A transient phreatic surface mound, evidenced by a strip of vegetation on an earth dam

Abstract

On the slopes of the embankment of the Al-Khod groundwater recharge-flood protection dam (Oman), a band of scrub vegetation community emerged after torrential rains and temporary filling of the dam reservoir. Species composition differs markedly on both sides of the embankment, with many exotics found on the reservoir side and more typical gravel-desert species on the outside. Hydro-ecologically, the vegetation is interpreted as the footprint of a temporary storage of water, which is a small-sized groundwater mound within the permeable shoulder of the levee. The levee, as an anthropogenic landform, induces a U-turn (gravitational slumping-lateral seepage-transpirational moisture ascent) topology of seepage. The Lembke method of successive variations of steady states is used in modelling the water table dynamics. In the early stage of the mound decay, outflow through a seepage face of the shoulder is modelled by the Barenblatt slumping parabola of the phreatic-zone part of the flow domain, which is perfectly matched with the Youngs exact solution for a purely horizontal flow through a porous wedge. At the stitching cross-section, the flow rates and saturated depths in the two zones coincide. The late stage of mound evolution is characterized by transpiration by the plant roots projected onto a shrinking free surface, with the Barenblatt and Youngs solutions conjugated but without the outcrop of the saturated mound on the levee slope. Ordinary differential equations for the sliding or descending locus of the intersection of the parabola and the triangle hypotenuse are integrated in a closed form or by the Runge-Kutta method. The dwindling saturated volume and the rate of drainage are obtained. They can be used in assessments of the hydro-ecological sustainability of slope-rooted shrubs (vegetation survival between rare rainfall episodes).Un dôme piézométrique transitoire révélé par une bande de végétation sur un barrage en terre Résumé Sur les pentes de la digue du barrage Al-Khod (Oman), construit pour la recharge de nappe et la protection contre les inondations, une bande de végétation arbustive est apparue après des pluies torrentielles et le remplissage temporaire de la retenue du barrage. La composition végétale diffère nettement des deux côtés de la digue, avec de nombreuses espèces exotiques sur le bord du réservoir et des espèces plus typiques des déserts caillouteux à l'extérieur. Hydro-écologiquement, la végétation est interprétée comme l'empreinte d'un stockage temporaire de l'eau, c'est-à-dire un petitdôme piézométriquedans un épaulement perméable de la digue. La digue, relief anthropique, induit une percolation en U (descente gravitationnelle-cheminement latéral-remontée par transpiration). La méthode de Lembke (1886) de successions d'états permanents est utilisée pour modéliser la dynamique de la nappe phréatique. Au stade précoce de baisse du dôme, le flux sortantau travers d'une surface de percolation de l'épaulement est modélisé par la parabole de décroissance de Barenblatt dans la partie phréatiqu...

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

“…A hydrologically similar phenomenon of impeding a vertical infiltration flux and channeling it towards the plant roots to make a clear band (strip) pattern of vegetation has been discovered on the slopes of the embankment of this dam (Kacimov and Brown, 2014). shows a distinct ecotone of lush vegetation rooted in a zone where a course dam filling and relatively fine subjacent soil are conjugated through a so-called seepage face (Strack, 1989), which vents evaporating water not intercepted for transpiration by the plant roots.…”

“…In this paper, we studied SMDaD in a unique and fascinating type of structural-textural heterogeneity of soils, which we have recently discovered in the field (Al-Ismaily et al, 2013, b;Kacimov et al, 2013;Kacimov and Brown, 2014). Noy-Meir (1973) conceptualized soil heterogeneity as a vertical soil textural stratification (i.e.…”

An exact analytical solution for steady seepage from a perched Aquifer to a low‐permeable sublayer: Kirkham‐Brock's legacy revisited

“…Therefore, flow in Figure c incorporates both a steady state phreatic surface, without any linearization or DF averaging, and refraction. The Youngs [] steady state wedge solution was extended by Kacimov and Brown [] as an analytic element in a transient problem of a slumping groundwater mound. Similarly, the KB wedge, as depleted by a slightly permeable substrate, can be employed in transient problems.…”

Phreatic seepage flow through an earth dam with an impeding strip

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