Groundwater Recharge Through Infiltration Process: A Case Study of Umudike, Southeastern Nigeria

Although water is a renewable resource for sustaining life and environment, excessive pumping of groundwater results in the ground water table being depleted. The major natural source of groundwater recharge is rainfall. In Umudike just like many other areas, the rate of natural recharge is lower than pumping rate. This is due to increasing economic and agricultural activities and also urbanization. Over exploitation of groundwater is a threat to the water quality and table and creates hydrological imbalance. This imbalance includes degradation in hydrological and hydro-chemical characteristics of the aquifer. Artificial recharge of water table aquifers becomes necessary to improve the hydrodynamic conditions of groundwater. A drop in piezometric level can be remedied by artificial recharge of groundwater through infiltration process using water from dams, lakes, rivers, runoff and sewage effluent. Results of water table survey conducted at Umudike show that it peaks at 85m (above sea level) before recharge and 95m after recharge. The recharge of groundwater is basically through rainfall and river water.

Managed Aquifer Recharge Using Infiltration Pond： Case Study of Ban Nong Na, Phitsanulok, Thailand

The Upper Chao Phraya River Basin, Thailand, has been facing continuous groundwater level decreases due to over-extraction for irrigation. MAR （managed aquifer recharge） using infiltration pond was investigated and constructed. A recharge experiment at the pilot site at Ban Nong Na, Phitsanulok Province, was conducted during 2009 to 2011 to mitigate the declining shallow groundwater level. The HELP3 and MODFLOW models were applied to explore the current groundwater recharge. The MODFLOW was used to simulate the recharge mechanism of the experiment in the 1,260 m2 infiltration pond during July to November, 2010. The simulated results showed the groundwater influx and outflux for the year 2010 were 1.34 Mm3 1.57 Mm3, respectively. The annual shallow groundwater extraction was 1.40 Mm3 resulting in the groundwater system deficit of 0.23 Mm3 and causing groundwater level decline at the rate of 0.25 m/yr. The critical zone with groundwater level deeper than 8 m from the ground surface covers 19% of the study area of 4.12 km2 and it would be increased up to 85% within the next 10 years （2020）. To achieve the groundwater system balance, the deficit amount of 0.23 Mm3 is needed and six infiltration ponds are required.

Evaluating Model Effectiveness for Soil Infiltration Attribute: Comparison of Green-Ampt, Horton and Modified Green-Ampt Infiltration Models

Soil infiltration is a very important concept in hydrology as well as irrigation, which plays a vital role in estimating surface runoff and groundwater recharge. It is a complicated process that varies with numerous factors. Accurate estimation of soil infiltration is required for future irrigation, and many other purposes. To estimate the infiltration process, there are numerous models. The majority of them have some presumptions, a unique calculation method, and some limitations. The purpose of the paper was to assess the model’s performance for a similar hypothetical scenario involving soil infiltration. It compared the infiltration rate, runoff rate, and incremental infiltration versus time for three different infiltration models: the Green-Ampt model (GA), the Horton model and the Modified Green-Ampt (MGA) model. A spreadsheet was used to calculate the Horton model, and HYDROL-INF (V 5.03) was used to simulate the other two models. Among those three models, the MGA model outperformed those three models, while the GA model produced greater infiltration rate than rainfall, which was insensible. The study showed that the MGA model, which provides useful infiltration predictions, outperformed the other two infiltration models. Since the Horton model does not consider ponding conditions, it is only applicable when the effective rainfall intensity exceeds the final infiltration capacity. Moreover, the GA model’s initial infiltration rate is irrational because it disregards the intensity of the rainfall. The results of this study will assist in selecting the most accurate method for estimating soil infiltration for agricultural purposes.

