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Rock gabion, rip-rap, and culvert treatments: Successes and failures in post-fire erosion mitigation, Schultz Fire 2010

Posted date: May 09, 2012
Publication Year: 
2011
Authors: Neary, Daniel G.; Koestner, Karen A.
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. 5 p.

Abstract

Following the Schultz Fire in June of 2010, several erosion mitigation efforts were undertaken to reduce the impacts of post-fire flooding expected during the 2010 monsoon. One treatment consisted of the placement of large rock rip-rap on targeted fill slopes of a high elevation forest road that contains a buried pipeline supplying water to the city of Flagstaff. Another treatment was culvert removal at 30 channel crossings on a forest road that transects the burn area at a lower elevation (Schultz Pass). On urbanized private lands below the fire, no road culverts were initially removed or upgraded. After initial post-fire flooding, a major, unarmored drainage ditch rated at a capacity of 14.2 m3 sec-1 was fitted with sixteen rock-filled wire cage gabions to reduce channel incision. Rainfall began in mid-July after the wildfire and produced multiple floods that caused substantial erosion, debris flows, and channel incision. The large rip-rap on the upper elevation road failed completely. Culvert removal at channel crossings within the forest functioned satisfactorily and prevented the addition of road fill and fill-breach surges to the stormflow. Road culverts in the urban area were grossly under capacity and were either buried or bypassed. The gabions in the drainage ditch functioned for a short time but were then bypassed, causing significant channel widening and transport of additional sediment. This paper takes a forensic look at these erosion control measures and discusses the reasons for failure or success. Recommendations are made for future use of these erosion control techniques.

Citation

Neary, Daniel G.; Koestner, Karen A. 2011. Rock gabion, rip-rap, and culvert treatments: Successes and failures in post-fire erosion mitigation, Schultz Fire 2010. 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. 5 p.