Intermediate-Scale Experiments to Evaluate Silt Fence Designs to Control Sediment Discharge from Highway Construction Sites

Abstract

Soil erosion occurring at highway construction sites can contribute large amounts of sediment to the local stream network and degrades overall water quality. The environmental impacts of the sediment-laden stormwater runoff can be mitigated by employing appropriate best management practices BMPs. Silt fence is one of the most widely used BMPs at highway construction sites. Numerous field studies have shown that silt fence installations at highway sites have a high degree of failure due to flow around the end of the fence, and due to concentrated erosion along the toe of the fence. To address these problems, erosion control manuals often recommend installing a tieback also known as j-hook at the down slope end of the fence. However, no one has systematically studied the sediment removal efficiency of tieback designs to develop a rational procedure for field installations. In this research, we quantified the effectiveness of silt fence systems installed with tiebacks by comparing its efficiency against systems installed without tiebacks. We completed this compari- son study using an intermediate-scale laboratory model that was designed to study the erosion processes occurring at highway construc- tion sites. The model allowed us to observe various erosion and sediment transport processes in a controlled setting. The results show that silt fence installations utilizing tiebacks remove sediment primarily through the process of sedimentation, not by filtration. Installation of a tieback improves the ability of the silt fence system to act as a temporary detention basin and greatly enhances the system's ability to remove suspended particles by sedimentation. Our experimental data shows that a well designed silt fence with tiebacks can remove up to 90% of solids transported by the runoff water.