Zlewni

Zlewni is the Polish term for a drainage basin or watershed—the land area from which precipitation drains toward a common outlet such as a river, lake, or coastal zone. The term is used in hydrology, geography, and environmental planning. It is common to refer to multiple basins with the plural form zlewni.

A zlewnia is bounded by topographic divides, typically ridges or high ground that separate it from neighboring basins. Inside the basin, a network of streams and rivers collects water from tributaries, while lakes, wetlands, and groundwater contribute to its storage and flow. The basin's hydrological boundary is defined by the landscape rather than political borders.

Basins vary widely in size and can encompass small catchments or large river systems. Hydrologists describe the internal structure of a zlewnia using concepts such as drainage density, river order, and sub-basins, which helps in understanding water flow and sediment transport.

Key processes include precipitation, infiltration, runoff, evapotranspiration, and groundwater exchange. The water balance of a basin depends on climate, soil characteristics, vegetation, and land use. Human activities such as agriculture, urban development, and damming alter flows, storage, and water quality within a basin.

Management of zlewni focuses on integrated watershed planning, flood mitigation, and sustainable use of water resources. Policies and practices aim to reduce flood risk, improve water quality, protect ecosystems, and maintain supplies for drinking and industry.

Examples include Poland's major basins drained by the Vistula and Oder rivers, and broader European basins such as the Rhine and Danube. Each basin presents unique hydrological characteristics and management challenges.

See also: Watershed, Drainage basin, River basin.