Geophysical Surveys over Karst Recharge Features,Illinois,USA

Karst aquifers supply a significant fraction of the world's drinking water. These types of aquifers are alsohighly susceptible to pollution from the surface with recharge usually occurring through fractures and solution openings at the bedrock surface. Thickness of the protective soil cover, macropores and openings within the soil cover, and the nature of the weathered bedrock surface all influence infiltration. Recharge openings at the bedrock surface, however, are often covered by unconsolidated sediments, resulting in the inadvertent placement of landfills, unregulated dump sites, tailing piles, waste lagoons and septic systems over recharge zones. In these settings surface geophysical surveys, calibrated by a few soil cores, could be employed to identify these recharge openings, and qualitatively assess the protection afforded by the soil cover. In a test of this hypothesis, geophysical measurements accurately predicted the thickness of unconsolidated deposits overlying karstic dolomite at a site about 100 km south of Chicago, Illinois. Zones of elevated electrical conductivity and high ground-penetrating radar (GPR) attenuation within the sediments coincided with subcropping solutionally-enlarged hydraulically active bedrock fractures. These fractures extend to over 12-m depth, as shown by 2-D inverted resistivity sections and soil coring. Anomalous electromagnetic (EM) conductivity and GPR response may be due to higher soil moisture above these enlarged fractures. An epikarstal conduit at 2.5-m depth was directly identified through a GPR survey. These results suggest that surface geophysical surveys are a viable tool for assessing the susceptibility of shallow karst aquifers to contamination.

Assessment of Groundwater Recharge from Rainfall in the Plain of Cai Phan Rang, Vietnam

This paper presents the quantitative assessment results of rainwater supply to groundwater in Cai Phan Rang River basin, Ninh Thuan province, Vietnam. In order to obtain the results, the authors developed two experimental areas with 10 wells which were monitored in one year to assess the infiltration supply of rainwater to groundwater. The results of this research assessed the amount of rainwater infiltrates into groundwater varies from 307.16-314.98 tam·year^-1, average is 311 mm·year^-1. The findings are significant in terms of science which identify sources of groundwater storage from the infiltration supply of rainwater. The findings are also practical in suggesting measures to reserve groundwater for the purpose of socio-economic development in the study area.

华北山前平原区厚包气带次降水入渗补给定量估算

降水入渗补给定量估算对于区域水资源评价具有重要作用。在干旱半干旱地区,年降水入渗补给量通常取决于年内几次集中的降水特性。因而,开展次降水入渗补给机理研究,建立次降水入渗补给量估算方法,有望提高干旱半干旱地区入渗补给量评估的科学性和准确性。本文以华北山前平原地下水深埋区为例,利用中国科学院栾城农业生态系统试验站和河北冉庄水资源实验站实测的土壤含水量、土壤水势、地下水补给量和降水量等长序列资料校准Hydrus-1D模型,模拟日降水入渗补给过程,构建具有物理意义的次降水入渗补给事件划分标准,深入研究华北山前平原地下水深埋条件下次降水入渗补给机理,定量估算次降水入渗补给量,建立次降水入渗补给量和次降水量间的定量关系。研究结果表明:次降水入渗补给量具有较大的变异性,次降水入渗补给量与次降水量或次总有效水量(次降水量+前期200 cm土壤储水量)呈显著相关关系(P<0.01),决定系数(R^(2))达0.801~0.962;但次降水入渗补给系数与次降水量无显著相关关系,这是由于次降水入渗补给系数不能反映降水前期土壤水分条件对补给的影响。因此,在地下水深埋区,不建议利用次降水入渗补给系数来估算次降水入渗补给量。本研究结果对区域地下水资源评价具有重要理论意义。

