Landscape Architecture Resource

Here's something that's very important that most home owners don't know about when paving their driveway, building a patio, or watering their garden.

Underneath the surface of the ground there is water. Virtually everywhere, if you drill deep enough you'll find ground water. Sometimes the ground water is just a few inches below ground, as at the beach. When the water level is above the ground, we call it a lake or stream or river, creek, pond, or spring. It's then surface water. It's all connected.

Where does ground water come from? Rain and melting snow, which percolate down through the soil until they reach and join the ground water. This is the ideal scenario. When rain is allowed to percolate through the soil it waters plants. Particulate matter like air pollution gets physically filtered from the water, while chemical pollutants get taken out and metabolized by bacteria in the soil. The end result is water pure enough to drink. Evian, for example, comes from springs in Evian, France. Springs are places where groundwater pours out of the ground, pure and clean.

To be clear, it's not as if there are underground rivers flowing as they do on the surface. In some areas this is true (limestone Karst topography), but in most areas ground water is just like wet sand where the water between sand particles moves about 50 feet per year. That's a very slow rate of flow, so it takes a while for impacts to be seen, and a lifetime for pollution to dissipate.

As mentioned before, rivers, lakes and streams are fed by ground water. Some comes from over-ground run-off, but the majority of water in a natural water body comes from ground water as it moves from below ground level to above ground level--or rather as ground level falls below the waterline.

This means that the water body is clean, and it also means that the water is cool. This is important, because cold water holds more oxygen than warm water, and thus cold water can support more diverse aquatic life and is less susceptible to nutrient imbalances like the ones that cause algal blooms and other problems.

But when you pave a piece of ground with something impermeable to water, like a driveway, a concrete patio, or a house (with its roof), the rain that falls is usually collected into a gutter or pipe and funneled into the sewer.

The sewer runs downhill, connecting to more and more sewers along the way from parking lots, roads, and everywhere else that rainwater is caught on its way down. This sewer water doesn't get a chance to be filtered by the earth, or cleaned by soil organisms, or cooled by the ground. It rushes down the sewer pipes collecting pollutants, silt, sand, oil, garbage, and everything else that gets washed off of our roads, driveways, and rooftops and is put down the sewer drain. Then it dumps straight into the lake or ocean, depending on where you live. Warm, polluted, and full of silt and debris that chokes fish, buries plants and habitat, and then... ultimately gets back into your body in your food and drinking water.

Meanwhile, the clean cool streams that should have been filling up on groundwater don't get a chance because the rain went into your gutter instead of into the ground. Sometimes when too much land gets paved it causes streams to dry up and the life that was once in them is killed. Fish, insects, plants and the birds and other animals that depend on them for food or habitat are gone. This can affect ecosystems further downstream including our lakes and oceans.

Sometimes wells dry up when too much land is paved and the ground water can't recharge as fast as it's being withdrawn. This happened where I grew up.

The solution is easy. As the saying goes, knowing is half the battle.

Disconnect your downspout. Let the water from your roof top trickle into your lawn and down into the soil to get re-purified as it recharges the ground water aquifer. Or better yet, collect it in a rain barrel and use it to water your garden. Save your potable tap water for drinking and cooking, and give your garden the rainwater that hasn't been treated with chlorine or your water softener.

And when paving, use permeable pavement whenever possible. Choose unit pavers (bricks or cobble stone) over concrete whenever possible. Choose gravel or permeable pavement over asphalt when ever you can. Don't make your driveway or patio any bigger than necessary. And pass on this message to help spread the word. Water quality is an important thing that we can all easily improve if we know our role in the hydrological cycle.