Abstract: Study on the characteristic of hydrogen and oxygen isotopes in precipitation is an important aspect of water cycle research. However, the production process of deuterium excess (D-excess) in rain water has not been fully explained. From the perspective of characteristics of air-liquid interface, the differences in isotopic fractionation between the processes of free water evaporation and rain water condensation are analyzed. The result shows that the two processes follow the kinetic fractionation and the equilibrium fractionation, respectively. This directly indicates the generation of D-excess in rain water, however, the interface effect of evaporation-condensation processes controls whether the diffusion process controls the fractionation or not. The free water evaporation process under natural conditions has a smaller specific interface area, the interface effect of isotopic fractionation is large, and the molecule diffusion is apparent. Thus, the free water evaporation is a non-equilibrium fractionation process; on the other hand, the process of rain water condensation has a larger specific interface area, the interface effect is ignorable, and the molecule diffusion does not affect the isotopic fractionation. This process is characterized as the equilibrium fractionation. Using the above result as the assumed conditions, the isotopic fractionation process of water cycle from seawater evaporation to precipitation condensation is simulated under different temperature conditions (10-40℃). The simulated result and the Global Meteoric Water Line (GMWL) coincide with each other, which supports the conclusion that the difference of the interface effects in the free water evaporation and the rain water condensation processes causes the D-excess in precipitation.
Abstract: A field survey is conducted on surface and groundwater samples collected from the Baiyangdian area in an effort to identify the scope and the impact of percolation of contaminated surface water on groundwater in the area, and to evaluate the groundwater quality for irrigation purposes. The pH, EC (Electric Conductivity) and ORP (Oxidation-Reduction Potential) values of water samples are measured, and their hydrogen and oxygen isotopic and major ion compositions are analysed. Using the linear discriminant analysis method and the RSA(Sodium Adsorption Ratio)index, the surface water leakage and its influence on groundwater are studied and discussed. Results show that the leakage from Baiyangdian Lake can lead to an increase in EC and a decrease in ORP with heavy isotopes being enriched in shallow groundwater. The concentrations of SO42- and Na+ in shallow groundwater around the Tang sewage reservoir have increased significantly. The extent of surface water leakages is sufficiently marked with δ18O values and the water table depth of shallow groundwater. The shallow groundwater is mainly recharged by Baiyangdian Lake. The groundwater quality around the Tang sewage reservoir area is affected by the percolation of reservoir water. The percolation of contaminated surface water has caused a general decline in groundwater quality in the area. The groundwater quality is not suitable for irrigation purpose in the west region of Baiyangdian Lake and the area around the Tang sewage reservoir.
Abstract: A constant-head injection test with wetting front observation is conducted to investigate the effect of coal mining subsidence on infiltration into unsaturated soils in sand drift areas. The test is done on two subsidence sites that are formed in 2004 and 2005, and the two sites are located in the Bulianta mining area of southeast Mu Us Sandy Land. Results show that towards the end of the observation period (0-175 min), bigger distances of wetting fronts can be observed at many lowland locations with a sustainable infiltration capacity compared to that of observations on soil slopes. At the 2004 subsidence site with no cracks, both mean vertical infiltration rate and 175-minute infiltration depth are significantly larger than that of observations on the corresponding soil slope (P<0.05) in a control area. The same is true for the mean lateral seepage rate at the 2005 subsidence site with no cracks. At the subsidence sites, the vertical infiltration rate increases during the first ten minutes of the test in lowland locations, and then decreases afterwards. The rate increase can be found during most of the test time on soil slopes. While for the lateral seepage infiltration rate, such an increase is found during the first ten to twelve minutes and followed by a decrease afterwards. The rate increase can also be found during most of the test time on soil slopes. The factor analysis reveals a high vertical inflation rate at lowland locations, and the same is true for the lateral seepage rate on soil slopes. The findings can be seen as the main infiltration characteristics of unsaturated soils in sand drift areas.
Abstract: We link the hydrological processes with the vegetation distribution across the Poyang Lake national nature reserve by creating histograms and calculating sensitivity index. Results show that the vegetation community types react differently to the hydrological conditions within the Poyang Lake national nature reserve. Specially, some communities like Carex community and Eremochloa ophiuroides community are able to tolerate a wide variety of mean water depth and percent time inundated, while other communities like Carex-Polygonum criopolitanum community, Carex-Phalaris arundinacea community and Phalaris arundinacea-Carex community could be found at locations with a relatively narrow range of hydrological conditions and they desire more humid environments. The Triarrhena lutarioriparia community is predominantly at more xeric environments. We suggest that these results would provide a new insight for evaluation of hydro-engineering projects on vegetation communities and wetland vegetation restoration.
