Full-Scale Performance Evaluations of Various Wire-Backed Nonwoven Silt Fence Installation Configurations

Abstract

Silt fences have long been a key component for controlling construction stormwater runoff; nonetheless, many silt fence installations fail to perform in the field as intended. Silt fences are temporary sediment control measures used to retain sediment by impounding runoff and allowing for sedimentation on-site, while simultaneously discharging stormwater runoff at a controlled rate. This study evaluated the performance of eight alternative configurations of the Alabama Department of Transportation (ALDOT) standard wire-backed, nonwoven silt fence. Standard installation parameters associated with the ALDOT silt fence include (1) 32-in. (81.3-cm) high fence, (2) 0.95 lb/ft (1.4 kg/m) support T-post, and (3) 10 ft (3.0 m) T-post spacing. Throughout the series of configurations tested, these standard parameters were varied individually and jointly in efforts to improve overall performance. Variations to the standard parameters include (1) 24-in. (61.0-cm) high fence, (2) 1.25 lb/ft (1.9 kg/m) support T-post, (3) 5 ft (1.5 m) T-post spacing, and (4) trench offsetting. Performance analyses were conducted on each configuration and results were evaluated to determine the best overall configuration to enhance the in-field performance of the ALDOT silt fence. Ultimately, the offset 24 in. (61.0 cm) fence with 1.25 lb/ft (1.9 kg/m) T-post spaced 5 ft (1.5 m) on-center resulted in the best overall improvement, retaining an average of 93% of sediment and deflection of only 0.18 ft (0.004 m) over the course of three simulated storm events.