Elementary Principles of Water
If you were ever lucky enough as a kid to play in the mud in a rainstorm, you probably observed a lot about hydrology without even knowing it. Grownups — if you weren't that lucky, it's not too late! Go outside in any downpour and watch as the land, usually stable and inanimate, comes alive as a conductor of water. A little observation in a rainstorm reveals the often forgotten power of water: erosion. Concentrated runoff from roofs, roads, and parking lots especially causes erosion, creating flows that cut against the natural topography of the land. This kind of erosion threatens to undermine our man made structures — San Luis Obispo County has spent millions of dollars constructing retaining walls to hold up roads and built pricey dikes to hold back water from homes and farm fields. Yet, the threat of erosion does not force a choice between sacrificing civilization to the underworld and paying dearly to create large, expensive means of controlling water and stabilizing structures. In fact, a simple saying nicely encapsulates the most effective way of dealing with excess water: slow it, spread it, sink it. It might even make a good nursery rhyme for kids to sing in a rainstorm.
Get Your Mind Out of the Gutter...
As a society, we have set our mind in the gutter when it comes to water. Even in dry areas, where water is a precious resource, it is pushed into a concrete gantlet that gets rid of it as quickly as possible. In the language of water, "gutters" are a mild insult. This way of controlling water does more to aggravate water's behavior than control it — wait for a 100 year rainfall event to see how. Of course, we need to control water. While most streets around the world deal with water by putting it in the gutter, at least one local group is working to make the gutter obsolete technology. Previously named as legalizers of sustainability in last month's column (Water: Part II), SLO Green Build has done it again. Working with local partners under the acronym SLO-COAT (the SLO Coalition of Appropriate Technology) they have unveiled their Manual for Low Impact Development. If you liked the Greywater Manual of last month, you'll love this. At the childish heart of their manual, our nursery rhyme: slow it, spread it, sink it.
Employing everything from trees to meandering swales, they find ways to keep a scarce resource around longer. Following the rule of thumb, these simple but creative technologies slow water down, lessening it's erosive power. They spread it out to increase evaporation and infiltration. They sink it into specially constructed cisterns and retention basins (swales) which store water in the soil itself. Check out their manual for design plans to help you put your water back in the air, into cisterns, into plants, into the soil — pretty much everywhere except into the gutter.
Oak Creek Commons Residents Digging a Swale to Hold Water from a Waterbar
- Photo by Greg Ellis
For those of us (myself included) who enjoy superimposing dollar signs on all of reality in a quest to understand and motivate human behavior, consider the following. SLO County receives an average of 21 inches of rainfall each year. For a simple 50 x 50 foot square lot this translates to nearly 33,000 gallons of water annually. Out of the tap, this water would cost anywhere from about $200 (in Paso Robles, based on future water rates) to about $400 (in San Luis Obispo)! So money is raining down from heaven — how can we keep it from going down the gutter?
Water in the 'Bank'
Oak Creek Commons co-housing, located in Paso Robles, has taken on a project to control erosion on a piece of it's 10 acre open space and hold water in the soil. The site consists of a pathway that goes up a small hill. The pathway has begun to deepen, scoured by water that concentrates along its compacted surface and runs downhill, carrying soil with it. A group of residents met early one morning in mid-August to beat the heat and begin construction on a water capturing and controlling device known as a waterbar. Consisting of a log dug-in crosswise to the trail, slightly inclined to one side to divert the water off the trial, a waterbar slows the water down, preventing erosion. Gravel placed on the uphill side of the log lessens the danger of tripping while still allowing water to flow. Once diverted off the trail, the water enters a swale — think of a ditch dug along the side of a slope on contour. The swale is not inclined and so holds the water instead of causing it to flow. Since the level swale is lower than the inclined waterbar, it holds water, spreading it out. Giving the water more contact with the soil helps it sink in. In addition, native plants (though a garden or fruit trees could be planted along a swale) will be seeded and transplanted to the sides of the swale, improving infiltration by loosening the soil with their roots. The benefit is two-fold: erosion is halted and precious water is stored in the soil.
Oak Creek Commons Residents Constructing a Waterbar – Photo by Greg Ellis
If you're interested in the swale, it has several variations: the Bioswale, the Keyline design and the Hugelkultur all offer much more diplomatic methods of controlling water, as well as keeping water in the 'bank'.
