Beyond Design Codes: An Integrated Analysis of Farmer-Built Dam Performance Using Geotechnical and Hydrological Methods

This study examines fourteen small, privately constructed water harvesting dams in the Sulaymaniyah Governorate of Iraq, which local farmers built without formal engineering design or oversight. The assessment encompasses dam geometry, geotechnical properties, slope stability, spillway performance, and cost efficiency. Field surveys, laboratory soil testing, and numerical modeling using GeoStudio SLOPE/W were employed to evaluate the structural and hydraulic behavior of these dams. The embankment soils were predominantly low-plasticity clays and clayey sands, with Plasticity Index values ranging from 7.6 to 13.6, borderline or marginal for safe dam construction according to standard guidelines. Slope stability analyses revealed that 86% and 71% of the dams exhibit factors of safety below the recommended thresholds on upstream and downstream slopes, respectively. Nonetheless, 79% of dam bodies have remained operational and stable for 7–13 years, suggesting that traditional 2D analyses may underestimate actual field stability by neglecting three-dimensional effects, vegetative reinforcement, and long-term soil behavior. Spillway inspections showed that five of the fourteen dams had partially or fully blocked spillways, raising concerns about flood safety during extreme events. Construction costs ranged from $2,667 to $40,000, representing 1% to 11% of the expenses of government-built dams, with no direct correlation between price and performance. The findings highlight the potential of integrating local knowledge with simplified engineering practices and performance-based assessments to enhance the safety, sustainability, and affordability of community-built water harvesting structures in semi-arid regions.