April 04, 2004

Permacultural Simplicity Illustrated

Category: Environment

swales.jpg

Tucson: The aerial photo above illustrates something both fascinating and incredibly simple. Sometime during the great depression, a works project went out into the desert near Tucson and built a series of swales. They're little more than mounds of dirt about 5 feet high and 100 feet long, built more-or-less perpendicular to the flow of water over that section of the desert. After that, they were forgotten.

Looking at the satellite photo, you can see where the swales are because of the vastly thicker vegetation that has grown up behind them. It doesn't take a genius to figure out that the swales slow the normally brisk desert floodwaters, giving plants more time to soak up the precious liquid, and over time a far more lush planted environment springs up in contrast to the more barren creosote drylands around it.

The purpose of these swales is lost in history, but the obvious effect they have on the water supply should be impressive enough to convince western cities and dryland agriculturalists to look beyond their standard (and wasteful) irrigation systems and consider the many free alternatives!

[more on dryland permiculture]

Posted by Nick at April 4, 2004 06:21 AM | TrackBack

Comments:

way cool! I assume this satellite photo is recent? do you know how long it took to get to this state (which I assume is now stable)?

Posted by: sam on April 5, 2004 03:49 AM

The swales were built in the 30s, so it's been 70 years or so. I'm not sure how recent that photograph is, but I went out to the swales in person, and there are a lot of full grown trees there at a vastly greater density than the surrounding area, it's like a mini jungle!

Posted by: Nick on April 5, 2004 04:56 AM

Its a cool image. What are the effects downslope? Are there swales and riparian areas near streams that were green and are now being deprived of that water?

Posted by: Ben the Geographer on April 7, 2004 04:23 PM

Yeah, good point - if you were to really go nuts with this, then you would probably deprive a certain amount of downstream use, but it's more of a "slowing" of water flow than an outright dam, in fact, it's possible to actually provide more water downstream - in the form of a smaller, but constantly flowing stream that seeps from the swales rather than the intermittant deluges that would otherwise result. I'll look for an example that proves this...

Posted by: Nick on April 12, 2004 08:19 PM

Agree completely with the alignment issue - such a simple concept so seldom seen and the explanation is unfortunately shallow. Developments are typically prepared first by urban planners who focus on regulatory codes, maximizing profit from land use, and coordinating with development entities. It is only downstream in the process where the engineer is handed a ‘bubble map’ and told to design the drainage system and utilities infrastructure for street alignments that nine times out of ten are perpendicular to natural flow lines, not to mention woefully inadequate for including the areal space required by modern code governing detention and water quality. This is where the bailing wire and bubble gum enter the design.

The segregation of technical disciplines is part of the reason ecosystem design is burdened by a bad reputation (aside from some initial enforcement aggressiveness that lacked the defensive technical strength .) The example cited is a terrific step forward since it indicates that technical IQ and disciplinary integration are penetrating a traditionally political process (especially the zoning and development issues) that was made even more partisan with the introduction of environmental legislation.

Regarding the use of swales for flood control purposes, it is not a popular concept except in isolated green areas of the country (Denver and Seattle are notable) because they require too much land to be cost effective relative to alternative channel linings, and working the ecosystem ‘benefits’ into a cost analysis is still little more than a wild guess (that contingency valuation may or may not improve upon.)

And, as noted upthread, any alteration in the existing hydraulics of flow conveyance impacts riparian water rights issues in a complicated way that is still largely analytically intractable, which is to say, a ‘sophisticated’ computer simulation model is used. As far as I know, I am still a minority opinion when I say that the mathematics is not appropriate for current demands posed by ecosystem simulations, most of which are so plagued by ‘butterfly‘ effects that a weather model type system run by supercomputers is required. Not many developers willing to fork over that kind of money for a few desert trees so it becomes incumbent on the engineering designer to work closely with an ecosystem specialist to develop a plan that is ‘not too expensive,’ but gives the developer green credits.

Too long, but there are many reasons why ecosystem design is usually found on the Simple Stupid side of the divide.

Posted by: Patience on April 24, 2004 11:13 PM
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