Abstract: River network connectivity is an important parameter for consideration in the context of regional flood control, water supply and ecological security. Based on graph theory, the natural river network might be represented by a graph model. Taking into account the variability in delivery capacity of different channel types, the hydraulic conductivity (or the reciprocal of the hydraulic resistance) is used to describe the degree of patency within a river channel. Using the ArcGIS platform with the degree of patency as a weighted factor, the graph model can then be represented by a weighted adjacency matrix. Using MATLAB, the degree of patency within a river channel can be estimated, and the connectivity in river channel networks can also be calculated. The quantitative analysis of river network connectivity can thus be achieved. The proposed approach has been tested on a river network of the Jiaxing Plain in the Taihu Lake Basin. The result shows that the river network connectivity is improved significantly after dredging. The study provides a useful tool for evaluating the river network connectivity.
Abstract: Farmland pipe drainage is one of new engineering measures to improve saline-alkali soils. It is important to simulating farmland water and salt migration for the construction and management of a pipeline system on farmlands. In this study, the basic principle and parameters of the water management model DRAINMOD-S are comprehensively introduced on the bases of mathematically modeling flows and salt migration in saturated-unsaturated soils. The DRAINMOD-S model is used with the weather, soil and crop data collected from typical saline lands along coastlines to simulate the groundwater level for different arrangements of subsurface pipe drainage. Using the calibrated parameters, the salinity profile of 0-80 cm soil layer is simulated with the DRAINMOD-S model. The result shows that the DRAINMOD-S model performs well for hydrological simulation. Both groundwater level and salinity profile are in good agreement with observation. The DRAINMOD-S model is able to predict the groundwater depth in saline-alkali soils and the salt content in soils. The model is a useful tool for the design and management of a pipeline system on farmlands.
Abstract: The impacts of irregular bedform in cross section on hyporheic exchange are studied by means of numerical simulation computations. The computation of the hyporheic exchange rate is done using the modular finite-difference ground-water flow model (MODFLOW) developed by the United States Geological Survey. Results show that more hyporheic exchange occurs on the part of the streambed in deeper-water areas. The bedform has less influence on the groundwater flow direction. However, the groundwater flow close to the streambed exhibits a strong velocity gradient due to terrain effects. The groundwater flow velocity in the deeper-water area is far greater than that in the shallower-water area. In comparison with the hydraulic conductivity and the water depth obtained from the field experiment, the heterogeneity in hydraulic conductivity in hyporheic zone is likely due to the effect of irregular bedform in cross section.
Abstract: Shock-capturing schemes are capable of solving the shallow-water equations with strong discontinuities. However, since the conservative form equations are employed, the water surface gradient term is split into two terms, the gradient of pressure and the bed slope source term. Nonphysical results will be produced if the latter two terms are not well balanced. Based on theoretical analysis a novel algorithm is proposed in this paper. The non-conservative form equations are utilized inside cells in the algorithm, which retains the water surface gradient term. While the conservative form equations of the conservative variables are utilized at cell interfaces to capture discontinuities. The proposed algorithm is verified using four benchmark problems, and the results demonstrate that it can successfully treat strong discontinuities and transcritical flows over varied topography, and it can also accurately reproduce the propagation of small perturbations.
Abstract: The devastating tsunami waves can mobilize a substantial amount of coastal sediments and considerably change the coastal morphology. Meanwhile, the study of grain size sorting on seabed is not only the core content for non-uniform sediment transport but also the key scientific issue in the study of sediment transport mechanics. A two-dimensional laboratory experiment is conducted to investigate the distribution change of sediment grain sizes under the influence of waves. The initial beach slope of 1/10-1/20 is exposed to the action of N-waves. The wave free surface elevations, processes of wave uprush, back wash and run-down jump, the change of cross-shore beach profile, the initial and final distribution of sediment grain sizes are observed and measured. Results show that there is a strong down-rush following the large run-up resulted in erosion on the foreshore and deposition seaward of wave run-down. The mean grain size increases in the deposition area. The beach profiles show bar type under regular and irregular wave actions in the experiment. The mean grain size decreases in the deposition area. This experimental result is in accord with the findings of Çelikoğlu that finer grains are winnowed from the seabed in most energetic areas by the turbulent process and then carried away to less energetic areas, resulting in coarsening of the median bed surface grain size in more energetic areas.
