Last week I discussed how cities can turn to gardens to help conserve water and reduce the strain on systems designed to take excess water to the sea. You can read the previous post here.

The photo above shows a variation on the classic ditch, part of a massive infrastructure project designed to master stormwater runoff in Seattle's Broadview neighborhood.

You remember ditches, right? They used to look like this:



Then people filled them in with dirt and gravel. This increased the parking. But the dirt compacted beneath the cars, and soon these surfaces too became impenetrable to water. That's why many streets now look like this:



The ecological future here is all about reconstructing the past. That's what engineers are realizing when it comes to stormwater management. The old world was squishy, absorbed the rain and let it out with a slow trickle and a sigh. The new world is fast like a waterslide, sending the whole storm sloshing into the ocean at once. So now that we know the old way worked better, we're trying to reconstruct it. The problem is, there's only a fraction of the land available to do that essential work. So the solutions must be highly engineered. And to my delight, those solutions look less like a public works project and more like a garden.

Seattle's Broadview neighborhood makes up much of the watershed feeding the creek running through Carkeek Park. The creek is a beautiful salmon spawning stream that runs through a lovely forest. But when there's a storm, the storm water mixes with sewage and coats the lovely estuary with toilet paper and you-know-what. Lawn fertilizers, weed killers, and pet waste all fed into the stream. The stream then meanders in picturesque oxbows across a beach where children play.


Carkeek Park, Photo by Jess, Beemouse Labs, shared via Flickr

So the city dug up all the streets and rebuilt them from scratch. The ditches are back, but their updated, radically more functional and beautiful than the old slots-in-the-yard that I remember from my youth.


Photo by Seattle Public Utilities

And while they are essentially infrastructure, they are also part ecological system, and part garden, because they provide such visual delight.



The flat streets were completely ripped up and rebuilt. Their new job was to collect rainwater. On the downhill side (left side of picture below), there's a big ditch, planted extensively with native plants and mulched heavily. There's no curb on this side, so that rainwater can sheet off into the ditch. The road slopes towards the ditch, rather than crowning in the middle as is typical. On the uphill side (right side of picture below), there's a sidewalk, then another, smaller ditch to catch the runoff from the yards on the uphill side.



Narrow new driveways were allowed where old ones existed, but everyone else was told to bring their cars in by the alley. Most alleys these days are underused and weedy, so this must have taken some getting used to. When the construction work wiped out everyone's mailboxes, the city replaced them by consolidating them in nodes, like the forest service consolidates heavily-used campsites in a pristine mountain wilderness.

Make no mistake, this was a bold decision, costing loads of money. A neighbor said it cost half a million dollars per block. And not everyone liked the idea. Ditches eliminated parking on one side of the street, and chopped some people's front yards in half (though only land in the right-of-way was reclaimed). There's an inherent conflict between accessing these houses and maintaining the continuity of the ditches. So the city built new concrete steps with welded tube-steel rails for everyone. Each city-built walkway is a little bridge, with a short section of culvert running below.



On the uphill-downhill streets, the ditches are larger. Here, the job was to accept run-off from the flat streets and slow it down as it went downhill. If possible, stormwater would be completely eliminated, allowed to seep into the groundwater. The ditches along the uphill-downhill streets contain chains of descending pools, built out of these elements:


A protected drain at the bottom;


dividing walls in the middle, separating the ditch into a series of terraced pools; and


a feeder culvert at the top, bringing in water from the side streets.

The project does have some problems. In some areas where there is no curb, vehicles are once again encroaching on the landscape. One neighbor complained that the city has no enforcement mechanism for protecting its plantings, and no funding to maintain them, though they're designed to require no maintenance. It seems the city still needs to clarify how much private property owners are responsible for maintaining the overall system. Below, a car compacts the new, highly-engineered soil.



People in the neighborhood have mostly come to appreciate the massive project. For one thing, it's eliminated a lot of basement flooding, according to one neighbor. He estimates the project increased his property value by quite a bit. As for myself, the neighborhood has become a major walking destination. I love to see how things are growing, how the city has slowly added new blocks to the project. I'm excited to learn the city plans to try a similar project in a very urban location next, much closer to downtown Seattle.

This project is forcing me to rethink what a garden can be. My garden works to provide my family with food, or flowers. This project is a garden too, for it also provides those things, though the food is mostly for wildlife. But there's a new inspiration in my garden diary these days. The hydrologic cycle, and stormwater management. These cycles are governed by their own unique rules. Leonardo DaVinci spent the last years of his life trying to discover those rules. When taken as inspiration, stormwater management can lead to new kinds of gardens with a fresh capacity to surprise and delight us.