Ali Al-Maktoumi

Can heterogeneity of the near-wellbore rock cause extrema of the Darcian fluid inflow rate from the formation (the Polubarinova-Kochina problem revisited)?

Darcian steady 2-D flow to a point sink (vertical well) placed eccentrically with respect to two circles demarcating zones of contrasting permeability is studied by the methods of complex analysis and numerically by MODFLOW package. In the analytical approach, two conjugated Laplace equations for a characteristic flow function are solved by the method of images, i.e. the original sink is mirrored about two circles that generates an infinite system of fictitious sinks and source. The internal circle of the annulus models formation damage (gravel pack) near the well and the ring-shaped zone represents a pristine porous medium. On the external circle the head (pressure) is fixed and on the internal circle streamlines are refracted. The latter is equivalent to continuity of pressure and normal component of specific discharge that is satisfied by the choice of the intensity and loci of fictitious sinks. Flow net and dependence of the well discharge on eccentricity are obtained for different annulus radii and permeability ratios. A non-trivial minimum of the discharge is discovered for the case of the ring domain permeability higher than that of the internal circle. In the numerical solution, a finite difference code is implemented and compared with the analytical results for the two-conductivity zone. Numerical solution is also obtained for an aquifer with a three-conductivity zonation. The case of permeability exponentially varying with one Cartesian coordinate within a circular feeding contour is studied analytically by series expansions of a characteristic function obeying a modified Helmholtz equation with a point singularity located eccentrically inside the feeding contour. The coefficients of the modified Bessel function series are obtained by the Sommerfeld addition theorem. A trivial minimum of the flow rate into a small-radius well signifies the trade-off between permeability variation and short-cutting between the well and feeding contour.

Infiltration into Two-Layered Soil: The Green–Ampt and Averyanov Models Revisited

Infiltration into a two-layered soil (continuum scale) is studied by the Green–Ampt (GA) model where the rate of infiltration (wetting front propagation) is a non-monotonic and discontinuous function of time. Both a constant ponding depth and a ponding level falling due to evaporation and infiltration are studied theoretically and in column experiments. The triads of saturated conductivity, porosity and front pressure in the two zones, as well as gravity, control vertical infiltration. Another model on the scale of a straight cylindrical capillary uses the Averyanov regime of a film flow, modified to include a front which is a quarter of a torus, rather than a spherical cap in a standard Washburn–Lukas model. The rate of front propagation is controlled by the Newtonian viscosity, tube-film sizes, surface tension, contact angle and gravity. For both scales, Cauchy problems for ODEs with respect to the front position are solved by computer algebra integration. In the field, pedon description and textural analysis of sedimentation-controlled layering are done. Of particular note is the thick cake deposited from a flash flood water pulse, which has very low permeability and can greatly inhibit infiltration. The infiltration rates measured by tension infiltrometers fluctuate, which is attributed to the mosaic and layered special distribution of hydraulic and capillary properties of the accrued sediments. Falling ponding depth laboratory experiments were conducted in four columns with a coarse substratum (sand) subjacent to a layer of thoroughly homogenized repacked dam silt. Imbibition front stopped at the interface between two texturally contrasting strata and the “waiting time” of the capillary barrier breakthrough was measured, as well as further oscillations of the infiltrations rate.

Impact of a Recharge Dam on the Hydropedology of Arid Zone Soils in Oman: Anthropogenic Formation Factor

AbstractA hydropedological study was conducted to investigate the impact of the construction of Al-Khoud recharge dam on soil development in a dry region of Oman. The study involved detailed descriptions of pedons, surface and subsurface soil textural analyses, and double-ring and tension infiltrometer tests in areas inside and adjacent to the dam. The reservoir area of this 25-year-old hydraulic structure has rapidly changed due to spatiotemporally variable deposition of sediments from the dammed water and intensive scraping of the silt cake. This resulted in the formation of multiple micro depressions and a nonflat shape of the reservoir bed. The subsurface soils of the bed showed heterogeneity and complex patterns of sediment deposition as a response to the human-induced changes in the soil development, geomorphology, and hydrological properties of the dam area. In most pedons, a sequence of Stokes’ law–generated porous layers indicates ponded conditions of flood events and reservoir filling correlated...

