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Stormwater, Impervious Surface, and Stream Health

Urban development is associated with an increase in impervious surfaces, that is, surfaces such as rooftops, sidewalks, and streets that prevent precipitation from infiltrating into the groundwater. Impervious surfaces increase the volume and energy of stormwater that reaches streams and can lead to adverse physical and water quality impacts, including erosions and increased nutrient runoff. In this video USGS scientist Tom Cuffney and Tom Schueler, director of the Chesapeake Stormwater Network, discuss the effects of impervious surfaces on stream health.

[train]

Jerry McMahon:

Impervious cover makes it easy for trash, nutrients, and stormwater to cause substantial problems in our urban streams.

Today, we'll visit the Patapsco River Watershed to get a first-hand look at these problems.

We'll be joined by students from Hammond Middle School, who will share their perspectives on urban streams.

Interviewer:

Why did you decide to do a river cleanup here?

Betsy McMillion:

Well, we do a lot of river cleanups and we do a lot of stream cleanups. We have stream watchers, about 60 of them, that keep an eye on the Patapsco River and streams. And any time there's so much trash or invasives that they can't remove, then we schedule a clean up.

Interviewer:

Why did you decide to bring your students out here today?

Jennifer Furman:

Well, part of the Chesapeake Bay Act of 2000 is that students go through a meaningful watershed experience related to the Chesapeake Bay so they can learn about the area in which they live, how pollution can affect our area and how they can remediate the effects of pollution on our Chesapeake Bay. So as a science teacher, I coordinated this with Betsy McMillion from the Patapsco Heritage Foundation so our kids could come out and actually get to do some service work where they clean up a river that feeds into the Chesapeake Bay

Jerry McMahon:

I'm Jerry McMahon, the team leader of a group of U.S. Geological Survey scientists, who are studying the effects of urban development on stream ecosystems.

Joining me today in our conversation is Tom Schueler, the coordinator of the Chesapeake Stormwater Network, and then, Tom Cuffney, a research biologist at the U.S. Geological Survey.

Interviewer:

So do you think that this stream is healthy?

(Various Students):

Ah, no, there's like trash every few feet everywhere we go, there's um, lots of bottles and tons of broken glass.

Well, yeah, it looks pretty healthy.

No.

There's a lot of pollution, I think, cause it looks pretty green.

Kind of.

Kind of sort of.

Tom Cuffney:

One of the things we look for is invertebrates that live under rocks. Normally in a healthy stream, if you picked up a rock, and flipped it over, you'd find all sort of things moving around, mayflies, stoneflies. Here all we see are an occasional midge in this stream. And midges typically in general are very tolerant organisms. And we're not seeing a lot of the organisms that we would normally think of as being sensitive to pollution. So, their absence really kind of indicates that this stream is not in the best of health.

Interviewer:

And what do you think would make a healthy stream?

(Various Students):

Um, I think we'd need a lot more vegetation and a lot cause I know a lot of the buffer zones are getting away, there's a lot of phosphorus, nitrogen, and chemicals that are getting into the river.

It would have some wildlife in it, like fish, turtles.

Cleaner water, no trash.

The absence of trash and these invasive plants.

Tom Schueler:

A really important element of a stream is their floodplain, which is an area where water is stored during floods and sediments are deposited. This is one of the last flood plains in Cooper's Branch that still exists. In many urban streams they're filled in and narrowed.

In addition to that you can see this bright green cover. It looks attractive but it's an invasive plant called lesser celandine that has completely carpeted the floodplain and has out competed the wildflowers we would normally see in the spring.

Interviewer:

And what do you think makes a healthy stream?

(Various Students):

Uh, just like clean water.

Well, a lot of creatures to balance out everything and healthier surroundings.

Tom Cuffney:

One of the important things for healthy stream ecosystems is to have a diverse and complex community of organisms. Streams that have the chemistry and physical conditions that support diverse communities can catch lots of energy in their plant life, pass that on to the invertebrates, which eat the plants, which are then in turn eaten by the fish. And the fish, of course, can be eaten by man.

Jerry McMahon:

Tom, what is impervious cover and why do we care about it?

Tom Schueler:

Impervious cover are all the hard surfaces in our urban landscape: the roads, the sidewalks, the rooftops, parking lots, and the like. And collectively, we measure the amount of impervious cover in a watershed so that we can determine its effect on streams.

The importance of impervious cover is that rainfall, when it strikes it, it runs directly off, so we produce an order of magnitude more runoff for the same rainfall event. And what that does is it runs through the connected stream - or down the curbs, into the gutters, and then into the stream where it acts like a fire hose, and the enormous power of that runoff shapes and degrades the quality of the stream, and carries with it a great deal of pollutants, sediment, nutrients, hydrocarbons and other things that can impair our drinking water.

Tom Schueler:

You note the concrete ledge across the stream. That used to extend at the same elevation across the entire stream. So that was the bottom of the stream 20 years ago. You can see the enormous cutting power of that runoff as it's really dropped the elevation here by at least 8 to 10 feet. And so it's taken an enormous quantity of sediment from the floodplain and sent it downstream to fill up our estuaries in the Chesapeake Bay. So this is kind of like a historic marker of the effect of stormwater on stream channel erosion.

Stream habitat from a fish-eye's view is a series of riffles, deeper pools, runs, complexity, root wads, large wooden debris. All of those create niches and habitats very characteristic of normal stream systems. In urban stream systems, as the watershed impervious cover increases, we begin to lose those features, streams become simplified, there's simply less habitat available for the wide diversity of aquatic insects and fish to make a home.

Tom Schueler:

If we want to protect our streams and rivers we need to do watershed management where we mitigate the impacts of impervious cover. We do that in a number of ways. We try to reduce how much impervious cover we create during land development. We also want to locate it in the right places in the watershed, away from our sensitive resources.

The second element of watershed planning are stream buffers; to have forests on both sides of the stream. We also have to be very careful during the construction stage that sedimients don't run off into our streams. And when we develop, what we want to do is to take that impervious cover and effectively eliminate it by disconnecting the system.

So here's an example of connected impervious cover where the rainfall goes to the gutters, into the storm drains as we see here, then directly shoots in the stream where it causes major problems.

So the alternative approach is to disconnect rooftop leaders over lawns into rain gardens, grassy swales and other ways to filter and infiltrate the rain water back into the ground rather than into a large storm drain pipe, which is really an admission of failure.

Interviewer:

And what do you think makes a healthy stream?

(Student):

A lot of people working together to get it clean.

Betsy McMillion:

And today, Hammond Middle School students picked up over 2 tons, which is 5,275 pounds… (applause from students)

[End of Audio]

Duration: 9:40 minutes