Electrical-hydraulic conductivity model for a weatheredfractured aquifer system of Olbanita, Lower Baringo Basin, Kenya Rift

Groundwater yield in the Kenya Rift is highly unsustainable owing to geological variability.In this study,field hydraulic characterization was performed by using geoelectric approaches.The relations between electrical-hydraulic(eh)conductivities were modeled hypothetically and calibrated empirically.Correlations were based on the stochastic models and field-scale hydraulic parameters were contingent on pore-level parameters.By considering variation in pore-size distributions over eh conduction interval,the relations were scaled-up for use at aquifer-level.Material-level electrical conductivities were determined by using Vertical Electrical Survey and hydraulic conductivities by analyzing aquifer tests of eight boreholes in the Olbanita aquifer located in Kenya rift.VES datasets were inverted by using the computer code IP2Win.The main result is that ln T=0.537(ln Fa)+3.695;the positive gradient indicating eh conduction through pore-surface networks and a proxy of weathered and clayey materials.An inverse(1/F-K)correlation is observed.Hydraulic parameters determined using such approaches may possibly contribute significantly towards sustainable yield management and planning of groundwater resources.

Saturated Hydraulic Conductivity Changes with Time and Its Prediction at SAR and Salinity in Quevedo Region Soils

Darcy’s law is applied to describe the steady flow processes in which the flux remains constant with time along the conducting system. Due to the dispersion and migration of colloidal particles and lodging in the soil pores the reduction in hydraulic conductivity occurs with time in particular when the soil and the percolating solution are affected by electrolyte concentration. Hence, the aim of this study is to find empirical equations that can be used to predict the flux with time. Data for the effluent volume versus time (up to 6 hours) which was collected for three soils (located at Quevedo-Los Rios region) treated by two salt solutions (5 and 50 meq/l) with different SAR values were used to test certain mathematical forms of equations. Only four empirical equations were found to perfectly fit the data (flux vs time) whereas, fitting the calculated and measured data of the hydraulic conductivity for all soils produced regression factors R2 ≥ 0.99. So, these equations can be applied to predict the hydraulic conductivity and to characterize the flow process at saturated conditions of the studied soils with great confidence. The Hoerl function model was the best of all equations for application as the fitting degrees were almost perfect for all studied soils at 5 and 50 meq/l. It was observed for all equations that one of the fitting parameters would always represent the initial hydraulic conductivity (Kos) that was evaluated graphically at zero time by extrapolation.

Assessing the Connectivity of a Regional Fractured Aquifer Based on a Hydraulic Conductivity Field Reversed by Multi-Well Pumping Tests and Numerical Groundwater Flow Modeling

Aquifer connectivity could greatly affect groundwater flow and further control the contaminant transport in fractured medium.However,assessing connectivity of fractured aquifer at regional scales is still a challenge because such connectivity is difficult to be measured directly.This study proposes a framework for assessing connectivity of a fractured aquifer,with Qitaihe area,Heilongjiang Province,northeastern China as an illustrating study area.The 3-D finite difference numerical models were established to interpret the results of three multi-well pumping tests and inversely estimate the distribution of hydraulic conductivity(K)in the fractured aquifer.A static connectivity metric of the minimum hydraulic resistance(MHR)was calculated,based on the optimized K-field,to evaluate the hydraulic connectivity in the aquifer,and the corresponding least resistance paths(LRPs)were identified.The results indicate a better horizontal connectivity in the fractured aquifer in the northeastern and middle parts than in the southwestern part of the study area.The identified LRP indicated that the preferential flow channels at regional scales were controlled mainly by aquifer connectivity instead of local high-K zones.The results of this study can provide a method for aquifer connectivity estimation at regional scales.

GIS-Based Hydrogeological-Parameter Modeling

A regression model is proposed to relate the variation of water well depth with topographic properties (area and slope), the variation of hydraulic conductivity and vertical decay factor. The implementation of this model in GIS environment (ARC/TNFO) based on known water data and DEM is used to estimate the variation of hydraulic conductivity and decay factor of different lithology units in watershed context.

