Arizona: Killer Flash-Flood near Payson

Anatomy of the Water Wheel Falls Flash Flood Tragedy:

On Saturday, July 15, 2017, at a popular swimming hole and recreational area near Payson, Arizona, a wall of water and debris surged down a stream, killing10 members of one extended family and injuring 4 others.  One of the bodies, that of a 27 year old man who was husband, father and brother of some of the others killed, was not found for several days.

The location of this tragedy is about 8 miles north of Payson, Arizona and about 6 miles south of the Mogollon Rim, the major east-west topographic dividing line that bisects central and eastern Arizona.  The swimming hole area, commonly referred to as Waterwheel Falls, is a popular and scenic recreational and hiking area near the confluence of two major streams, the East Verde River and Ellison Creek.  The watershed above the two drainages has many tributaries that reach northward to the Mogollon Rim.  The terrain south of ‘The Rim’ is deeply incised by canyons and drops precipitously about 1,000 to 1,500 feet, then drops less steeply along the major drainages such as Ellison Creek, which channeled much of the floodwater. Ellison Creek joins the East Verde River a short distance below the falls, where flood waters from both of these major streams combined.

25-0713_to_0806

The watershed area (circled). Ellison Creek comes in from the east, meeting the East Verde River which comes down from the north, forming the confluence of the two streams near Water Wheel Falls (smaller circle). Many small tributaries from the steep and deeply incised rim country feed into both streams. The numbered purple dots represent springs.

The recreational hiking and swimming-hole area extends from a half mile below the confluence of the two streams, adjacent the main Forest Service parking area for day use, to above the confluence and up both tributaries, but a much greater distance up Ellison Creek. The actual falls is another half mile above the confluence, eastward up Ellison Creek, or about a mile in total from the parking area.  Online accounts suggest hordes of people visit the area on hot summer days, particularly on weekends.

In June of this year, a wildfire, dubbed the Highline Fire, burned over 7,000 acres, a good portion of which was within the steeply eroded upper part of the Water Wheel Falls watershed along and just south of the Mogollon Rim. The Forest Service has even closed access to a portion of a major hiking trail within the watershed, the Highline Trail, that borders the wildfire area, as well as the area within the wildfire zone itself.  Notice of this closure can be seen on the Tonto National Forest website.

On the Tonto National Forest website, a public notice, ‘Highline Fire Public Safety Closure Order’ reads in part: “AREA DESCRIBED: All lands and trails South of the Mogollon Rim to the Highline Trail (trail #31) from Dry Dude Creek to the unnamed drainage just east of Ellison Creek. The Highline Trail is closed from Dry Dude Creek to Ellison Creek. PURPOSE: The purpose of the temporary Area Closure Order is to protect National Forest visitor and firefighter health and safety by eliminating potential for members of the general public entering into the Highline Fire burned area due to potential snag/falling trees hazards, re-ignitions, flash flooding and conflict with firefighting operations.” However, the notice and access restrictions were limited to the immediate wildfire zone and not the heavily used recreational and swimming area in the major drainages just downstream.

On Saturday, July 15, the southwestern ‘summer monsoon’ was kicking into high gear following a couple of months of very hot ‘pre-monsoon’ weather in the region. Thunderstorms were developing all along the rim that day.  In particular, a small but intense thunderstorm developed over the the rim adjacent the Waterwheel Falls watershed.  The storm very quickly grew and moved over the watershed, dropping heavy rain simultaneously into all the tributaries above Water Wheel Falls and on into the two major streams.   The run-off from the many small, steep tributaries just below the rim very quickly converged into a huge surge of water and debris down Ellison Creek and on toward its confluence with the East Verde River, which also flash flooded.

Initially the surge coming down Ellison Creek was more of a debris flow with rocks, logs, dirt and soot, as is typical of flash-floods in the Southwest. In this case, however, the amount of debris and rainfall runoff was greatly increased by the recent wildfire in the upper part of the watershed. This surging mass of water and debris roared down the canyons and through the Water Wheel Falls area at a high rate of speed, likely deepened and speeded up by the narrowness of the canyons within the busy recreational area. This, combined with the long period of hot, dry weather from which many young people from the Phoenix area were by this time seeking respite, added up to a ‘perfect storm’ for a flash flood tragedy.

Except for a few private inholdings, the entire drainage area, including the Water Wheel Falls site, is on the Tonto National Forest. One news interview I saw on a local TV station indicated no signage present for the hazard of flash-flooding at the parking area. Looking at Google photos of the site, of which there are some 150, two show the same informational sign at the parking area. On this informational sign are warnings in the form of posted pieces of paper protected by a plastic overlay about the hazards of bears, rattlesnakes, information on self-pay for day use per vehicle ($9.00), packing out your garbage, keeping your dog on a leash, ‘welcome to your national forest,’ but nothing visible about flash floods or even so much as a posted map of the area.  Online accounts indicate the access trails are relatively undeveloped, with most people rock scrambling up the East Verde River from the parking area, then turning east at the confluence up Ellison Creek to reach the falls. A close-up view on Google Maps reveals, as well, an ad-hock network of trails accessing the falls directly, bypassing the drainage after an initial crossing of the East Verde River from the parking area. Also, within this hodgepodge, there is a private inholding of land from the confluence area of the two streams westward a short distance up the East Verde River (USFS online map), with fencing and no-trespassing signs visible along the East Verde drainage (as described in comments on the area on trails.com).

