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981.
膜下滴灌棉花根系发育特征及其与土壤水盐分布的关系 总被引:4,自引:0,他引:4
为探讨膜下滴灌条件下水分和盐分对棉花根系空间发育的影响,在花铃期选择相同灌溉制度、咸淡水灌溉的两个膜下滴灌处理田块采集距滴灌带不同距离、不同深度上的根系样品144 件。用1 mm 土筛和手拣将棉花根系从土壤中筛分出来,去除死根,冲洗干净后用扫描仪扫描成tif 格式图像,再用DT-SCAN 软件计算根长密度。对比分析发现膜下滴灌及盐胁迫条件下,咸水灌溉的根系分布范围较大,其总根长密度比淡水大31.69 mm/cm3,根系生长深度也远大于淡水灌溉。咸水灌溉根系分布主要受盐分胁迫,淡水灌溉根系分布主要受水分胁迫。水平方向上距滴头40 cm以远,水分胁迫对根系发育起主导作用。土壤体积含水率在20% 以上、电导率在2 000 μs/cm 以下时可以满足根系的正常生长发育。 相似文献
982.
The three-dimensional groundwater flow patterns in a gravel bar at the Danube east of Vienna were investigated and are discussed in this paper. The observed groundwater level gradients are highly dynamic and respond very quickly to changes in the river water levels. A variably saturated groundwater model was calibrated to the data to describe the complex dynamics of flow in the gravel bar. The model results suggest that short-term (6–48 h) fluctuations of river water levels cause variations in the exchange flow rates from − 35 l/s to 82 l/s. The highest rates occur during brief infiltration after rapidly rising river water levels. Simulations of different scenarios indicate that riverbank clogging will decrease the exchange fluxes by up to 80%, while clogging of both riverbank and riverbed essentially stops the flow exchange. The groundwater model is also used to simulate the transport of a conservative tracer. The variation of river water levels over time is shown to increase the extent of the active river–aquifer mixing zone in the gravel bar. These dynamic factors significantly enhance the dilution of conservative tracer concentrations in this zone. 相似文献
983.
Irina Kouznetsova Xiaomin Mao Clare Robinson D.A. Barry Jason I. Gerhard Perry L. McCarty 《Advances in water resources》2010
Simulation of biodegradation of chlorinated solvents in dense non-aqueous phase liquid (DNAPL) source zones requires a model that accounts for the complexity of processes involved and that is consistent with available laboratory studies. This paper describes such a comprehensive modeling framework that includes microbially mediated degradation processes, microbial population growth and decay, geochemical reactions, as well as interphase mass transfer processes such as DNAPL dissolution, gas formation and mineral precipitation/dissolution. All these processes can be in equilibrium or kinetically controlled. A batch modeling example was presented where the degradation of trichloroethene (TCE) and its byproducts and concomitant reactions (e.g., electron donor fermentation, sulfate reduction, pH buffering by calcite dissolution) were simulated. Local and global sensitivity analysis techniques were applied to delineate the dominant model parameters and processes. Sensitivity analysis indicated that accurate values for parameters related to dichloroethene (DCE) and vinyl chloride (VC) degradation (i.e., DCE and VC maximum utilization rates, yield due to DCE utilization, decay rate for DCE/VC dechlorinators) are important for prediction of the overall dechlorination time. These parameters influence the maximum growth rate of the DCE and VC dechlorinating microorganisms and, thus, the time required for a small initial population to reach a sufficient concentration to significantly affect the overall rate of dechlorination. Self-inhibition of chlorinated ethenes at high concentrations and natural buffering provided by the sediment were also shown to significantly influence the dechlorination time. Furthermore, the analysis indicated that the rates of the competing, nonchlorinated electron-accepting processes relative to the dechlorination kinetics also affect the overall dechlorination time. Results demonstrated that the model developed is a flexible research tool that is able to provide valuable insight into the fundamental processes and their complex interactions during bioremediation of chlorinated ethenes in DNAPL source zones. 相似文献
984.
