Practical Silt Fence Enhancements for Enhanced Stability and Dewatering

Many of today’s construction sites rely on perimeter control practices to capture and treat sediment-laden stormwater emanating from disturbed lands. Silt fence systems are a common sediment control practice often specified by stormwater designers to be installed as perimeter control applications. While design considerations are often given to the location and placement of these systems within the boundaries of a site, design characteristics of the silt fence itself (e.g., post size, post spacing, fence height, etc.) are rarely taken into consideration. As a result, silt fence systems often become overloaded and fail due to insufficient support or lack of effluent flow capability. Thus the goals of this study were to: (1) design and evaluate a silt fence system that had the ability to effectively discharge flow at controlled rates while maintaining sediment retention and water quality standards, (2) determine the structural capacity of common support posts used during the construction of silt fence systems, and (3) develop guidance for specifying post spacing distances based on manufactured post specifications. Results from full-scale testing suggest the inclusion of a dewatering mechanism resulted in 96% sediment retention and effluent water quality data similar to results associated with standard silt fence installations. Silt fence dewatering time was reduced from over 24 hours to four hours with minimal downstream disturbance of soil and vegetation. Finally, structural analysis data from five common silt fence support posts was used to determine post spacing based on structural load limits. Using this data and in-field observations, recommended distances for post spacing were developed for each support post type evaluated.