The drainage or runoff of water, especially from rain or melting snow, flowing away from a surface or area.
From 'flow' + 'off' (Old English 'of'). This compound describes the literal flowing away of water, particularly in environmental and engineering contexts.
Urban flowoff is actually a major pollution crisis—instead of soaking into soil to be filtered naturally, concrete city streets channel all water directly into streams, carrying oil, chemicals, and trash and overwhelming ecosystems!
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