北方岩溶区降水入渗补给系数及补给机制:以羊庄岩溶水系统为例

为建立北方岩溶区水文地质参数系列,提高岩溶地下水可采资源计算精度,笔者团队于20世纪80年代开始,在山东羊庄封闭式泉排型岩溶水系统开展了岩溶水均衡试验研究,积累了40余年的监测试验数据。根据长期野外水均衡要素观测资料,推导出裸露型、半覆盖型和覆盖型岩溶区降水入渗补给系数计算公式,建立了岩溶区降水入渗补给系数α与降水量P和地下水位埋深D的相关方程,以及可调控的最大降水入渗补给系数系列,揭示了降水入渗补给过程与α变化机制。结果表明:α随水位埋深D的改变而改变,每个降水量P段分别对应一个最大降水入渗补给系数α_(max)和最大降水入渗补给量即补给极限G_(max),相应的水位埋深便是最佳水位埋深D_(critical)。D>D_(critical)时,包气带截留量随着水位埋深的增大而增大,α<α_(max);D<D_(critical)时,地表径流量随着地下水位埋深的减小而增大,α<α_(max)。不同的降水量段对应不同的D_(critical),降水量增大时,对应的α_(max)及D_(critical)也增大。在任意水位埋深时,G_(max)为蓄满产流临界降水量与包气带最大截流量之差。本研究解决了岩溶区降水入渗补给的关键科学问题,即揭示降水入渗补给机制、建立降水入渗补给系数与降水量和水位埋深的定量关系,提升了我国北方岩溶水资源基础性研究水平。

典型引黄灌区包气带与地下水动态响应试验

【目的】开展银川平原引黄灌溉引起的包气带和地下水的动态响应试验,研究“灌溉水-包气带水-地下水”的转换过程和规律。【方法】以典型引黄灌区水田为研究对象,运用水文地质学、土壤水动力学等学科理论对原位试验观测资料数值分析,借助Origin、SPSS等统计分析软件进行数据处理,利用Hydrus-1D、Surfer等数值模拟软件进行拟合和插值分析。【结果】结果得出,灌溉过程中包气带各埋深层位的水分和负压变化呈显著相关性,相关系数达0.9以上;运用Hydrus-1D拟合田间土壤水分特征曲线,发现叠加各埋深层位可得到较连续的拟合曲线;在多次灌溉入渗试验中,第1次灌溉入渗引起的地下水动态响应最快,灌溉后响应时间为388.8 min;运用地下水灌溉响应法定量测算灌溉入渗能力,算得田间灌溉入渗系数均值为0.202;对地下水位动态进行插值分析,发现回灌逐步形成“水丘”中心,地下水流场也随之发生变化;通过地下水补给源项分析,引黄灌区内灌溉水对地下水的年灌溉补给贡献率达79%。【结论】通过原位田间试验,进一步厘清引黄灌区的包气带特性和地下水响应过程,发现引黄灌溉对灌区地下水的补给和流场特征有着决定性的作用,为提高引黄水量利用率和包气带-地下水资源评估、管理及调控提供一定科学支撑。

Spatiotemporal Evolution Characteristics Study on the Precipitation Infiltration Recharge over the Past 50 Years in the North China Plain

The spatiotemporal evolution characteristics of precipitation infiltration recharge during the past 50 years are discussed in this paper. This research is significant for groundwater resource rational utilization. The distribution of precipitation infiltration recharge coefficients in the 1960 s, 1980 s, and 2000 s can be obtained using unsaturated zone lithology and depth to water table at different times. The amount of precipitation infiltration recharge in the 1960 s, 1980 s, and 2000 s can be calculated using precipitation infiltration recharge coefficients and precipitation data from the Ministry of Water Resources of China. Results show that the change in the precipitation infiltration recharge coefficient is closely related to the water table decrease. From the 1960 s to the 1980 s, the precipitation infiltration recharge coefficient clearly increased in all units. From the 1980 s to the 2000 s, the value slightly increased in the ancient Yellow River alluvial-proluvial and eastern alluvial-marine plains and slightly decreased in the piedmont alluvial-proluvial and central alluvial-lacustrine plains. The piedmont alluvial-proluvial and ancient Yellow River alluvial-proluvial plains exhibited a large precipitation infiltration recharge coefficient for the coarse lithology. The amounts of precipitation infiltration recharges were 16.23×109（1960s）, 19.11×109（1980s）, and 19.42×109 m3/a（2000s）. The amount of precipitation infiltration recharge increased from the 1960 s to the 1980 s then decreased from the 1980 s to the 2000 s in the piedmont alluvial-proluvial and the central alluvial-lacustrine plains. However, this value increased from the 1960 s to the 2000 s in the ancient Yellow River alluvial-proluvial and eastern alluvial-marine plains.

