Hell and high water

Photos of Houston afflicted by Hurricane Harvey reminded us of the worst that stormwater can do. It’s been pointed out that Houston’s unrestrained development created a set-up for flooding.

Flooding in Houston

Developers have been building in flood plains and paving over wetlands and prairies, reducing the chance for rain to soak into the ground. Smarter urban planning could have lessened the catastrophic effects of the hurricane.

Wetlands around Houston used to absorb stormwater--photo by Daniel Ray

    Did you know that China is a leader in this environmental area? They’re developing “sponge cities,” engineering ways to keep rainwater for use by water-poor cities, rather than letting it run off.  Besides cutting down on impermeable paved surfaces, they’re collecting rainwater in ponds and tanks and circulating it into the cities’ water supplies, either for non-potable uses or purified as drinking water.

    I hope it never happens, but if we got 50 inches of rain (a year’s worth) in a few days, the amount that fell on Houston, we’d want to let it soak through every possible surface.

Our deck and stone path, wet but permeable

Even without a huge hurricane, it’s better to keep rainwater on your property, because if it rushes down the street, it carries pollutants with it into nearby waterways. Here are some ways we gardeners can make our yards more sponge-like.

•    Make hard surfaces permeable. This is probably the most important change you can make. For us, the driveway is the main impermeable surface. By replacing a section of our asphalt driveway with porous paving material, we’ve enabled water to soak into the ground. 

Water sinks into the darker porous paving

A nice-looking alternative is to make a driveway out of stones with spaces between them where water can soak in. 

Paving stones let water soak through

Spaces between the stones of our new walkway similarly allow water to reach the soil below.

•    Direct water where you want it to go. If you’re an enterprising digger, you can create swales—basically trenches--to send water to your garden beds or to low-lying areas, where it will gradually percolate into the soil. 

Bioretention swale in Seattle during a 100-year storm

David Del Porto, an environmental visionary who designed an eco-friendly house and landscape called the Urban Ark 30 years ago, told me he used this approach to direct rainwater from his roof to the right spots in his vegetable garden, obviating the need for irrigation with purified drinking water. 

•    Plant a rain garden. This is a shallow depression, ideally at the lowest area of your yard, where water can collect and filter into the soil. Plants in the rain garden will soak up water and help purify it. Heavy soils may need to be amended with sand or gravel to make them drain faster in the rain garden; our sandy soil drains fast already.

A rain garden in Leeds, MA--photo U.S. Air Force

I like to think that we designed a rain garden without meaning to, because the land slopes down from the fence lines, making the center of the yard a collecting site for rainwater. I’d still plant a rain garden if I had a place for it. It’s a great excuse for a new planting project.

Water barrel dreams

As I’ve shifted toward more sustainable gardening, I’ve become more aware of stormwater runoff. To keep rain from running down the driveway into the street, two years ago I hooked up a rain barrel to the downspout at the corner of the house and got two strips of porous paving dug into the driveway. 

            The barrel feeds a soaker hose that waters a clump of shrubs near the street. When heavy rain fills the barrel, the porous paving lets the overflow soak down into the soil. During rainstorms it’s quite an amazing and satisfying sight to see sheets of water disappear into the ground as they hit the porous paving, instead of puddling in the gutter. It’s good to be doing my part to prevent stormwater from running into the storm drains, but I’ve started to wish I could capture that water for use in the garden.

            Ken Dews, an expert in rainwater harvesting systems, told me that he got started in the field when he set up a rain barrel at his house and saw it fill up and overflow after one heavy rain. His reaction to the overflow was, “That’s my water!”

            I feel the same. The rain barrel has me thinking differently about rain. Suddenly it seems silly to be using tap water for irrigation. If  I can water one small bed with rainwater, why not the whole garden? I could be solving two problems at once—irrigation and runoff—if I captured the rain falling on our roof, stored it, and used it in the garden. Massachusetts hasn’t yet made it easy to get permits to set up a greywater system, using water from the shower, dishwasher and clothes washer for irrigation. But I could arrange to drain water from house gutters into an underground cistern in the backyard and run the garden sprinkler system off that water supply.  

            Today it rained heavily. As I watched water pour out of the overflow of the rain barrel, I thought it was high time to make the investment in that rainwater harvesting system.