HydrionisGlobal Water Intelligence
Diagram

A river catchment

A catchment is the area of land from which all rainfall drains to a single point. It is the natural unit for managing water — and rarely matches any administrative boundary.

A river catchment

A catchment is the area of land from which all rainfall drains to a single point. It is the natural unit for managing water — and rarely matches any administrative boundary.

A river catchmentA schematic catchment. Rain falls across the whole area. Water flows from the upland headwaters through tributaries into a main river, past a gauging station, an abstraction point and a discharge point, and finally to the outlet. The dashed catchment boundary follows the ridge line, dividing this catchment from its neighbours.return flowrunoffHeadwatersupland, high rainfallTributaryTributaryMain riverAbstractionto water treatmentEffluent dischargefrom wastewater worksGauging stationGauging station: Where flow is measured. Flow statistics belong to the gauge, not to the river as a whole.Outletestuary or confluenceFarmlanddiffuse pollution
Catchment boundary
Follows the topographic ridge. Rain on one side reaches this river; rain on the other reaches a different one.
Why catchments matter
Everything that happens upstream reaches everything downstream. This is why water is managed by river basin rather than by county.
Return flow
Water abstracted upstream and discharged after treatment is available again downstream. A river can supply the same water several times over.

Text description

A schematic catchment. Rain falls across the whole area. Water flows from the upland headwaters through tributaries into a main river, past a gauging station, an abstraction point and a discharge point, and finally to the outlet. The dashed catchment boundary follows the ridge line, dividing this catchment from its neighbours.

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