Flash Flood at Galloway Wash
November 10, 2014
Seven of the ten U.S. states with the most flood fatalities per capita are in the dry areas of the West; especially the desert southwest. How can these relatively dry regions have so many flood deaths? They're subject to summer monsoon storms that can dump several inches of rain in just a couple of hours. Soils are thin and rocky, so there's relatively little vegetative ground cover and rainwater runs off quickly. With on-going recent plate tectonic activity, streams have steep gradients and flow fast, especially when at flood stage. Fortunately, local zoning has been relatively successful in preventing damage to homes and properties. The major cause of these fatalities has been drivers foolishly (and often illegally) attempting to cross flooded stream-level crossings.
The above photos were taken from the same position at Cave Creek, Arizona, just one week apart. The stream volume in this flood is estimated to be roughly equal to half the flow of the Colorado River through the Grand Canyon. Yet, Galloway Wash is bone dry about 95 percent of the time. This is a privately owned bridge to just one property. At the public road, just 300 ft (97 m) downstream from here, stream level traffic was halted a few hours. There are about a thousand citizens who are completely blocked from access to their homes by flooding at this crossing. But it seems most of them don’t want a bridge as they consider this a normal part of life in Cave Creek. Photos taken on August 19, 2014 (top) and August 26, 2014 (bottom).
Photo details: Camera Model: Canon PowerShot SX50 HS; Focal Length: 4.3mm; Aperture: f/3.4; Exposure Time: 0.0040 s (1/250); ISO equiv: 160.