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Rill and gully formation following the 2010 Schultz Fire

Posted date: May 09, 2012
Publication Year: 
2011
Authors: Neary, Daniel G.; Koestner, Karen A.; Youberg, Ann; Koestner, Peter E.
Publication Series: 
Paper (invited, offered, keynote)
Source: Paper presented at the 24th Annual Symposium of the Arizona Hydrological Society; Watersheds near and far: Response to changes in climate and landscape; September 18-20, 2010; Flagstaff, AZ. 6 p.

Abstract

The Schultz Fire burned 6,100 ha on the eastern slopes of the San Francisco Peaks across moderate to very steep ponderosa pine and mixed conifer watersheds. There was widespread occurrence of high severity fire, with several watersheds classified as over 50% high severity. This resulted in moderate to severe water repellency in most soils, especially those on steep slopes. Prior to the fire there were no rills or gullies as the soil was protected by a thick O horizon. This protective organic layer was consumed leaving the soil exposed to raindrop impact and erosion. A series of flood events beginning in mid-July 2010 initiated erosion from the upper slopes of the watersheds. Substantial amounts of soil was eroded from hillslopes via a newly formed rill and gully system, removing the A horizon and much of the B horizon. The development of an extensive rill and gully network fundamentally changed the hydrologic response of the upper portions of every catchment. The intense, short duration rainfall of the 2010 monsoon interacted with slope, water repellency and extensive areas of bare soil to produce flood flows an order of magnitude in excess of flows produced by similar pre-fire rainfall events. Rill networks now cover much of the upper slopes and gullies are cutting to bedrock. Sediment delivery to the channel systems is likely to continue unabated for many years and hydrologic response will continue to be flashy.

Citation

Neary, Daniel G.; Koestner, Karen A.; Youberg, Ann; Koestner, Peter E. 2011. Rill and gully formation following the 2010 Schultz Fire. Paper presented at the 24th Annual Symposium of the Arizona Hydrological Society; Watersheds near and far: Response to changes in climate and landscape; September 18-20, 2010; Flagstaff, AZ. 6 p.