Mean Hydraulic Conductivity Research Articles

Hydrodynamic Characterization of Carbonate Aquifers Using Atypical Pumping Tests without the Interruption of the Drinking Water Supply

The Gran Sasso carbonate aquifer is the largest and most productive in the Apennines. Its hydrogeological structure has been studied since the middle of the last century for the springs’ characterization for drinking purposes and for a motorway tunnel. Meanwhile, its hydrodynamic parametrization is less developed and has been limited to monitoring the discharge and chemical and isotopic parameters. Secondary porosity characterizes the aquifer, and an underlying impermeable marly complex represents the basal aquiclude. It might appear inappropriate to characterize the hydraulic properties via pumping tests, as their reliability has been proven in homogeneous and isotropic media. However, the high extent of the aquifer, the wells’ location, the scarcity of information available and the lack of alternatives has forced the estimation of hydrodynamic parameters as in porous aquifers and the experimental testing of the aquifer, especially in maximum pumping conditions, for a possible exploitation increase. Since aquifer testing was performed during the normal well field’s activities, it was not possible to perform typical tests. Therefore, the step-drawdown test was conducted by turning on an increasing number of wells over time and keeping the observation points fixed. As results, a mean hydraulic conductivity of 5 × 10−3 m/s and a mean transmissivity of 0.3 m2/s were established without interrupting the water supply; meanwhile, the influence radius and flow directions were also estimated.

Development and Application of a New Exponential Model for Hydraulic Conductivity with Depth of Rock Mass

Hydraulic conductivity generally decreases with depth in the Earth’s crust. The hydraulic conductivity–depth relationship has been assessed through mathematical models, enabling predictions of hydraulic conductivity in depths beyond the reach of direct measurements. However, it is observed that beyond a certain depth, hydraulic conductivity tends to stabilize; this phenomenon cannot be effectively characterized by the previous models. Thus, these models may make inaccurate predictions at deeper depths. In this work, we introduce an innovative exponential model to effectively assess the conductivity–depth relationship, particularly addressing the stabilization at greater depths. This model, in comparison with an earlier power-like model, has been applied to a globally sourced dataset encompassing a range of lithologies and geological structures. Results reveal that the proposed exponential model outperforms the power-like model in correctly representing the stabilized conductivity, and it well captures the fast stabilization effect of multiple datasets. Further, the proposed model has been utilized to analyze three distinct groups of datasets, revealing how lithology, geological stabilization, and faults impact the conductivity–depth relationship. The hydraulic conductivity decays to the residual hydraulic conductivity in the order (fast to slow): metamorphic rocks, sandstones, igneous rock, mudstones. The mean hydraulic conductivity in stable regions is roughly an order of magnitude lower than unstable regions. The faults showcase a dual role in both promoting and inhibiting hydraulic conductivity. The new exponential model has been successfully applied to a dataset from a specific engineering site to make predictions, demonstrating its practical usage. In the future, this model may serve as a potential tool for groundwater management, geothermal energy collection, pollutant transport, and other engineering projects.

Assessment of engineering geology and grouting applications in Yalnızardıç Dam Site (Antalya, Türkiye)

The Yalnızardıç roller compacted concrete (RCC) dam, constructed in 2015, is located in the Mediterranean region of Turkey, intended for electric power production. It is approximately 303 m long and 92 m in height. In this paper, it is aimed to determine the performance of the grouting method, conducted to control the water seepage and improve the foundation of the Yalnızardıç dam. The engineering properties of the site were introduced by geological mapping, drilling, and laboratory tests. The seepage of the foundation was determined by the in-situ Lugeon test method, also referred to as a water pressure test, which is estimate the mean hydraulic conductivity of rock mass. As a result of the tests, high-permeable and permeable zones were determined in the dam axis area. To make a barrier layer for these permeable zones, grout curtains were built in the left abutment, thalweg and right abutment with two lines of grouting holes which is proposed according to the Lugeon test and rock quality designation (RQD) results. Consolidation grouts were built to increase the density of the soil which makes the strength of the dam's foundation. After the groutings, check boreholes were drilled and water pressure tests were performed to control the seepage along the foundation and dam site. The results indicated that average Lugeon (LU) values reduced, and the values were within the recommended limit. The process shows considerable accuracy in evaluating grouting efficiency.