Morphed block-crack preferential sedimentation in a reservoir bed: a smart design and evolution in nature

Abstract A pedological study of the reservoir bed of Al-Khoud Dam, Oman, revealed an unusual sedimentation pattern which evolved into an intricate composition of silt blocks surrounded by vertical cracks and horizontal layers filled with a “proppant” sand. The discovered soil morphology reflects the complex topology of water motion (infiltration–seepage–evaporation) through the sand-filled cracks/layers and blocks during both the rare flood events and ensuing periods of ponding, and the long, intervening dry periods. These naturally formed soils demonstrate an ability to preserve a large quantity of water inside the silty blocks at depths of 0.5 to 1.5 m, despite the high temperature and dryness of the topsoil. The hydrological optimality and “smartness” of these soils is attributed to the unique block-crack system. Natural, lush vegetation was found in adjacent zones of the reservoir bed, and acted as a footprint of the shallow “fractured perched aquifer”. Planted “ivy” (Convolvulaceae) in the vertical face of one pedon showed intensive growth without irrigation. Soil moisture content data confirmed the hydrological immobility of water in the blocks if not depleted by transpiration. The novel phenomena reported unveil the possible alteration of soil heterogeneity for optimization of the soil–water system in arid zone soils. Editor D. Koutsoyiannis; Associate editor F.F. Hattermann Citation Al-Ismaily, S.S., Al-Maktoumi, A.K., Kacimov, A.R., Al-Saqri, S.M., Al-Busaidi, H.A., and Al-Haddabi, M.H., 2013. Morphed block-crack preferential sedimentation in a reservoir bed: a smart design and evolution in nature. Hydrological Sciences Journal, 58 (8), 1779–1788.

Soil substrate as a cascade of capillary barriers for conserving water in a desert environment: lessons learned from arid nature

Interaction between soil pedogenesis, subsurface water dynamics, climate, vegetation and human ingenuity in a desert environment has been found to result in a unique ecohydrological system with an essentially three dimensional sedimentation structure in the bed of a recharge dam in Oman. A 3-D array of silt blocks sandwiched by dry sand-filled horizontal and vertical fractures was studied in pot experiments as a model of a natural prototype. Pots are filled with a homogenous sand-silt mixture (control) or artificially structured (smart design, SD) soil substrates. Rhodes grass and ivy (Ipomea, Convolvulaceae) were grown in the pots during the hottest season in Oman. Soil moisture content (SMC) was measured at different depths over a period of 20 days without irrigation. SD preserved the SMC of the root zone for both ivy and grass (SMC of around 25%–30% compared to <10% for control, 3 days after the last irrigation). Even after 20 days, SMC was around 18% in the SD and 7% in the control. This, similar to the case of a natural prototype, is attributed to the higher upward capillary movement of water in control pots and intensive evaporation. The capillary barrier of sand sheaths causes discontinuity in moisture migration from the micro-pores in the silt blocks to sand pores. The blocks serve as capillarity-locked water buffers, which are depleted at a slow rate by transpiration rather than evaporation from the soil surface. This creates a unique ecosystem with a dramatic difference in vegetation between SD-pots and control pots. Consequently, the Noy-Meir edaphic factor, conceptualizing the ecological impact of 1-D vertical heterogeneity of desert soils, should be generalized to incorporate 3-D soil heterogeneity patterns. This agro-engineering control of the soil substrate and soil moisture distribution and dynamics (SMDaD) can be widely used by desert farmers as a cheap technique, with significant savings of irrigation water.

Research-based learning for undergraduate students in soil and water sciences: a case study of hydropedology in an arid-zone environment

Abstract This article reports the efficacy of a research-based learning (RBL) exercise on hydropedology of arid zones, with guided and open research projects (OPR) carried out by teams of undergraduate students in Oman. A range of activities and assessments was used to support student learning during the three-month course. Assessment included monitoring of field trip and lab activities, attendance recording, scrutiny by a panel of written reports and open oral presentations. Students’ feedback through teaching evaluation is compared with other courses in the Department-College, illustrating high level of students’ satisfaction. OPR best fit the scaffold of RBL.

