排序方式： 共有29条查询结果，搜索用时 15 毫秒
21.
This paper investigates the impact of heterogeneity of the transmissivity field on the interpretation of steady-state pumping test data from aquifer systems delimited by constant head boundaries such as aquifers adjacent to lakes or rivers. Spatially variable transmissivity fields are randomly generated and used to simulate the drawdown due to a pumping well located at different distances from a constant head boundary. The steady-state drawdown simulated at different observation wells are then interpreted using the Hantush method (Hantush 1959). The numerical simulations show that, in contrast to the case of infinite aquifer domains, the interpreted transmissivity varies depending on well locations and the separation distance between pumping well and boundary relative to the correlation length. The ensemble-averaged estimated transmissivity varies between the geometric mean and the arithmetic mean, and can even exceed the arithmetic mean in a narrow domain adjacent to the boundary. It approaches the geometric mean of the underlying transmissivity field only if the distance between the pumping well is more than 20 times the characteristic length of the transmissivity field. 相似文献
22.
The spatial variability of each parameter affecting storm runoff must be accounted for in distributed modelling. The objective of the work reported here is to assess the effects of using distributed versus lumped hydraulic roughness coefficients in the modelling of direct surface runoff. A spatially variable data set composed of Manning roughness coefficients is used to model direct surface runoff. To assess the information content (as measured by entropy) of spatially variable data and its significance in distributed modelling, various degrees of smoothing are applied. The error resulting from smoothing the hydraulic roughness coefficients is determined by modelling overland flow using a finite element solution. The Manning roughness coefficients were taken from field measurements of the Manning roughness coefficient at 0.6 m on a 14 m hillslope. These values were then used in a numerical simulation of outflow hydrographs to investigate the dependence of error on spatial variability. Our study focuses on the characteristics of spatial data used in distributed hydrological modelling. The field sites have fractal dimensions of ≈? 1.4, which is close to a Brownian variation. The sampling interval that captures the essential spatial variability of the Manning roughness coefficient does not seem to matter due to its Brownian variation in the field sites. Hence due to the nearly uniform random distribution, measurements at 0.6 m intervals are not necessary and larger intervals would yield results that are just as acceptable provided the mean value together with a uniformly random distribution is maintained for any size of finite element or sampling resolution. Because detailed measurements of hydraulic roughness are not practically available for deterministic catchment modelling, it is important to know that larger sampling resolutions may be used than 0.6 m. 相似文献
23.
Farhad Nadim Shili Liu Ph.D. George E. Hoag Ph.D. 《Ground Water Monitoring & Remediation》2001,21(1):89-96
The presence of headspace and air bubbles in volatile organic analysis sampling vials lowers the actual aqueous concentration of these compounds due to the partitioning of solutes into the gaseous phase. This could make the sample invalid for analysis.
In this work, the effects of air bubbles and headspace on the aqueous concentration of 60 volatile organic compounds listed in U.S.Environmental Protection Agency (U.S. EPA) Method 8260 were evaluated experimentally and theoretically. The results showed that for air to water ratios of 1 to 20 and less, there was no significant effect on the aqueous concentrations of target organic solutes in the sampling vials. When the air to water ratio was increased to 1 to 10, the recovery rates of four organic compounds were lower than the control. Laboratory experiments on sampling vials showed that the presence of air bubbles or headspace with the volumetric air to water ratios of 1 to 20 and less do not produce any significant effect on the original concentrations for most targeted volatile organic compounds.
The experimental results also indicated that in 40 mL sampling vials with headspace range of 2 to 8 mL, the recovery rates of most volatile organic compounds with high values of Henry's law constant (> 0.01 Atm m3 /mol. at 25°C) were larger than the calculated rates. 相似文献
In this work, the effects of air bubbles and headspace on the aqueous concentration of 60 volatile organic compounds listed in U.S.Environmental Protection Agency (U.S. EPA) Method 8260 were evaluated experimentally and theoretically. The results showed that for air to water ratios of 1 to 20 and less, there was no significant effect on the aqueous concentrations of target organic solutes in the sampling vials. When the air to water ratio was increased to 1 to 10, the recovery rates of four organic compounds were lower than the control. Laboratory experiments on sampling vials showed that the presence of air bubbles or headspace with the volumetric air to water ratios of 1 to 20 and less do not produce any significant effect on the original concentrations for most targeted volatile organic compounds.