Unraveling the hydraulic properties of loess for landslide prediction:A study on variations in loess landslides in Lanzhou,Dingxi,and Tianshui,China

Loess has distinctive characteristics,leading to frequent landslide disasters and posing serious threats to the lives and properties of local re sidents.The involvement of water repre sents a critical factor in inducing loess landslides.This study focuses on three neighboring cities sequentially situated on the Loess Plateau along the direction of aeolian deposition of loess,namely Lanzhou,Dingxi,and Tianshui,which are densely populated and prone to landslide disasters.The variations in hydraulic properties,including water retention capacity and permeability,are investigated through Soil Water Characteristic Curve(SWCC)test and hydraulic conductivity test.The experimental findings revealed that Tianshui loess exhibited the highest water retention capacity,followed by Dingxi loess,while Lanzhou loess demonstrated the lowest water retention capacity.Contrastingly,the results for the saturated permeability coefficient were found to be the opposite:Tianshui loess showed the lowest permeability,whereas Lanzhou loess displayed the highest permeability.These results are supported and analyzed by scanning electron microscopy(SEM)observation.In addition,the water retention capacity is mathematically expressed using the van Genuchten model and extended to predict unsaturated hydraulic properties of loess.The experimental results exhibit a strong accordance with one another and align with the regional distribution patterns of disasters.

Coupled hydro-thermo-mechanical modeling of hydraulic fracturing in quasi-brittle rocks using BPM-DEM

This paper presents an improved understanding of coupled hydro-thermo-mechanical(HTM) hydraulic fracturing of quasi-brittle rock using the bonded particle model(BPM) within the discrete element method(DEM). BPM has been recently extended by the authors to account for coupled convective econductive heat flow and transport, and to enable full hydro-thermal fluidesolid coupled modeling.The application of the work is on enhanced geothermal systems(EGSs), and hydraulic fracturing of hot dry rock(HDR) is studied in terms of the impact of temperature difference between rock and a flowing fracturing fluid. Micro-mechanical investigation of temperature and fracturing fluid effects on hydraulic fracturing damage in rocks is presented. It was found that fracture is shorter with pronounced secondary microcracking along the main fracture for the case when the convectiveeconductive thermal heat exchange is considered. First, the convection heat exchange during low-viscosity fluid infiltration in permeable rock around the wellbore causes significant rock cooling, where a finger-like fluid infiltration was observed. Second, fluid infiltration inhibits pressure rise during pumping and delays fracture initiation and propagation. Additionally, thermal damage occurs in the whole area around the wellbore due to rock cooling and cold fluid infiltration. The size of a damaged area around the wellbore increases with decreasing fluid dynamic viscosity. Fluid and rock compressibility ratio was found to have significant effect on the fracture propagation velocity.

基于GIS的城市建筑内涝损失和风险定量计算方法

从城市内涝的致灾因子、承灾体暴露性和承灾体脆弱性属性出发,研究基于GIS的城市建筑内涝损失及风险定量计算方法.方法整合了来自内涝模拟淹水深度、建筑物空间分布以及其脆弱性属性多方面风险影响因素,对城市内涝风险进行定量评估.对北京左安东路片区的建筑内涝损失计算实例表明,该计算方法能建立单个建筑物尺度、具有空间分布属性的内涝损失和风险量化结果,为工程减灾和制定内涝管理对策提供基础依据.

基于GIS的给水管网动态水力计算模型的建立与应用

基于GIS和给水管网水力计算方法,采用一种新的更符合实际的节点流量分配方法,建立了给水管网动态水力计算模型,实现了模拟结果和GIS图形信息的良好结合,解决了工况结果难以在GIS中显示和输出的问题。将模型应用于天津市津南区咸水沽镇供水管网,并将计算结果与MIKENET模拟值、EPANET2.0计算值进行比较,验证了模型的实用性。

基于边坡单元的三维滑坡灾害评价的GIS方法

利用一个新的基于地理信息系统(GIS)栅格单元的三维定量模型,并且以边坡单元(slope unit)作为研究对象,利用三维安全系数指标进行滑坡灾害的分区。假定初始滑动面为椭球体的下半弧面,滑坡的最危险滑动面通过Monte-Carlo模拟方法搜索最小三维安全系数的方法获得。本模型既可适应于单一土层,也可适应于多层地层的情况,还可考虑地下水和不连续面的影响。所有的计算过程和数据结果显示均在一个名为3DSLOPEGIS的系统内完成。在该系统中,使用一个GIS组件来实现所有的GIS功能和空间分析功能。

基于GIS的供水管网水力计算模型

供水管网是将水从单一或多个水源地输送到用户的管线网络。文中就基于地理信息系统(Geographic InformationSystem,GIS)的供水管网水力计算模型的有关概念、建模方法、理论、实现等问题做了阐述,它将使管网工况分析工作从繁琐耗时变的简单快捷。

利用中间层技术实现GIS与水力模型的无缝连接

针对在给水管网管理信息系统建设中水力模型和地理信息系统的结合问题,提出了基于GIS的利用数据挖掘和数据检查技术建立中间层,并以之作为水力模型数据来源的方法,从而避免了水力模型会继承GIS中的数据缺陷和数据错误等不足,同时实现了GIS与模型的无缝连接和同步更新。实际应用情况表明,通过中间层来建立和维护水力模型简单、可靠、高效;与传统方法相比,模型更新及时、维护费用低,且适用于多种GIS平台,通用性好。

