输沙能力模式在坡面非恒定输沙过程中的应用

在坡面土壤侵蚀输沙计算中,可选用的输沙能力模式较多,但这些模式多运用于恒定输沙,在非恒定输沙中运用不多。建立了坡面土壤侵蚀非恒定输沙数学模型,模型中的输沙能力运用水流切应力、水流功率、单位水流功率3种模式,对模型过程采用有限差分格式离散求解。根据实测水沙资料进行模型参数率定,运用3种输沙能力模式于不同降雨强度、不同坡度的非恒定坡面输沙过程中。结果表明:在坡面非恒定输沙计算中,不同输沙能力模式对计算结果有明显影响,在降雨强度较小时,单位水流功率模式结果较其他两个模式为好,而在雨强较大时,切应力模式计算结果较好。     

On the use of enriched finite element method to model subsurface features in porous media flow problems

In this paper, a new enrichment scheme is proposed to model fractures and other conduits in porous media flow problems. Inserting this scheme into a partition of unity based method results in a new numerical method that does not require the mesh to honor the specific geometry of these subsurface features. The new scheme involves a specially designed integration procedure and enrichment functions, which can capture effects of local heterogeneity introduced by subsurface features on the pressure solution. The new method is also capable of modeling fractures with low as well as high conductivity. Another feature of the proposed scheme is that, even though two enrichment functions are used to model the permeability change at the two rock/fracture interfaces of a fracture, only one element partition is made for numerical integration. To demonstrate the accuracy and effectiveness of the proposed approach, production problems for wells that were stimulated or completed by longitudinal fracture, transverse fractures, and perforations are studied.     

国内外泥石流活动关键指标估算方法之比较

泥石流流体容重、流速、冲击力是表征泥石流活动特征众多指标中的三个关键指标.本文在分析国内外对这些指标评估现状的基础上,总结了应用较普遍的估算公式,对比了不同公式的特点及其适用性.比较结果认为:由于泥石流组成和运动状态的复杂性以及影响因素的多样性,对于这三个指标,目前的估算公式都不具有普适性.在当前的认知水平下,建立基于各个地区泥石流特点的指标估算经验公式是最为实用的途径.在各个指标经验公式的建立方法上,考虑各个粒组的多变量容重统计分析方法相对较为合理;泥石流流速估算公式的建立途径在我国、前苏联和欧美国家之间有显著差异,前二者基于曼宁公式,后者基于强迫涡流公式、以弯道超高为主要参数;泥石流冲击力的估算方法国内外都以动量理论为基础,区别主要体现在经验系数取值上,巨石冲击力的计算则都考虑了拦挡建筑物的特点.     

The use of environmental isotopic and hydrochemical tracers to characterize the functioning of karst systems in the Tlemcen Mountains,northwest Algeria

The functioning of karst systems in the Tlemcen Mountains, Algeria, was studied using environmental isotopic and chemical parameters. The weakly enriched values of ¹⁸O suggest a fast infiltration of water through the karst systems. The deuterium (²H) excess in groundwater and tritium (³H) in precipitation show that the region is subjected to Mediterranean and Atlantic influences with a predominance of the former. The isotopic gradient, in combination with topographic and geologic criteria, allows the recharge areas of the main karst systems to be estimated. The results of ¹³C, ¹⁴C and ³H analysis show that the majority of present waters come from perched systems and mixture waters influenced by three clusters (“ante-thermonuclear” waters, “thermonuclear” waters, and present waters) that generally emerge from semi-confined systems. The oldest waters are relatively rare and are stored in deeply confined systems. These results are consistent with the hydrochemical and the hydrogeological findings. The results have important implications in groundwater protection.     

Permeability generation and resetting of tracers during metamorphic fluid flow: implications for advection-dispersion models

