Scientists Say: Runoff | Science News for Students

Scientists Say: Runoff

When water hits soil, it doesn’t stop there
May 21, 2018 — 6:30 am EST

Water flowing out of these concrete pipes is runoff.


Runoff (noun, “RUN-off”)

This is water that flows off the land. It may come from rain, snow or ice. Runoff can also arise when people apply too much water somewhere, such as on a farm field or lawn. Water may run off soil because the soil is too soaked to hold more. Or it might run off of a paved road or driveway because it can’t penetrate the hard surface. Runoff eventually ends up in streams, ponds, rivers, lakes and oceans. Before it gets there, the water can pick up dirt, pollutants and even medicines. All of those substances can end up in the waterways where the runoff pours in and may cause problems for creatures living within them.

In a sentence

The ditches farmers use to drain their fields may also carry runoff full of pollutants.

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Power Words

(more about Power Words)

pollutant     A substance that taints something — such as the air, water, our bodies or products. Some pollutants are chemicals, such as pesticides. Others may be radiation, including excess heat or light. Even weeds and other invasive species can be considered a type of biological pollution.

runoff     The rainwater that runs off of land into rivers, lakes and the seas. As that water travels through soils, it picks up bits of dirt and chemicals that it will later deposit as pollutants in streams, lakes and seas.

sea     An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.