Saturday, May 20, 2017

Revisiting the 2006 debris flow of Santa Catalina Mountains

Bouldery debris flow levee, Santa Catalina Mtns. 

Historic rainfall precipitates 100s of debris flows | For five days in late July 2006, the mountains of southern Arizona received unusually heavy rainfall.  A final burst of precipitation on the morning of 31 July produced over 400 hillslope failures in the Santa Catalina Mountains of Pima County (Fig. 1).  In drainages near Sabino Canyon, a popular hiking and tourist destination, masses of unconsolidated soil, rock and vegetation coalesced into debris-flows that traveled to the mouths of several canyons.  

Fortunately, the 2006 debris-flows did not result in any injuries. There was, however, considerable damage to some canyon roads, outbuildings, and hiking trails.  At Gibbon, Soldier, and Bird Canyons debris flows nearly reached or spilled out of canyon mouths. The 2006 debris-flows were much larger than any that had occurred historically in the Santa Catalina Mountains, raising new concerns about the potential for damage to roads and homes near many canyon mouths in the Catalina Foothills.  

Map showing distribution and ages of debris flows.
Debris flows have occurred before and will occur again at the canyon mouths of the Catalina foothills. (Phil Pearthree, then AZGS chief of environmental geology.)

Mapping Shows 20,000-year History of Debris Flow Activity | In addressing homeowners concerns, the Pima County Regional Flood Control District contracted  the Arizona Geological Survey (AZGS) and the US Geological Survey (USGS) to map and date debris-flow deposits in 15 canyons along the southern face of the Santa Catalina Mountains  (Fig. 2).  AZGS research scientist Ann Youberg headed a team of mappers to produce high resolution, 1:6,000-scale maps on a color aerial photographic base. (At 1:6,000-scale, one inch on the map equals 500 feet on the ground.)

This post was cribbed from "A 20,000 year record of debris flows in the Santa Catalina Mountains of southern, Arizona". 
Posted 5/20/2017

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