Horizontal Hydraulic Conductivity Research Articles

Heterogeneity of hydraulic conductivity and Darcian flux in the submerged streambed and adjacent exposed stream bank of the Beiluo River, northwest China

Recognizing the heterogeneity of hydraulic conductivity and hyporheic flow is critical for understanding contaminant transfer and biogeochemical and hydrological processes involving streams and aquifers. In this study, the heterogeneity of hydraulic conductivity and Darcian flux in a submerged streambed and its adjacent exposed stream banks were investigated in the Beiluo River, northwest China. In the submerged streambed, Darcian flux was estimated by measurement of vertical hydraulic conductivity (Kv) and vertical head gradient (VHG) using in-situ permeameter tests. On exposed stream banks, both horizontal hydraulic conductivity (Kh) and Kv were measured by on-site permeameter tests. In the submerged streambed, Kv values gradually decreased with depth and the higher values were concentrated in the center and close to the erosional bank. Compared to the exposed stream banks, the Kv values were higher in the streambed. From stream stage to the topmost layer of tested sediment, through increasing elevation, the Kh values increased on the erosional bank, while they decreased on the depositional bank. The values of VHG along the thalweg illustrate that downwelling flux occurred in the deepest area while upwelling flux appeared in the other areas, which might result from the change of streambed elevation. The higher value of the Darcian flux in the submerged streambed existed near the erosional bank.

Variation of the hydraulic conductivity of Boom Clay under various thermal-hydro-mechanical conditions

In this paper, an experimental study is presented that intended to investigate (1) the anisotropy properties of hydraulic conductivity of Boom Clay, (2) the effect of heating-cooling cycle on the hydraulic conductivity and intrinsic permeability of Boom Clay, and (3) the effect of loading-unloading cycle on the hydraulic conductivity and intrinsic permeability of Boom Clay. Constant-head tests were carried out in a temperature-controlled triaxial cell. First, the anisotropic characteristic of hydraulic conductivity of Boom Clay with respect to its bedding was confirmed. The horizontal hydraulic conductivity (parallel to bedding) is larger than the vertical hydraulic conductivity (perpendicular to bedding). Second, there was a positive and reversible relationship between the hydraulic conductivity and temperature and a negative and irreversible relationship between the hydraulic conductivity and hydrostatic pressure. Specifically, for both horizontal and vertical hydraulic conductivity, the value at 80°C is approximately 2.4 times larger than that at room temperature (23°C). However, it appears that the hydraulic conductivity is not sensitive to heating rate. Data analysis reveals that under variable temperature conditions, the changes in viscosity and density of water with temperature are the main factors affecting the change in hydraulic conductivity of Boom Clay with temperature, although other factors may have an effect to some extent.

Groundwater sustainability assessment in coastal aquifers

The present work investigates the response of shallow, coastal unconfined aquifers to anticipated overdraft conditions and climate change effect using numerical simulation. The groundwater flow model MODFLOW and variable density groundwater model SEAWAT are used for this investigation. The transmissivity and specific yield estimated from the existing database range from 10 to 810 m 2/day and 0.08% to 10.92% respectively. After successful calibration with Nash–Sutcliffe efficiency greater than 0.80, the values of horizontal hydraulic conductivity and specific yield of the unconfined aquifer were set in the range 1.85–61.90 m/day and 0.006–0.24 respectively. After validating the model, it is applied for forecasting the aquifer’s response to anticipated future scenarios of groundwater draft, recharge rate and sea level rise. The findings of the study illustrate that saltwater intrusion is intensified in the area adjoining the tidal rivers, rather than that due to the sea alone. Of all the scenarios simulated, the immense negative impact on groundwater quality emerges due to overdraft conditions and reduced recharge with the areal extent of seawater intrusion exceeding about 67% (TDS >1 kg/m 3). The study also arrives at the conclusion that, regional sea level rise of 1 mm/year has no impact on the groundwater dynamics of the aquifer.

