures. Many researchers have conducted various studies to predict the maximum depth and length of scour holes and to develop new methods in order to control this phenomenon. In the methods that have recently been examined, embedded buried plates are used to control the scour in the erosive beds. In this study, using a physical model, the effect of buried plates in erosive beds on the depth of scour downstream of a hydraulic jump was studied. Several experiments were performed in which plates were buried at 50 and 90 angles at different distances from the apron in open channels with horizontal and reverse bed slopes. The result of experiments in which the scour profiles were drawn in dimensionless forms showed that the angle and position of the plates are very important to controlling and reducing scour depth. In fact, by reducing the angle of buried plates, the maximum depth of scour is also reduced. Also, comparing the results of a single buried plate and double buried plates, it can be concluded that using two buried plates at the distances of 30 and 45 cm from the non-erodible bed is more effective in reducing the scour depth. The best distances of the buried plates with angles of 90 and 50 from the non-erodible bed are 45 cm and 30 cm, respectively, in the condition with a single buried plate.
Abstract: In this study, FLUENT software was employed to simulate the flow pattern and water depth changes in a 120° sharp bend at four discharge rates. To verify the numerical model, a 90° sharp bend was first modeled with a three-dimensional numerical model, and the results were compared with available experimental results. Based on the numerical model validation, a 120° bend was simulated. The results show that the rate of increase of the water depth at the cross-section located 40 cm before the bend, compared with the cross-sections located 40 cm and 80 cm after the bend, decreases with the increase of the normal water depth in the 120° curved channel. Moreover, with increasing normal water depth, the water depth change decreases at all cross-sections. At the interior cross-sections of the bend, the transverse water depth slope of the inner half-width is always greater than that of the outer half-width of the channel. Hence, the water depth slope is nonlinear at each cross-section in sharp bends. Two equations reflecting the relationships between the maximum and minimum dimensionless water depths and the normal water depth throughout the channel were obtained.
