tormwater runoff. Sounds vaguely familiar, right? We have all heard the word, but what is it? Why should we care?

Stormwater runoff is water that flows across the landscape from rain and snowmelt. Much of the runoff is absorbed into the soil, where it is taken up by plants. Soils act as a sponge, releasing the water slowly over time, so it gradually seeps into nearby waterways. Soils and natural habitats such as forests and wetlands also filter this water, removing impurities before it reaches a stream or a lake.

Humans, however, have changed the landscape, by creating “impervious” surfaces, such as concrete, blacktop and roofs, that do not absorb water. Instead, rainwater flows towards the lowest point in the landscape, often a storm drain or, in some cases, the nearest basement. This becomes an especially big problem when rains become more intense, and water gathers speed, rushing like a torrent through low-lying streets. As the stormwater flows, it picks up trash, chemicals, oils and dirt, and carries it all into the nearest stream or lake.

Fast-flowing stormwater can cause erosion, washing out soil as it rushes through. Stormwater flowing into the stream at Bird Park was routinely washing away the stream bank, requiring a large remediation project to slow the flow and stabilize the stream banks. Capturing this water before it becomes a problem is cheaper and much more efficient.

We can all take steps to reduce stormwater runoff. You can even get a one-time cash credit from the municipality for some of these measures, and save money on your stormwater bill (visit the Public Works Department’s  section Stormwater Fee page for details). Some tips:

• Get rid of some of your lawn and plant native shrubs, trees and perennials.

• Mow your grass no shorter than 3 inches and leave grass clippings in place after mowing. This helps soil and root development which leads to better water absorption.

• Install rain gardens or bioswales in areas where water tends to gather.

• Install rain barrels and/or other methods of rainwater harvesting; as a bonus you can use this stored water for your garden.

• In your next construction project, reduce the paved areas around your home by adding permeable materials that allow stormwater to pass into the soil where it can be absorbed. Consider permeable pavers for your patio or driveway.

The Mt. Lebanon Nature Conservancy is hosting its inaugural native plant sale from 9 a.m. to 3 p.m., Saturday, May 7, at Sunnyhill Unitarian Universalist Church, 1241 Washington Road. Visit www.lebonature.org, and see Facebook posts for more information and online presale ordering.