A multiscale approach to determine hydraulic conductivity in thick claystone aquitards using field, laboratory, and numerical modeling methods

AbstractCharacterizing the hydraulic conductivity (K) of aquitards is difficult due to technical and logistical difficulties associated with field‐based methods as well as the cost and challenge of collecting representative and competent core samples for laboratory analysis. The objective of this study was to produce a multiscale comparison of vertical and horizontal hydraulic conductivity (Kv and Kh, respectively) of a regionally extensive Cretaceous clay‐rich aquitard in southern Saskatchewan. Ten vibrating wire pressure transducers were lowered into place at depths between 25 and 325 m, then the annular was space was filled with a cement‐bentonite grout. The in situ Kh was estimated at the location of each transducer by simulating the early‐time pore pressure measurements following setting of the grout using a 2‐D axisymmetric, finite element, numerical model. Core samples were collected during drilling for conventional laboratory testing for Kv to compare with the transducer‐determined in situ Kh. Results highlight the importance of scale and consideration of the presence of possible secondary features (e.g., fractures) in the aquitard. The proximity of the transducers to an active potash mine (∼1 km) where depressurization of an underlying aquifer resulted in drawdown through the aquitard provided a unique opportunity to model the current hydraulic head profile using both the Kh and Kv estimates. Results indicate that the transducer‐determined Kh estimates would allow for the development of the current hydraulic head distribution, and that simulating the pore pressure recovery can be used to estimate moderately low in situ Kh (<10−11 m s−1).

Technical Note: Three-dimensional transient groundwater flow due to localized recharge with an arbitrary transient rate in unconfined aquifers

Abstract. Most previous solutions for groundwater flow induced by localized recharge assumed either aquifer incompressibility or two-dimensional flow in the absence of the vertical flow. This paper develops a new three-dimensional flow model for hydraulic head variation due to localized recharge in a rectangular unconfined aquifer with four boundaries under the Robin condition. A governing equation describing spatiotemporal head distributions is employed. The first-order free-surface equation with a source term defining a constant recharge rate over a rectangular area is used to depict water table movement. The solution to the model for the head is developed with the methods of Laplace transform and double-integral transform. Based on Duhamel's theorem, the present solution is applicable to flow problems accounting for arbitrary time-dependent recharge rates. The solution to depth-average head can then be obtained by integrating the head solution to elevation and dividing the result by the aquifer thickness. The use of a rectangular aquifer domain has two merits. One is that the integration for estimating the depth-average head can be analytically achieved. The other is that existing solutions based on aquifers of infinite extent can be considered as special cases of the present solution before the time when the aquifer boundary had an effect on head predictions. With the help of the present solution, the assumption of neglecting the vertical flow effect on the temporal head distribution at an observation point outside a recharge region can be assessed by a dimensionless parameter related to the aquifer horizontal and vertical hydraulic conductivities, initial aquifer thickness, and the shortest distance between the observation point and the edge of the recharge region. The validity of assuming aquifer incompressibility is dominated by the ratio of the aquifer specific yield to its storage coefficient. In addition, a sensitivity analysis is performed to investigate the head response to the change in each of the aquifer parameters.

A field proof-of-concept of tomographic slug tests in an anisotropic littoral aquifer

Hydraulic tomography is increasingly recognized as a characterization approach that can image pathways or barriers to flow as well as their connectivity. In this study, we assess the performance of a transient analysis of tomographic slug test head data in estimating heterogeneity in horizontal hydraulic conductivity (Kh), hydraulic conductivity anisotropy (the ratio between vertical and horizontal hydraulic conductivity – Kv/Kh) and specific storage (Ss) under actual field conditions. The tomographic experiment was carried out between two wells in a moderately heterogeneous and highly anisotropic silt and sand littoral aquifer. In this field proof-of-concept, the inversion of the two-dimensional (2D) head dataset was computed with a 2D radial flow algorithm that considers Kh, Kv/Kh, Ss and wellbore storage effects. This study demonstrated that a transient analysis of tomographic slug tests is able to capture the key features of the littoral environment of the test: the vertical profiles of Kh and Kv are indeed in agreement with those from other field and laboratory tests, and Ss values exhibit physically plausible profiles. Furthermore, the simulation of independent inter-well hydraulic tests (slug and pumping tests screened over the entire aquifer) using resolved Kh, Kv/Kh and Ss tomograms produce responses very close to field observations. This study demonstrates that the effects of fine scale heterogeneity that induces K-anisotropy at larger scales can be captured through a transient analysis of tomographic slug tests, which are very difficult to quantify otherwise with conventional hydraulic tests, thus allowing a better representation of properties controlling flow and transport in aquifer systems.