Round empty core infiltration and anti-filtration recharge wells and laboratory recharge tests

Anti-filtration recharge wells are commonly installed in river channels and irrigation canals on the Shandong Peninsula,China,and can be used as an important recharge facility for underground reservoirs.However,during recharge,as the running time increases,the recharge capacity gradually decreases.This study was undertaken to develop a new recharge well and mitigate this deficiency.A round empty core infiltration and antifiltration recharge well and laboratory recharge test equipment were developed.Subsequently,1:25 models of the recharge pond,a round empty core recharge wellhead,and an artificial recharge well were prepared.Using equal recharge levels and ambient groundwater levels,laboratory steady-flow recharge tests on the existing anti-filtration recharge well,the new round empty core infiltration and anti-filtration recharge well,and an artificial recharge well were carried out.Experimental data on the measured groundwater table and single-well recharge quantity were also collected and analyzed.The results showed that compared with the existing anti-filtration recharge well,the new round empty core infiltration and anti-filtration recharge well had stronger anti-deposition and anti-scouring properties,and the single-well recharge quantity increased by 403%.With an increase in the number of recharge tests,the single-well recharge quantity gradually decreased and tended to stabilize as a whole.

裂隙及强降雨入渗对堆积体滑坡渗流场及稳定性的影响

降雨入渗导致滑坡地下水位以上的非饱和区水压力暂时升高,坡体基质吸力减小,抗剪强度降低;同时,滑坡内的裂缝又为雨水下渗提供快速通道,雨季强降雨将在坡体裂隙较发育的部位汇集形成暂态水源,连续补给产生高孔隙动水压力,并导致深层滑坡的地下水位上升。这种瞬态的地下水运动及暂态附加水荷载成为非饱和边坡在雨季失稳的控制因素。以某大型堆积体滑坡为研究对象,采用土体饱和—非饱和渗流理论和有限差分方法,研究强降雨在坡体的裂缝末端形成的暂态水源对滑坡渗流场和地下水位的影响机制,通过强度折减方法计算暂态补给水对滑坡稳定性带来的不利影响。这些研究可为堆积体滑坡的预防和排水治理设计提供科学依据。

潜水稳定井流的剖面二维数值模拟方法

经典Dupuit井流模型与考虑入渗的改进Dupuit井流模型,都受到Dupuit假定的影响,可能存在系统误差。建立反映三维流或轴对称二维流特性的潜水井流数值模型,是检验Dupuit模型可靠性的重要手段。提出一种模拟潜水稳定井流的剖面二维数值模拟方法,通过参数转换把柱坐标系的渗流方程变换为等效的直角坐标系方程,利用MODFLOW方体网格有限差分模型实现剖面二维流场模拟。数值模型以抽水井的井中水位为已知条件,渗出面的排水量按照Darcy定律差分公式计算,潜水面则通过MODFLOW对干-湿单元的处理加以识别,抽水流量经水均衡计算得到。通过采用精细化网格建立典型案例模型,获得模拟精度很高的结果,使反算抽水井流量的相对误差不超过0.2%。以此检验Dupuit井流模型,发现解析公式得到的水位线总体与数值模拟结果一致,仅在抽水井附近由于没有考虑水跃而偏低,且误差受到含水层渗透系数各向异性的影响。在有入渗的情况下,分水岭附近的渗流违反Dupuit假定。然而,改进的Dupuit井流公式计算的分水岭水位相对误差低于1%。这一数值模拟方法简单实用,但也受到MODFLOW本身局限性的约束。

