黄土区坡地土壤水分运动与转化机理研究进展

土壤水分是作物生长、植被恢复以及生态环境建设的主要限制性因素.从降雨入渗及再分布、土壤水量转化以及土壤水分动态变化等几方面概述了黄土区坡地土壤水分运动与转化研究进展,认为应该把坡面土壤—植物—大气作为一个物理上的连续统一体,以大气水、地表水、植物水和土壤水相互转化过程和机制为基础,研究坡面土壤—植被—大气界面水分运动和转化规律,为植被恢复重建提供理论依据.     

地下水位在非饱和水流数据同化中的应用

为理解地下水位观测信息在非饱和水流数据同化中的数据价值,建立了基于地下水位动态观测信息的一维饱和-非饱和水流集合卡尔曼滤波,通过虚拟数值实验检验了地下水位观测信息在非饱和水力参数估计和水分校正中的潜在价值。研究结果表明:在以地下水位为唯一观测数据时,同时更新参数和水头比仅更新水头能更好地校正土壤剖面的水头分布;当多层单个水力参数未知时,地下水位观测可以为参数估计提供有效信息;当多层多个参数未知时,地下水位与多层多个参数之间的复杂关系导致观测信息难以估计出最优的(唯一的)参数值;地下水位可作为辅助信息,与含水量观测等信息联合运用改善参数估计和含水量预测精度。     

Modeling root water uptake when calculating unsaturated flow in the vadose zone and groundwater recharge

This paper considers models of the transpiration root water uptake and principles for substantiating their parameters when calculating unsaturated flow in the vadose zone and estimating infiltration groundwater recharge. The possible use of generalized parameters for different landscape and soil conditions is substantiated based on analyzing the natural patterns of water balance formation in the vadose zone and the sensitivity of transpiration models. Recommendations are given for selecting the models of transpiration water uptake and substantiating their parameters, which enables one to minimize the errors in estimating infiltration groundwater recharge.     

Preferential flow,diffuse flow,and perching in an interbedded fractured-rock unsaturated zone

Layers of strong geologic contrast within the unsaturated zone can control recharge and contaminant transport to underlying aquifers. Slow diffuse flow in certain geologic layers, and rapid preferential flow in others, complicates the prediction of vertical and lateral fluxes. A simple model is presented, designed to use limited geological site information to predict these critical subsurface processes in response to a sustained infiltration source. The model is developed and tested using site-specific information from the Idaho National Laboratory in the Eastern Snake River Plain (ESRP), USA, where there are natural and anthropogenic sources of high-volume infiltration from floods, spills, leaks, wastewater disposal, retention ponds, and hydrologic field experiments. The thick unsaturated zone overlying the ESRP aquifer is a good example of a sharply stratified unsaturated zone. Sedimentary interbeds are interspersed between massive and fractured basalt units. The combination of surficial sediments, basalts, and interbeds determines the water fluxes through the variably saturated subsurface. Interbeds are generally less conductive, sometimes causing perched water to collect above them. The model successfully predicts the volume and extent of perching and approximates vertical travel times during events that generate high fluxes from the land surface. These developments are applicable to sites having a thick, geologically complex unsaturated zone of substantial thickness in which preferential and diffuse flow, and perching of percolated water, are important to contaminant transport or aquifer recharge.     

Distribution of groundwater salinity and formation mechanism of fresh groundwater in an arid desert transition zone

This study reviews the distribution of groundwater salinity in an arid desert transition zone. By combining field experiments and computer simulation models we make a comprehensive analysis of the formation mechanism of fresh groundwater in relation to the paleogeographic conditions of lithofacies, the geochemical characteristics of the aquifer media, salt deliverability in the vadose zone and prevailing hydrodynamic conditions. The results demonstrate that (1) the lacustrine facies deposition stratum of the Huanhe formation in the Cretaceous system provides a brackish-salt groundwater environment; (2) the average salinity of parent rocks are approximately 440 mg/kg and 4 371 mg/kg in the Quaternary eolian sand and the Cretaceous Huanhe formation respectively, suggesting that parent rocks are the principal controlling factor in the distribution of groundwater quality given that mineral and chemical composition of the eolian sand is simpler than that of the Huanhe formation; (3) average groundwater flow rates are approximately 0.25 m/d and 0.1 m/d in eolian sand and Huanhe formation aquifers respectively, indicating that hydrodynamic conditions play an important role in driving in the formation and evolution of fresh groundwater; (4) The salinity deliverability in the vadose zone overlying the aeolian sand and Huanhe formation aquifers are approximately 15.97 mg/L and 220.42 mg/L respectively, signifying that the combination of lithology and salt content of vadose zone, rainfall infiltration, evapotranspiration and concentration heavily influence the formation, distribution and evolution of groundwater quality. This study can provide a scientific basis for the sustainable development and utilization of groundwater resources in arid areas.     

