drainage

Drainage refers to the removal of surface and subsurface water from an area to manage water in the landscape for agriculture, construction, flood control, and environmental protection. Effective drainage lowers the water table, reduces waterlogging and soil salinity in irrigated soils, stabilizes foundations, and prevents damage to roads and other infrastructure.

Drainage can be categorized into surface drainage and subsurface drainage. Surface drainage uses open conveyance channels such as ditches, swales, and graded slopes to move excess water to outlets like streams or retention basins. Subsurface drainage uses buried pipes, often perforated and surrounded by gravel or filter material, to collect water from the soil and carry it away. In urban contexts, drainage systems encompass stormwater runoff systems, separate or combined sewer networks, catch basins, and engineered storage facilities such as detention or retention basins, sometimes integrated with green infrastructure.

Design of drainage systems considers climate and rainfall, soil permeability and stratification, topography, land use, and the desired outlet. Key concepts include drainage density, which relates to how extensively an area is drained, and the required outlet capacity to prevent water buildup. Maintenance issues such as sedimentation, root intrusion, and pipe collapse affect performance.

In agriculture and civil engineering, drainage practices must balance effective water removal with environmental protection, groundwater sustainability, and water quality.