Effectiveness of straw bale check dams at reducing post-fire sediment yields from steep ephemeral channels.

Robichaud PR, Storrar KA, Wagenbrenner JW. 2019. Effectiveness of straw bale check dams at reducing post-fire sediment yields from steep ephemeral channels. Science of the Total Environment 676 (2019) 721–731. https://doi.org/10.1016/j.scitotenv.2019.04.246

Keywords: Straw bale, Check dam, Trap efficiency, Erosion, Silt fence, Rainfall intensity

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Abstract: Post-fire flooding and elevated sediment loads in channels can pose hazards to people and structures within the wildland-urban interface. Mitigation of these hazards is essential to protect downstream resources. Straw bale check dams are one treatment designed to reduce sediment yields in small ephemeral catchments (b2 ha). This study investigated their effectiveness in five paired catchments burned at high severity during the 2010 Twitchell Canyon Fire in Utah. Rainfall, ground cover and hillslope erosion rates were also measured during the two-year study. Adjacent paired catchments were physically similar and ranged in size from 0.2 to 1.6 ha across pairs. Within pairs, one catchment was an untreated control and the other treated at a rate of four strawbale check dams ha-1. High intensity rainfall, erodible soils and slowregrowth contributed to the observed high hillslope sediment yields (N 60 Mg ha-1). 1- and 2-yr I30 return period rain events early in the study quickly filled the strawbale check dams indicating the treatment did not statistically reduce annual sediment yields. First year annual sediment yields across all catchments were 19.6 to 25.7 Mg ha-1. Once the check dams were full, they had limited storage capacity during the second post-fire year, allowing 3.8 to 13.1 Mg ha-1 of sediment to pass over the check dams. The mean mass of sediment trapped by individual straw bale check dams was 1.3 Mg, which allowed them to trap a mean of 5.9 Mg ha-1 of sediment at the given treatment rate. Straw bale check dams trapped b50% of the total mass delivered from catchments with efficiency decreasing over time. Increasing straw bale check damtreatment rate in stable channels may improve trap efficiency. Application of this treatment in areas with lower expected rainfall intensities and less erodible soils may be justifiable.

Moscow FSL publication no. 2019e