Seepage

Seepage refers to the gradual movement of water through porous media such as soil, rock, or engineered materials, driven by differences in hydraulic head. It can occur below the ground surface as groundwater flow, or through the body of structures where moisture moves along pores and cracks. Seepage is common in natural settings, including seepage through hillsides and at springs, and in engineered systems such as dams, levees, foundations, tunnels, and earthworks where water is present.

Movement is governed by permeability, porosity, and hydraulic gradient. In many cases, water flow in soils is described by Darcy's law for laminar flow, where discharge is proportional to hydraulic gradient and the material's permeability. The seepage path depends on the pore structure and anisotropy of the medium. Seepage can create seepage pressure; in confined conditions, it can generate pore-water pressures that reduce effective stress and shear strength.

Impacts of seepage can include erosion along seepage paths, internal erosion or piping, settlement, heave, or undermining of structures. It may lead to damp zones, salt intrusion, or groundwater mounding near discharge points, and can influence slope stability and foundation performance.

Control and mitigation involve assessing seepage with field instruments such as piezometers and flow nets, and implementing drainage, cut-off walls, curtain grouting, proper backfill, and low-permeability liners. The design objective is to maintain stable seepage conditions, minimize concentrated flows, and reduce risks to structures, soils, and surrounding ecosystems.