Abstract: Using the fractal cluster growing model, the effect of turbulent flow on the flocculation velocity, the average diameter and the fractal dimension of flocs are studied. The model simulates the collision, the bonding and breakage of sediment particles under the action of Brown motion, gravity settling and turbulent flow in a three-dimensional space. The results show that the process of flocculation and average diameter of flocs can be divided into three stages: accelerating section, uniform section and descending section. The flocculation duration of uniform section appears to be first increasing then decreasing as the turbulent intensity increased, and so do the growth of average diameter. Moreover, the flocculation velocity and the flocs average diameter are smallest in the central region. The fractal dimension of flocs increases with the turbulent intensity increasing, and is finally stabilized. Besides, the fractal dimension of flocs appears to be first increasing then decreasing with time. The fractal dimension of floc is largest in the lower region, followed by the upper region, and the lowest value is found in the middle region.
Abstract: The spatial distribution characteristics of nutrients and diffusion fluxes at the sediment-water interface were analyzed in the three sites of the Licun River estuary in the summer of 2010. The results showed that the nutrient contents in interstitial water were different within the investigated sites, which decrease with the distance from the inner Licun River estuary. The concentration of NH4+-N was 26.21-53.10 mg/L, which was the main form of nutrients in interstitial water of sediment. The organic matter decomposition was completed in anaerobic condition. The nutrients concentration profile in sediment interstitial water was influenced by the concentration of organic matter and the oxidation-reduction environment. The diffusion of nutrients in tidal flat area was from pore water into overlying water, except NO3--N. The sediment in tidal flats was the important sources for nutrients in bottom water.
Abstract: In order to analyze transportation and diffusion characteristics of contaminants at flow confluence, this paper presents the results of a series of experiments that were conducted and the numerical simulation study for probing distribution rules at flow confluence. A two-phase flow model applicable to confluences was established, and it was verified by experimental results. Experiments and numerical simulation were performed for different conditions. The results indicate that: A long and narrow contaminated zone is formed near the tributary side; and, the smaller junction angle and flow ratio (momentum ratio) are narrower with contaminated zone; within the contaminated zone, the gradient of concentration is great; and, contaminants distribution at the confluence is mainly determined by the effects of transportation and diffusion. These study results can provide a scientific basis for environmental evaluation, management and pollution control of river confluence.
Abstract: In order to predict the effects on the hydrodynamic and sediment environment caused by the artificial islands of the Hong Kong-Zhuhai-Macao Bridge, the physical model for the bridge is built to analyze the changes of the tidal level, tidal current and seabed evolution caused by the artificial islands. The physical model is based on the characteristics of the flows and sediment transportation in the project sea area. The experimental results show that the drag force on flow is increased and the flow section area is decreased by the two large artificial islands built in the sea. Near each end of the artificial islands, the velocities of tidal currents increase and the local scour holes form. At the downstream side of the artificial islands, there is the recirculation zone with many vortexes in different scales, which have a periodic change from formation to disappearance. Affected by the topography, hydrodynamic and sediment conditions in the project sea area, as well as by the position, shape and scale of the artificial islands, the changes of hydrodynamics and sediment environment by both the west and east artificial islands are similar in the change rules and different in the forms.
Abstract: Six empirical formulae of the wind drag coefficient were considered in a MIKE21 hydrodynamic model to study properties of wind-driven flow in a shallow lake in the northern city (Dongchang Lake in Liaocheng, Shangdong, China) under a real wind condition. Moreover, the influence of ice cover area on simulated result was also analysed. The results showed that the accuracy was improved about 20% when the wind drag coefficient was varied with real wind field than when it was constant. That is, the model with real wind could accurately describe the wind-driven flow process of the Dongchang Lake. Among the six formulae of the wind drag coefficient, the one proposed under breeze condition was best. Freezing water has significant effected on numerical simulation of wind-driven flow, especially in the zone of ice cover. The influence of wind stress on water flow has been weakened or counteracted under water freezing. Compared with the traditional wind-driven flow simulation, it was necessary to consider ice condition or to adjust the wind drag coefficient in MIKE21 in a northern shallow lake. The results might give a reference for the water resources management in a northern shallow lake.
Abstract: A predictable hydrodynamic model was established to evaluate the impact of the Three Gorges Reservoir on hydrodynamics along the tidal reach of the Yangtze River. With merely upstream discharge boundary condition, the model was able to provide the downstream boundary condition considering interaction between the river runoff and the ocean tide. Quantitative analysis was achieved with 10-year continuous simulations of a one-dimensional (1D) unsteady numerical model of channel network in tidal reach of the Yangtze River from Datong to Xuliujing before and after the impoundment of the Three Gorges Reservoir. Statistical result indicates that runoff regulation of the reservoir plays an important role in both cumulative frequencies of tidal level and seasonal hydrodynamic processes.
