A critical review of groundwater budget myth, safe yield and sustainability

The principle of water balance is well known, but its application often causes controversy. One recent debate is the use of the water balance equation to determine the safe yield and sustainable yield. Two extreme opinions exist on natural groundwater recharge. One misconception is that the development of groundwater is considered to be safe if the pumping rate does not exceed the rate of natural recharge. Another is that the sustainable pumping rate has nothing to do with natural recharge, but depends on the increased recharge and decreased discharge (called capture) induced by pumping. The truth is that both the natural recharge and dynamic development of the capture determine the safe yield or sustainable yield of a groundwater basin. This paper clarifies the water budget controversy and uses the water balance equation to critically analyse the concepts of safe yield and sustainable yield. Numerical simulation of a hypothetical case was used to demonstrate the natural groundwater balance, effects of pumping and the dynamic development of the capture.     

Magma yield stress and permeability: Insights from multiphase percolation theory

Magmas often contain multiple interacting phases of embedded solid and gas inclusions. Multiphase percolation theory provides a means of modeling assemblies of these different classes of magmatic inclusions in a simple, yet powerful way. Like its single phase counterpart, multiphase percolation theory describes the connectivity of discrete inclusion assemblies as a function of phase topology. In addition, multiphase percolation employs basic laws to distinguish separate classes of objects and is characterized by its dependency on the order in which the different phases appear. This paper examines two applications of multiphase percolation theory: the first considers how the presence of bubble inclusions influences yield stress onset and growth in a magma's crystal network; the second examines the effect of bi-modal bubble-size distributions on magma permeability. We find that the presence of bubbles induces crystal clustering, thereby 1) reducing the percolation threshold, or critical crystal volume fraction, ?_c, at which the crystals form a space-spanning network providing a minimum yield stress, and 2) resulting in a larger yield stress for a given crystal volume fraction above ?_c. This increase in the yield stress of the crystal network may also occur when crystal clusters are formed due to processes other than bubble formation, such as heterogeneous crystallization, synneusis, and heterogeneity due to deformation or flow. Further, we find that bimodal bubble size distributions can significantly affect the permeability of the system beyond the percolation threshold. This study thus demonstrates that larger-scale structures and topologies, as well as the order in which different phases appear, can have significant effects on macroscopic properties in multiphase materials.     

Flood‐based analysis of high‐magnitude sediment transport using a non‐parametric method

Upland erosion and the resulting reservoir siltation is a serious issue in the Isábena catchment (445 km² Central Spanish Pyrenees). During a three‐month period, water and sediment fluxes have been monitored at the catchment outlet (Capella), two adjacent subcatchments (Villacarli, 41 km²; Cabecera, 145 km²) and the elementary badland catchment Torrelaribera (8 ha). This paper presents the results of the monitoring, a method for the calculation of a sedigraph from intermittent measurements and the derived sediment yields at the monitored locations. The observed suspended sediment concentrations (SSCs) demonstrate the role of badlands as sediment sources: SSCs of up to 280 g l^?1 were encountered for Villacarli, which includes large badland areas. SSCs at the Cabecera catchment, with great areas of woodland, barely exceeded 30 g l^?1. SSCs directly at the sediment source (Torrelaribera) were comparable to those at Villacarli, suggesting a close connection within this subcatchment. At Capella, SSCs of up to 99 g l^?1 were observed. For all sites, SSC displayed only a loose correlation with discharge, inhibiting the application of a simple sediment rating curve. Instead, ancillary variables acting as driving forces or proxies for the processes (rainfall energy, cumulative discharge, rising/falling limb data) were included in a quantile regression forest model to explain the variability in SSC. The variables with most predictive power vary between the sites, suggesting the predominance of different processes. The subsequent flood‐based calculation of sediment yields attests high specific sediment yields for Torrelaribera and Villacarli (6277 and 1971 t km^?2) and medium to high yields for Cabecera and Capella (139 and 410 t km^?2) during the observation period. In all catchments, most of the sediment was exported during intense storms of late summer. Later flood events yield successively less sediment. Relating upland sediment production to yield at the outlet suggests considerable effects of sediment storage within the river channel. Copyright © 2008 John Wiley & Sons, Ltd.     

The behavior of specific sediment yield in different grain size fractions in the tributaries of the middle Yellow River as influenced by eolian and fluvial processes

Based on data from 35 stations on the tributaries of the Yellow River, annual specific sediment yield (Y_s) in eight grain size fractions has been related to basin‐averaged annual sand–dust storm days (D_ss) and annual precipitation (P_m) to reveal the influence of eolian and fluvial processes on specific sediment yield in different grain size fractions. The results show that Y_s in fine grain size fractions has the highest values in the areas dominated by the coupled wind–water process. From these areas to those dominated by the eolian process or to those dominated by the fluvial process, Y_s tends to decrease. For relatively coarse grain size fractions, Y_s has monotonic variation, i.e. with the increase in D_ss or the decrease in P_m, Y_s increases. This indicates that the sediment producing behavior for fine sediments is different from that for relatively coarse sediments. The results all show that Y_s for relatively coarse sediments depends on the eolian process more than on the fluvial process, and the coarser the sediment fractions the stronger the dependence of the Y_s on the eolian process. The Y_s–D_ss and Y_s–P_m curves for fine grain size fractions show some peaks and the fitted straight lines for Y_s–D_ss and Y_s–P_m relationships for relatively coarse grain size fractions show some breaks. Almost all these break points may be regarded as thresholds. These thresholds are all located in the areas dominated by the coupled wind–water process, indicating that these areas are sensitive for erosion and sediment production, to which more attention should be given for the purpose of erosion and sediment control. A number of regression equations were established, based which the effect of rainfall, sand–dust storms and surface material grain size on specific sediment yield can be assessed. Copyright © 2007 John Wiley & Sons, Ltd.     