Cascade of proppant-sandwiched silt blocks as a double-continuum: From discovery to mathematical modeling

A new naturally morphed soil structure has been discovered at 2 out of 33 pedons excavated in Oman, inside and in the vicinity of a flood-protection/recharge dam, subject to a rapid geomorphological changes, caused by sediment loads from a wadi-transported runoff. Low permeable cascades of soil blocks are interspersed by highly permeable fractures filled by a natural “proppant” (sand). Different time scales (ponding with infiltration/seepage—evaporation/transpiration), the pore pressure contrast between fractures and block, capillarity (mostly of blocks), gravity (similar to oil-gas gravity drainage in reservoir engineering of fractured rock), climatological factors and transpiration of the plant roots—all control the topology of water motion in this porous double-continuum medium. Infiltration in layered soils is modeled by the Green–Ampt model with front propagating across an interface between layers of contrasting conductivity, porosity and capillarity. The goal of this work is to explain qualitatively and using a mathematical model the macroscale observations (infiltration) by a pore-scale model.

Water Resources in Arid Areas: The Way Forward

The red sand dunes appear along the south east, -west coast of Tamil Nadu, India between the latitudes and longitudes of 8°07′56′′N to 8°22′11′′N; 77° 19′84′′E to 77°53′40′′E. The dune sands from this region were studied through magnetic methods such as magnetic susceptibility measurements and acquisition of isothermal remanent magnetization, geochemistry and X-ray diffraction methods. Optically stimulated luminescence (OSL) dating method was used to constrain the chronology of deposits. Three sections were excavated up to 5–9.5 m with one inland deposit (TPV) and two near coastal sections (THOP and MUT). Celeste Gomes—deceased A. Vidyasakar (&) S. Srinivasalu Department of Geology, Faculty of Science and Humanities, Anna University, Chennai, India e-mail: a.vidyasakar@gmail.com A. Vidyasakar H. Sant’Ovaia Pole of the Faculty of Sciences, Earth Sciences Institute, Rua do Campo Alegre, Porto 4169-007, Portugal L. Alappat Department of Geology and Environmental Science, Christ College, Irinjalakuda 680125, Kerala, India P. Morthekai Luminescence Dating Laboratory, Birbal Sahni Institute of Palaeobotany, 53 University Road, Lucknow 226007, India A.K. Singhvi Planetary and Geoscience Division, Physical Research Laboratory, Ahmedabad 380009, India F. Jorge LaboratórioNacional de Energia e Geologia, I.P/Rua da Amieira, Apartado 1089, S. Mamede de Infesta, Porto 4466-901, Portugal C. Gomes CGUC, Department of Earth Sciences, Faculty of Sciences and Technology, University of Coimbra, Largo Marquês de Pombal, Coimbra 3000-272, Portugal

Estimating Groundwater Mounding in Sloping Aquifers for Managed Aquifer Recharge

Design of managed aquifer recharge (MAR) for augmentation of groundwater resources often lacks detailed data, and simple diagnostic tools for evaluation of the water table in a broad range of parameters are needed. In many large-scale MAR projects, the effect of a regional aquifer base dip cannot be ignored due to the scale of recharge sources (e.g., wadis, streams, reservoirs). However, Hantushs (1967) solution for a horizontal aquifer base is commonly used. To address sloping aquifers, a new closed-form analytical solution for water table mound accounts for the geometry and orientation of recharge sources at the land surface with respect to the aquifer base dip. The solution, based on the Dupiuit-Forchheimer approximation, Greens function method, and coordinate transformations is convenient for computing. This solution reveals important MAR traits in variance with Hantushs solution: mounding is limited in time and space; elevation of the mound is strongly affected by the dip angle; and the peak of the mound moves over time. These findings have important practical implications for assessment of various MAR scenarios, including waterlogging potential and determining proper rates of recharge. Computations are illustrated for several characteristic MAR settings.

Management options for a multipurpose coastal aquifer in Oman

Using MODFLOW 2005, this study numerically evaluated the effects of managed aquifer recharge (MAR) using treated wastewater (TWW) in managing the Al-Khawd coastal aquifer northeast of Oman. Our primary objective is to increase the urban water supply and to sustain the aquifer service with the lowest possible damage to the aquifer. A number of managerial scenarios were simulated and progressively developed to reduce seawater intrusion and outflow of the groundwater to the sea. An economic analysis was conducted to characterize the trade-off between the benefits of MAR and seawater inflow to the aquifer under increased abstraction for domestic supply. The results show that by managing irrigation wells and relocating public wells in conjunction with MAR practices, the abstracted volume for drinking purposes could be doubled. Even though injection of TWW is more expensive (due to the injection cost), it was observed to result in greater benefits. The results indicate that managing the aquifer would produce a net benefit ranging from