某油田地下水污染特征及其机理分析

在对某油田石油类污染物分布特征研究的基础上,对其进入地下水的途径进行分析。研究表明,除石油类外,CODMn、Cl-、NO3-N和TDS具异常变化,这些异常变化已成为石油类污染的参考指标。含水层污染程度主要以严重污染和中度污染为主,下段含水层中的石油类污染物的浓度明显高于上段含水层。地下水遭受污染的途径类型分为地表渗透型和优势通道渗漏型,但地表渗透型污染对研究区地下水的威胁性相对来说较小。由构造活动、地下水开采引发的地裂缝形成的优势通道渗漏型污染是地下水污染的主要途径。     

Patterns in groundwater chemistry resulting from groundwater flow

 Groundwater flow influences hydrochemical patterns because flow reduces mixing by diffusion, carries the chemical imprints of biological and anthropogenic changes in the recharge area, and leaches the aquifer system. Global patterns are mainly dictated by differences in the flux of meteoric water passing through the subsoil. Within individual hydrosomes (water bodies with a specific origin), the following prograde evolution lines (facies sequence) normally develop in the direction of groundwater flow: from strong to no fluctuations in water quality, from polluted to unpolluted, from acidic to basic, from oxic to anoxic–methanogenic, from no to significant base exchange, and from fresh to brackish. This is demonstrated for fresh coastal-dune groundwater in the Netherlands. In this hydrosome, the leaching of calcium carbonate as much as 15 m and of adsorbed marine cations (Na⁺, K⁺, and Mg²⁺) as much as 2500 m in the flow direction is shown to correspond with about 5000 yr of flushing since the beach barrier with dunes developed. Recharge focus areas in the dunes are evidenced by groundwater displaying a lower prograde quality evolution than the surrounding dune groundwater. Artificially recharged Rhine River water in the dunes provides distinct hydrochemical patterns, which display groundwater flow, mixing, and groundwater ages. Received, May 1998 · Revised, August 1998 · Accepted, October 1998     

Analyzing unsaturated flow patterns in fractured rock using an integrated modeling approach

Characterizing percolation patterns in unsaturated fractured rock has posed a greater challenge to modeling investigations than comparable saturated zone studies due to the heterogeneous nature of unsaturated media and the great number of variables impacting unsaturated flow. An integrated modeling methodology has been developed for quantitatively characterizing percolation patterns in the unsaturated zone of Yucca Mountain, Nevada (USA), a proposed underground repository site for storing high-level radioactive waste. The approach integrates moisture, pneumatic, thermal, and isotopic geochemical field data into a comprehensive three-dimensional numerical model for analyses. It takes into account the coupled processes of fluid and heat flow and chemical isotopic transport in Yucca Mountain’s highly heterogeneous, unsaturated fractured tuffs. Modeling results are examined against different types of field-measured data and then used to evaluate different hydrogeological conceptualizations through analyzing flow patterns in the unsaturated zone. In particular, this model provides clearer understanding of percolation patterns and flow behavior through the unsaturated zone, both crucial issues in assessing repository performance. The integrated approach for quantifying Yucca Mountain’s flow system is demonstrated to provide a practical modeling tool for characterizing flow and transport processes in complex subsurface systems.     

A comparison of field-monitored and numerically predicted moisture movement in unsaturated soil

This paper presents the results of the application of a numerical model of flow of water in unsaturated soil to simulate real field behaviour. Numerical predictions are compared with field-monitored results as part of an assessment of the approach adopted. The numerical approach is based on a finite element solution of Richards' theoretical formulation, adopting a finite difference recurrence relationship to model the transient nature of the problem. The field results have been collected by British Gas in Kimmeridge clay at a site in Swindon. The simulation addressed the autumn wetting of the soil during 1983. Comparisons of volumetric moisture content readings from the field and numerical predictions give good correlation. It is concluded that the numerical model has adequately represented field behaviour over the depth of interest. Taken in conjunction with previous results, it is claimed that the model should now be capable of use in a predictive mode.     

地下水分层勘查技术在地下水流系统研究中的应用

地下水流是一种运动流体,空间上分布连续且能传递压力,在能量(势)差驱使下发生从水头高处向低处的运动.通常在补给(势源)区,地下水垂向上由上向下运动,而在排泄(势汇)区地下水由下向上运动,即地下水整个生命过程中总是由源到汇、向着能量减小的方向做径流运动,无论是在单个或多个透水岩层中都是如此.地下水分层勘查技术使在垂向上分...     

Evaluation of probabilistic flow in two unsaturated soils

A variably saturated flow model is coupled to a first-order reliability algorithm to simulate unsaturated flow in two soils. The unsaturated soil properties are considered as uncertain variables with means, standard deviations, and marginal probability distributions. Thus, each simulation constitutes an unsaturated probability flow event. Sensitivities of the uncertain variables are estimated for each event. The unsaturated hydraulic properties of a fine-textured soil and a coarse-textured soil are used. The properties are based on the van Genuchten model. The flow domain has a recharge surface, a seepage boundary along the bottom, and a no-flow boundary along the sides. The uncertain variables are saturated water content, residual water content, van Genuchten model parameters alpha (α) and n, and saturated hydraulic conductivity. The objective is to evaluate the significance of each uncertain variable to the probabilistic flow. Under wet conditions, saturated water content and residual water content are the most significant uncertain variables in the sand. For dry conditions in the sand, however, the van Genuchten model parameters α and n are the most significant. Model parameter n and saturated hydraulic conductivity are the most significant for the wet clay loam. Saturated water content is most significant for the dry clay loam. Electronic Publication     

