Galloway Wash Boulders
March 18, 2008
This photo shows the normal conditions along Galloway Wash in Cave Creek, Arizona. Flooding is a formidable hazard in the desert southwest. Monsoon thunderstorms can fill dry washes with fast-moving muddy water in a matter of minutes. A police officer was swept to his death in a rescue attempt in Galloway wash about 30 years ago. Many local roads cross these washes without bridges for two reasons. The washes are dry nearly all of the time, and sound bridges are expensive because they must be built to withstand unusual forces.
A major flood, estimated to be a “100 year event,” occurred here on July 31, 2007. It's believed that 5,000 cfs (cubic feet per second) of water was rushing through this location at a depth of 5 feet (just over 1.5 m) and a speed of 9 mph (just under 15 km/h). The hundreds of people who live north of this crossing were stranded on one side or the other for several hours.
The power of the water is illustrated by this two hundred pound boulder, which was lifted about 4 feet (just over 1 m) and left stranded on a well anchored but stripped cottonwood tree. In fact, during this flood, spectators could clearly hear and actually feel boulders bouncing across the road. Large sections of concrete and pavement from a major crossing about half a mile (0.8 km) upstream were also scattered about. A million dollar bridge in this location is currently under consideration to allow emergency access for the homes to the north.