基于GIS和随机森林算法的宁东土壤饱和导水率分布与预测

为探明宁东土壤饱和导水率(Ks)的空间分布特征,在宁东采集136个原状土,采用经典统计和地统计方法分析土壤Ks的空间结构特征,并以地形因子、土壤属性等作为辅助变量,运用随机森林法(RF)、普通克里格法(OK)和逐步回归克里格法(RK)对区域土壤Ks进行预测并对3种方法的预测结果进行精度评价。结果表明:Ks介于0.05~7.13 mm/min,平均值为1.46 mm/min,变异系数为106.86%;Ks与容重、孔隙度、高程、坡度、坡向、平面曲率和剖面曲率在不同滞后距离下具有自相关关系和交互相关关系;土壤Ks块金值为38,表明随机因素引起的土壤Ks变异性较大,空间异质比为15.32%,在空间上呈现强变异性;RF法的预测精度最高,其平均相对误差(MRE)和均方根误差(RMSE)绝对值均为最小,相比OK和RK方法预测精度分别提高了5.53%和2.49%,且对局部细节的描述更准确、模拟效果最佳。RF法可以较为准确的预测宁东土壤Ks,为了解研究区土壤水文过程及林草植被建设提供数据参考。

雷电冲击下GIS外壳暂态电位升的研究

为了计算雷击GIS单相套管外引线时,GIS外壳暂态电位升高,建立了GIS电路模型。利用电磁场理论和多导体传输线理论提取了GIS主要元件参数,建立了GIS主要元件的电路模型。以某220 kV GIS智能开关设备为研究对象,计算了智能组件传感器安装处GIS外壳TEV,并进行了试验验证。所得的仿真结果为下一步智能组件端口骚扰电压的研究提供基础。

GIS技术在水力学模型构建中的应用

以无结构不规则网格水力学模型和ArcGIS软件为例,介绍了GIS技术在水力学模型构建的数据前处理中的应用,包括网格拓扑关系的建立、网格高程和建筑物面积属性提取、道路高程和宽度的提取、河道宽度及河段上下游关系提取等的方法和技巧,充分利用软件中的分析工具,避免了手工逐一提取存在的耗时和误差问题,为提高水力学模型构建效率和准确性提供了参考。

Experimental study and modeling of hydromechanical behavior of concrete fracture

In this study, the hydromechanical behavior of a concrete fracture under coupled compressive and shear stresses was investigated. A special experimental device was designed to create a planar fracture in a cylindrical sample and to carry out different kinds of hydromechanical tests on the fracture. Four series of laboratory tests were performed on an ordinary concrete sample. Hydrostatic compression tests were first conducted to characterize the normal compressibility of the fracture. In the second series, direct shear tests were conducted on the fracture under different normal stresses. The maximal shear stress of the fracture was determined as a function of the normal stress. In the third series, fluid flow tests were carried out in view of characterizing the overall hydraulic conductivity of the fracture as a function of its opening and closure. Shear tests with a constant fluid pressure were finally performed to investigate the influence of fluid pressure on the deformation behavior of concrete fractures. Based on the experimental investigation, an elastoplastic model is proposed. This model takes into account the nonlinear elastic behavior of a fracture under normal compression and the plastic deformation and failure due to shear stress. The model was coupled with the classical Darcy's law to describe the fluid flow along the fracture by considering the variation of permeability with fracture aperture. Numerical results agree with experimental data from various laboratory tests.

BIM与GIS集成的三维建模方法在水利工程管理中的应用

当前水利工程管理的信息化需求与日俱增,结合表面分析能力强大的三维GIS与几何语义丰富的BIM数据,形成集成宏观地理环境数据与微观建筑信息数据的水利工程精细化三维模型,是实现水利工程的精细化、智慧化管理的重要方式.本文概述了多种集成方法,主要介绍了基于SuperMap软件平台实现两者集成的方法,并以江西省峡江水利枢纽工程为例,展示集成结果.其中,精细模型数据由Revit软件构建,并提出精细三维模型与当前物联网等新技术结合后的综合应用构想,说明BIM与GIS集成后产生的精细三维模型在水利工程管理方面的应用场景.