The experimental results also indicated that in 40 mL sampling vials with headspace range of 2 to 8 mL, the recovery rates of most volatile organic compounds with high values of Henry's law constant (> 0.01 Atm m
24.
A conceptual framework for quantitative estimation of physical vulnerability to landslides 总被引：5，自引：0，他引：5
The paper illustrates a method for scenario-based, quantitative estimation of physical vulnerability of the built environment to landslides. The rationale and main features of the procedure are presented in the context of quantitative risk estimation. Vulnerability is defined quantitatively as a function of landslide intensity and the susceptibility of vulnerable elements. Reference terminology is presented and discussed. Models for the quantification of intensity and susceptibility for some categories of elements at risk such as structures and persons are proposed. An example application is illustrated. 相似文献
25.
Sina Maghami Nick Nadim K. Copty Selen Deviren Saygın Hasan Sabri Öztürk Burak Demirel S. Mehdi Emadian Günay Erpul Majid Sedighi Masoud Babaei 《水文研究》2024,38(3):e15135
Soil salt accumulation is a widespread problem leading to diminished crop yield and threatening food security in many regions of the world. The soil salinization problem is particularly acute in areas that lack adequate soil water drainage and where a saline shallow water table (WT) is present. In this study, we present laboratory-scale column experiments, extending over a period of more than 400 days that focus on the processes contributing to soil salinization. We specifically examine the combined impact of soil compaction, surface water application model and water quality on salt dynamics in the presence of a saline shallow WT. The soil columns (60 cm height and 16 cm diameter) were packed with an agricultural soil with bulk densities of 1.15 and 1.34 g/cm−3 for uncompacted and compacted layers, respectively, and automatically monitored for water content, salinity and pressure. Two surface water compositions are considered: fresh (deionized, DI) and saline water (~3.4 mS/cm). To assess the sensitivity of compaction on salt dynamics, the experiments were numerically modelled with the HYDRUS-1D computer program. The results show that the saline WT led to rapid salinization of the soil column due to capillarity, with the salinity reaching levels much higher than that at the WT. However, compaction layer provided a barrier that limited the downwards moisture percolation and solute transport. Furthermore, the numerical simulations showed that the application of freshwater can temporarily reverse the accumulation of salts in agricultural soils. This irrigation strategy can help, in the short-term, alleviate soil salinization problem. The soil hydraulic properties, WT depth, water quality, evaporation demand and the availability of freshwater all play a role in the practicability of such short-term solutions. The presence of a saline shallow WT would, however, rapidly reverse these temporary measures, leading to the recurrence of topsoil salinization. 相似文献
26.
27.
Computational Fluid Dynamics (CFD) numerical analysis was employed to analyze the situations tested experimentally, as described in Part I. The methodology and results of the CFD analyses are discussed and compared with the observations made from the experiments. The numerical model performed satisfactorily with regard to obtaining the impact forces exerted on the model pipe as well as simulating the hydroplaning phenomenon and estimating slurry flow heights. The experimental results were combined with the results of the CFD analyses to develop a practical method to compute the drag force caused by a submarine debris flow impact on a pipeline. The CFD analyses provided some insight to the separated region characterization, but the attempt to analyze the vortex shedding phenomenon as observed in the experiments was unsuccessful. Additional studies are required for better understanding of both the separated region characteristics and vortex shedding. 相似文献
28.
29.
A data set was derived for the Åknes rock slope, Norway, with the main focus on deriving input parameters for the Barton–Bandis shear strength criterion. Back-calculations of a 100,000 m3 rock slide were performed for evaluation of the data set. The limit equilibrium analysis showed that the joint roughness coefficient (JRC) has the greatest effect on the calculated safety factor of the slide. Probabilistic computations showed that the JRC stands out as the most important contributor to the total uncertainty over the whole set of variables and that the computed failure probability of the 1960 slide was very high, which may be interpreted that the input variables and the Barton–Bandis shear strength criterion are reasonable for the slide. JRC was measured on 0.25 m scale and on 1 m scale. The results from the two scales were different. 相似文献