Use of tritium in characterizing the leachate migration from a landfill – Central de tratamento de resíduos sólidos (CTRS) BR040 (Belo Horizonte, Minas Gerais, Brazil)

Landfills often become a source of environmental impact due to the percolation of the leachate (liquid resulting from the decomposition of buried waste), which can eventually disperse and contaminate the soil and water bodies. This study aimed to evaluate quantitatively and spatially the leachate plume from the former Belo Horizonte landfill in the Coqueiros and Taiobas watersheds by using tritium (3H) concentration in nineteen (19) sampling points: 14 groundwater, 4 surface water and 1 leachate. Among the methodologies applied to determine the 3H content in the leachate, pre-filtration proved to be the most effective due to the ease treating of the sample, as well as the identical results obtained compared to the traditional method. The 3H contents resulted in concentrations up to thirty times higher in the leachate (=96,19 to 111,87 TU) and ten times in groundwater (PM23/3 = 45,06 TU), compared to the calculated threshold (TS) of rainfall tritium (TS_3Hrain = 3,41 TU). Temporal series results indicate no trend and no influence of seasonality regarding the entry of pluvial tritium, leachate liquid level and wells water level. The 3H contour maps shows a transport of the mixture (water and leachate) towards the Coqueiros stream, with a higher concentration of leachate in wells closer to the landfill slope (PM13, PM14, PM15, and PM23) and in the southwest margin of the Coqueiros stream (PM17). In the furthest portion of the landfill, 3H levels are higher than the base threshold only at the deepest level of PM20 (=3,90 TU), possibly due to factors such as: i) denser character of the leachate compared to groundwater; ii) greater influence of recharge for regions further away from the landfill slope; and iii) the presence of the rock about 50 m from the surface. Based on the hydrogeological conceptual model, the transport of the leachate water mixture in the groundwater water compartment of the Coqueiros watershed basin seems to follow a piston or dispersion flow, with a small Peclet number (Pd = 0,05, as an example), as indicated by the high correlation coefficient values (R2 ≈ 0,85 to 0,99) from graphic interpolation. The mixture of water and leachate results in a transient time (tt) ≈ 30 years and linear velocity (Vl) ≈ 3–14 m/year in the interpolated sections. These indicate a coherent correlation with the mean hydraulic conductivity (K ≈ 29,34 m/year), as they result in effective porosity values between (Ne) ≈ 0.16 to 0.36, which corresponds to Ne range for unconsolidated sediments, similar to the wells lithotype profiles. Time series evaluation combined with lumped parameter approach suggest to be an interesting way to better understanding the HCM, and, therefore, to determine hydrodynamic parameters using tritium as a tracer.

Limited recharge of the southern highlands aquifer on early Mars

To determine plausible groundwater recharge fluxes on early Mars, we developed analytic and numerical solutions for an unconfined steady-state aquifer beneath the southern highlands. We showed that the aquifer’s mean hydraulic conductivity, K, is the primary constraint on the plausible magnitude of the mean steady recharge, r. By using geologic constraints, a mean hydraulic conductivity of K∼10−7m/s, and varying shoreline elevations and recharge distributions, the mean recharge must be of the order of 10−2 mm/yr. Recharge for other values of K can be estimated as r∼10−5K. Our recharge value is near the low end of previous estimates and significantly below published precipitation estimates. This suggests that, in a steady hydrologic cycle, most precipitation forms runoff as opposed to infiltrating into the subsurface. Alternatively, high rates of runoff production combined with a sufficiently slow transient aquifer response to recharge may limit major groundwater upwelling prior to the cessation of climatic excursions causing precipitation.

