Year of Award

2013

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Resource Conservation

Department or School/College

College of Forestry and Conservation

Committee Chair

Peter R. Robichaud

Commitee Members

Andrew Wilcox, Cara Nelson, Mike Patterson

Keywords

BAER team, soil erosion, treatment, wildfire

Abstract

Increased sedimentation caused by post-fire flooding is a risk to people, homes, and buildings. The USDA Forest Service installs straw bale check dams in ephemeral channels to reduce sedimentation rates from small catchments. We set out to study if straw bale check dams effectively reduce sedimentation rates from five paired catchments following the 2010 Twitchell Canyon Fire in south central Utah. Each pair consisted of two adjacent catchments that had similar physical characteristics and areas, with catchment areas ranging from ~0.2 to 1.6 ha (~0.5 to 4.0 ac). For each pair we treated one catchment with four straw bale check dams per ha (two per ac) and left the other catchment untreated as a control. Sediment yields produced from catchments during 2011 and 2012 were measured as well as the mass of sediment trapped by individual straw bale check dam structures. We found straw bale check dams did not significantly reduce annual catchment sediment yields produced by 30-minute rainfall intensities (I30) equal to or less than 14 mm hr-1 (0.5 in hr-1), a 1-year return period event at the study area. The straw bale check dams were filled to sediment holding capacity early in the first post-fire year from sediment yields produced by 1- and 2-year I30 return period rain events, or by two rain events having less than 1-year I30 intensity return periods. Three of the five paired catchments did not capture the total 2011 annual sediment yields because sediment retention structures used to measure catchment yields were overwhelmed by sediment during large rain events, however reliable measurements indicate annual sediment yields of 19.53 to 25.71 Mg ha-1 [8.71 to 11.47 t ac-1] passed over already full straw bale check dams. Straw bale check dams were non-functioning during the second post-fire year, allowing 3.74 to 13.12 Mg ha-1 [1.67 to 5.85 t ac-1] of sediment to pass over structures. The mean mass of sediment trapped by individual straw bale check dams is 1.26 Mg (1.40 t). At a treatment rate of four straw bale check dams ha-1 (two ac-1), they trapped 5.87 Mg ha-1 (2.62 t ac-1) of sediment.

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