233 publications from this institution
Single sink depths providing maximum ground‐water table decrease during a fixed time interval within a selected area are found for the 2‐D and 3‐D cases. The curve of the maximal phreatic surface position (underflooding curve) in the aquifer from flood induced variation in water level of the ground‐water reservoir is calculated. Well‐known analytical solutions based on nonlinear and linear potential theories and the Dupuit‐Forchheimer approximation are applied to calculate the objective function, decision variables, and boundary of the fully saturated zone. In the linear case, an explicit analytic solution gives the unique maximum of the water table decrease at the compliance point for a given pumping duration. For small values of sink depth, the linear approach is invalid. In the nonlinear case, complex analysis and series expansions are used. For small values of drain depth, the series technique becomes untenable. For the reservoir‐aquifer problem the spreading phreatic surface is a rotating straight line and the underflooding curve is a parabola.
Saturated hydraulic conductivity and wetting front pressure head (as soil properties) on an abrupt Green-Ampt front are assumed to increase and decrease with depth of a porous heterogeneous soil subject to a constant ponding or infiltration-evaporation depleted ponding on the surface. The corresponding Cauchy problem for a nonlinear ordinary differential equation describing the wetting front propagation in the soil profile is solved by computer algebra routines. Sensitivity of the cumulative infiltration to variation of hydraulic conductivity and capillarity is studied. A concave-convex infiltration graph is obtained for some values of parameters of the assumed exponential growth/decay of conductivity/capillarity. Texture of soil samples collected from a pedon is used for calculation of conductivity from a pedotransfer function. Synthesis of heterogeneity resulting in a specified front dynamics is discussed.
The continuous and frequent occurrence of the Shallow Water Table (SWT) in urban regions aggravates the severity of geotechnical and environmental problems. Exploring possible measures that effectively reduce the negative impact of SWT in urban aquifers is of extreme importance. This research investigated the effectiveness of bioengineering techniques in lowering SWT in the framework of hydropedological factors (soil structure in the vadose zone, where most pore water fluxes take place). The methodology includes physical models (sand tank experiments) and field-scale studies. A total of nine sand tanks were utilized, segmented into three distinct groups, to investigate the reduction of the water table through different mechanisms: (1) evapotranspiration drawdown by soil water uptake by the roots of vegetation (specifically Reeds), (2) evaporation by bare homogeneous topsoil, and (3) evaporative “soil siphoning” in tanks that were made as “smart composites” with a fine-textured vertical “moisture chimney”. The dynamics of SWT were monitored over 6 months (March–September 2023). Each tank measures 100 cm in length, 70 cm in height, and 15 cm in width. All tanks were packed with two horizontal soil layers (sand and clay) to simulate a perched aquifer, common prototypes of which were explored in Muscat, Oman. In the siphoning experiment, a small trench was made and packed with silt loam soil. This trench extended the entire thickness of the aquifer to enhance capillarity and, hence, evaporation. Analysis of the results showed that the drawdown of the water table ranged from 75% to 300% (winter to summer seasons) in the tanks containing plants (Reeds) compared with the control tanks. In addition, the SWT in the tanks with “soil siphons” was reduced in the range of 22%-46% compared with the control tanks. Another experiment with Reeds was conducted on a larger field scale using Concrete Agricultural Basins (CABs) with dimensions of 1000 cm length, 200 cm width, and 60 cm depth. The experiment spanned three months (June-September 2023) and aimed to investigate the impact of Reeds on SWT levels in larger-scale 3D pore water dynamics (in sand tank experiments flows were 2D). Overall, the large-scale experiment showed that over the three months, the evapotranspiration from Reeds reduced the water level by 16.7%, 66.7%, and 116.7% more than evaporation from bare soil during the first, second, and third months, respectively.This investigation highlights the significant influence of bioengineering through phreatophytic Reeds, seasonal variations of weather conditions, and the hydropedology of the root zone on checking the SWT levels. The influence of fine-textured soil lenses, strata, and engineered soil siphons in controlling water levels was studied. While the presence of Reeds plays a crucial role in influencing water levels, seasonal fluctuations, usually modeled by ET0-ETc, also contribute, with drastic differences between summer and winter. The investigated drainage techniques are ecologically and environmentally benign: no electricity or fuel is used for the reduction of waterlogging because only soil capillarity and solar energy maintain the processes of evaporation and transpiration; the Reeds’ biomass, accumulated during the ecoengineering process, additionally intercepts and sequesters CO2.
