Permeable Beauty
Jeffrey Bale
Pennsylvania Blue Stone laid on 1/4 minus gravel |
Garden symposiums seem to be focusing more on environmental issues these days, especially in California where the wise use of water is becoming not just important, but essential. I was asked to address the topic of permeable pavements. Permeability doesn’t sound like the most exciting topic, but when you think about it, most of the life in a garden is underground where we cant see it. When we learn to nurture that, we benefit the environment that sustains us. It is not just a matter of engineering to get water to drain in to the ground, it is an opportunity to provide for the earth and enrich the architecture of our gardens at the same time. I’ve selected images of the best examples of work that I’ve built or seen around the World that show how pavement can be permeable and beautiful at the same time.
It has always been important to me that the Earth be allowed to breath and replenish, even when paved. This is seldom accomplished in typical hardscape, where driveways cover enormous areas, walkways drain on to sidewalks and in to the gutters on the street, and patios are impervious slabs. If you were to look at an aerial view of your home, how much square footage is made up of house roof and impermeable lifeless pavement? It is a large amount of space we occupy at the expense of natural ecosystems. The runoff flows in to storm drains carrying pollutants that collect on surfaces such as oil and airborne grit, and without biological systems to filter and purify it, degrades waterways.
Where I live in Portland, Oregon you can see curb swales that have been installed in some neighborhoods to catch the runoff from streets. The water that would normally go down the storm drain is allowed to be absorbed in to the ground. The swales become wetlands during the rainy season. Healthy wetlands are some of the most productive on Earth. So what was once asphalt is becoming a crucible for life. Oil and dust are cleaned from the water by microorganisms and plants, rather than pouring in to the river, so the negative impact that we have by paving large areas is reduced. That moisture is made available to the roots of trees, and local aquifers are replenished. People are also being encouraged to disconnect their downspouts to reduce runoff in to storm water systems, which during heavy rainfall sometimes cause the city’s sewage system to overflow directly in to the Willamette River. The city has pledged to meet a federal deadline to stop that from happening. The most responsible and proactive way to do that is to increase permeability.
When it comes to the garden, run off can be most easily put back in the ground by having gaps in the pavement that allows the water to reach the soil. This doesn’t necessarily have to be gaping swale that you can fall in to. A simple couple of inches of open space at regular intervals can absorb average rainfall.
Gaps in this mosaic pavement allow for permeability |
My main garden area, which is quite small, is paved in these small pebbles. I love how clean it is. I can wash things on it and it drains right in to the ground. Self sowers come up along the edges but not where there is traffic. I mix in pebbles I have collected in my travels to add color and interest. The gravel dries quickly, and I like to lay Oriental carpets over it in the summer to recline on with pillows. It makes a great space to stretch and do yoga, or lounge with friends. Its also nice that the legs of garden furniture will settle in to it so you don’t have wobbly tables and chairs. And I’ve even brushed bright blue paint on the pebbles and raked them in to add a dash of color.
Carpets on my round rock patio in summer |
When paving an area with stone or brick, laying the material in sand and not mortaring the joints allows water to reach the underlying soil. When moisture and air can get to the ground, life has a better chance of manifesting itself. Live soil is far better than dried out, oxygen starved soil for the root systems of trees and shrubs needing to capitalize on the soil under their canopies, which are often times paved.
If pavement is solid, like a cement pour, or stone set on a sub slab or mortared together, then gaps or holes in the pavement are the best way to allow water to drain in to the ground. It is common for pavements to be unbroken, but even a 1 inch gap will allow water to seep in. I use wooden form boards when I build with mortared stone that can be removed after the work cures. The design benefit is that expanses of pavement can be broken up to make them feel less imposing and softer. The eye will stop along the length of a path rather than heading down a runway like stretch. Pavement pads that connect sidewalks to the street curb will drain in to the ground if there is a gap left between them. If repairs need to be made to sidewalk or curb then the pad wont need to be disturbed, and tree roots are less likely to push up from underneath because water and air can reach them.
Path and Small Patio in Portland |
Driveways are usually the most offensive part of a home garden, especially in the suburbs where parking for numerous cars seems to be a requirement. I’ve worked on several homes where the driveway took up more than half of a front yard, dominating these homes and looking more like a parking lot. They often crack, because the expanse of pavement is too big. Few people can say they have an attractive driveway. By breaking up the area with gaps, cracks are less likely to form, and water can drain in to the ground to the benefit of ground dwelling organisms and root systems. When pouring a new driveway, add forms that are the full thickness of the pavement and can be removed, and then fill the gaps with permeable material. There are pavers on the market that can be laid for driveways to be permeable as well. The trick is laying them so that they aren’t ugly. A pleasing shape and creating a complimentary pattern are the tricks to solving this problem. Try to be as imaginative with materials as well as utilitarian. Use the touch of an artist rather than the Army Corp of Engineers. Concrete strips that only cover the area for tires to run on with an open strip of lawn or low ground covers used to be far more common than today’s expansive driveways. If you want to make openings in an existing slab, a concrete cutter can be hired to cut lines and remove sections of pavement at relatively modest expense. Doing this where the driveway meets the sidewalk or street can significantly reduce the amount of water that flows down the drain. The gaps could be planted with tough low growing herbs rather than turf grass, which is far more appealing than vast areas of pavement.
You might just start hanging out in your driveway rather than just parking on it if you make it more appealing to look at. When you hose off your patio and paths, the water will have somewhere to run besides a drain. Life will have a chance to flourish, our waterways will be cleaner, and your garden will become a healthier, vital, and more beautiful place .