The inherent complexity of soil and its interactions with Earth’s diverse spheres, including the atmosphere, biosphere, hydrosphere, lithosphere within the ecosphere, and anthroposphere, requires that soil science specialists and students develop not only a profound understanding of soil science, but also the ability to collaborate across various disciplines to address these complex challenges. Equipping students with the necessary knowledge, skills, and attitudes to tackle the intricate and dynamic issues of the 21st century, spanning soil science, water sciences, hydropedology, geology, agronomy, geotechnical engineering, sedimentation, waste management, recycling, and environmental management, is of paramount importance. In response, innovative pedagogical approaches that integrate classroom learning from diverse soil science courses with practical skills and field-based competencies are needed. This paper suggests merging our own “Soil Skills” (SSK) pedagogical method with the “Soil Judging Contest” (SJC), a teaching approach supported by the American Society of Agronomy and the Soil Science Society of America since 1961. This integration aims to enhance the holistic, harmonized, interdisciplinary, and enthusiastic nature of soil science education. Both the SSK and SJC approaches received positive feedback from students and demonstrated significant improvements in academic performance. Our study begins with an in-depth exploration of the SSK contest, followed by an overview of the pertinent aspects of the SJC. Subsequently, we offer a comparative analysis of the complementarity of these two approaches. Finally, in the concluding remarks, we summarize the strengths of the implemented SSK and outline prospective applications. Our findings underscore the unique advantages of combining SSK and SJC approaches in delivering comprehensive, problem-based, and practical field-learning experiences. This combination approach closely aligns with applied scenarios that demand multidisciplinarity and interdisciplinarity perspectives, preparing students for their future professional careers, and enabling the practical application of their soil science knowledge in real-world contexts.
Steady, Darcian, one‐phase, phreatic surface flow of groundwater into a horizontal well with a pancake lens of light nonaqueous phase liquid (LNAPL) accumulated in the water table trough is studied by the method of complex analysis. A sharp interface model assumes groundwater capped by two isobaric limbs (groundwater–vadose zone interfaces) of a free surface with an in‐between cambered segment of an immiscible LNAPL‐water interface, along which pressure is hydrostatically increasing with the depth of the LNAPL “channel.” The complex potential polygon is mapped onto an auxiliary half plane where the complex physical coordinate of the flow domain is represented in terms of singular integrals as a solution of the Keldysh‐Sedov problem. The shapes of semi‐infinite “wings” of the water table contacting the vadose zone gas and of a finite length LNAPL‐groundwater interface are found from parametric equations that involve the sink strength and location with respect to the pancake surface, the ordinate of the lowest trough point, and the volume of LNAPL accreted in the lens. Critical conditions, corresponding to the lens contour cusping toward the sink, are found. The Riesenkampf solution contains a free parameter, which is fixed by specifying either a point on the free surface or the volume of the trough‐intercepted LNAPL.
We consider solutions to two boundary values problems for the Poisson equation on plane domains. We prove several estimates for integrals of solutions using geometric characteristics of domains.
Said S. Al-Ismaily*a, Anvar R. Kacimova, Ali K. Al-Maktoumia & Hamad A. Al-Busaidiaa Department of Soils, Water and Agricultural Engineering, Sultan Qaboos University, Al-Khoud 123, Sultanate of Oman
Two-dimensional flows near cavities were studied by superposition of the Philip solution for an isobaric cylindrical cavity in an infinite unsaturated soil and vertical infiltration. Depending on the radius of the cavity and the intensity of the net infiltration, the cavity irrigates the surrounding soil forming a plume of seeping moisture (source regime), drains the descending infiltration forming a capture zone (sink regime), or admits water through its upper section and releases water through its bottom (dipole regime). The separatrices, i.e., the lines, which divide the incoming, outgoing, and passing-by portions of the flow, were found. For the dipole regime, the values of flow rates through the admitting and releasing sections of the cavity and streamlines were calculated. The supercritical flow regime is characterized by a permeable blunt upstream section of the cavity and watertight downstream segments. For elongated cavities, this regime was modeled as a combination of a permeable isobaric segment and a part of the adjacent separatrice. Analogies with saturated flows in confined aquifers near a circular constant head boundary and with contaminant transport from a circular isoconcentric source were discussed.
