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

A 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 with the hydrographs of the gaging station that feeds the reservoir. Textural analysis indicates the difference of ponding depth durations and sediment load is highly variable for pedons inside the reservoir and in the off-dam adjacent zones, both upstream and downstream of the embankment. The formation of a unique three-dimensional cascade of silt blocks, sandwiched by sand-filled horizontal and vertical fractures, was discovered. The propagation of silt entrained by infiltrated water into an originally coarse parent alluvium and the ensuing reduction of permeability were detected. Cumulative infiltration and infiltration rate curves and saturated hydraulic conductivities are related to the soil hydraulic-capillary properties.