Hydrogeophysical Investigation in Parts of the Eastern Dahomey Basin, Southwestern Nigeria: Implications for Sustainable Groundwater Resources Development and Management

Geoelectrical resistivity measurements were conducted in five locations within the eastern portion of the Dahomey basin for the purpose of subsurface evaluation and detecting saturated zones. The locations are Covenant University (L1), Bells University (L2), Oju-Ore-Ilogbo Road (L3), Obasanjo-Ijagba Road (L4), and Iyana Iyesi (L5). The study was carried out to avert the common challenges of drilling low-yield groundwater boreholes in the area. A total of 30 Vertical Electrical Soundings (VES) and five two-dimensional Electrical Resistivity Tomography (ERT) data sets have been acquired along the study areas. The geoelectrical resistivity results were integrated with the borehole logs to generate the spatial distribution of the subsurface lithologies in the area. The delineated subsurface lithologies include the topsoil (lateritic clay), clayey sand, sandy clay, fine silty sand, coarse sand, and shale/clay units. The fine silty sand and coarse sand units were identified as the two main aquifer units within the area. The depths to the upper aquifer unit in the area include 31.7–96.7 m, 38.5–94.0 m, 30.7–57.5 m, 39.1–63.4 m, and 46.9–57.5 m for locations L1, L2, L3, L4, and L5, respectively. At the same time, the depths to the lower aquifer unit in the area include 43.4–112.7 m, 52.2–108.0 m, 44.2–72.5 m, 53.7–78.5 m, and 63.5–72.9 m for locations L1, L2, L3, L4, and L5, respectively. The estimated hydraulic parameters for both aquifers show they are highly productive with mean porosity, mean hydraulic conductivity, and mean transmissivity of 20–22%, 12.4–17.0 × 10−2 m/s, 1.56–2.18 m2/s for the upper aquifer, and 48–50%, 371–478 × 10−2 m/s, 50.00–62.14 m2/s for the lower aquifer. By focusing on these aquifer systems during exploration, sustainable groundwater resources can be secured, providing relief to homeowners within the study area who might otherwise face the frustration of drilling unproductive and low-yield boreholes. However, it is crucial to consider the presence of sub-vertical faults in the study area, as these faults can significantly impact groundwater development and management. These sub-vertical structural faults may lead to changes in the permeability, hydraulic conductivity, and transmissivity of the delineated aquifers, affecting their productivity across the divide and ultimately influencing the overall water availability in the area. Careful consideration of these geological factors is essential for effective aquifer management and sustainable groundwater utilisation.

Bleb geometry and morphology after Preserflo Microshunt surgery: Risk factors for surgical failure.

To investigate the possible risk factors for treatment failure in patients who had undergone Preserflo Microshunt (PMS) implantation, using anterior-segment optical coherence tomography (AS-OCT) to analyze the internal structures of the bleb. The PMS blebs of 54 patients were evaluated with AS-OCT. A mathematical model was used to calculate the total filtering surface of the episcleral fluid cavity (EFC) and the hydraulic conductivity (HC) of the bleb wall. Complete and qualified success were defined as IOP between 6 and 17 mmHg with or without glaucoma medication. The relation between baseline characteristics and probability of bleb success was analyzed by bivariate and multivariate logistic regression. The main outcome measures were mean bleb wall thickness (BWT), reflectivity (BWR), HC, mean horizontal and vertical diameter and total filtering surface (TFS) of the EFC. Blebs from 74% patients were considered as complete success and 26% as failure. BWR and BWT increased linearly up to the first year in both groups. BWR was higher in the group failure (p = 0.02) and BWT in the group success (p<0.001). EFC was wider and shorter in the success group (p = 0.009, p = 0.03). Higher TFS showed a negative correlation with IOP (r = -0.4, p = 0.002). Higher baseline IOP was associated with success of PMS by multivariate analysis (p = 0.01). Mean HC, 0.034 ± 0.008 (μL/min)/mm2/mmHg, was negatively correlated with bleb surface (r = -0.5, p<0.0001) and wall´s thickness (r = -0.3, p = 0.01). AS-OCT revealed that successful PMS blebs could show either thick hyporreflective walls or wide filtering surfaces with thin capsules. A higher baseline IOP increased the probability of surgical success.

