29 Jun 2008

Acequias -- Community Irrigation

Irrigated agriculture has existed for thousands of years, and interesting institutional solutions have sprung up to deal with location- and community-specific water conditions.

In areas colonized by the Spanish, these organizations are called acequias (NM acequias association), and we can learn about sustainability from observing how they managed scarce water over the centuries, and how they are dealing with modern problems of water transfers, oil drilling, legal jurisdiction, etc.

I particularly like this description of the unintended consequences of "efficient" canal lining:
When the water is pulled out of the river and placed in canals within a mile (usually much less) along the valley floor and run through flood irrigated fields it is never really leaving the system, just being channeled and any excess is returned to the river via drains and groundwater recharge. This channeling mimics the flood plain of the river.... Also I think there is some evidence to support the idea that the lined ditches are not much more water efficient.*

I grew up on an acequia (ditch) that had all the characteristics of a small stream. It was lined the native Rio Grande cottonwood with native plants and foodstuffs, including onions, wild marijuana, berries, etc...you could even catch trout in it. A little microclimate existed along the ditch and as kids we spent our spare time in the cool, shady strip along the ditch.

When I was a kid up until my teens every spring people along the acequias in the valleys worked to clean the acequias readying them for the seasons water. Men and young boys dug them out and cleaned them and women along the way kept them the men fed and watered. It was a kind of social event and I remember the boys in high school talking about it and looking forward to it. It was also an opportunity for the girls to see what guys were good workers, you got to see them working with their shirts off, the guys would work in competition to impress the girls, you got to take them water or food that maybe you made (a chance to show off your cooking abilities)... it was a cultural ritual every spring in the north where the acequias still exist.

Then sometime when I was in college somebody decided it would be more water efficient and perhaps labor efficient to cement line the acequia. Within a few years all the cottonwoods died and eventually fell down, the plants along died and the acequia is little more than a dry, hot parched cement channel running through the valley with zero aesthetic appeal and probably significant evapotranspiration occurring with no significant natural habitat or wildlife corridors. And so died a cultural tradition on that acequia.
Bottom Line: Just because its old doesn't mean it's not useful.

* Canal lining concentrates water in one area by reducing seepage to other areas. The areas that capture more water through lining are better off, but the system as a whole may not be. This result shows up in the controversial lining of the All-American Canal, which hurts the Mexicans and environment but supplies cities near San Diego with "extra" water.

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