Modelling blue and green water resources availability in Iran

Knowledge of the internal renewable water resources of a country is strategic information which is needed for long‐term planning of a nation's water and food security, among many other needs. New modelling tools allow this quantification with high spatial and temporal resolution. In this study we used the program Soil and Water Assessment Tool (SWAT) in combination with the Sequential Uncertainty Fitting program (SUFI‐2) to calibrate and validate a hydrologic model of Iran based on river discharges and wheat yield, taking into consideration dam operations and irrigation practices. Uncertainty analyses were also performed to assess the model performance. The results were quite satisfactory for most of the rivers across the country. We quantified all components of the water balance including blue water flow (water yield plus deep aquifer recharge), green water flow (actual and potential evapotranspiration) and green water storage (soil moisture) at sub‐basin level with monthly time‐steps. The spatially aggregated water resources and simulated yield compared well with the existing data. The study period was 1990–2002 for calibration and 1980–1989 for validation. The results show that irrigation practices have a significant impact on the water balances of the provinces with irrigated agriculture. Concerning the staple food crop in the country, 55% of irrigated wheat and 57% of rain‐fed wheat are produced every year in water‐scarce regions. The vulnerable situation of water resources availability has serious implications for the country's food security, and the looming impact of climate change could only worsen the situation. This study provides a strong basis for further studies concerning the water and food security and the water resources management strategies in the country and a unified approach for the analysis of blue and green water in other arid and semi‐arid countries. Copyright © 2008 John Wiley & Sons, Ltd.     

黏性土剪切带的形成与其屈服的内在联系的探索

为了深入了解黏性土的应力应变特性,对黏性土进行了量测侧向变形的不排水平面应变压缩试验。分析试验结果发现,黏性土局部化变形的起始点与黏性土样中的孔隙水压力的突然增长的转折点非常接近,而孔隙水压力开始急剧增长变化的转折点为其屈服点,说明黏性土剪切带开始形成的偏应力为其屈服点,超过此点后黏性土局部化变形加剧,这个发现将有助于土体在强度理论、变形和稳定分析等方面的深入研究。     

建筑垃圾填埋场沉降计算中模型参数灵敏度分析

建筑垃圾土的变形机理复杂,它不同于传统意义上的土体。通过大量的非线性有限元计算,找到了双屈服面模型中影响建筑垃圾填埋场沉降的主要参数,并给出了各参数与沉降之间的定性关系,为建筑垃圾填埋场沉降计算和参数灵敏度分析奠定了基础。     

粘弹塑本构模型及用于冻土数值计算的柔度矩阵

随着寒区经济发展及冻结法施工技术在工程中的推广应用,对冻土蠕变的深入研究显得尤为重要.对冻土单轴流变试验结果分析,用非线性牛顿体替代线性牛顿体,从而对西原模型进行了改进,得到了冻土三向应力状态下的本构方程;并利用D-P屈服准则推导出应用与数值计算的柔度矩阵.通过有限元程序的二次开发,将本构模型添加到大型非线性程序ADINA中.用三轴蠕变试验检验了粘弹塑本构模型,获得相应的试验拟合曲线.结果表明:三轴蠕变试验与理论计算结果吻合良好,说明粘弹塑本构模型可以描述冻土在高应力下反映的非衰减性蠕变变形特征.     

岩石变形破坏的熵突变过程与破坏判据

在岩石的变形破坏过程中,当进入不稳定的破裂发展阶段之后,系统不断调整结构抵抗外力的扰动,裂纹向局域集中的有序方向发展,应变能不断耗散,并以应变能的耗散为媒介,使系统与外扰动所追加的负熵流产生能量流通,也使系统熵值和系统的维数逐次降低,这一阶段岩石系统远离平衡态,岩石的破坏是系统熵的突变过程。基于这一认识,并在验证应变能分布与结构块度分布模式的一致性的基础上,推导出包含了结构因素和能量分布的熵表达式;对熵表达式进行平衡分析获得局部突变的分岔集,得到了岩石局部破坏的熵折迭突变破坏准则;同时,探讨了熵表达式所表征的结构有序度的尖点突变性,解出岩石系统的分岔集,这个分岔集就是岩石系统熵突变的整体破坏准则。     

岩土介质三维快速拉格朗日数值分析方法研究

研究了FLAC3D（fast lagrangian analysis of continua in 3 dimensions）的特点,并与有限单元法作了比较。FLAC3D方法以结点运动方程为支配方程,追踪了介质从受荷到达到平衡状态的过程,而有限元法是根据介质力学平衡方程直接求解,这是二者主要区别。FLAC3D没有采用介质真实的阻尼特性和结点质量,给出的不是介质所经历的真实过程,不能正确反映过程的影响,因此给出的介质应力和变形计算结果的物理意义是不甚明确的。求解过程中的介质振动,是一种噪音,可引起弹塑性介质计算结果误差,而弹性介质的计算结果几乎不受影响。研究指出了FLAC3D方法的优缺点。还通过算例作了四个方面的研究：(1) Drucker-Prager屈服准则与Mohr-Coulomb屈服准则比较;(2) 膨胀角取值对计算结果的影响;(3) 大变形与小变形对计算结果的影响;(4) 精度设置对计算结果的影响。研究表明,Drucker-Prager准则与Mohr-Coulomb准则结果差异颇大;膨胀角取值对结果的影响是敏感和显著的;一般情况下,取小变形模式是合适的,计算精度取10-5是足够的。