Mosaic 3-D cascade of parallelepiped-shaped silt blocks, which sandwich sand- lled cracks, has been discovered in the eld and tested in lab experiments. Controlled wetting-drying of these blocks, collected from a dam reservoir, mimics field ponding-desiccation conditions of the topsoil layer subject to caustic solar radiation, high temperature and wind, typical in the Batinah region of Oman. In 1-D analytical modelling of a transient Richards’ equation for vertical evaporation, the method of small perturbations is applied, assuming that the relative permeability is Avery-anov’s 3.5-power function of the moisture content and capillary pressure is a given (measured) function. A linearized advective dispersion equation is solved with respect to the second term in the series expansion of the moisture content as a function of spatial coordinates and time. For a single block of a nite thickness we solve a boundary value problem with a no- ow condition at the bottom and a constant moisture content at the surface. Preliminary comparisons with theta-, TDR- probes measuring the moisture content and temperature at several in-block points are made. Results corroborate that a 3-D heterogeneity of soil physical properties, in particular, horizontal and vertical capillary barriers emerging on the interfaces between silt and sand generate eco-niches with stored soil water compartments favourable for lush vegetation in desert conditions. Desiccation significantly increases the temperature in the blocks and re-wetting of the blocks reduces the daily average and peak temperatures, the latter by almost 15°C. This is important for planning irrigation in smartly designed soil substrates and sustainability of wild plants in the region where the top soil peak temperature in the study area exceeds 70°C in Summer but smartly structured soils maintain lash vegetation. Thee layer of dry top-blocks acts as a thermal insulator for the subjacent layers of wet blocks that may host the root zone of woody species.
A model is outlined that predicts NAPL which is held in pore wedges and as films or lenses on solid and water surfaces and contributes negligibly to NAPL advection. This is conceptually referred to as residual NAPL. Since residual NAPL is immobile, it remains in the vadose zone after all free NAPL has drained. Residual NAPL is very important because it is a long-term source for groundwater contamination. Recent laboratory experiments have demonstrated that current models for predicting subsurface NAPL behavior are inadequate because they do not correctly predict residual NAPL. The main reason for the failure is a deficiency in the current constitutive theories for multiphase flow that are used in numerical simulators. Multiphase constitutive theory governs the relations among relative permeability, saturation, and pressure for fluid systems (i.e., air, NAPL, water). In this paper, we outline a model describing relations between fluid saturations and pressures that can be combined with existing multiphase constitutive theory to predict residual NAPL. We test the revised constitutive theory by applying it to a scenario involving NAPL imbibition and drainage, as well as water imbibition and drainage. The results suggest that the revised constitutive theory is able to predict the distribution of residual NAPL in the vadose zone as a function of saturation-path history. The revised model describing relations between fluid saturation and pressures will help toward developing or improving numerical multiphase flow simulators.
A zero-pressure isobar is reconstructed in a potential Laplacian field generated by a sink–source pair that models steady-state Darcian seepage from a ponded soil surface to a cavity draining a homogeneous isotropic half-plane. At sufficiently small flow rates (cavity depths under the soil surface) the obtained contour is almost spherical. For a given "sphere" its depth under a constant-head plane is found providing minimal inflow rate.
A discussion of a paper with the aforementioned title by H.M. Hathoot, published in this journal (Volume 124, Number 2, March/April 1998), is presented. The discusser maintains that the author's use of the steady problem solution for calculation of water-table drawdown, the corresponding design of drain spacing, and optimization of the mole drain array step are interesting, both practically and mathematically. He questions, however, the assumption of the existence of infinitely high depth of soil above the drain arrays. He maintains that employment of sinks requires a posteriori expressions of the depth of the drain through the depth of the sink and that generally, the two depths do not coincide. In application to the flow pattern, he believes it is unclear for what stages of decrease of the water table the half-sink approximation is valid. Finally, he contends that optimization of drain spacing did not include precise formulation of the mathematical problem. Discussion is followed by closure from the author.
A porous barrier bounded by two confocal ellipses is filled with material of a hydraulic conductivity different from the ambient one in order to control the flow rate inside. Optimization problems are solved by describing the flow through a medium consisting of zones of different properties. For three-component composites, viz. three zones demarcated by two confocal ellipses, an explicit rigorous solution of refraction problems for potential fields of Darcian 2-D saturated flows is used. An aquifer, an elliptical 'core' and an elliptical annulus, which serves as a liner of the core, have contrasting hydraulic conductivities (control variables). The magnitude of the velocity in the core, total flow rate, travel time along streamlines, hydraulic gradient in the core are objectives in optimization. A single maximum of the magnitude of velocity in the 'core' is found at a certain conductivity of the annulus, similarly to the Strack circular annulus refracting a unidirectional flow. This maximum can be higher or lower than the velocity at infinity, i.e. the liner can amplify or lessen the incident flow. Applications to in situ ore leaching, permeable reactive barriers, porous waste repositories, aquifer permeameters and formation damage due to suffusion in the vicinity of pumping wells are discussed.Abbreviations: ISL: in situ leaching; RAF: reduction–amplification factor.
