Seepage beneath dams is one of the most important hydraulic phenomena affecting dam safety and stability, as water moves from the high-pressure upstream side toward the downstream side through soil pores and rock fissures in the foundation. Engineering studies have shown that most failures of earth and rockfill dams have been associated with uncontrolled water flow. For this reason, the aim of design is not to prevent seepage completely, but to control its quantity, velocity, and path within safe limits. Seepage analysis relies on Darcy's law, which relates discharge to the hydraulic gradient and soil permeability, while flow nets and numerical software such as SEEP/W are used to determine the distribution of pressures and discharges in complex geometric sections. Among the most significant hazards caused by seepage are hydraulic heave in the downstream zone when the exit gradient approaches its critical value, and piping, which begins with the erosion of fine particles and gradually progresses until it leads to dam failure. Seepage also produces uplift pressure that reduces the dam's resistance to sliding and overturning, and it can dissolve foundation minerals in gypsum and limestone formations. To address these hazards, several measures are used, including grout curtains in fractured rock foundations, cutoff walls and trenches that intersect permeable layers, upstream impervious blankets that lengthen the flow path, and relief wells, filters, and drains that reduce uplift pressures and prevent particle migration. The theories of Bligh and Lane likewise estimate the creep path length required to ensure safety against internal erosion in concrete dams built on permeable foundations. Design is incomplete without a monitoring system that includes piezometers, weirs for measuring discharge, and checks on the turbidity of seepage water, since these instruments reveal any malfunction early and confirm that the dam's performance matches the design assumptions. In light of this, the success of seepage control depends on a careful geological investigation of the foundation, a combination of barriers and drains, and continuous monitoring throughout the dam's operational life, thereby ensuring structural safety and efficient water resources management. Presented by Asst. Lect. Farah Hamid Abdulkhudhur M.Sc. in Civil Engineering Source: Cedergren, H. R. Seepage, Drainage, and Flow Nets, 3rd ed., Wiley, 1989.