The Utah backcountry is a wild and uncontrolled place. This is good. But there are lots of ways of getting yourself in trouble, and a prudent visitor will be prepared to manage the risks. Managing the following hazards well will enable you to return for more fun.
Flash Flooding is an important problem for every canyoneer to understand. Almost every adventure has some element of Flash Flood Danger; the key thing to understand is floods are predictable and avoidable. Since this is an important and rarely analyzed subject, I shall spew forth in detail:
Here's how Flash Floods work:
One of those impressive late-summer thunderstorms builds up, sucking all the moisture into the sky, making huge, grand and impressive thunderheads.
The thunderstorms get too big, too tall, "overdeveloped." The thunderhead collapses, and all that moisture falls out of the sky in an amazingly intense rain, often accompanied by hail.
The storm drops a very large amount of water over a small area, in a small time. The desert soil, baked by the summer heat, does not absorb much of anything, and the water runs off.
Runoff collects in gulleys, which lead to washes that lead to canyons. Because water runs faster when deeper, the water collects into a bit of a leading wave. Downcanyon, we hapless hikers are trapped in the narrow canyon when the water reaches us, concentrated by the narrow canyon walls. Death or discomfort occur.
It need NOT storm where you are to flash flood the canyon you are in, it only needs to storm somewhere in the watershed above you. This can be quite a distance. For example, in the San Rafael Swell, the lower part of Eardley Canyon/Straight Wash is fed by a large area near I-70, up to 12 miles away; in another especially difficult case, the Chute of Muddy Creek is fed by Upper Muddy Creek, which has a very large collection area from the central Swell to the Wasatch Plateau, 50 miles away. Bluebird skies above may provide no hint of the storm cell pounding the distant headwaters.
A flash flood does not arrive in one big wave, like on TV. Instead, it tends to arrive in numerous small waves, building quickly to a massive, churning maelstrom. I once just missed seeing the Muddy River rise from 1 foot deep and 15 feet wide to 6 feet deep and 30 feet wide, charging like a mad locomotive with big trees churning up and down - all in 15 minutes! Yikes! I almost spent the night across the river in my shorts and sandals, and some friends were almost swept away in the middle of the night. In that case, the thunderstorm was many miles away and a couple hours earlier.
Protect yourself from flash flooding: Be smart.
During certain times of the summer (May-October), an annual weather pattern sets up bringing moist air in from the Pacific off Mexico, and big thunderstorms form almost every day. This is known as 'The Monsoon'. Pay attention to the weather forecast. Pay attention to the sky.
Do NOT go Canyoneering during the Monsoon.
Do NOT go Canyoneering when there are big thunderstorms forming.
That's pretty much it. It is pretty easy to predict that it WILL thunderstorm, but difficult to predict exactly where. But you don't really need to know that. Basically, you can predict with fair certainty, that 3 or 4 canyons will flash somewhere in the Swell. Now, call me timid, but knowing that, I'm heading to Ray's Tavern for a day of shooting pool and $1.50 Bud longnecks, rather than playing Canyoneering Roulette with Mr. Thunderstorm.
Some Flash Flood Rules of Thumb:
If the Thunderheads are already forming by noon, things are going to be bad.
If you cannot see through the rain falling from a thunderstorm, it is strong enough to create a flash flood.
Once the rain begins, flash flood conditions can develop in less than 5 minutes.
If your inner gut says 'no', listen to it. Go do something else.
However high you think you need to be to be safe from the flood, go at least twice as high.
If getting caught, do not try to outrun the flood unless you are very close to the end. Instead, find a place where you can climb out of the canyon or to a secure place HIGH on the canyon wall.
When camping in a narrow canyon, camp high above the canyon floor, above any signs of previous floods. Camp somewhere with safe pathways to go higher if needed.
Read more about flash flood examples and stories, below.