Mauro Sulis Steven B. Meyerhoff Claudio Paniconi Reed M. Maxwell Mario Putti Stefan J. Kollet 《Advances in water resources》2010
Problems in hydrology and water management that involve both surface water and groundwater are best addressed with simulation models that can represent the interactions between these two flow regimes. In the current generation of coupled models, a variety of approaches is used to resolve surface–subsurface interactions and other key processes such as surface flow propagation. In this study we compare two physics-based numerical models that use a 3D Richards equation representation of subsurface flow. In one model, surface flow is represented by a fully 2D kinematic approximation to the Saint–Venant equations with a sheet flow conceptualization. In the second model, surface routing is performed via a quasi-2D diffusive formulation and surface runoff follows a rill flow conceptualization. The coupling between the land surface and the subsurface is handled via an explicit exchange term resolved by continuity principles in the first model (a fully-coupled approach) and by special treatment of atmospheric boundary conditions in the second (a sequential approach). Despite the significant differences in formulation between the two models, we found them to be in good agreement for the simulation experiments conducted. In these numerical tests, on a sloping plane and a tilted V-catchment, we examined saturation excess and infiltration excess runoff production under homogeneous and heterogeneous conditions, the dynamics of the return flow process, the differences in hydrologic response under rill flow and sheet flow parameterizations, and the effects of factors such as grid discretization, time step size, and slope angle. Low sensitivity to vertical discretization and time step size was found for the two models under saturation excess and homogeneous conditions. Larger sensitivity and differences in response were observed under infiltration excess and heterogeneous conditions, due to the different coupling approaches and spatial discretization schemes used in the two models. For these cases, the sensitivity to vertical and temporal resolution was greatest for processes such as reinfiltration and ponding, although the differences between the hydrographs of the two models decreased as mesh and step size were progressively refined. In return flow behavior, the models are in general agreement, with the largest discrepancies, during the recession phase, attributable to the different parameterizations of diffusion in the surface water propagation schemes. Our results also show that under equivalent parameterizations, the rill and sheet flow conceptualizations used in the two models produce very similar responses in terms of hydrograph shape and flow depth distribution. 相似文献
985.
Despite the presence of gas in river beds being a well known phenomenon, its potential feedbacks on the hydraulic and thermal dynamics of the hyporheic zone has not been widely studied. This paper explores hypotheses that the presence of accumulated gas impacts the hydraulic and thermal dynamics of a river bed due to changes in specific storage, hydraulic conductivity, effective porosity, and thermal diffusivity. The hypotheses are tested using data analysis and modelling for a study site on the urban River Tame, Birmingham, UK. Gas, predominantly attributed to microbial denitrification, was observed in the river bed up to around 14% by volume, and to at least 0.8 m depth below river bed. Numerical modelling indicates that, by altering the relative hydraulic conductivity distribution, the gas in the river bed leads to an increase of groundwater discharge from the river banks (relative to river bed) by a factor of approximately 2 during river low flow periods. The increased compressible storage of the gas phase in the river bed leads to an increase in the simulated volume of river water invading the river bed within the centre of the channel during storm events. The exchange volume can be more than 30% greater in comparison to that for water saturated conditions. Furthermore, the presence of gas also reduces the water-filled porosity, and so the possible depth of such invading flows may also increase markedly, by more than a factor of 2 in the observed case. Observed diurnal temperature variations within the gaseous river bed at 0.1 and 0.5 m depth are, respectively, around 1.5 and 6 times larger than those predicted for saturated sediments. Annual temperature fluctuations are seen to be enhanced by around 4 to 20% compared to literature values for saturated sediments. The presence of gas may thus alter the bulk thermal properties to such a degree that the use of heat tracer techniques becomes subject to a much greater degree of uncertainty. Although the likely magnitude of thermal and hydraulic changes due to the presence of gas for this site have been demonstrated, further research is needed into the origins of the gas and its spatial and temporal variability to enable quantification of the significance of these changes for chemical attenuation and hyporheic zone biology. 相似文献
986.
