Erosion and Sediment Control
Designing Silt Fence Sediment Barriers: A Performance Based Approach
Silt fence is one of the most commonly used sediment barriers on construction sites. Often times silt fence fails due to inadequate design or improper installation and maintenance. This presentation will explore a new silt fence design and installation approach developed by the IECA Standards and Practice Committee targeted at improving the field performance of sediment barriers. The design guidance has been developed after a compressive state-of-the-practice review of design guidance and performance-based research results. The presentation will include design and implementation examples through a user-friendly spreadsheet-based design tool that has been developed to assist professionals in the proper design and implementation.
Construction sites have the potential to discharge considerable amounts of sediment into receiving water bodies, which poses an environmental risk to the aquatic ecosystem. Silt fence works as a sediment control which treats stormwater onsite to minimize sediment-laden discharge. Silt fence is a temporary practice consisting of a geotextile material with or without reinforcement supported by posts. Most design professionals rely on state guidance manuals, which are primarily based on industry rule-of-thumb guidance, with little scientific design rationale. Site specific factors (i.e., topography, precipitation, soil type, etc.), needs to be considered for appropriate design and implementation of sediment controls. A need currently exists to develop a simple, reliable, and widely applicable design guidance for the application of silt fence on construction sites. This design and installation technical paper provides guidance on the proper implementation of silt fence used as a sediment barrier for construction applications. Silt fence installations achieve water quality improvements by intercepting and containing sediment-laden runoff to form impoundment pools that convert kinetic overland flow energy to potential energy, allowing suspended soil particles to settle out of suspension. To be successful, silt fence must be designed and installed in a manner that creates a containment system, allowing suspended particles to be deposited. A comprehensive literature review was conducted to evaluate the state-of-the-practice in silt fence designs and performance-based research conducted across the U.S. Through the IECA Standards and Practice Committee, a design approach was developed that considers site-specific parameters to determine the proper placement and installation criteria for silt fence sediment barriers. This technical paper is intended to provide an overview of the developed design and installation criteria for proper application and use of silt fence in three common installation configurations: (1) linear, (2) “J” Hooks, and (3) “C” Configurations. Developed design guidance calls for silt fence segments be designed to impound the runoff volume from the local 2-yr, 24-hr rainfall event. Effectively designing, sizing, and configuring silt fence segments to satisfy the capacity required by the upslope watershed, can help reduce the occurrence of failures. In addition, this paper explores a spreadsheet-based design tool that has been developed to assist professionals in the implementation of a proper silt fence design. The tool allows practitioners to determine a silt fence design and placement based on site-specific hydrologic parameters (i.e. soil hydrologic condition, precipitation data, topography, etc.). The technical paper and accompanying presentation will include design examples developed from site plans.