Catchment area

A catchment area is land from which water drains to a specified outlet, such as a river channel, lake, reservoir, or monitoring point. Its boundary follows divides that separate flows toward different outlets.

Watershed divide: A topographic boundary separating land whose water drains to different outlets. Divides mark the catchment’s outer boundary by separating flows headed for neighboring outlets.
Drainage basin: An area of land whose water drains to a common outlet through a river system. It is a closely related term, often used for larger river systems.
Hydrological modeling: The mathematical representation of water movement and storage in a landscape or river system. Models use catchment boundaries to define where inputs and runoff are calculated.
Groundwater basin: An area of subsurface aquifers and groundwater flow bounded by geological or hydraulic features. Its subsurface boundaries may not match the catchment’s topographic divides.
Surface runoff: Water that flows over land when rainfall or snowmelt exceeds infiltration or storage. Runoff carries water across the catchment toward channels and its outlet.
Watershed: A term that can mean either a drainage area or the boundary separating drainage areas, depending on regional usage. Its meaning varies by region, unlike the more consistently area-focused catchment area.
Flood forecasting: The prediction of flood timing, extent, or magnitude using observations and models. Rainfall over a catchment becomes a key input to forecasts at its outlet.
Urban watershed: A drainage area shaped by built surfaces, storm sewers, and engineered channels in an urban landscape. Urban drainage infrastructure can redirect water beyond natural catchment boundaries.
Infiltration: The process by which water at the ground surface enters soil or porous rock. Infiltration determines how much precipitation becomes surface flow within a catchment.
Stream order: A ranking system that describes the branching hierarchy of channels in a river network. Stream order helps characterize the channel network draining a catchment.

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