Soil Importation and Wadi Channel Narrowing for Agricultural Expansion Alter Sediment Patterns and Soil Chemistry in Arid Oman

Wadis—ephemeral watercourses in arid regions—serve as vital ecohydrological corridors, supporting both biodiversity and water resource functions. Yet, these fragile systems are increasingly threatened by human interventions. Impacts of agricultural expansion, particularly soil importation and wadi occlusion, on sediment dynamics and surface-soil properties in Wadi Al-Khoud, Oman are investigated. Sampling at three transects across the wadi (n = 48), combined with laboratory analysis, is done. Spatial statistics was used to assess soil texture, topsoil chemistry, and downstream nabkhas as geomorphic landforms. The imported “alien” soils—often mixed with waste like construction debris, crashed rock from local quarries and stripped asphalt—altered soil composition, with concentrations of Na+, NO3;−, and K+ increased by 249.11%, 32.71% and 103.93%, respectively, compared to the control. Texture at the anthropogenically impacted site showed a significant increase in fine silt content by 4.28 folds compared to control. Semivariogram analysis corroborated disrupted spatial texture patterns. Over a decade of 2010–2020, wadi's average width contracted by 73 m, amounting to approximately 95,838 m3 of imported material. This narrowing induced a Venturi contracta effect, which increases the flow velocities, and consequently scoures more sediments, thereby intensifying flood-driven erosion and contaminant dispersal. The formed nabkhas reflect ecological shifts in the wadi/floodplain. Nabkhas buffer sediment loss but alarm the instability of the upstream sediments. Legal frameworks akin to urban landscaping regulations are urgently needed to protect wadis as “natural hydraulic veins” and critical environmental assets in Oman's rapidly urbanizing drylands.