High Water Everywhere
So high the water was risin' our men sinkin' down
Man, the water was risin' at places all around,
boy, they's all around
It was fifty men and children come to sink and drown
A verse from Charley Patton’s 1929 High Water Everywhere recalling the devastating
1927 Mississippi River flood, which killed nearly 250 people and displaced 700,000 more.
Floods and Debris Flows
Floods are among the most common of geologic hazards in the U.S. They occur in every state and cost upwards of six billion dollars annually.
On average, most river systems flood every year or two. A flood occurs when water leaves its confining channel and flows outward onto the adjacent floodplain. There are two types of floods: regional floods that last for weeks or months, and flash floods that occur suddenly and last only hours. Both floods are dangerous and capable of doing substantial damage to homes, property and infrastructure. Each year about 140 people are killed by floods in the U.S.
Arizona is home to both regional and flash floods. While regional floods can involve large and small river systems, it is Arizona’s perennial rivers – the Colorado, Salt, Gila and Verde Rivers – that are most heavily impacted.
Read Kyle House’s excellent review article, Floods 1993, recalling the severe statewide flooding linked to the 1993 El Nino. Flood damage that year was estimated at about 50 million dollars. US Highway 95, just east of Yuma, Arizona, closed for nearly six months as the swollen Gila River slowly drained of flood waters.
Flash floods rarely cause major economic impact, but they can be murderous (See a local flash flood video here). On 12 August 1997, 11 tourists hiking in Antelope Canyon near Page, Arizona, were killed by a flash flood that had its origin in a distant, unseen cloudburst. Flash floods commonly occur during Arizona’s monsoon season, usually driven by local, short-lived rainfall events. In the event of a flash flood: to stay safe, stay out of the water. The Arizona Legislature enacted the “Stupid Motorist” law (statute 28-910) to penalize drivers who drive around barricades in a foolish attempt to cross flooding streams.
Debris Flows in Arizona
Imagine a flood comprised largely of coarse particles -- sands, cobbles and boulders -- and containing only about 20% water. That is a debris flow; a viscous flood with the consistency of a wet concrete slurry.
Debris flows characteristically occur on steep slopes where loose, unconsolidated Earth materials – soils, vegetation, regolith, and rocks – are set in motion during heavy rains or snowmelt. Debris flows move downslope rapidly, easily attaining velocities of 20+ miles per hours; their fine-grained relative, mudflows, have been clocked traveling at 90 miles per hour in steep mountain canyons. Debris flows are capable of great damage and loss of life.
For an excellent article on recent debris flows in Sabino Canyon, Tucson, Arizona, read Phil Pearthree’s and Ann Youberg’s Recent Debris Flows and Floods in Southern Arizona 2006.