呼和浩特盆地地下水流系统变异机制及其资源效应

几十年的高强度开采致使呼和浩特盆地地下水流系统发生了很大变化。在对含水系统结构特征分析的基础上,结合地下水流场及水位动态特征,对地下水流系统演化模式进行了分析总结,基本可归纳为3个演化阶段,地下水人工开采及沟谷水利工程的修建是地下流系统变异的主要驱动因子。采用均衡法对现状条件下地下水均衡情况进行了定量计算,通过与历史时期均衡情况对比分析,发现在不同水流系统演化阶段,各含水层地下水补排量差异较大,从而导致地下水资源量发生变化,与历史时期相比,潜水含水层资源量明显减小,承压含水层资源量有所增加,但总资源量一定程度减小,地下流系统变异的资源效应明显。     

Seasonal variations and mechanisms of groundwater nitrate pollution in the Gaza Strip

Nitrate represents one of the major pollutants of groundwater in the Gaza Strip. Several cases of blue babies disease were reported in the last couple of years. The present study is an investigation of the seasonal variations in nitrate concentration to better understand the mechanisms and parameters controlling this perilous pollutant. Nitrate was analysed in 100 wells (47 agricultural and 53 domestic) in five governorates. The results showed that 90% of the tested wells have nitrate far beyond the allowed values set by the World Health Organization (WHO). The average concentration of nitrate in domestic wells is 128 mg/L in June-July and 118 mg/L in Jan-Feb, and for the agricultural wells, the average is 100 mg/L in June-July, and 96 mg/L for Jan-Feb. The results suggest that the seasonal differences in nitrate concentrations of the domestic wells are slightly more observable than those of the agricultural wells. The environmental factors that control nitrate in groundwater are: a partially-confined aquifer, lack of a sewage system, population density, the presence of refugee camps, the presence of fertilizers and the annual rain. The variations in nitrate concentration of the domestic wells are not of considerable values. It is suggested that concrete policies in pollution control and/or prevention measures could be formulated upon better understanding of the environmental factors.     

降水和开采变化对石家庄地下水流场影响强度

为能精确识别降水和开采对石家庄地下水流场影响强度,应用小波变换和相关分析等研究方法,对区域平均地下水位、地下水降落漏斗面积及中心水位与降水和开采变化之间的互动特征进行了研究。结果表明:① 1961—1973年期间,平均地下水位随降水量增大呈幂函数递减趋势;1974—2010年期间,降水量每减小100 mm,漏斗中心水位下降速率增大7.35 m,平均地下水位下降速率增大2.15 m;② 1961—1973年期间,开采量每增加1亿m3,平均地下水位下降0.28 m,漏斗面积扩大11.74 km2,中心水位下降0.52 m,1974年以来累计超采量每增加1亿m3,漏斗面积增幅1.52 km2,中心水位降幅0.18 m;③ 降水量每减小100 mm,降水贡献度减弱3.0%,人类开采影响强度增大2.76%。     

非饱和流节点间导水率估计及达西平均分析

针对由Gardner-Russo函数描述的特征土壤,在双饱和度坐标系中,探讨了常规节点间导水率估计与量纲一水平达西平均(k*_H)和量纲一垂直达西平均(k*_V)的差异.k*_H是相邻两节点饱和度的函数,而k*_V也是空间步长(Δx)和特征参数(α)的函数.对水平非饱和流,算术平均高估导水率,而几何与调和平均低估导水率;从相对误差空间分布看,几何平均优于算术和调和平均.对垂直非饱和流,随Δx(或α)的增大,常规估计的相对误差空间顺(或逆)时针旋转并缩小,从而降低模型准确性.k*_H等值线具有对称性,而k*_V不具对称性;仅当Δx或α足够小时,k*_H才趋近于k*_V.因此,为提高非饱和流数值模拟的准确性,必须采用精确的达西平均来计算节点间导水率.     

A mathematical model for predicting coupled heat and water movement in unsaturated soil

An investigation was conducted to develop a comprehensive moisture model for predicting non-isothermal moisture conditions in soils. An extensive literature review indicated that a model based on the Philip and de Vries equations for non-isothermal moisture movement and heat conduction would give the best results. By using numerical methods, the implicit finite difference approximations to the moisture movement and heat-transfer equations were programmed for computer solution of water content and temperature in the soil with time. Validation studies indicate that the moisture model can be used to predict accurately moisture conditions in the soil. The model was validated by using hydraulic data from laboratory studies conducted on soil columns compacted with AASHO A-3 and AASHO A-4 soil. The application of the moisture model to the study of non-isothermal moisture movement in the field is demonstrated. The influence of parameters such as water table depth, precipitation, and soil hydraulic properties on soil moisture content are shown by use of the moisture model. The model is shown to be applicable to a wide range of boundary conditions and that it predicts the moisture-temperature regime with time in soils utilizing climatic input data.