井塘结合入渗补给地下水的包气带水流模拟

为探究井塘结合模式在含水层补给管理中的应用潜力,利用HYDRUS软件构建了二维轴对称模型。通过对已有文献中实际场地有井无塘模式复现验证了本文建模过程的准确性,并进一步分析比较了不同塘半径下(5、15、25 m和35 m)井塘结合、有井无塘和有塘无井3种模式的补给效果,以及不同包气带质地(砂土、壤质砂土、砂质壤土和壤土)和井深(33、38、43 m)对井塘结合模式入渗和补给效果的影响。模拟结果表明:(1)复现值与文献值吻合较好,决定系数R 2均在0.98以上;(2)不同塘半径下井塘结合模式的补给效果均优于其他两种模式,但渗透塘半径为5 m时,井塘结合模式730 d的累计补给量分别为有井无塘和有塘无井模式的1.02倍和36倍,而当渗透塘半径增大到35 m时,井塘结合模式730 d的累计补给量则为有井无塘和有塘无井模式的2.6倍和1.54倍;(3)不同包气带质地下井塘结合模式累计入渗量随入渗时间呈线性增大的趋势,而累计补给量则分别在26.3 d、38.9 d、81.9 d和164.4 d时(湿润锋达到稳定状态)才随时间增加呈线性增大的趋势,随包气带渗透系数K s的增加,湿润锋首次到达补给区域的时间分别为0.75、1.38、3.63 d和8.63 d;(4)井深每增加5 m,井塘结合模式730 d的累计入渗量分别增加5.5%和5.9%,累计补给量分别增加9.5%和9.8%,湿润锋首次到达补给区域的时间则分别减少31.8%和25.6%。研究结果可为地下水人工补给调蓄工程的优化设计提供参考。

有入渗补给的层状非均质含水层圆岛潜水井流模型

作为圆岛状均质含水层稳定井流模型,经典的Dupuit井流模型既没有考虑普遍存在的降水入渗补给,也不适用于层状非均质含水层系统,有必要加以完善。在考虑降水入渗补给改进Dupuit井流模型的基础上,进一步将其拓展到层状非均质潜水含水层。引入Гиринский(吉林斯基)势函数,根据水均衡原理建立极坐标下的地下水流微分方程,再依边界条件解析得到了相应的流量方程、水位方程和分水岭公式。以双层结构为例,观察30组不同参数条件的典型水位曲线组,发现不同渗透系数的水位曲线交于一点的特殊现象并从理论上给出了证明。解析模型仍引入Dupuit假定,且没有考虑抽水井的井壁“水跃”现象,为判断这些条件对解析公式适用能力的影响,建立轴对称剖面二维流数值模型并做了对比研究。除抽水井附近外,水位解析方程产生的相对误差一般低于4%,在最偏离Dupuit假定的分水岭处,距离和水位的解析误差均小于0.1%。Dupuit假定并没有严重影响解析模型的适用性。

科尔沁沙地樟子松人工林土壤水分动态及其对降雨的响应

在科尔沁沙地采用“两行一带”种植模式低密度栽培樟子松进行生态修复后,林地土壤水分动态及其对降雨的响应影响了同类型地区是否可以持续使用樟子松进行生态修复。为了研究科尔沁沙地南缘植被修复后土壤水分动态特征,本研究综合运用原位观测、数值模拟的方法,基于土壤水分实测数据校正Hydrus-1D模型,探究降雨-土壤水分响应关系。结果表明:(1)樟子松人工林显著改变了地区水分分布,裸沙地2.0 m处深层渗漏量占降雨量的44.16%,而樟子松林地深层渗漏量仅占降雨量的0.7%。(2)监测期内,0.4 m深度以下土壤水分对小雨无响应,土壤水分对中雨的响应深度可达1.0 m,对大雨和暴雨的响应深度涉及整个观测剖面。随着土壤深度的增加,水分波动幅度呈现减小的趋势。(3)降雨量和深度较浅的土壤体积含水量之间存在较强的相关关系,周期为周、半月的累计降雨量与各层土壤体积含水量显著相关;降雨量大于50 mm时,能保证对2.0 m处土壤水分的补给。(4)模型的决定系数范围在0.61~0.85,均方根误差范围在0.0061~0.0096 cm^(3)·cm^(-3),能较好地模拟研究区土壤水分的动态变化特征,且深层模拟精度高于浅层。研究结果对科尔沁沙地雨养型植被造林、生态恢复和水资源管理具有重要的意义。