Scale Effect on Hydraulic Properties of Pore-Fissure Deep Rock Formations and Its Importance for the Mining Shaft-Sinking Process

The problem of hydraulic parameters estimation lies in the depth: the deeper the rock formation, the more expensive and difficult the field tests and samples acquisition, and the more challenging the technical issues. The article assesses the Triassic sandstone’s drainage potential at the stage of shaft sinking. It focuses on parameter analysis in varied scales, from drill-core sample laboratory testing, through a single well drawing test, to long-term pumping and recovery tests in the well with observation piezometers. The obtained results are compared to the values estimated in the past using different methods. Finally, the paper states whether it is reliable to forecast pore-fissure sandstone drainage potential based only on core samples’ laboratory tests. This research proved that lab tests underestimate pore-fissure rocks’ hydraulic parameters (mean hydraulic conductivity k = 9.79 × 10−8 m/s) tenfold more than long-term pumping tests (mean k = 4.45 × 10−7 m/s). However, it can be concluded that the group of so-called “witness samples”, 10% of all core samples with a top value of the hydraulic conductivity tested in the laboratory, can be representative of the aquifer and comparable to the values obtained in pumping tests. With this in mind, we recommend using the highest values of hydrogeological parameters from laboratory tests based on the worst-case scenario. Therefore, it is possible to forecast inflows to the shafts reliably. This methodology is recommended only for rocks of porous and pore-fissure character.

Influence of long-term tillage and diversified cropping systems on hydro-physical properties in a sandy loam soil of North-Western India

A study was conducted to determine the combined effects of three tillage practices and four maize (Zea mays L.)-based cropping systems on physical, saturated, and near-saturated hydraulic properties in a sandy loam soil of North-Western India. Split-plot experimental design was adopted with tillage [conventional tillage (CT), zero tillage (ZT), and permanent raised bed (PB)] as the main plot treatments and intensified crop rotations [Maize (Zea mays L.)-Wheat (Triticum aestivum)-Greengram (Vigna radiata L.) (MWGg), Maize-Chickpea (Cicer arietinum L.)-Sesbania (Sesbania aculeata) (MCpSb), Maize-Mustard (Brassica juncea) -Greengram (MMuGg) and Maize-Maize-Sesbania (MMSb)] as subplot treatments. The saturated and near-saturated soil hydraulic conductivity were derived from steady-state infiltration rates measured using a hood infiltrometer on the surface soil at 0, − 1, and − 3 cm pressure heads. The long-term (10 years) study revealed that the bulk density (BD) of the soil under conservation agriculture (CA) practices (PB and ZT) was significantly (P ≤ 0.05) lower than that in CT practices. The soil BD in the MCpSb cropping system was measured to be the lowest (1.24 g cm−3) among all the cropping systems. The soil aggregate mean weight diameter (MWD) under PB and ZT was determined to be 31% and 27% higher than in the CT treatments. In tillage × cropping systems interactions, the highest MWD was observed in the PB×MWGg. The saturated and near-saturated hydraulic conductivity (K(h)) were estimated to have higher values in CA practices (PB and ZT) than in the CT treatments. In the case of cropping systems, the soil's mean field saturated hydraulic conductivity was estimated to be significantly (P < 0.05) higher under the MWGg, MCpSb, and MMuGg than the MMSb. The present study indicates that conservation agriculture-based crop management with diversified maize-based rotation (MCpSb, MWGg, and MMuGg) could be promising alternatives to conventional tillage practices (CT). Among the cropping system choices, MWGg was more effective in improving the soil's hydro-physical properties in the study area.