Advection-dispersion fluid flow models implicitly assume that the infiltrating fluid flows through an already fluid-saturated medium. However, whether rocks contain a fluid depends on their reaction history, and whether any initial fluid escapes. The behaviour of different rocks may be illustrated using hypothetical marble compositions. Marbles with diverse chemistries (e.g. calcite + dolomite + quartz) are relatively reactive, and will generally produce a fluid during heating. By contrast, marbles with more restricted chemistries (e.g. calcite + quartz or calcite-only) may not. If the rock is not fluid bearing when fluid infiltration commences, mineralogical reactions may produce a reaction-enhanced permeability in calcite + dolomite + quartz or calcite + quartz, but not in calcite-only marbles. The permeability production controls the pattern of mineralogical, isotopic, and geochemical resetting during fluid flow. Tracers retarded behind the mineralogical fronts will probably be reset as predicted by the advection-dispersion models; however, tracers that are expected to be reset ahead of the mineralogical fronts cannot progress beyond the permeability generating reaction. In the case of very unreactive lithologies (e.g. pure calcite marbles, cherts, and quartzites), the first reaction to affect the rocks may be a metasomatic one ahead of which there is little pervasive resetting of any tracer. Centimetre-scale layering may lead to the formation of self-perpetuating fluid channels in rocks that are not fluid saturated due to the juxtaposition of reactants. Such layered rocks may show patterns of mineralogical resetting that are not predicted by advection-dispersion models. Patterns of mineralogical and isotopic resetting in marbles from a number of terrains, for example: Chillagoe, Marulan South, Reynolds Range (Australia); Adirondack Mountains, Old Woman Mountains, Notch Peak (USA); and Stephen Cross Quarry (Canada) vary as predicted by these models. Received: 3 February 1997 / Accepted: 26 June 1997     

吉大一院基础工程在粘性土层水文地质求参的尝试

本文着重在粘性土(隔水)层中进行水文地质抽水试验,通过施工6眼试验井,测得地层渗透系数、涌水量等水文地质参数,为深基坑开挖工程提供安全、可靠的设防,并满足抗浮设计计算所需的准确数据。     

On the evaluation of sediment transport models in tidal environments

The application of numerical models for the simulation of coastal hydro-and sediment dynamics requires model verification, calibration and validation with field data. Yet, no commonly accepted rules for the evaluation of sediment transport models exist. This paper discusses the significance of statistical parameters and their limitations considering common time lags in tidal environments. It is shown that the occasionally used discrepancy ratio lacks quantitative and qualitative information on model performance, as the time context information on time series characteristics is lost. As an initial measure of association, the simple linear correlation coefficient r² is proposed. To account for time lag errors in suspended transport models, a separate cross-correlation analysis for the flood and ebb tidal phase is proposed. For a comparison with other model applications, a concluding rating of model performance can be expressed by a dimensionless error definition which takes into account the quality of field data.     

裂隙地下水反分析中若干问题探析

本文以反演介质参数为例,讨论了模型的建立、反问题数值计算中实际参数采集及其对成果的影响,有关数值法的适用性、唯一性。     

On some problems of the genesis of hydrothermal deposits

Some important problems of the theory of hydrothermal ore formation that were discussed as early as in the works of F.I. Wolfson are briefly considered.     

Deuterium composition and flow path analysis as additional calibration targets to calibrate groundwater flow simulation in a coastal wetlands system

A conceptual model of the Lake Warden coastal wetlands system, Western Australia, was developed using hydraulic, chemical and stable isotopic data, and formed the basis for a groundwater flow model using the finite element numerical code (FEFLOW). The system to be modeled is complex. The surface water and groundwater within the wetlands system show varying salinity and isotopic composition over short distances and time frames. As a first step, the flow model was calibrated to observed groundwater levels measured since 2001 for both steady state and transient stresses. Particle tracking analysis was conducted to test the source areas of water discharging to the lakes within the wetlands system. The analysis was able to delineate the connectivity between the lakes in the wetland and the flow path. Enrichment of isotopic concentration is evident along a NE–SW transect and the data set provides a means for calibrating a detailed transport model. The study incorporates the varying deuterium composition of the water bodies directly into a transport model and a good match between observed and simulated temporal variations along the transect indicates that the model closely simulated the dynamics of water exchange between the lakes and groundwater within the system.     

Use of multiple age tracers to estimate groundwater residence times and long-term recharge rates in arid southern Oman

Multiple age tracers were measured to estimate groundwater residence times in the regional aquifer system underlying southwestern Oman. This area, known as the Najd, is one of the most arid areas in the world and is planned to be the main agricultural center of the Sultanate of Oman in the near future. The three isotopic age tracers ⁴He, ¹⁴C and ³⁶Cl were measured in waters collected from wells along a line that extended roughly from the Dhofar Mountains near the Arabian Sea northward 400 km into the Empty Quarter of the Arabian Peninsula. The wells sampled were mostly open to the Umm Er Radhuma confined aquifer, although, some were completed in the mostly unconfined Rus aquifer. The combined results from the three tracers indicate the age of the confined groundwater is < 40 ka in the recharge area in the Dhofar Mountains, > 100 ka in the central section north of the mountains, and up to and > one Ma in the Empty Quarter. The ¹⁴C data were used to help calibrate the ⁴He and ³⁶Cl data. Mixing models suggest that long open boreholes north of the mountains compromise ¹⁴C-only interpretations there, in contrast to ⁴He and ³⁶Cl calculations that are less sensitive to borehole mixing. Thus, only the latter two tracers from these more distant wells were considered reliable. In addition to the age tracers, δ²H and δ¹⁸O data suggest that seasonal monsoon and infrequent tropical cyclones are both substantial contributors to the recharge. The study highlights the advantages of using multiple chemical and isotopic data when estimating groundwater travel times and recharge rates, and differentiating recharge mechanisms.     

