Effectiveness of Current BMPs in Controlling Sediment Discharges from Small Construction Sites

Stormwater runoff from construction sites has become an increasingly major contributor of fine inorganic sediment input into streams and rivers. The negative impacts of excess fine sediment loads extend to all segments of the aquatic ecosystems from microbes to fish. While large construction projects represent single major potential pollution sources and are usually more visible, smaller construction sites (<5 acres) are both more numerous and are less likely to employ adequate erosion control best management practices (BMPs). The most common BMPs employed at such sites are silt fences. Few field studies have been performed to evaluate the effectiveness of these BMPs, especially as affected by physical site and rainfall characteristics.The objectives of this project were to evaluate the effectiveness of currently-employed best management practices (i.e., silt fences) in controlling sediment discharges from small construction sites, and to evaluate the extent to which the addition of vegetated buffer strips improved control. Additionally, the sensitivity of a number of biological metrics to stress associated with sedimentation effects was also investigated. The study was carried out in the upper Cahaba River watershed in north central Alabama.The mean count of small particles below silt fences was approximately 54% less than that from areas with no erosion control measures. However, even though the fences appeared to be properly installed and in good order, the variability between samples was sufficiently great that the difference between these means was not statistically significant. The silt fences did not reduce particle counts to levels comparable to nearby undisturbed sites. For every variable measured, the mean values of samples taken below silt fences were significantly higher (p