Abstract: To discuss the greenhouse gas flux at water-air interface in different impoundment stages and to elucidate the reconstruction of aquatic ecosystem after impoundment, partial pressure of CO2p(CO2) at water surface and CO2 diffusive flux FCO2 were compared between 2004 (the 1st year after impoundment) and 2008 (the 5th year after impoundment) in the backwater area of the Pengxi River (PBA), a typical tributary of the Yangtze River in the Three Gorges Reservoir. It was found that annual p(CO2) and FCO2 in 2004 were (101.9±7.5)Pa and (13.99±1.58)mmol/(m2·d) respectively, and the values in 2008 were (129.1±16.4)Pa and (19.92±3.55)mmol/(m2·d). Impoundment of the reservoir created more organic carbon to be degraded in the new flooded land. This increased the level of p(CO2) and FCO2 in the PBA from 2004 to 2008. However, with the reconstruction of aquatic ecosystem, increase in primary production and growth of phytoplankton regulate the seasonal variations of p(CO2) and FCO2 obviously.
Abstract: The commonly used methods for the identification of chaotic characteristic of runoff time series are the correlation dimension method, the largest Lyapunov exponent method and Kolmogorov entropy method, which are based on the phase space reconstruction. Recently, a novel test approach for chaos detection in time series named zero-one (0-1) test has been proposed. This method applies directly to time series data; therefore, the phase space reconstruction is not required. Moreover, the non-chaotic and chaotic motions can be decided by means of the parameters Kc approaching asymptotically either to zero or one. Case studies of Logistic map, daily runoff series of Jinsha River in China and Umpqua River in America are implemented. The chaotic characteristics are identified and verified by using the 0-1 test algorithm. Then, based on the phase space reconstruction, five nonlinear dynamic methods are employed: ① phase space reconstruction; ② the false Nearest Neighbor (FNN) algorithm; ③ correlation dimension method; ④ Lyapunov exponent method; and, ⑤ Kolmogorov entropy. The comparative results show the effectiveness and reliability of the 0-1 test algorithm. The results from these methods provide cross-verification and confirmation of the existence of a mild low-dimensional chaos in the two daily runoff time series.
Abstract: Based on the surface morphology of sea ice in the Weddell Sea measured by a helicopter-borne laser altimeter during the Winter Weddell Outflow Study 2006, form drag on ice ridges and its contribution to total drag, and air-ice drag coefficient Cdn(10) corresponding to 10m altitude under a neutral stability condition are studied using the drag partition theory. The results revealed that, for compacted ice field, form drag on ridges and its contribution to total drag both increase with ridging intensity (the ratio of mean sail height to mean spacing), while decrease with increasing roughness length. And this ratio to the total drag was 35% corresponding to the typical ridging intensity and roughness length in the winter Weddell Sea, indicating an important impact of form drag on ridges to the momentum exchange at the air-ice interface. Besides, there is an increasing trend of the drag coefficient Cdn(10) with increasing ridging intensity. Meanwhile, Cdn(10) increases for the smaller ridging intensities, whereas decreases for the larger ridging intensity, with increasing roughness length, which is mainly attributed to the change of dominance of form drag on pressure ridges and skin drag over rough ice surface.
Abstract: Due to the existing faults, fractures and penetrating wells in the cap rock, the deep stored CO2 can leak into a shallow aquifer, change the acidity and the distribution of hazard components concentration in groundwater. According to the literature, the studies in this area are in their infancy, and the results from lab and field experiments, numerical simulations and natural analogues studies show that, the intrusion of CO2 into a shallow aquifer would decrease the pH and elevate the trace metal components concentrations significantly. However, the concentrations rarely exceed the drinking groundwater limits. Because of the significant differences between the mineralogy in different aquifers, detailed studies should be done on the risk assessment of carbon dioxide leakage of special aquifers, and point out that further study is needed based on the limitations of the current studies.
Abstract: Recently, an effective approach based on the Continuous Time Random Walk (CTRW) theory has been proved successful in accounting for the behavior of solute transport in heterogeneous porous media in numerical, laboratory, and field experiments. This study presents a brief overview of the development and theoretical basis of the CTRW framework. The differences between CTRW and others based on the advection-dispersion equation and other approaches have been stated. We then exhibit the application of the CTRW to measured breakthrough curves from both laboratory and field experiments. Some key issues have been analyzed particularly in prospect of modeling of reactive solute transport. Further extension of the CTRW formulations to account for the transport behavior of reactive solute and in complicated system are areas for future research, which are critical and challenging problems.