锡林浩特多年生草本根部导管性状与植株生态策略的相关特征

PDF HTML阅读 XML下载 导出引用 引用提醒 锡林浩特多年生草本根部导管性状与植株生态策略的相关特征 DOI: 10.5846/stxb202108262399 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金重大项目（41991233）；国家自然科学基金面上项目（41877539，42071125） Vessel traits of main roots are linked to ecological strategies of the perennial herbs in Xilinhot of China Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:干旱半干旱区植物的木质部输水系统对维持植物生长发育有重要作用。以中国干旱半干旱区的草本植物为研究对象，旨在探究草本物种根系导管解剖结构与植物生长之间的关系。用石蜡切片法，将在锡林浩特草原采集的草本物种的主根样品制作成切片，得到固定面积内导管解剖结构参量（导管数量、导管分数、平均导管面积、平均水力传导率和水力直径），然后用逐步回归法和Pearson相关分析各导管解剖性状与植物生长特征（年龄、生长速率和平均高度）之间的关系。结果发现（1）生长速率与导管数量（R=-0.494，P<0.01）和导管分数（R=-0.255，P<0.05）显著负相关，与平均导管面积（R=0.274，P<0.05）、平均水力传导率（R=0.263，P<0.05）和水力直径（R=0.245，P<0.05）显著正相关，表明生长快的草本具有大而少的导管，需要较高的水分传输能力，而生长慢的草本具有小而多的导管，水力安全性较高；（2）植株的高度与导管数量（R=-0.354，P<0.01）显著负相关，与平均导管面积（R=0.293，P<0.05）、平均水力传导率（R=0.289，P<0.05）和水力直径（R=0.278，P<0.05）显著正相关，表明高大的植株以较少的导管补偿较大的导管以维持一定的机械强度，而矮小植株的水力安全性较高。 Abstract:The hydraulic system plays an important role in supporting plant growth and development in arid and semiarid regions. In this study, we explored the relationship between vessel anatomical traits and growth characteristics of herbaceous species. We used paraffin sectioning method to make taproot sections, and acquired the characteristics of vessel anatomical structures (including number of vessels, vessel fraction, mean vessel area, mean hydraulic conductivity, and hydraulic diameter) in a fixed area. Pearson correlation and stepwise regression methods were used to analyze the relationship between vessel anatomical traits and plant growth characteristics (age, growth rate, and mean height). The results indicated that (1) the growth rate was significantly negatively correlated with vessel number (R=-0.494, P<0.01) and vessel fraction (R=-0.255, P<0.05), whilist, significantly positively correlated with mean vessel area (R=0.274, P<0.05), mean hydraulic conductivity (R=0.263, P<0.05), and hydraulic diameter (R=0.245, P<0.05), which may indicate that fast-growing herbs form larger and fewer vessels to increase the hydrualic efficiency, while slow-growing herbs form smaller and more vessels to increase hydraulic safety. (2) Mean height was significantly negatively correlated with vessel number (R=-0.354, P<0.01), whilist, significantly positively correlated with mean vessel area (R=0.293, P<0.05), mean hydraulic conductivity (R=0.289, P<0.05), and hydraulic diameter (R=0.278, P<0.05), which may suggest that in order to maintain the mechanical strength, high plants usually form few vessels to compensate for large vessels, while short plants form smaller and more vessels to increase hydraulic safety. 参考文献 相似文献 引证文献

Hydro-physical, Hydrophobicity and Chemical Characterization of Drip Irrigated Soil Using Aquaculture Wastewater under Sweet Pepper/Okra Intercrop

ABSTRACT Studies that comprehensively investigated the mechanism by which aquaculture wastewater improve crop productivity are very few. Irrigation water from raw aquaculture water, treated aquaculture water and borehole water were applied at two water application levels to cultivate Okra/SweetPepper under three cropping patterns (Okra alone, Sweetpepper alone, and Okra/Sweetpepper intercrop). A mini disc infiltrometer with suction rate of −2 cm was used to determine the unsaturated hydraulic conductivity. The soil water sorptivity to water and ethanol were also determined in each of the water source treatment. Soil physico-chemical properties were determined using standard procedure. Results showed that the mean hydraulic conductivity mostly showed a decreasing trend in the order: Raw aquaculture water < Treated aquaculture water < Ground water, while the hydrophobicity index, R, mostly showed increasing trend in the order; Ground water < Treated aquaculture water < Untreated Aquaculture water. Pooling the soil properties together, soil hydraulic properties and hydrophobicity index significantly (P < .05) correlated well with the soil nutrients, organic matter and carbon in most cases, while moisture contents showed no correlation with the hydraulic and hydrophobicity properties. Overall, organic matter influence the infiltration characteristics of the soil, thus enhancing plant nutrient uptake.

