233 publications from this institution
Two boundary value problems are solved for potential steady-state 2D Darcian seepage flows towards a line sink in a homogeneous isotropic soil from a ponded land surface, which is not flat but profiled. The aim of this shaping is ‘uniformisation’ of the velocity and travel time between this surface and a horizontal drain modelled by a line sink. The complex potential domain is a half-strip, which is mapped onto a reference plane. Either the velocity magnitude or a vertical coordinate along the land surface are control variables. Either a complexified velocity or complex physical coordinate is reconstructed by solving mixed boundary-value problems with the help of the Keldysh-Sedov formula via singular integrals, the kernel of which are the control functions. The flow nets, isotachs and breakthrough curves are found by computer algebra routines. A designed soil hump above the drain ameliorates an unwanted ‘preferential flow’ (shortcut) and improves leaching of salinised soil of a cropfield during a pre-cultivation season.
Steady, essentially two-dimensional, tension-saturated seepage from a flat-bottomed soil channel in an arid environment is studied analytically. Physically, the action of capillary spreading, evaporative drive to the atmosphere both from the near-channel banks and capillary fringe boundary, Darcian resistance of the matrix and gravity are juxtaposed and result in trifurcation of infiltrated water into deep percolation and semi-infinite evaporation "wings" with two hinge points on the soil surface and two dividing streamlines. Mathematically, free boundary problem is solved by conformal mappings and the Polubarinova-Kochina boundary-value problem method. The dependence of deep percolation losses and evaporative return flow on the channel width, conductivity, static capillary rise height, and intensity of evaporation is found.
Abstract An impermeable boundary of the grout cutoff has been found that maximizes the seepage flow for a specified grouting volume. The shape of a trench has been defined that maximizes the quantity of fluid entering the ground‐water flow from the trench. The seepage characteristics of the grout cutoff and the trench which have arbitrary shapes are estimated in terms of the derived exact analytical solutions of variational problems.
The common assessment of soil salinity posits a linear function, which transfers the electrical conductivity (EC) of highly diluted extracts to the standard state of soil paste. Our study examines this assumption and explains its limitations in a wide range of EC for highly saline soils of the Aral region in Uzbekistan. For a comparative EC assessment in the liquid phase from standard soil pastes and 1:5 aqueous extracts we used portable EC–meters. The dependences of EC, total dissolved solids (TDS), and soil-water potential on the pore water content were evaluated using centrifugation to separate the liquid phase from the soil matrix. The non-linearity of the relationship between the EC of water from soil pastes and 1:5 water extracts for both average and median data over a broad (0.4–160 dS/m) range of their variation is detected. A strong retention and concentration of electrolytes in fine pores and water films resistant to vacuum extraction, as well as the nonlinear EC versus TDS relationship in highly saline soils are attributed to this nonlinearity. A comprehensive statistical analysis showed that despite the general non-linearity, in the EC range from 0 to 30–35 dS/m, the results for 1:5 extract can be reliably converted to the standard state using the dilution model for the liquid phase of the soil with one basic parameter of soil bulk density. For hypersaline soils (EC > 30–35 dS/m), conversion based on the dilution theory is unacceptable due to a strong underestimation of TDS.
Conformal mappings and integral representations of the Dirichlet boundary value problem for analytic functions are employed to solve explicitly the problem of steady, two‐dimensional, Darcian seepage from a reservoir with fresh water to a sea in a confined aquifer of a finite thickness. A sharp interface between moving fresh and stagnant saline water forming a wedge is determined depending on one dimensionless parameter, which includes the difference in water elevations between the reservoir and the sea, the contrast in water densities, and the aquifer thickness. If the acting head reaches some critical (minimal) value, saline water will always stay at some depth; that is, the wedge will have an infinite width. In this case the interface coincides with the Saffman‐Taylor shape of a finger in a Hele‐Shaw apparatus.
Steady, two-dimensional, viscous, fully developed, laminar flows are studied by the methods of isoperimetric estimations, complex analysis, and asymptotic approximations. The Carman-Kozeny averaging of velocity over the cross-sectional area of a tube is shown to become meaningless for some fractures deviating from "normal" convex shapes. Permeability of constituting tubes is estimated from above and below using a novel characteristic, the momentum of the flow domain about its boundary. Poiseuille-type flows in double-connected and misconnected domains are discussed. Longitudinal and transversal flows through a nonplanar zigzag fracture composed of annular segments are studied by an asymptotic solution of the Poisson equation and an exact solution of the Navier-Stokes equation, correspondingly. The lubrication theory approximation is compared with the case of a nonparabolic velocity profile within the fracture. The influence of tortuosity on permeability is established by calculation of the flux ratio through curved and planar fractures. For the Stokes approximation, a double-periodic combination of plane fractures and circular enlargements is studied using the Rayleigh solution and its generalization. A two-dimensional Darcian flow through a system with regular square occlusions is studied and kinematic channeling is quantified by the travel time along the fastest streamline.
Sidr (Christ-thorn) phreatopytic-xerophitic wild trees growing in the reservoir area of the Al-Khoud groundwater recharge/flood protection dam in Muscat (Oman) were surveyed. Trees’ loci, heights and stem diameters were measured. Soil profiles were described in two pedons (trenches) excavated near two pilot trees. A remarkable increase in infiltration rate was observed when double-ring infiltrometers were placed near the tree stems and at the bottom of the trenches. Sap flow metering conducted on one tree over a period of 9 months resulted an average rate of 12.5 L/d. This value was used to evaluate the reservoir water balance, considering it as the difference between infiltration of ponded post-flash-flood water and transpiration. Sidr trees are recommended as excellent eco-engineers, that can alleviate the negative impact of reservoir bed siltation by enhancing the infiltration-recharge of the underlying aquifer.
Analytical solutions for the maximum area of the cross section of a drain ditch and a mole drain are obtained. In the case of seepage to a ditch from an underflooded soil surface, the extreme curve is represented by a semicircle, with a constant value of flow velocity along the curve. Seepage to a system of empty horizontal drains is studied for one of three possible patterns of water tables. At low values of infiltration to a phreatic surface, the drain of a maximum area is nearly circular.
