Drainage (water management)

Drainage is the practice of removing excess water—from rainfall, irrigation, or groundwater—from a specific location to elsewhere. The purpose is to prevent water from collecting on the land surface, to allow plant roots to access air, and to prevent water damage to structures.

Drainage systems work according to how water moves, ranging from open drains to underground pipes. When water is not removed, stagnant pools, soil salinity, or structural deterioration can result.

Types of drainage

Surface drainage relies on ditches, canals, and shallow embankments to direct rainwater away. Subsurface drainage uses perforated pipes or tile drains laid underground to lower the water table. Pumped drainage is used when the land is too low; pumps force water upward.

Irrigation and drainage

Irrigation and drainage are interconnected. Irrigated land without drainage causes water to rise and salt to accumulate at the surface (salinization), reducing crop yields. For this reason, large irrigation schemes typically include canals that return excess water to a river or sea.

Cities

In cities, the hard surfaces of pavement and roofing prevent water from penetrating the soil, so rainwater collects and pools rapidly in low-lying areas, causing flooding. Urban drainage systems include street drains, underground pipes, and retention basins that store and gradually release water. Some cities use separate systems so that rainwater and wastewater do not flow through the same pipes, preventing sewage overflow.

Management and health

Drainage has two-sided effects. On one hand, it reduces stagnant water where disease vectors breed, which relates to disease control. On the other hand, draining wetlands destroys habitat, and water removed from fields or containing nitrogen from fertilizer must be managed carefully before it enters waterways.