Why it floods every year in the Salt River Valley
If you never leave Phoenix, Arizona looks like a big, flat, empty desert that goes on forever. If you fly over it, you see that it's far from that. And since most people in Arizona live in Phoenix, and rarely get away, it's understandable.
For reference, in the photo above, at the top are the San Francisco Peaks of Flagstaff. At just about center is the Salt River Valley, where Phoenix and its surrounding communities are. If you know your geography well enough, you can find South Mountain, running mostly east and west, next to the much bigger Estrella Mountain Range, which runs mostly north and south.
Since Phoenix is in a desert, it doesn't rain much there. So if you've ever wondered why it floods, take a look at what is just uphill from it. Those areas, which in addition to getting rain, gets melting snow, drains directly into the Salt River Valley, going southwest. Arizona tips to the southwest, and mostly to the west, so all of that water drains down through the valley, and ultimately to the Gulf of California.
I've lived in Phoenix since I was a teenager, and I don't remember a time when it didn't rain, and snow, up in the northeast in the winter. And my research has shown that this uplifted area has been like this for millions of years, and even though it was cooler 10,000 years ago, during the last ice age, it still got warm enough in the valley to flood.
And the reason most people don't know anything about this isn't ignorance, it's engineering. Some of the most spectacular engineering on the planet has been done in Arizona to gather up the water, and control flooding. It's a fascinating study, and if you've done much hiking around the Valley, you have seen a lot of it. If all you've ever done is driven, it's mostly hidden. I've known people who have crossed the bridge over the Arizona Diversion Channel many times, and have never noticed it. Amazing that something that big can be hidden!
Personally, I find all of this fascinating, as I am interested in Phoenix history. So, no, there has never been a drought in the Salt River Valley, and yes, it has flooded every year for at least 10,000 years. The Hohokam would have known that, and the Phoenix pioneers would have known it, too. And if you don't, just thank the engineers, who are still working on it, holding back the flood waters.
Posted by Brad Hall