Arizona Geological Survey OPEN-FILE REPORT OFR 08-06

Arizona Geological Survey
A direct comparison of study canyon morphometrics with reported data describing debris‐flow prone
basins is difficult, as reported data are either from regions with very different climates (Wilford and
others, 2004) or from highly disturbed basins (Cannon and Gartner, 2005). In addition, all of the study
canyons have evidence of past debris‐flow activity. These data are more useful for assessing the
influence of basin size and channel gradient on debris‐flow conveyance and potential runout distances.
A review of Table 1 shows that the largest basins also have the lowest channel gradients: Aqua Caliente,
La Miligrosa, Molino, Bear and Sabino Canyons. Three of these canyons – Molino, Bear, and Sabino –
had debris flows in 2006 (Webb and others, 2008). Debris flows in these canyons formed on steep
sideslopes, flowed into the main channel and either terminated at the channel junction or traveled a
short distance downstream before depositing.
In contrast, six smaller, steeper basins with debris flows in 2006 behaved differently. These canyons
include Soldier, Gibbon, Bird, Esperero, Ventana, and Rattlesnake Canyons. Debris flows in Esperero and
Ventana Canyons were limited to the upper watersheds (Webb and others, 2008), while debris flows in
Soldier, Gibbon, Bird and Rattlesnake exited or almost exited the mountain front. In Rattlesnake Canyon
slope failures coalesced into a debris flow which traveled 2.4 miles downstream into Sabino Canyon
where 15 ‐20 feet of sediment was then deposited (Webb and others, 2008). Debris flows in both
Gibbon and Soldier Canyons exited the mountain front and deposited in developed areas. Debris flows
in Bird Canyon also exited the mountain front but were confined within a deeply incised channel. Basin
responses to the 2006 rainfall indicates that smaller, steeper basins have a greater potential for exiting
the mountain front than those generated in larger basins with lower‐gradient channels.
Figure 12. Stream profile plots of the three largest study basins. Bear and Sabino Canyons has debris
flows in 2006. Sabino and Bear Canyons had debris flows in 2006.
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