河北平原典型小流域降雨入渗补给规律研究

准确计算降雨入渗补给量是评价平原区地下水资源量的基础,传统的年补给系数法未考虑降雨特征、土壤墒情等因素影响,导致评价结果精度不高。本研究以河北平原下博和沧县运西两个典型小流域为例,采用动态分析法研究次降雨的入渗补给过程。结果显示以7 d为时间间隔适合作为划分次降雨的标准,次降雨量加土壤含水量(P+SW)与降雨入渗补给量(Pr)相关性最好,优于次降雨量(P)和次降雨量加前期雨量(P+Pa);动态分析法计算的降雨入渗补给量较传统降雨入渗系数法,精度提高22%~40%,且年补给系数法高估了河北平原区的年地下水补给量。本研究为河北中东部平原准确评价降雨入渗补给量提供了技术参考,对支撑区域的地下水合理开发利用及地下水超采综合治理具有较强的科学和实践意义。

海绵城市建设对地下水的补给量化研究进展

地下水回补量与水位埋深变化趋势成为了评估海绵城市建设效益的关键。雨水设施的存在使得地表水-地下水的水分运移过程复杂化,如何在雨水设施下对地下水的补给量化成为了难题。故综述了目前国内外应用最广泛且普遍的量化方法,通过分析其原理、优缺点、适用范围,为我国海绵城市建设地下水的补给量化提供参考依据和评价标准。最后,进行了展望,建议与气候变化模型相结合,优化地表水-地下水数值模型的耦合结构,全方位分析水分的运移过程,促使计算结果精准化。

降水补给地下水过程中包气带变化对入渗的影响

采用野外试验和室内试验方法,通过对不同降水量的入渗过程中岩土含水率和水势变化规律分析,发现入渗水流在包气带内下渗过程的岩土吸水、过水(即水分通量不变、且不等于零)和脱水的不同阶段,当岩土水势的梯度分别大于、等于和小于1cmH2O/cm(厘米水柱/厘米)时,岩土含水率分别表现为增加、稳定和减少。对包气带不同埋深的岩土含水率和水势变化特征分析表明,随着地下水位不断下降,包气带增厚对降水入渗补给地下水的影响程度和方式都发生改变。当包气带厚度小于潜水蒸发极限深度时,包气带的增厚使得岩土水分亏缺累积量增大,导致入渗速率和地下水获取的总入渗补给量减小;当包气带厚度大于潜水蒸发极限深度时,随着包气带厚度增大,入渗速率趋于稳定,无限时间内地下水获取的总入渗补给量不因包气带增厚而变化,但是有限时间内地下水获取的入渗补给量趋小。这是因为入渗途径的延长导致入渗所需时间增加,以至在有限时间内包气带内过剩的入渗水分尚未充分排出补给地下水。

流动沙丘水分深层入渗量与降雨的关系

为分析流动沙丘水分深层入渗与降雨的关系,采用YWB-01型水分深层渗漏记录仪,运用土壤水动力学原理,研究了毛乌素沙地流动沙丘降雨入渗水分传递过程及地表以下150 cm深度入渗补给特征。结果表明：流动沙丘深层土壤水分来源主要为降雨入渗,2010年入渗补给量为141.4 mm,2011年为355.8 mm,分别占同期降雨量的55.1%和68.2%。深层入渗主要补给期为5—11月,期间补给量占全年总量的95%。当土壤水分条件保持在田间持水量范围之内时,降雨过程对土壤150 cm深度的补给作用主要受降雨量和降雨强度的影响,入渗量与降雨量呈极显著正相关（P〈0.01）,降雨通常在30~48 h后渗透补给到150 cm深层土壤,入渗补给速率在前3~5 h呈快速上升趋势,3~8 h左右达到最大值,此后缓慢下降,整个入渗补给过程可以持续96 h以上。