三维GIS在水利工程规划设计中的应用

传统二维的CAD设计图不能直观表达水利工程规划设计方案,因此针对三维GIS在水利工程规划中应用的技术流程进行了阐述,并就规划阶段水工建筑物的特点,提出了两种地物模型的建模策略,结合Geoprocessing工具搭建ModelBuilder模型实现管线数据的参数化建模,最后以某水库为例试验论证了该方法在工程规划阶段具有良好的实用性。

基于GIS的公路综合排水系统设计方法研究

为了从系统工程的角度设计公路排水系统,提出了基于GIS的公路综合排水系统设计方法。通过建立数字高程模型,基于GIS平台构建资料管理库系统,结合水文分析计算,进行地表水模拟。对地下水进行数值模拟计算,借助VisualBasic进行设计径流量和水力计算,通过排水设施图形库来进行排水设施模拟,流域集成后推荐排水设施设置情况,构建公路综合排水设计系统结构。

准饱和细砂在圈闭气体溶解过程中渗透系数的变化

准饱和含水层的渗透系数会随着圈闭气体饱和度的增大而变小,但受限于试验操作和测量精度,通过传统驱替试验很难获得大量连续的圈闭气体饱和度数据,因此限制了小圈闭气体饱和度及其对应的准饱和渗透系数之间关系的准确刻画。研究设计了一个以氧气代替天然圈闭过程中空气的准饱和细砂圈闭气体溶解试验,通过精确测量溶解过程中水中可溶性氧和相应的渗透系数得到了大量连续的圈闭气体饱和度及其准饱和渗透系数的数据。试验结果表明,在小于5%圈闭气体饱和度的区间,圈闭气体进入到无效孔隙中,因此不影响渗透系数的大小;圈闭气体饱和度在5%~6%时会形成孔喉阻塞效应,对渗透系数的影响加剧。在此基础上,构建了预测准饱和渗透系数的van Genuchten模型。与传统Faybishenko幂律模型相比,新构建的模型很好地表征了小圈闭气体饱和度对渗透系数影响不大的特征;在其他圈闭气体饱和度时,新模型与传统模型的预测性能相当。新构建的准饱和渗透系数模型为深入研究准饱和水流和溶质运移奠定了基础。

有机物料还田对草甸土孔隙结构及玉米产量的影响

为了研究有机物料还田对草甸土孔隙结构及玉米产量的影响,优化草甸土耕作层结构、提高作物产量,2019年以吉林省公主岭市的草甸土为试验地,在玉米播种前设置了秸秆浅混还田(CT,0~15cm)、秸秆深混还田(STS,0~35cm)、秸秆和有机肥深混还田(STSM,0~35 cm)、无秸秆还田常规耕作(CK)4个处理。对玉米收获后的土壤进行取样分析,测定0~35 cm土层土壤物理性质和孔隙结构,并采用结构方程模式、Mantel test和随机森林方法分析土壤孔隙结构调控玉米产量的途径。结果表明,经CT、STS和STSM处理后的0~15 cm土层土壤容重与CK处理相比显著下降了5.2%~7.8%(P<0.05),而田间持水量和饱和导水率均呈现上升趋势,分别显著增加了7.8%~16.6%和77.5%~325%(P<0.05);STS和STSM处理进一步显著改变了>15~35 cm土层上述3个土壤物理性质。CT扫描结果显示,有机物料还田显著改善了相应土层土壤结构。与CK处理相比,CT、STS和STSM处理显著增加了0~15 cm土层>1000µm孔隙数量和孔隙度;与CT处理相比,STS和STSM处理>15~35 cm土层>1000µm孔隙数量和孔隙度分别显著增加了1.2倍~1.3倍和47.5%~58.9%(P<0.05)。有机物料还田增加了土壤孔隙的复杂性和连通性。与CK处理相比,CT、STS和STSM处理显著增加了0~15 cm土层的各向异性和分形维数,降低了欧拉数(P<0.05);STS和STSM处理显著改善了15~35 cm土层土壤孔隙结构。不同处理间玉米产量表现为STSM>STS>CT>CK。结构方程模型结果显示,0~15 cm土层土壤孔隙结构可以直接影响玉米产量或者通过影响容重和饱和导水率间接影响玉米产量,而15~35 cm土层土壤孔隙结构只能通过影响田间持水量间接影响玉米产量。0~35 cm土层土壤物理性质和孔隙结构能够解释玉米产量的81.9%,15~35 cm土层对玉米产量的贡献大于0~15 cm土层。有机物料深混还田通过改变0~35 cm土层草甸土物理性质和孔隙分布,增加孔隙结构的复杂性和连通性,优化耕层结构,具备提高玉米产量的潜力,其中秸秆和有机物配合施用的效果优于单独秸秆还田。如果草甸土分布区有机肥源充足,建议利用秸秆和有机肥料进行深混还田可建立良好的土壤肥力,可以有效增加玉米产量。