What Is It & Why Do We Care?

So what is stormwater?

Stormwater runoff is simply rain or melting snow that “runs off” the land and into storm drains and creeks.

Anytime it rains, water accumulates on hard surfaces such as streets, sidewalks, driveways. When you see it flowing down the side of the street—that is stormwater runoff. Even if that water flows into a storm drain, that storm drain will eventually discharge the water into a stream or river. 

Things that affect stormwater runoff (and sometimes make it difficult to manage—either in volume or in terms of our water quality)—include the following:

· heavy rainfall

· too much impervious surface

· inadequate or poorly designed drainage basins.

The possible negative outcomes (and you’ve seen them, probably with increasing frequency and degree) include all of these:

· flash flooding

· pollutants and debris entering our local waterways

· streambank erosion

· unhealthy sediment buildup in stream beds

· depleted aquifers

· various threats to human health

· possible restrictions on recreational use of water resources.

If your home has 2,000 square feet of impervious surfaces (roof, driveway, etc.), that equals 1,246 gallons of stormwater runoff that needs to be managed (about the volume of water in an “average” 

10’x10’ pond). And that’s just for a typical rainstorm. 

While our state (literally, “Penn’s Woods”—sylvaniais Latin for “forest land) is about 60% covered by woodlands and relatively stable at that level (roughly, 16-17 million acres), parcelization of private lands and deforestation leads to “an estimated 28,000 acres of forest being lost to residential and industrial development annually” (Pennsylvania Statewide Forest Resource Assessment June 2010, PA DCNR). 

To appreciate the value of trees in stormwater management, consider this: a single large tree with a crown 33 feet wide can capture and retain as much as 332 gallons of water. (USDA) Some of that water is used by the tree. Some evaporates. Some trickles down the trunk into the soil. And that slower process allows the water to infiltrate and not quickly run over the surface of the soil. If not enough water is infiltrating the soil, our groundwater “bank account” can become depleted, which can contribute to deterioration of water quality, reduction of water in streams and lakes, increased pumping costs, and land subsidence.

Click these links for more on ways stormwater can be a problem and how to mitigate that. 

For further reading on this topic:

The Homeowner’s Guide to Stormwater (Penn State Extension):

Go to the website (includes an interactive tool to map your property and stormwater flow and calculate stormwater to be managed)

Download the PDF

Stormwater Basics resource materials (Penn State Extension)

A Green Solution to Stormwater Management (Penn State Extension)

Pennsylvania Statewide Forest Resource Assessment June 2010, PA DCNR

Various video case studies of innovative solutions being applied all over the state (StormwaterPA)

Groundwater: A Primer for Pennsylvanians (DEP)

Northampton County Hometowner’s Guide to “Green” Lawn and Yard Practices(Northampton Co. Conservation District)

Green Gardens Clean Water (PSU Ext Master Gardeners)