台塬塬顶裂缝对黄土斜坡水文响应的影响 总被引:1,自引:0,他引:1
针对黑方台黄土滑坡,从现场灌溉试验监测数据和数值模拟分析着手,研究灌溉过程中台塬斜坡的水文响应以及对黄土斜坡稳定性的影响。结果表明:短期的灌溉并不能对地下水位形成有效的补给,但是却容易引起斜坡浅部范围内体积含水量增加,从而使得抗剪强度降低,最终在台缘顶部发生滑塌,台塬顶部裂缝的存在会使得浅部体积含水量增加速度加快,加速土体弱化,更易发生台塬顶部的滑塌;从长期灌溉模拟来看,裂缝的存在会加速地下水位的上升。从数据上论证了黄土斜坡受裂缝的影响特性,为研究黄土滑坡与地表水入渗的关系提供数据参考。此外,数值模拟与监测数据有很好的对应关系,用其模拟灌溉引起的斜坡水文响应是可行的。 相似文献
987.
Inverse modeling is widely used to assist with forecasting problems in the subsurface. However, full inverse modeling can be time-consuming requiring iteration over a high dimensional parameter space with computationally expensive forward models and complex spatial priors. In this paper, we investigate a prediction-focused approach (PFA) that aims at building a statistical relationship between data variables and forecast variables, avoiding the inversion of model parameters altogether. The statistical relationship is built by first applying the forward model related to the data variables and the forward model related to the prediction variables on a limited set of spatial prior models realizations, typically generated through geostatistical methods. The relationship observed between data and prediction is highly non-linear for many forecasting problems in the subsurface. In this paper we propose a Canonical Functional Component Analysis (CFCA) to map the data and forecast variables into a low-dimensional space where, if successful, the relationship is linear. CFCA consists of (1) functional principal component analysis (FPCA) for dimension reduction of time-series data and (2) canonical correlation analysis (CCA); the latter aiming to establish a linear relationship between data and forecast components. If such mapping is successful, then we illustrate with several cases that (1) simple regression techniques with a multi-Gaussian framework can be used to directly quantify uncertainty on the forecast without any model inversion and that (2) such uncertainty is a good approximation of uncertainty obtained from full posterior sampling with rejection sampling. 相似文献
988.
989.
在地应力连续测量方法"渗透率法"的基础上,设计了一种对观测系统进行标定的方法。经对原有推导结果进行数学转换,给出了新的计算公式以及其中有关参数的测定方法。结果表明,经过标定之后,原有的连续相对测量方法可转换为抗干扰性强、灵敏度高、经济简便且物理意义确切的有效正应力连续测量方法。 相似文献
990.
基于FEFLOW和GIS技术的矿区地下水动态模拟及预测 总被引:2,自引:0,他引:2
矿区地下水动态研究是山西亟待解决的重大需求问题。针对山西矿区水资源短缺与水环境恶化等现状,通过分析气象、水文、地质地貌、开采现状等监测数据资料,以FEFLOW模型和GIS技术为平台,构建山西矿区三维地下水数值模型,进行地下水动态研究,模拟并预测了4种不同情境下矿区地下水动态过程,从而定量分析采矿活动对地下水动态的影响,揭示矿区开采对地下水系统的作用机制。结果表明:当矿区开采强度提高10%、30%、50%时,地下水整体流场和运动趋势没有大的变化,但在矿区南部地下水流场发生突变,等值线形变,且在东南部形成一个水位变化剧烈的低水位带,迫使地下水流向发生偏转。水位分析表明采矿活动会造成地下水位整体下降,下降幅度与开采强度呈正相关关系。地下水系统均衡分析表明,当开采强度保持现状或提高10%,地下水系统仍然处于正均衡,补给量大于排泄量,当开采强度提高30%、50%时,系统转为负均衡状态,补给量小于排泄量,地下水水量大幅度减少。研究成果可为矿区制定合理的开采方案,保护矿区地下水资源提供参考依据,为有效遏制矿区水环境恶化、确保矿区水安全提供科技支撑。 相似文献