Trap efficiency of silt fences used in hillslope erosion studies

Robichaud, P.R.; McCool, D.K.; Pannkuk, C.D.; Brown, R.E.; Mutch, P.W. 2001. Trap Efficiency of Silt Fences Used in Hillslope Erosion Studies. Presented January 3-5, 2000, Honolulu, HI. In: Ascough II, J.C.; Flanagan, D.C., eds. Soil erosion for the 21st century: proceedings of the international symposium. St. Joseph, MI: ASAE. 541-543. ASAE Pub. No. 701P0007.

Keywords: Soil erosion, Geotextiles, Sediment control, silt fence

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Abstract: Renewed interest in land management practices, such as conservation tillage techniques on agricultural lands and timber harvesting, prescribed fires and wildfires on forested lands, has made it desirable to measure hillslope soil erosion. Measuring soil erosion is generally costly and time consuming requiring expensive equipment, many site visits and laboratory analyses. The objective of the study was to determine the suitability of silt fences for measuring onsite hillslope erosion. Silt fences are low-cost and easy to install. They commonly are used as an erosion control device for construction projects and therefore generally available. For this study a silt fence was installed at the base of an existing long-term hillslope erosion plot at the Agricultural Research Service's Palouse Conservation Field Station at Pullman, WA. Two seasons of erosion data were collected. The silt fence was installed by making a cavity facing upslope such that runoff could not go around the silt fence. Also, the silt fence was folded to form a pocket to collect the sediment and eliminate the possibility of undermining the silt fence. Silt fences were installed across the width of the plot. The trap efficiency was determined by measuring the collected runoff and sediment that flowed through the silt fence compared to the sediment trapped by the silt fence. Results indicate that the mean trap efficiency was 93 percent the first year when measured on a storm-by-storm basis and 92 percent efficient the second year when only measured at the end of the runoff season. Thus various time intervals can be used depending of the detail of the erosion rates that are of interest, for example after every storm or seasonally without compromising its trap efficiency.

Moscow FSL publication no. 2001g