Impermeable Surfaces Create a Multitude of Problems for Waterways

What are impermeable surfaces?

Have you ever noticed that little stream running down the road after a heavy rainstorm? These are created by impermeable (or impervious) surfaces, and they contribute to a variety of problems including increased run-off and pollution. An impermeable surface is any solid surface that will not allow water to penetrate through such as asphalt, concrete, stone, brick, roofing, or extremely compacted ground like a soccer field. These areas are particularly numerous in urban and suburban areas where lots of problems with impermeable run-off can occur as a result. As you increase the number of paved roads and buildings then you decrease the vegetation and therefore decrease the amount of water absorbed into the ground. The water has nowhere else to go but follow along the impermeable surface.

Why are impermeable surfaces bad for water?

The aquifers in the ground are not being replenished as fast as they are being used since most of the water cannot penetrate through the surface. The water is unable to penetrate directly through to the ground, so it travels along the impermeable surface and picks up various chemicals/pollutants along the way before entering a drain. However, sometimes the surface is not done correctly, and the water can puddle up instead of flow, and this creates further problems such as breeding areas for insects. The contaminated water that can move then flows into larger bodies of water and pollutes them as a result.

Since the water was not able to absorb into the ground, and much more of it ran-off into the streams and rivers, it will increase the likelihood of flooding and bank erosion in these areas. The increased stormwater run-off can cause vast amounts of property damage and increase sediment deposits in waterways. The water also gets superheated on the dark surfaces and this can stress or even kill various stream inhabitants. All inhabitants are harmed in some way by impermeable surfaces, but some are much more sensitive than others, such as amphibians, fish, and macroinvertebrates. Any stream that has above 10% impervious surface has a drastically less aquatic life and can only support very tolerant insects. Anything above 20% impervious surface has no chance of sustaining life and has become too polluted and damaged because of the run-off.

This graphic shows how impermeable surfaces impact stream health. From: Maryland Department of Natural Resources

What are ways I can reduce impermeable surfaces' impacts on my property?

One of the most obvious, but not always easiest, is to just reduce the number of impermeable surfaces on your property. You can reduce the amount of concrete and paved areas and increase the amount of non-compacted soil and plant growth. This will decrease the amount of run-of caused by the impermeable surfaces while also encouraging more groundwater absorption. There are also a variety of structures or additions you can do to your property to further mitigate impermeable surface impacts. Some examples of this include rain barrels, rain gardens, or green roofs. Rain gardens will funnel stormwater and planting water-loving plants will help to absorb pollutants from the water and gradually absorb it into the ground. Rain barrels can store large amounts of water for later use and reduces the amount of water that would otherwise run-off.

What are some new innovations that help to reduce impermeable surface impacts?

Permeable paving systems are a fast-growing and environmentally friendly alternative to traditional paving methods. These are specially designed surfaces that will replace asphalt and other traditional materials by utilizing pore gaps between the material that allows water the filter through into the ground. There are a large variety of materials that qualify as permeable pavement including porous asphalt, plastic grids, porous turf, or permeable clay pavers. These permeable paving methods are often laid down on top of gravel or sand in order to allow for gradual seepage into the ground. This alternative greatly reduces the amount of run-off and therefore reducing the amount of chemicals being carried into the waterways. As a result, it eliminates the need for retention basins and other water collection areas which can save lots of money in addition to helping reduce pollution. Some examples of large-scale use of permeable paving are recreational water parks, parking lots, and permeable sidewalks.

Where can I find more information on reducing stormwater impact on my property?

You can find a variety of information on the Penn State Extension website including a webinar titled "A Homeowner's Guide to Stormwater" as well as more information and articles about rain barrels and rain gardens. All these tools can be very useful in helping you assess the impact of stormwater on your property and how you can mitigate the impacts of impermeable surfaces on your property.