Said Al-Ismaily

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.

Environmental Soil Microbiology: A Novel Research-Oriented Laboratory Course for Undergraduate Students

Laboratories curricula are considered to have a central and distinctive role in science education (Hofstein & Lunetta, 2004; Bruck and Towns, 2013). In order to bridge theory with practice several universities have made the laboratory session as an important companion for undergraduate programs where theory and practice can coalesce for students (Fennessy et al. 1992; Kotiw et al. 1999; Russell & Weaver, 2008). Science laboratory is of benefit and becomes a meaningful learning experience only if students are given opportunities to learn research methods and techniques that will increase their ability in investigating scientific phenomena and their engagement in solving problems (Tobin, 1990; Hodson, 1993; Skoumios et al., 2013). However, some educators are seriously questioning and scrutinizing the pedagogical effectiveness of the laboratory courses in providing such opportunities to students (see, for example, Bates, 1978; Tobin, 1990; Mamlok-Naaman et al., 2012). Hodson (1990) has claimed laboratory classes to be unproductive and confusing since there are often given without any clearly thought-out purpose. This led The National Science Education Standards (National Research Council [NRC], 1996) and education literature (Lunetta, 1998; Bybee, 2000) to call for a reform of the laboratory curriculum in science teaching. This is especially true as due to the current “information explosion” on cognition and student’s learning behavior (Bransford et al. 1999). In addition, laboratory work in undergraduate teaching is considered to play a potential role in advocating learning by inquiry; which the latter defined by the NRC (1996) as “Inquiry is a multifaceted activity that involves making observations; posing questions; examining books and other sources of information to see what is already known; planning investigations; reviewing what is already known in light of experimental evidence; using tools to gather, analyze, and interpret data; proposing answers, explanations, and predictions; and communicating the results. Inquiry requires identification of assumptions, use of critical and logical thinking, and consideration of alternative explanations”.

Progressing from direct instruction to structured and open inquiry-based teaching in a bachelor of soil sciences program: Experience at the National University in Oman

Abstract Revising standard structured academic programs by incorporating research throughout the curriculum is a modern trend at universities worldwide. There are numerous publications on inquiry-based learning (IBL) in individual courses, but few provide evidence both of success at the program level and of synergy in the teaching–research nexus. Our strategy in inquiry-based teaching (IBT) relies on three intertwined premises: (a) advancing the soil BSc program from direct instruction through structured learning toward IBL, (b) including outreach activities executed by undergraduates, and (c) facilitating students’ initiatives to compete for and fulfill grants from national research agencies. Our evaluation is based on students’ self-reported evaluations in program courses, data obtained from the questionnaires administered at two workshops organized by students, and the progress of elite students who won a research grant. Students reported improved confidence and perception of an increase in teamwork skills.