Bank filtration for climate resilience: potentiality of a new site along the Ismailia Canal in Egypt

Abstract Bank filtration (BF) is a nature-based solution that can provide safe drinking water at a low cost, in being a green technology that benefits from natural ecosystem services and saves energy as well. The objective of the present paper is to evaluate the potentiality of a new site for bank filtration along a surface water source that experiences periods of both high and low flow. This site is located along the Ismailia Canal in the eastern Nile Delta fringe of Egypt. The present evaluation is based on exploratory drilling, installation of monitoring infrastructure and monitoring of both water level and water quality parameters for one year. The site has favourable hydrogeological conditions; the mean hydraulic conductivity of aquifer materials (sand and gravel) is 18.98 m/day. Moreover, there is a hydraulic connection between canal and aquifer; under steady conditions, the canal feeds the aquifer. Using different tracers, such as Cl, EC, Sr and SO4, the average bank filtration share is in excess of 95%. BF has reduced the particulates (turbidity) by 96%, total coliform by 99 % and total organic carbon (TOC) expressed as ultra-violet absorbance at 254 wavelengths (UVA254) by 44%. In addition, BF reduces concentrations of disinfection by-products due to its ability to remove organic matter. The potential degradation of TOC in the canal bed sediments may cause the release of iron (Fe) and manganese (Mn) to the bank filtrate water; this process is exaggerated during low-flow periods. Compared to conventional water treatment, BF is a cost-effective green technology, because no chemicals are used and no waste products are generated.

Impact of layered heterogeneity on thermal response test interpretation performed on a standing column well operated without bleed

This paper presents a comprehensive field testing programme conducted in Mirabel, Quebec, that aims to demonstrate the thermal effectiveness of a standing column well installed in a pervious layered aquifer. The first-order approximation of the infinite line source model of a thermal response test in the absence of bleed suggested that heat conduction alone could not explain the thermal response obtained at a test standing column well. To further investigate this hypothesis, a numerical model that couples the state equations for heat transfer and groundwater flow is developed and exploited to assess the contribution of advective heat transfer. A comparative study involving four cases is presented to analyse the effect of the aquifer heterogeneity in terms of hydraulic and thermal conductivity on the thermal response of test well. The results show that in contrast to the work currently available in the literature, the advective heat transfer mechanism can have a large contribution to the thermal response in specific geological environment, even without bleed. In this particular case, advection is approximately 265 times more important than conduction. This shows that layered heterogeneity and mean hydraulic conductivity can significantly impact the thermal response of a standing column well operating without bleed. The results presented in this study show that hydrogeological conditions should be given greater consideration by incorporating local hydrogeological features to replicate the experimental measurements of the thermal response test.

Using maize to evaluate the Mohammadi–Khataar (M–K) model as a salinity weighting function (

Context Soil water availability, as characterised by the integral water capacity, uses weighting functions based on models not yet evaluated using plants, especially in the context of saline soils. Without plant evaluation such weighting functions remain theoretical at best. Aims We aimed to use maize plants to evaluate Mohammadi and Khataar’s (2018) conceptual model for a salinity weighting function, against those used in Hydrus 1D. Methods We conducted glasshouse experiments with large columns of two sandy loams planted with maize irrigated using different salinities, and repeated without plants. Soil matric suction ranged between saturation and 100 cm, and we measured or predicted plant height, transpiration, evaporation, drainage, storage, and solute concentration over time. The soil water retention curve was measured and the weighted mean hydraulic conductivity was obtained using the van Genuchten model. Key results We found a correlation between our salinity weighting function and the relative transpiration rate of maize (grown in two different soils using irrigation water of three different salinities), particularly in the first few days of growth but not thereafter; errors were related to uncertainties in predicting drainage, salt concentration, and soil water storage in planted columns. Conclusions The deviation of transpiration rate from that predicted by our salinity weighting function at higher salinities may relate to the linear nature of the Maas–Hoffman salinity weighting function plus heterogeneity of soil water and solute distributions. Implications Improving the estimates of drainage and soil water storage in future would make our physical model more useful in larger scale hydrological predictions.

Assessment of Geologic Controls of Flooding in Parts of OBIO/AKPOR L.G.A., Rivers State, Nigeria