Structural and statistical characterization of joints and multi-scale faults in an alternating sandstone and shale turbidite sequence at the Santa Susana Field Laboratory: Implications for their effects on groundwater flow and contaminant transport

This paper describes the properties of faults and fractures in the Upper Cretaceous Chatsworth Formation exposed at Santa Susana Field Laboratory and its surroundings (Simi Hills, California), where groundwater flow and contamination have been studied for over three decades.The complex depositional architecture of this turbidite consisting of alternating sandstones and shales, interacting with formative stress conditions are responsible for multi-scale fault hierarchies and permeable fractures in which nearly all groundwater flow occurs.Intensity and distribution of background fractures and their relation to bedding thickness are established for sandstones, the dominant lithology. The architecture of faults with increasing displacement is described, and relationships among fault dimensional parameters captured.Data from ∼400 boreholes and piezometers reveal the effect of faults and fractures on groundwater flow. Large hydraulic head differences, observed across fault zones with shale-rich cores, indicate these structures as cross-flow barriers. Moreover, hydraulic head profiles under ambient conditions, and pumping tests suggest strong hydraulic connectivity in all directions to depth of hundreds of meters.This outcrop-based structural characterization relates the horizontal hydraulic conductivity to the observed well-connected fracture network, and explains the strong vertical connectivity across low-hydraulic conductivity shales as faults and sheared fractures provide flow pathways.

Sensitivity Analysis of a Physically Based Distributed Model

The objective of this study is to perform a sensitivity analysis of the SHETRAN model on the example of the torrential Lukovska River catchment in Serbia. The sensitivity analysis of the model was performed for the following parameters: the vertical saturated hydraulic conductivity of the subsurface soil, the horizontal saturated hydraulic conductivity in the saturated zone, the Strickler roughness coefficients for overland flow and for streams, the available water content in the soil and the erodibility coefficients due to rain and due to overland flow. It can be concluded that the water and sediment discharge are very sensitive to the values of the vertical saturated hydraulic conductivity of the subsurface soil in the range of 0.001 to 0.1 m/day; to the values of the horizontal saturated hydraulic conductivity in the saturated zone in the range of 0.01 to 5 m/day and to the values of the Strickler’s coefficients for overland flow and for rivers in the range of 0.1 to 100 m1/3s-1 and 15 to 40 m1/3s, respectively. The sediment concentrations in a flow and sediment discharge are very sensitive to the values of erodibility coefficient due to overland flow in the range of 0.5 to 1.5 mg/m2s and to the values of erodibility coefficient due to rain in the range between 0.1 and 40 J-1. The obtained results could be used to simplify the parameter calibration procedure and to facilitate estimation of parameters in ungauged mountainous basins of similar characteristics.

Approximate analysis of three-dimensional groundwater flow toward a radial collector well in a finite-extent unconfined aquifer

Abstract. This study develops a three-dimensional (3-D) mathematical model for describing transient hydraulic head distributions due to pumping at a radial collector well (RCW) in a rectangular confined or unconfined aquifer bounded by two parallel streams and no-flow boundaries. The streams with low-permeability streambeds fully penetrate the aquifer. The governing equation with a point-sink term is employed. A first-order free surface equation delineating the water table decline induced by the well is considered. Robin boundary conditions are adopted to describe fluxes across the streambeds. The head solution for the point sink is derived by applying the methods of finite integral transform and Laplace transform. The head solution for a RCW is obtained by integrating the point-sink solution along the laterals of the RCW and then dividing the integration result by the sum of lateral lengths. On the basis of Darcy's law and head distributions along the streams, the solution for the stream depletion rate (SDR) can also be developed. With the aid of the head and SDR solutions, the sensitivity analysis can then be performed to explore the response of the hydraulic head to the change in a specific parameter such as the horizontal and vertical hydraulic conductivities, streambed permeability, specific storage, specific yield, lateral length, and well depth. Spatial head distributions subject to the anisotropy of aquifer hydraulic conductivities are analyzed. A quantitative criterion is provided to identify whether groundwater flow at a specific region is 3-D or 2-D without the vertical component. In addition, another criterion is also given to allow for the neglect of vertical flow effect on SDR. Conventional 2-D flow models can be used to provide accurate head and SDR predictions if satisfying these two criteria.

