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, water all around

With Massachusetts’ drought officially over as of May 10,  I’m feeling more comfortable about watering my garden. 

Nice to see rain on the hostas

I’m happy when it rains, even though some of my annual plants, most noticeably the tomatoes, are slow to take off this spring because of fewer sunny days. 

     With plentiful rain comes other problems, though. During last week’s heavy rain, water streamed down the street in front of our house toward the storm drains.

Rainwater heading for the storm drain

    Rainwater running off roofs and down driveways in our neighborhood could be carrying toxic chemicals from both surfaces into storm drains and through them to rivers and Boston Harbor. The EPA, the Massachusetts Department of Environmental Protection, and local government all advocate keeping rainwater at home, not letting it wash into the street.

     Our section of town backs up against the Charles River, which is one of our area’s most beautiful and prized natural resources. 

A quiet spot along the Charles

Years of effort have gone into restoring it from a toxic waste stream to a place where people and wildlife can enjoy the benefits of clean water. 

     At this point, storm water runoff is most of what pollutes the Charles by carrying oil, grease, gasoline, pet waste, detergents, pesticides, fertilizer, and trash into the river. 

Overgrowth of algae in a river caused by fertilizer runoff

Rain should be soaking into the soil to replenish groundwater, but with more areas paved or covered with lawns that slope toward the street, it flows into storm drains instead. 

     Not wanting to be part of the problem for the river, in 2013 we agreed to install two 14-foot strips of porous paving in our driveway. One runs from a downspout at the corner of the house toward the street. The other crosses the width of the driveway alongside the sidewalk. 

     This material looks like asphalt but allows water to flow through to a layer of crushed stone which holds the water while it gradually percolates into the subsoil. When it rains, we can see that water no longer flows down the driveway into the street. As the water reaches the porous paving, it disappears into the ground.

Water drains through the darker porous paving

     Our sandy soil drains fast. We never see flooding in our yard. Rainwater falling on soil sinks into the ground and doesn’t flow toward the neighbors’ paved parking area behind our lot. So the porous paving in the driveway is enough to prevent storm water from running off our property.

Rainwater doesn't flow off the berm at the back of the yard

     Rainwater streaming from downspouts and driveways into the street now looks to me like a waste. Instead of watering with purified tap water, we could be collecting storm water and using it in our gardens. I calculate that the rain falling annually on our 1,900-square-foot roof could supply just about all the water I use for irrigation. 

     So have I been harvesting water that falls on the roof? No, I’m sorry to say I haven’t. The obstacles are cost and the prospect of digging a huge hole in the garden for an underground cistern. Maybe 

someday. Meanwhile, I’m enjoying the irrigation that’s falling from the sky.

Diverting some rainwater with a rain barrel