Excerpt from Valley 101: A Slightly Skewed Guide to Living in Arizona, a collection of Clay Thompson’s columns for The Arizona Republic. (Originally published July 11, 1999.)

Q: What are the canals for, and how do they work?

A: Bibbity, bobbity boo. Next question, please.

Oh, all right, we’ll tell you: Farms and gravity.

Really.

The miles and miles of canals maintained by the Salt River Project were put there to bring water to thirsty acres of alfalfa, cotton, citrus and dates. Although there are a few pumping stations along the way, nearly all the system operates on the principle that water flows downhill.

That’s what worked for the Hohokam, who dug the first canals about 1,300 years ago to water their corn, beans and squash.

Canal System near Shea & Frank Lloyd Wright in Scottsdale. Photo Credit: Kevin Korycanek

The ancient ones had quite a little civilization going—check out the Pueblo Grande Museum in east Phoenix — before they vanished about 500 years ago, probably chased off by a long drought. By the time the Europeans arrived, the desert had reclaimed the Hohokams’ 135 miles of canals.

In 1867, Jack Swilling, a former Confederate soldier living in Wickenburg, realized what those lines in the sand meant. He formed the Swilling Irrigation Canal Co. and dredged out one of the canals. A meager harvest resulted and—voila!—agriculture was reborn in the Valley, and Phoenix had a reason for being.

The subsequent flood of farmers expanded and improved the canal system, but they lacked what the Hohokam had lacked: a way to tame the Salt, which actually had water in it in those days. The problem was, it either had too much water or not enough.

Enter the Salt River Project, an interesting animal. It is really two entities: the Salt River Valley Water Users Association and the Salt River Project Agricultural Improvement and Power District.

This gets a little confusing, so pay attention. The water side of SRP is a private corporation. The electric side of SRP is a political subdivision of the state of Arizona. That’s why, depending on what part of town you live in, you find candidates for the board of directors on the ballot when you go to vote for governor or county supervisor.

The Water Users Association was founded in 1903 by landowners who wanted the feds to build a dam on the Salt. They basically pledged their land against the cost of building Roosevelt Dam, which was completed in 1911 and named for President Teddy Roosevelt, who had signed the enabling legislation and turned up for the dedication. (Amazing true fact: The first water over the spillway of the new dam was bottled and used to christen the USS Arizona, which met an untimely end at Pearl Harbor.)

Anyway, in 1937, when the Depression was making it tough for farmers to meet the debt payments for the dam (which wasn’t paid off until 1955), the Legislature established the power side of SRP as a political subdivision of the state. That enabled the district to sell tax-free municipal bonds to help pay off the dam debt.

If you live within the boundaries of the SRP’s water district, which are not necessarily the same as the power district’s boundaries, you get SRP irrigation water from the canals. That’s why in some older parts of the Valley you see berms built up around the lawns—to hold in the irrigation water.

Of course, growing Bermuda grass wasn’t what the canals were built for, but most of the cropland that once covered the Valley has given way to houses and Home Depots.

The major canals actually are owned by the federal government, but maintained by SRP. They are mostly controlled today by computers and remote sensors, but in the old days, keeping the canals flowing was the job of zanjeros — ditch riders — who patrolled the canal system. Some irrigation services still call their workers zanjeros.

Now the real newcomer question — the one you’re too embarrassed to ask: Where does the water come from?

In the years after construction of Roosevelt Dam, a series of five dams—three on the Salt and two on the Verde—were built to help store water from the rivers’ 13,000-square-mile watersheds.

Those dams created the various lakes—Canyon, Saguaro, etc.—where you go to fish or water-ski.

That’s why there’s no water in the Salt — not counting Tempe’s new Town Lake: It’s all damned up upstream. The water enters the SRP canal system at the Granite Reef Diversion Dam below the confluence of the Salt and Verde in the far East Valley.

And that is why, even though you came here to get away from the snow, you should care how much snow falls in Arizona’s central and eastern mountains. That snowmelt keeps the lakes filled.

The watershed is not the Valley’s sole source of water. SRP and various cities pump groundwater and the Central Arizona Canal, a huge undertaking, delivers Arizona’s share of Colorado River water to the Valley and Tucson.