Monsoon Mayhem in Moab
Today’s post was supposed to be a look at heat inequality—from space! But then the flash floods came and washed it all away. Okay, not really, but the massive flash flooding that hit Moab this weekend, and all of the crazy videos of the same, were a serious distraction. So, we’ll save heat inequality for next time and take a quick look at what happened in Moab instead.
First, a bunch of rain fell on ground that had already been hit by some good monsoonal flow this summer. The weather data’s a little strange for the area right now, so determining exactly how much rain fell where is a bit tough. The National Weather Service’s Moab station shows measurable precipitation, but nothing remarkable (the gauge is at the airport, and the flooding came from the other side of town). One of the stations in Canyonlands, at The Neck, is better, clocking a total of 2 inches of rainfall on Aug. 19 and 20. That’s a crapload of rain for Canyon Country, by the way: That same weather station normally gets about .8 inches of rain during the entire month of August; so far this year it has received 3.8 inches. So, yeah, it’s a big monsoon, in case you hadn’t noticed. The Salt Lake Tribune reports that nearly 1 inch of precipitation fell on the area in a 30 minute period on the evening of Aug. 20.
On Saturday at 6 p.m., the USGS’s Mill Creek streamflow gage at the Sheley Tunnel (an irrigation diversion nine miles upstream from Moab) recorded a flow of 15 cubic feet per second—a gurgling little stream about the size of an irrigation ditch—and the gage height was 3.5 feet. Within an hour, the creek had swollen into a raging, 1,160-cubic-feet-per-second monster, with the gage height registering nearly 10 feet. It took about two hours for the surge to reach the streamflow gage just above where it joins the Colorado River (just downstream from Moab), where Mill Creek ballooned from just 8 cfs at 8:15 p.m., to 1,120 cfs at 10 p.m. It’s safe to assume the stream was even larger as it barreled through town, since some of its waters were diverted by, well, Main Street.
All of which is to say: In less than an hour, an irrigation-ditch-sized stream grew to something resembling the San Juan River as it runs through Bluff.
Had it just been water flowing down the creek, things might not have been too bad. But the water was also filled with debris, from branches and mud to rocks and entire cottonwood trees. In one video, a car floats by. It’s likely that some of the debris (except for the car) came from last year’s Pack Creek Fire burn scar, which is in the Mill Creek watershed. In at least one place, the debris piled up behind a bridge over the creek, creating a sort of dam that diverted a good portion of the massive flow onto nearby streets. Before long, the main drag was a river. The video below is a good, quick look at Highway 191/Main Street through Moab.
While local officials are deeming this a 100-year flood event, it’s not unprecedented. According to USGS records, Mill Creek at the Sheley Tunnel ran nearly as big in 2010, 1993, 1991, and 2009. I looked back at weather records for those years, and precipitation patterns are similar—a string of dry days followed by an intense downpour. The temperatures, however, were markedly cooler back then.
Still, the damage it caused does appear to be unprecedented. Here’s a great video by Michael Grindstaff showing the aftermath of the floods.
Several businesses were inundated by floodwaters, water was shut off to parts of town, and, as the above video shows, there is a lot of mud and debris all over the place.
Utah, in general, has been battered by extreme weather this summer. First it was drought, then high temperatures, and now heat combined with intense downpours. The mercury in Salt Lake City has topped 100 degrees F on 24 days so far this summer and has been in the 90s on most other days. Bluff’s temperature was in the triple digits on 13 days in July. And the state’s National Weather Service office has issued more than 77 flash flood warnings this summer, putting it on pace to beat the record, set last year, of 118.
One of those warnings was for the Zion National Park area on Aug. 19. Heavy rains caused the Virgin River, which runs through the park, to shoot up from about 80 cfs to nearly 3,000 cfs in a matter of hours. One of the the park’s most popular trails, the Narrows, actually is in the river. Several hikers were caught in the flood. One person remains missing.
But, of course, the monsoon mania and flash flooding have not been constrained to Utah, by any means. Even as Zion National Park teams searched for the missing hiker, about 200 people were stranded by flash flooding at Carlsbad Caverns National Park in southern New Mexico. The roads to Chaco Culture National Historical Park are open, but are reportedly “in very bad shape,” and shouldn’t be attempted without a 4x4. And if and when it rains next? They’ll become slippery-as-snot mudbogs once again.
Heavy rain hammered the Albuquerque area on Sunday night and into Monday morning, causing urban arroyos to fill up rapidly. The North Floodway Channel, a concrete drainage feature, shot up from 80 cfs to 4,000 cfs last night.
Oh, and get this! They have live arroyo cams in Albuquerque! Yet another way for me to procrastinate!
Apparently some intrepid souls in Tucson didn’t get the stay-away-from-arroyos memo:
And with that, we give you a few more streamflow gages from around the Southwest so you can see how the monsoon is playing out in the arroyos and rivers.
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