Simulação numérica do fluxo de águas do sistema aquífero urucuia na bacia hidrogeológica do Rio Corrente (BA)

<p>Com o objetivo de quantificar o balanço hidrológico e compreender a dinâmica do fluxo das águas subterrâneas do Sistema Aquífero Urucuia (SAU), na bacia hidrogeológica do rio Corrente, realizou-se uma simulação do fluxo dessas águas, em regime permanente. O SAU aloja-se na bacia hidrográfica do São Francisco e é composto pelo conjunto de aquíferos interligados, cujo arcabouço é formado pelas rochas do Grupo Urucuia. O sistema é do tipo poroso granular, com geometria de um espesso tabuleiro, constituído essencialmente por arenitos. O método de elementos finitos foi utilizado na simulação numérica, empregando-se o algoritmo computacional FEFlow<em> (Finite Element Subsurface Flow e Transport Simulation System</em>). Por meio da simulação numérica foram estimados os parâmetros hidrodinâmicos: recarga máxima de 267 mm/a e mínima de 142 mm/a; condutividade hidráulica horizontal e vertical de 9,7 x 10<sup>-5</sup> m/s; fluxo de base de 1,26 x 10<sup>7</sup> m³/dia. Os resultados ressaltam a importância da bacia do rio Corrente na manutenção da vazão do rio São Francisco e confirmam a natureza homogênea e isotrópica do SAU.</p>

Determination of Anisotropic Saturated Hydraulic Conductivity of a Macroporous Slope Soil

For a steeply sloped part of the “Heumoser”, a creeping landslide in Vorarlberg (Austria), it is postulated that subsurface macropore flow results in high pore water pressures at the base of the slope and thus triggers mass movement or may even cause slope failure. To quantify saturated hydraulic conductivity and anisotropy in a soil containing macropores, a novel method was required to obtain a “very large” (L/W/H ≈ 30/30/60 cm) undisturbed soil sample. A square column was carved out from the slope, wrapped in cling wrap, surrounded with timber walls on the four lateral sides and stabilized by injection of polyurethane foam. The sample was then cut off at the base and carefully transported to the laboratory where it was installed in a constant head permeameter to obtain values for vertical hydraulic conductivity (Kᵥ). After completing the vertical flow measurements, the sample was divided into two cubes with approximately 30 cm side length and the respective vertical hydraulic conductivities were determined. Then the cubes were turned by 90° to obtain the horizontal saturated hydraulic conductivities (Kₕ). This new method allowed thus for a directional characterization of the hydraulic conductivity of soils containing macropores. It could be shown that the vertical hydraulic conductivity decreased by a factor of two from the upper sample to the lower sample. A similar anisotropy factor (Kₕ/Kᵥ) of approximately 0.5 was determined for both layers, in other words, it was shown that macropores can reverse the expected “natural” anisotropy (Kₕ/Kᵥ > 1).

Anisotropic hydraulic conductivity and critical hydraulic gradient of a crushed sandstone–mudstone particle mixture

ABSTRACTThis paper describes the development of a modified instrument used to measure the anisotropic hydraulic conductivity of coarse soils. Then, based on this modified instrument, horizontal and vertical hydraulic conductivities and critical hydraulic gradients of a crushed sandstone–mudstone particle mixture are measured. Using this data, we investigate the effects of particle size on the anisotropic hydraulic conductivity. The testing results indicate that the anisotropic hydraulic conductivity coefficient, which is defined as the logarithm value of the ratio of the horizontal hydraulic conductivity to the vertical conductivity, ranges from 0.079 to 0.358. This means the horizontal hydraulic conductivity is 1.20 to 2.28 times to that of the vertical conductivity. The anisotropic coefficient decreases as the uniformity coefficient increases. Meanwhile, the critical hydraulic gradient increases with an increase in fine particle content.

Analysis of transient seepage into equally spaced ditch drains from a ponded field

An analytical solution is proposed for simulating transient seepage into a system of ditch drains placed in parallel in a homogeneous and anisotropic soil confined by an impermeable layer and receiving water from an infinitely extended ponded field. The solution assumes the ponding depth over the surface of the soil to be uniform and the soil fluid to be of constant density. The model can be applied for both equal and unequal water levels in adjacent drains. The accuracy of the developed solution is checked by comparing for a flow situation the hydraulic heads and streamlines as obtained from the proposed model with the corresponding results obtained from an available steady state solution of the problem as provided by Kirkham [14]. A numerical check on the proposed solution is also performed for a particular flow configuration of the problem in the transient zone. The study shows that flow in a ponded ditch drainage system is greatly influenced by anisotropy and directional conductivities of soils. The uniformity of surface flux distribution is found to be quite sensitive to the anisotropy ratio (the ratio of horizontal and vertical saturated hydraulic conductivities of soil) of a soil column – a higher anisotropy ratio favors and a low anisotropy ratio weakens this distribution. Furthermore, the time to attain steady state by a ditch drainage system can be considerable, particularly for situations where the drains are dug relatively deeper into a soil having a high anisotropy ratio. The analytical model presented here is significant as it can be used to design ditch drainage networks for reclaiming a salt-affected and/or waterlogged soil within a specified time.