Flooding of Municipal areas is a frequent environmental occurrence in Rivers State that occurs when rainfall runoff meets land surfaces with low water absorbing capacity or when it overwhelms drainage channels. In order to assess the flood situation in the study area, an integrated method which involves Field-measurement, Geographic information system (GIS), Laboratory analysis of soil samples and topographic studies were employed. Digital Elevation Model of the study area reveals that the flooded areas are situated in areas with elevations lower than its surrounding, thereby acting as a natural basin to retain flood waters after rainfall. Four holes were drilled to depth of 3m to obtain soil samples at 1 m sampling interval, from which laboratory analysis was carried out to determine some geotechnical parameters such as soil’s particle size, specific gravity, bulk density, porosity, moisture content, permeability and hydraulic conductivity. Results from the analysis show that permeability, hydraulic conductivity and porosity diminishes with respect to depth. The soil in the flooded areas have high fines content (silt and clay), high bulk density which increase with depth and a specific gravity that is typical of organic rich soils that contain sand mixed with a considerable amount of fines. At Nkpolu, mean permeability rates of 0.003cm/sec, 0.009cm/sec and 0.033cm/sec were obtained at 1, 2 and 3m respectively. At Eneka, mean permeability rates of 0.011cm/sec, 0.018cm/sec and 0.014cm/sec were obtained at 1, 2 and 3m respectively, while at Rukpokwu, mean Permeability rates of 0.021cm/sec was obtained at 1m, while 0.006cm/sec was obtained at 2 and 3m respectively. The Mean hydraulic conductivity for the locations under study is of the order of 10-4ft/day. This study has shown that the flooded areas are located in low lying urban areas which act as basins, therefore, the top soil is crusted with highly compacted soil horizons beneath. With high and frequent rainfall in the region which generates a lot of runoff, in addition to poor drainage system, flooding of the study area occurs frequently. Therefore, construction and maintenance of efficient drainage channels for an effective solution to urban pluvial flooding in the study area are thereby recommended.

Conditional mean, effective, and realizations of hydraulic conductivity fields

This study first discusses the conditional mean, realizations, and effective hydraulic conductivity in a theoretical framework. It then introduces Monte Carlo simulation (MCS) algorithms for constraining the outcome by either hydraulic conductivity (K) samples or hydraulic head (h) measurements from the hydraulic tomographic survey (HT). It demonstrates that kriging using K measurements leads to a conditional mean K field, while inverse modeling using successive linear estimator (SLE) with head measurements of HT yields the conditional effective K field. The effects of conditioning using K measurements are different from those using heads. Besides, the conditional effective K leads to the unbiased prediction of the head that honors the observed head at measurement locations. More importantly, the study reveals that the harmonic and geometric means of conditional realizations of K fields of MCS, given head measurements, are equivalent to the conditional effective K in one- and two-dimensional flows, respectively. The first-order approximation in the SLE results in a conditional covariance similar to that from MCS with smaller magnitudes. Despite the difference, all approaches predict unbiased conditional mean head behaviors.

Effects of soil heterogeneity on subsurface water movement in agricultural fields: A numerical study

This study aims to numerically examine the effects of soil heterogeneity on subsurface water movement in agricultural fields under wheat (Triticum aestivum L.) and rice (Oryza sativa L.) crop covers. The 3-D Richards equation that accounts for root water uptake was coupled with a random field generation method to produce realizations of soil hydraulic properties, and the effects of soil heterogeneity were analyzed under realistic atmospheric boundary conditions. Four soil types and three different soil heterogeneity levels were considered to investigate the response of soil heterogeneity on soil water dynamics. It was observed that the effect of soil heterogeneity varies across soil types and its effect was more pronounced in silty clay loam soils. Further, an increase in soil heterogeneity level can increase or decrease the mean soil moisture, hydraulic conductivity, and flow velocity based on land cover, upper boundary condition, and atmospheric demand, and its effect was higher during irrigation periods. A maximum difference of 30% in soil moisture values was observed near the surface soil layers due to an increase in soil heterogeneity on irrigation days. The mean soil moisture content under rice crop cover was always lower than that of wheat crop cover due to higher atmospheric demand in the former. Soil layering effect on soil moisture dynamics, which is related to capillary and hydraulic barrier formation, was found to depend on the layering configuration, available soil moisture, and land cover. The numerical experiments provided useful insights into the complex soil moisture dynamics in agricultural fields.