建设用地地质灾害危险性评估中几个问题的思考

结合工作实践，就建设用地地质灾害危险性评估及其成果审查工作中经常遇到的5个问题——评估灾害类型的确定原则，评估区环境条件分析深度的把握，现状、预测及综合地质灾害危险性评估内容的侧重点，土地适宜性评价的依据以及优秀评估成果的判定标准，提出了个人的理解和认识。供从事类似工作的同志参考。     

Groundwater arsenic biogeochemistry-Key questions and use of tracers to understand arsenic-prone groundwater systems

Over 100,000,000 people worldwide are exposed to high arsenic groundwater utilised for drinking or cooking.The consequent global avoidable disease burden is estimated to be of the order of 100,000 avoidable deaths or more per annum from just direct exposures — i.e.excluding indirect exposure(from rice and other foods)and excluding morbidity.Notwithstanding 1000 s of papers published on arsenic(hydro)(bio)geochemistry,there remain a number of key outstanding questions to be addressed in relation to arsenic geoscience-these include questions related to:(i)the role of human activities —irrigation,agriculture and other land uses — on arsenic mobilisation in groundwaters;(ii)the specific sources,nature and role of organics,minerals and microbial communities involved in arsenic mobilisation;(iii)the relationship to microscopic to macroscopic scale geological(including tectonic)and evolution processes;(iv)unravelling the over-printing of multiple processes in complex highly heterogeneous aquifer systems and(v)using increasing understanding of the controls of arsenic mobility in groundwaters systems to informing improved locally-relevant remediation and mitigation approaches.This article further summarises how the 9 further papers in this Special Issue address some of these questions through the use of chemical and/or isotopic tracers.     

An efficient quasi-Newton approximation-based SORM to estimate the reliability of geotechnical problems

The first order reliability method (FORM) is efficient, but it has limited accuracy; the second order reliability method (SORM) provides greater accuracy, but with additional computational effort. In this study, a new method which integrates two quasi-Newton approximation algorithms is proposed to efficiently estimate the second order reliability of geotechnical problems with reasonable accuracy. In particular, the Hasofer–Lind–Rackwitz–Fiessler–Broyden–Fletcher–Goldfarb–Shanno (HLRF–BFGS) algorithm is applied to identify the design point on the limit state function (LSF), and consequently to compute the first order reliability index; whereas the Symmetric Rank-one (SR1) algorithm is nested within the HLRF–BFGS algorithm to compute good approximations, yet with a reduced computational effort, of the Hessian matrix required to compute second order reliabilities. Three typical geotechnical problems are employed to demonstrate the ability of the suggested procedure, and advantages of the proposed approach with respect to conventional alternatives are discussed. Results show that the proposed method is able to achieve the accuracy of conventional SORM, but with a reduced computational cost that is equal to the computational cost of HLRF–BFGS-based FORM.     

Conceptual model of recharge to southeastern Badain Jaran Desert groundwater and lakes from environmental tracers

Sources of groundwater recharge to the Badain Jaran Desert in China have been investigated using geochemical and isotopic techniques. Stable isotope compositions (δ¹⁸O and δ²H) of shallow groundwater and surface water from oasis lakes evolve from a starting composition considerably depleted compared to local unsaturated zone moisture, confirming inferences from chloride mass balance that direct infiltration of precipitation is not a volumetrically important source of recharge to the shallow aquifer in the study area. Shallow phreatic and deeper confined groundwater bodies appear unconnected based on chemical composition and radiocarbon activities. Hydrogeologic evidence points toward a bordering mountain range (Yabulai) as a likely recharge zone, which is consistent with tracer results. A mean residence time in the range of 1–2 ka for the desert’s southeastern margin is inferred from radiocarbon. These results reveal that some replenishment to the desert aquifer is occurring but at a rate much lower than previously suggested, which is relevant for water resources planning in this ecologically sensitive area.