Reducing impervious surfaces
What are impervious surfaces?
Impervious surfaces include driveways, sidewalks, patios, and rooftopsany surface that doesnt allow rainwater to percolate into the ground.
Why should I reduce
Impervious surfaces alter the natural water balance in a watershed. As you replace forests and wetlands with roads, driveways, parking lots and buildings, you increase the amount of rainfall that flows over land and reduce the amount of rainfall that percolates in the soil or is consumed by plants and trees. Increasing the amount of rainfall that runs off the land leads to flooding.
As water flows over these paved surfaces, it collects soil, pet wastes, salt, fertilizers, oils, and other pollutants. It doesnt matter if your house is not on a stream or riverthe rainwater flows down the street into a catch basin. Storm sewers carry this runoff from your neighborhood directly to the nearest body of water, taking dirt and pollutants along with it. This runoff is the greatest source of pollution in many streams.
How do I reduce stormwater runoff from my yard?
One way you can help to reduce stormwater runoff is to minimize the amount of impervious surfaces on your property. As you add or rebuild patios and garden pathways, consider alternative techniques to the traditional concrete or asphalt. For instance, paving blocks, permeable pavements, wood decks, wood chips, and crushed rock allow rainwater to soak through and help to reduce stormwater runoff.
Paving blocks: There are many types of grid or lattice paving blocks that have holes in the concrete blocks. These holes can be filled with soil and planted with grass, or they can be filled with gravel. A small fraction of stormwater runoff is trapped in the shallow depressions in the paving blocks, and some may actually infiltrate into the soil. Not only do paving blocks help to reduce runoff, but also they often serve as a very attractive alternative to pavement. They typically come in different colors, shapes, and patterns. Paving blocks can be found at most major home centers. Also, traditional bricks can be used. As you lay them out, leave space in between the bricks. You can fill this space with sand or moss and the effect will be the same as using paving blocks. Just dont cement the bricks together!
Permeable pavement: Permeable pavement or concrete is similar to traditional pavement and concrete used on our sidewalks and roads, except that the gravel used in the mix is larger, which results in larger pore spaces in the pavement itself. The rainwater can then percolate through these pore spaces. Most pavement contractors should be able to provide you with more information about this option.
Wood decks: Wood decks allow rainfall to flow between the boards and percolate into the soil underneath. However, you should be careful in your selection of lumber for your decka lot of wood is treated with chemical preservatives and can contain toxics such as arsenic, which can leach into groundwater.
A Few things to consider
Before you replace driveways or sidewalks with grid pavers or permeable pavements, check with the building department of your community. Most cities have regulations regarding the types of paving materials that may be used for driveways and sidewalks.
As you are laying out your new patio or pathway, grade the surface so that it slopes to natural areas, such as garden beds. You dont want rainwater flowing off of this surface to head towards the street or the foundation of your house!
When it comes times to clean your patio, deck, sidewalk or driveway, use a broom rather than a stream of water. This will prevent the pollutants that have accumulated on the surface from entering the catch basin. Also, this will save literally hundreds of gallons of water every time.
Tips for helping urban streams
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