Characterization of the hydraulic conductivity of glacial till aquitards

Pleistocene-aged glacial sediments are found in many parts the Northern Hemisphere and are often composed of clay-rich tills which form aquitards that can control drainage and influence groundwater movement and contaminant transport. Site-scale investigations have characterized the hydraulic properties of till aquitards; however, the hydraulic conductivity of these units has not been quantitatively described at a regional scale of tens of kilometers. This study constrains regionally representative hydraulic conductivity estimates and characterizes the hydrogeological properties of Pleistocene-aged till aquitards from data collected at 15 sites compiled from 21 studies. The data quantify the scale dependence of hydraulic conductivity measurements in till aquitards and further define the relationship between hydraulic conductivity and depth. Data from centimeter-scale laboratory tests remained generally constant with depth, with a geometric mean hydraulic conductivity of 7.0 × 10−11 m/s and a standard deviation of 0.4 orders of magnitude, while the meter-scale in-situ tests had a geometric mean of 4.9 × 10−9 m/s and a standard deviation of 1.0 orders of magnitude at depths less than 10 m, and 3.7 × 10−11 m/s and 0.2 order of magnitude at depths greater than 23 m. The results support the existence of a shallow fractured zone of higher hydraulic conductivity and a deeper zone characterized by matrix permeability. The observed data variability occurred primarily at the site scale, while the central tendency and variability of the data were consistent between sites separated by hundreds of kilometers suggesting that statistically derived, depth-defined regional hydraulic conductivity estimates can be meaningful.

Seepage Analysis of Railway Earthen Embankment in Mokama Using RFEM Considering Random Hydraulic Conductivity Field

In this study, seepage through the body of an earthen embankment for construction of railway lines in Mokama in Bihar is estimated using finite element method. Seepage of water through the body of earthen embankment adversely affects its stability. In order to check the reliability of the constructed railway embankment stretching for a long distance, Random Finite Element Method (RFEM) originally developed by Fenton and Griffiths (Fenton and Griffiths, 1996) is used. The influence of variability in spatially distributed hydraulic conductivity/permeability field of the embankment is investigated by carrying out seepage analysis. Local Averaging Subdivision (LAS) technique is used to build the random field of hydraulic conductivity of soil domain under consideration. Afterwards, Monte Carlo simulation is performed for 1000 such random fields. The mean of total flow rate $$\left( {m_{Q} } \right)$$ , mean of logarithmic of total flow rate $$\left( {m_{\ln Q} } \right)$$ and variance of logarithmic of total flow rate $$\left( {s_{\ln Q}^{2} } \right)$$ from seepage analyses for 1000 realizations of random field are reported. The results show that as the correlation length decreases, the output parameters $$m_{Q}$$ , $$m_{\ln Q}$$ and $$s_{\ln Q}^{2}$$ follow a decreasing trend and vice versa. These variations are studied for the embankment with and without drain. The effect of drain on the mean hydraulic conductivity and hydraulic gradient standard deviation of the embankment are investigated in which the embankment with drains is found safer than embankment without drain.

Modelling the permeability characteristics of an earth reservoir

Particle size distribution and void ratio of a soil are considered as the direct information that can be used in a relatively easy manner for hydraulic conductivity estimation. Estimation of hydraulic conductivity from particle size distribution can be used to check permeability values obtained from other methods. Therefore, this paper attempts to relate the particle size distribution to hydraulic conductivity. The study was carried out on 24 soil samples which were collected from the embankment of an earth reservoir and subgrade at the toe. The investigation was carried out in accordance with the standard procedure given in BS1377. A series of hydraulic conductivity tests were carried out on optimum moisture content (OMC) compacted soil samples using the falling head method. The mean sizes of particles in each sample from particle size distribution curves were determined and used to generate regression models for the flow. Linear, exponential, polynomial and logarithmic models were used to test the validity; however, the best was adopted for this study. The findings of this study show that there is variability in the particle sizes of the soil material which in turn results to variation in the hydraulic conductivity. The hydraulic conductivity was found to increase with an increase in mean particle size. The relationship between mean particle size and hydraulic conductivity yielded coefficients of determination (R2 ) of stronger correlation when the plastic and non-plastic samples were separately analyzed. However, all values of R2 (0.9949, 0.9968 and 0.8918 for samples 1 to 16, 17 to 24 and 1 to 24 respectively) can be considered satisfactory. In addition, generalized models for the flow were generated for the plastic, non-plastic and the combined samples. The generated models can be used to predict the hydraulic conductivity of different soil samples.Keywords: Model, Hydraulic Conductivity, Mean Particle Size, Earth Reservoir