Steady two-dimensional groundwater flow in a porous low-permeable trough is studied by the method of boundary-value problems for holomorphic functions. In the overlying highly permeable aquifer the hydraulic head varies linearly, i.e. flow is unidirectional. The exchange of groundwater between aquifer and trough does not affect the flow in the aquifer. It is assumed that through a horizontal aquifer–trough interface the head is transmitted into the trough, where the bounding effect of the bed causes circulatory seepage. Triangular troughs are studied and an isosceles form with a base angle of 38° is proved to have the highest circulation rate at a given cross-sectional area. In the class of arbitrary forms, solution to this optimal shape design problem is obtained by tackling the Schwartz and Signorini singular integrals and a unique and global maximum of the rate is found. The extreme curve coincides with an optimal soil channel of minimal seepage losses having depth to width ratio of 0.371. The global maximum differs from that one for the triangular class in 3% only that corroborates stability and robustness of the optimization criterion and makes possible isoperimetric estimates of the seepage intensity through arbitrary troughs.
Permeable reactive barriers (PRBs) are a popular technology for passive contaminant remediation in aquifers through installation of reactive materials in the pathway of a plume. Of fundamental importance are the degree of remediation inside the reactor (residence time) and the portion of groundwater intercepted by a PRB (capture width). Based on a two‐dimensional conformal mapping approach (previously used in related work), the latter is studied in the present work for drain‐and‐gate (DG) PRBs, which may possess a collector and a distributor drain (“full” configuration) or a collector drain only (“simple” configuration). Inherent assumptions are a homogeneous unbounded aquifer with a uniform far field, in which highly permeable drains establish constant head boundaries. Solutions for aquifer flow fields in terms of the complex potential are derived, illustrated, and analyzed for doubly symmetric DG configurations and arbitrary reactor hydraulic resistance as well as ambient groundwater flow direction. A series of practitioner‐friendly charts for capture width is given to assist in PRB design and optimization without requiring complex mathematics. DG PRBs are identified as more susceptible to flow divergence around the reactor than configurations using impermeable side structures (e.g., funnel‐and‐gate), and deployment of impermeable walls on drains is seen to mitigate this problem under certain circumstances.
Steady, 2D Darcian seepage in a homogeneous isotropic porous medium under an impervious structure is studied by the methods of complex analysis. The geometry of the structure is studied focusing on the travel time of a marked (neutral tracer) particle from the upper pool to the tailwater. In the Verigin problem, the angle of inclination of a sheetpile resulting in minimal time along the bounding streamline is π∕2 . If the maximum of the minimum of the travel time is searched between all streamlines originated in the upper pool, then the optimal angles are found to be 0.404π and 0.596π . The minimization of the total volume of fluid that arrives from the upper pool to the tailwater during a prescribed time span is also considered. For arbitrary geometry, structure optimization with respect to travel time is carried out explicitly for the bounding streamline with a constraint on the wetted perimeter of a depressed structure. The minimal-time shape is found to be the Voshinin semicircular structure, which is mathematically generated by a line vortex.
The known formulae of Freeze and Cherry, Polubarinova–Kochina, Vedernikov for flow rate during 2-D seepage into horizontal drains and axisymmetric flow into cavities are examined and generalized. The case of an empty drain under ponded soil surface is studied and existence of drain depth providing minimal seepage rate is presented. The depth is found exhibiting maximal difference in rate between a filled and an empty drain. 3-D flow to an empty semi-spherical cavity on an impervious bottom is analysed and the difference in rate as compared with a completely filled cavity is established. Rate values for slot drains in a two-layer aquifer are 'inverted' using the Schulgasser theorem from the Polubarinova–Kochina expressions for corresponding flow rates under a dam. Flow to a point sink modelling a semi-circular drain in a layered aquifer is treated by the Fourier transform method. For unsaturated flow the catchment area of a single drain is established in terms of the quasi-linear model assuming the isobaric boundary condition along the drain contour. Optimal shape design problems for irrigation cavities are addressed in the class of arbitrary contours with seepage rate as a criterion and cavity cross-sectional area as an isoperimetric restriction. © 1998 John Wiley & Sons, Ltd.
Abstract A tension-saturated water slug descends through a homogenous soil after a rainfall (irrigation) event and shrinks due to transpiration by a distributed root-sink and evaporation. The upper (drainage) and lower (imbibition) sharp fronts of the slug separate it from the superjacent and subjacent vadose zones, where water is immobile. In the slug, the hydraulic conductivity is constant according to the Green-Ampt model. The capillary pressures as well as effective porosities on the fronts are given (generally, different) constants that can be viewed as a kind of hysteresis. A volumetric sink models mild (no desaturation of the slug) soil water withdrawal by the plant roots. The sink intensity varies with the depth from the soil surface and with time. Mathematically, the hydraulic head is immediately expressed by double integration of a governing 1-D flow equation. The pressure and kinematic conditions on the fronts result in a Cauchy problem for a system of two ODEs, which is solved by computer algebra routines. Editor D. Koutsoyiannis Citation Kacimov, A. and Obnosov, U., 2013. Pseudo-hysteretic double-front hiatus-stage soil water parcels supplying a plant–root continuum: the Green-Ampt-Youngs model revisited. Hydrological Sciences Journal, 58 (1), 1–12.