PVD improvement of soft Bangkok clay with and without vacuum preloading using analytical and numerical analyses

This paper presents the performance of improved soft Bangkok clay with prefabricated vertical drains (PVDs) combined with embankment preloading (conventional PVD method) and vacuum preloading (vacuum PVD method). The performance was evaluated in terms of settlements and flow parameters using analytical methods and numerical simulations in the ABAQUS software. The horizontal coefficient of consolidation (Ch), the ratio (kh/ks) between the horizontal hydraulic conductivity in the undisturbed zone (kh) and the horizontal hydraulic conductivity in the smeared zone (ks), and the final settlement (Sf) were back-calculated using the measured data. The sensitivity analysis was performed by varying the values of kh/ks. The vacuum PVD method was confirmed to have a higher rate of settlement than the conventional method. In particular, Ch increased from 4Cv to 5Cv, kh/ks decreased from 8 to 7, and the consolidation time required to obtain a settlement of 1.30 m decreased from 300 days to 100 days. In addition, the calculated results from both the analytical method and FEM simulations for the conventional PVD agreed with the measured data. However, the results from the vacuum PVD method demonstrated that the FEM simulations yielded more reasonable results compared with the corresponding results obtained from the analytical methods.

Experimental Study on the Anisotropic Hydraulic Conductivity of a Sandstone–Mudstone Particle Mixture

AbstractThis study focuses on the anisotropic hydraulic conductivity of a sandstone–mudstone particle mixture. Permeameter tests were performed in the laboratory. The effects of the mixture’s dry bulk density and mudstone particle content on its anisotropic hydraulic conductivity were investigated accordingly. Both the horizontal and vertical hydraulic conductivities were compared based on the calculation results from empirical grain-size formulas and tests. The best predictive formula for the hydraulic conductivities was found to be the Terzaghi empirical formula. It was found that the average horizontal hydraulic conductivity is about 2.0 times more than that of the vertical one. The anisotropy ratio initially increases and then decreases with the increase of the mudstone particle content by weight. A maximum ratio of 2.946 was obtained when the mudstone particle content reached about 60% by weight.

Dual-Screened Vertical Circulation Wells for Groundwater Lowering in Unconfined Aquifers.

A new type of vertical circulation well (VCW) is used for groundwater dewatering at construction sites. This type of VCW consists of an abstraction screen in the upper part and an injection screen in the lower part of a borehole, whereby drawdown is achieved without net withdrawal of groundwater from the aquifer. The objective of this study is to evaluate the operation of such wells including the identification of relevant factors and parameters based on field data of a test site and comprehensive numerical simulations. The numerical model is able to delineate the drawdown of groundwater table, defined as free-surface, by coupling the arbitrary Lagrangian-Eulerian algorithm with the groundwater flow equation. Model validation is achieved by comparing the field observations with the model results. Eventually, the influences of selected well operation and aquifer parameters on drawdown and on the groundwater flow field are investigated by means of parameter sensitivity analysis. The results show that the drawdown is proportional to the flow rate, inversely proportional to the aquifer conductivity, and almost independent of the aquifer anisotropy in the direct vicinity of the well. The position of the abstraction screen has a stronger effect on drawdown than the position of the injection screen. The streamline pattern depends strongly on the separation length of the screens and on the aquifer anisotropy, but not on the flow rate and the horizontal hydraulic conductivity.

Numerical analysis of vertical drains accelerated consolidation considering combined soil disturbance and visco-plastic behaviour

Soil disturbance induced by installation of mandrel driven vertical drains decreases the in situ horizontal hydraulic conductivity of the soil in the vicinity of the drains, decelerating the consolidation rate. According to available literature, several different profiles for the hydraulic conductivity variation with the radial distance from the vertical drain, influencing the excess pore water pressure dissipation rate, have been identified. In addition, it is well known that the visco-plastic properties of the soil also influence the excess pore water pressure dissipation rate and consequently the settlement rate. In this study, a numerical solution adopting an elastic visco-plastic model with nonlinear creep function incorporated in the consolidation equations has been developed to investigate the effects of disturbed zone properties on the time dependent behaviour of soft soil deposits improved with vertical drains and preloading. The employed elastic visco-plastic model is based on the framework of the modified Cam-Clay model capturing soil creep during excess pore water pressure dissipation. Besides, nonlinear variations of creep coefficient with stress and time and permeability variations during the consolidation process are considered. The predicted results have been compared with V<TEX>$\ddot{a}$</TEX>sby test fill measurements. According to the results, different variations of the hydraulic conductivity profile in the disturbed zone result in varying excess pore water pressure dissipation rate and consequently varying the effective vertical stresses in the soil profile. Thus, the creep coefficient and the creep strain limit are notably influenced resulting in significant changes in the predicted settlement rate.

