…it lands on paved streets, rooftops and parking lots.

These are impervious surfaces that water cannot soak into. Instead of soaking into the ground, the water runs-off the pavement.

With more developments, there are more impervious surfaces. Not much field left! How does this affect runoff?

This chart shows how the amount of stormwater increases dramatically * cfs = cubic feet /second, a measure of stream flow with more development. This can be because of more impervious surfaces.

Where does this water go ?

In most neighborhoods, the water goes into storm sewers. Where to next?

The storm sewers quickly move the water into a detention basin.

The purpose of a detention basin is to reduce downstream flooding.

Detention basins are designed to hold storm water for 24 – 48 hours, and then…

… release the stormwater to the stream it would have gone into before the development was build.

What does this do the amount of water in the stream

Increases it!! ~~because less water soaks into the ground…

What can be the result of more water in the stream after a storm?

More water in the stream can result in flooding where none existed before!

Besides more stormwater runoff, there are other problems caused by traditional storm detention basins.

1. Traditional designs result in basins that provide very little aesthetic value to the community. Don’t know what “aesthetic” means? Right click it!

2a. Required regular mowing increases maintenance costs.

2b. Mown grasses develop shallow root systems which can lead to erosion in high velocity flows. 2c. Mown grass has little ability to filter storm water. Why do you think this is so?

low flow channel. This is called a low flow channel. Another problem with traditional basin design is the concrete low flow channel.

3. Because they are shallow, concrete low flow channels heat runoff and quickly transport it through a basin, without filtering it.

4. A traditional detention basin puts more water in the stream, so stream bank erosion is a common result, which alters or decreases stream habitat.

5. As water runs over impervious surfaces, it picks up various pollutants, including a) oil and grease from cars…

5b) fertilizers, herbicides and pesticides from lawns…

5c) fecal matter from pet waste and malfunctioning septic tanks …&…

5d) heavy metals from tires, shingles, paints, and metal surfaces.

But there are new methods to help alleviate some of these traditional stormwater problems.

A naturalized stormwater detention basin has more environmental, economic, and aesthetic benefits.

A naturalized stormwater detention basin is attractively landscaped, using native trees, shrubs and wildflowers.

In what ways are naturalized basins better than traditional basins?

Wildflower and tall grass meadow plants have deeper root systems.

Stormwater is slowed down and filtered by these deep-rooted plants.

This reduces flooding and keeps pollutants out of the stream.

Slower moving stormwater can recharge groundwater supplies.

Naturalized basins tend to have vegetation that requires only annual mowing. This decreases maintenance costs.

A natural low flow channel helps to remove pollutants from stormwater and is more aesthetic.

Native plants increase water quality by trapping sediment and many pollutants found in runoff.

There are other methods to enhance existing stormwater basins which can further improve water quality.

Removing concrete low flow channels helps to decrease water temperatures and allows for more infiltration.

Adding a sediment forebay improves water quality.

Forebays collect debris, sediments, and other pollutants.

allows for pollutants and sediments to settle out into the basin, Altering outlet structures so that runoff is held in the basin longer

…and limits downstream flooding and erosion.

What can you do to help stormwater leave your neighborhood safely?

Gardening organically, and reducing use of pesticides and fertilizers will lessen chemical pollutants in stormwater and local streams.

Planting trees and shrubs along streamside property helps prevent erosion, increase stormwater quality and reduce flooding.

How would reducing lawn areas by planting native trees, flowers and shrubs reduce stormwater runoff?

This will allow more stormwater to infiltrate into the ground. This also saves maintenance time and money.

With a little care and conscious thought, we won’t have to worry about the answer to this question:

The following slides will help you with your neighborhood survey. The answers to their questions can earn you 3 points extra credit on your Digital Field Trip worksheet.

Perhaps you have been near a stream and seen storm sewer access ports like these. 18. Why do you think the storm sewers run right next to the stream?

19. Some developments have pumphouses. What do you think they are for?

Some neighborhoods have markings like these on the curb. 20. What do you think they are for?

Improving Stormwater Basins, Naturally. (pamphlet) Lower Providence Township, Perkiomen Watershed Conservancy, Montgomery County Planning Commission, Philadelphia Suburban Water Co. Sam Huffer, Northampton Township(PA) Municipal Authority. cook_center_parking_lot.htm Compiled by: Tina Spiegel, 2003.