It would appear that much more effort is needed by the Forest Service to properly develop the popular area for such highly concentrated recreational use as now exists. This might include, at the very least, park service-quality flash-flood interpretive and warning signs at the parking area and a properly developed hiking path and perhaps even a bridge, not to mention a buyout of the private inholding and removal of fencing. Of course, this all takes funding, funds probably not allotted the agency, even for such a dire local recreational need.

Hopefully, to prevent inevitable future such occurrences, such improvements will be considered.  (However, I wouldn’t hold my breath!)

As for rainfall amounts from the storm, nearby observers in Payson on the CoCoRaHS network reported about 0.90 inches of precipitation. S imilar amounts were recorded from automated personal weather stations in the area as seen on Weather Underground. These stations showed that most of the rain – around three quarters of an inch – fell in a period of a half hour, which is more than ample for significant flash flooding in this type of terrain.  As in much of the Southwest, probably all it would take for some degree of flash flooding in these drainages is a quick one quarter of an inch.

Below are radar images and satellite photos which graphically show the event.  What is striking is the rather mundane nature of the offending storm – one of many that develop over the southwest each day in the ‘summer monsoon’ season.   In particular, this event was spawned by a rather ordinary wave of scattered upland thunderstorms that developed over the Mogollon Rim and then spread southwestward toward the Phoenix Valley, yet ultimately resulted in the untimely deaths of 10 young people who happened to be in a very dangerous place when thunderstorms are brewing.

15-0713_to_0806

Here the drainage area is circled with a small but intense thunderstorm developing adjacent, just north of the rim. The cross hatch on the oval shaped circle represents the approximate location of the confluence and the falls.

16-0713_to_0806

22 minutes later, the storm, though still relatively small, is seen to be rapidly increasing in size and is pushing southwestward into the watershed area. The confluence and falls area is probably just outside the storm area (‘X’), but huge quantities of water are already falling onto the denuded and steep slopes to the north.  The flash flood is no doubt rapidly developing.

17-0713_to_0806

About 16 minutes later, a large lobe of the storm hangs over the Ellison Creek drainage, while a narrow arm of the developing storm extends westward. The falls area would be near the beginning of the narrow arm of the storm just off the larger lobe.

18-0713_to_0806

About 22 minutes after the previous image, the storm continues to grow and is moving into the town of Payson.  However, a major portion of the storm is hanging back over the watershed of both major drainages. Meanwhile, at the local Payson Airport (+ PAN) at a date/time of 15/2115Z the automated observation shows winds of 40 MPH, gusting to 54 MPH with a visibility of 3/4 of a mile in heavy rain with thunder.

19-0713_to_0806

About 17 minutes following the previous image, rain is lightening up over the drainage area as the storm moves southwestward. However, the Payson airport (+ PAN) at 2135Z reports visibility of 1/4 mile and a 400 foot ‘overcast’ (vertical visibility), both indicating extremely heavy rain.  There is no rain gauge at this lower-tier automated aviation wether observing site, but the temperature has dropped to 63 degrees from 90 degrees an hour earlier. The elevation at Payson is about 5,000 feet.

20-0713_to_0806

An hour and a half before the start of the storm, convective cumulous build-ups are developing all along the Mogollon Rim. The vicinity of Waterwheel Falls is circled. From the falls one would at this time merely see some billowing or towering cumulous off to the north and northeast, a common sight on summer afternoons.

21-0713_to_0806

An hour later and little less than a half hour before the first radar image when the storm is pushing in, clouds can be seen building further, with anvil tops indicating thunderstorms both northwest and southeast of the Water Wheel Falls area along the Mogollon Rim. Billowing tops in the circled area near the falls indicate rapid development and incipient storms. From the falls one might see tall billowing clouds nearby to the north and northeast, with anvil tops farther afield northwest and southeast  If one was weather wise and knowledgeable of flash floods at all, this would be the time to think about immediately evacuating the drainage area.

22-0713_to_0806

The storm is in progress over the drainage area, dumping heavy amounts of rain. If the flash flood has not yet reached the falls and confluence area, it is about to at any minute.

23-0713_to_0806

The heavy rain is done in the drainage and the flash flood has taken place. The storm has also mostly moved across the town of Payson but with light rain and thunder continuing there. A volunteer observer with the CoCoRaHS network located very near the falls reported 0.88 inches, with another observer in that network reporting 0.93 inches near the Payson Airport.

24-0713_to_0806

The storms continue to develop and push southwestward, later wreaking havoc with strong wind and heavy rain on Lake Pleasant, northwest of Phoenix.  A few locations in the Phoenix Valley were also eventually hit with flash flood magnitude rains, especially the far northwest valley near Sun City and also a small area west of the Scottsdale Airport, with both localized areas receiving around 8 tenths of an inch of rainfall in a short period.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s