Trap Efficiency of Silt Fences Used in Hillslope Erosion Studies

Abstract

Renewed interest in land management practices, like conservation tillage techniques on agricultural lands andtimber harvesting, prescribed fires and wildfires on forested lands has made it desirable to measure hillslope soilerosion. Measuring soil erosion is generally costly and time consuming requiring expensive equipment, many sitevisits and laboratory analyses. The objective of the study was to determine the suitability of silt fences for measuringonsite hillslope erosion. Silt fences are low-cost and easy to install. They commonly are used as an erosion controldevice for construction projects and therefore generally available. For this study a silt fence was installed at the baseof an existing long-term hillslope erosion plot at the Agricultural Research Service-Palouse Conservation FieldStation, Pullman, WA. Two seasons of erosion data were collected. The silt fence was installed by making aconcave cavity facing upslope such that runoff could not go around the silt fence. Also, the silt fence was foldedto form a pocket to collect the sediment and eliminate the possibility of undermining the silt fence. Silt fences wereinstalled across the width of the plot. The trap efficiency was determined by measuring the collected runoff andsediment that flowed through the silt fence compared to the sediment trapped by the silt fence. Results indicate thatthe mean trap efficiency was 93 percent the first year when measured on a storm-by-storm basis and 92 percentefficient the second year when only measured at the end of the runoff season. Thus various time intervals can beused depending of the detail of the erosion rates that are of interest, for example after every storm or seasonallywithout compromising its trap efficiency.