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Author Keywords

forest fire, Rosgen field methods, stream bank alteration, Dixie National Forest, East Fork Virgin River watershed, monsoon-dominated stream systems

Abstract

The alteration of a stream’s morphology and recovery following a watershed fire is well documented in streams where high flow events occur during spring runoff. However, there are very little data regarding the alteration and natural recovery of streams that have high flow events during the late summer monsoon rains. Stout Canyon, a tributary to the East Fork of the Virgin River, is located approximately 30 miles southeast of Cedar City, Utah, and is a monsoon-dominated stream system whose watershed was burned by the Shingle Fire of 2012. Employees of the Dixie National Forest have monitored Stout Canyon since 2002, using Rosgen Field Methods. The alteration and recovery of Stout Canyon after the fire were documented using the same methods. The comparison of the pre-fire and post-fire data demonstrates how the fire altered the morphology of Stout Canyon. The data were also compared to similarly collected data from three snow-melt-runoff-dominated streams in the Rocky Mountain area whose watersheds have also been disturbed by fires. Bank full indicators began to reappear at Stout Canyon three years after the fire, suggesting that the stream is just beginning to redevelop its floodplain. Some results match the general trends that occur in spring runoff-dominated systems. However, major differences between Stout Canyon and other streams appear in bank geometry. In most streams, the largest changes in bank geometry occur within the first year after the fire with minor alteration occurring in the subsequent years, with bank re-stabilization within about three years. Stout Canyon’s banks, however, saw the most alteration during the second year after the fire and it is continuing to undergo major alteration with no signs of stabilizing three years after the fire. This may be a result of the fact that monsoon-caused high-water-events vary greatly from year to year, whereas snowmelt-runoff-caused high-water-events are generally more consistent. Through the course of the study, monsoonal rains led to erosion rates that were ten times greater than spring runoff. The inconsistent high water events on streams like Stout Canyon make it difficult for the stream banks to stabilize as efficiently and quickly as observed on other streams in the Rocky Mountain Region. The information presented here may be applied to other monsoon-dominated-systems to determine proper preventative and restoration methods.

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