Practical Silt Fence Design Enhancements for Effective Dewatering and Stability

Abstract

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. Although 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, and fence height, among others) 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, this research effort sought to identify and evaluate practical methods for managing the discharge of impounded stormwater and improving the structural stability of silt fence systems. Results from full-scale testing suggest the inclusion of a plywood 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 to 4 h with minimal downstream disturbance of soil and vegetation. Finally, structural analysis data from five common silt fence support posts were used to determine post spacing based on structural load limits. Using these data and in-field observations, recommended distances for post spacing were developed for each support post type.