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

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

With more developments, With more developments, there are more impervious there are more impervious surfaces. surfaces.

Not much field left!

How does this affect runoff?How does this affect runoff?

This chart shows how the This chart shows how the amountamount of stormwater of stormwater increasesincreases dramatically dramatically

* cfs = cubic feet /second,a measure of stream flow

with more with more developmedevelopment.nt.This can be This can be because of because of more more impervious impervious surfaces.surfaces.

Where Where does this does this water gowater go ??

In most neighborhoods, In most neighborhoods, the water goes into the water goes into storm sewers.storm sewers.

Where to next?

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

The purpose The purpose of a of a

detention detention basin is to basin is to

reduce reduce downstream downstream

flooding.flooding.

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

… release the stormwater to the stream it would have gone into

before the development was build.

What does What does this do the this do the amount of amount of

water in the water in the streamstream

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

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

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

Besides more stormwater runoff, Besides more stormwater runoff, there are other problems caused there are other problems caused by traditional storm detention by traditional storm detention basins.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?Why do you think this is so?

This is called a low flow low flow channel.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 But there are new methods to help alleviate some of these help alleviate some of these traditional stormwater traditional stormwater problems.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 There are other methods to enhance existing stormwater enhance existing stormwater basins which can further basins which can further improve water quality.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 fertilizerswill 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 theirquestions 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.

www.dillard.edu/about_d/ cook_center_parking_lot.htmwww.greenworks.tv/stormwater www.pvwatershed.orgwww.montcopa.org/olancom

Compiled by: Tina Spiegel, 2003.