A preliminary analysis of the hydrogeological conditions and groundwater flow in some parts of a crystalline aquifer system: Afigya Sekyere South District, Ghana

A steady state groundwater flow model was calibrated to simulate the complex groundwater flow pattern in some crystalline aquifer systems in north-central Ghana. The objective was to develop the general geometry of the groundwater system and also estimate spatial variations in the hydraulic conductivity field as part of efforts to thoroughly investigate the general hydrogeology and groundwater conditions of aquifers in the area. The calibrated model was used in a limited fashion to simulate some scenarios of groundwater development in the terrain. The results suggest the dominance of local groundwater flow systems resulting from local variabilities in the hydraulic conductivity field and the topography. Estimated horizontal hydraulic conductivities range between 1.04m/d and 15.25m/d, although most of the areas consist of hydraulic conductivities in the range of 1.04m/d and 5.5m/d. Groundwater flow is apparently controlled by discrete entities with limited spatial interconnectivities. Recharge rates estimated at calibration range between 4.3% and 13% of the annual rainfall in the terrain. The analysis suggests that under the current recharge rates, the system can sustain increasing groundwater abstraction rates by up to 50% with minimal drawdown in the hydraulic head for the entire terrain. However, with decreasing groundwater recharge as would be expected in the wake of climate change/variability in the area, increased groundwater abstraction by up to 50% can lead to drastic drawdowns by more than 25% if recharge reduces by up to 50% of the current levels. This study strongly recommend the protection of some of the local groundwater recharge areas identified in this study and the promotion of local recharge through the development of dugouts and other conduits to encourage recharge.

An iterative method for estimating solute travel times to ditch drains under steady recharge and ponded conditions

An iterative procedure is worked out for estimating solute travel times in a subsurface system by making use of the velocity and streamline distributions pertinent to the system. The developed method is then being applied to study the solute travel times to ditch drains originating from a field being subjected to a uniform (1) recharge and (2) ponding field over the surface of the soil. For case (1), both single and layered soils are being considered to estimate the travel times. The developed mathematical procedure is simple to use, robust, reasonably accurate even if being used with a lesser division of a streamline and completely eliminates the necessity of determination of any integrals for estimating the travel times—integrals which, in the methods generally been employed for estimating the travel times from steady-state analytical groundwater models, would otherwise need be evaluated. The study shows that travel times of water particles traversing through a layered soil being subjected to a uniform recharge at the surface are sensitive to the directional conductivities, anisotropy ratio (defined here as the ratio between horizontal and vertical hydraulic conductivities of soil) and thickness of individual layers of a soil profile as well as to the magnitude of the steady-state recharge on the surface of the soil. For the ponded drainage scenarios also, directional conductivities and thickness of a soil profile, extent of partial penetration and width of the ditch drains, levels of water head at the surface of the soil as well as on the ditches are observed to influence the travel times in a noticeable way. The proposed method is important as it provides simple and accurate estimations of migration times of pollutants to subsurface drains under different drainage situations; it can also be used to assess the time of reclamation of a salt-affected or waterlogged soil being drained by a network of subsurface drains being installed for the purpose from the available hydraulic theory relevant to the concerned drainage situation.

Physical and Biochemical Properties of Apple Orchard Soils of Different Productivities

Physical and biochemical properties of apple orchard soils of different productivities (orchard A: 30 t&#183haǃ orchard B: 20 t&#183ha&#451) were analyzed. Most of the physical properties were similar in both orchards. In orchard A, the horizontal saturated hydraulic conductivity at 10-cm depth was 16.42 cm&#183day&#451, and was about four times higher than that in orchard B (4.41 cm&#183day&#451). Total carbon, total nitrogen, and total phosphorus were about two times higher in orchard B soil, whereas total potassium, bacterial biomass, nitrification, and phosphorus mineralization activities were similar in both orchards. Excess nutrients accumulated on the top 15 cm layer of orchard B soil because the topographical and physical conditions were associated with reduced apple productivity. Appropriate management of fallen leaves and reduction of chemical fertilizer seem necessary for a high level of apple productivity.