What Happens to Stormwater Runoff
Launch library · evergreen read
Stormwater is rain that falls onto hard surfaces like roads, roofs and pavements and drains away rather than soaking into the ground. In most urban systems, it flows into gutters and underground pipes that lead directly to a local creek, river or the sea, generally without any treatment along the way.
This is different from wastewater from sinks and toilets, which is a common point of confusion. Because stormwater bypasses treatment, anything that enters a street drain, from litter and vehicle fluids to garden chemicals, has an almost direct path to a waterway, which is why storm drains are often marked accordingly.
During heavy rain, the sheer volume of runoff can also cause its own problems, eroding stream banks and carrying large amounts of sediment downstream in a short burst. Urban design features that slow and filter this flow, such as rain gardens and retention basins, address both the pollution and the volume issue together.