Effectiveness of forestry BMPS for stream crossing sediment reduction using rainfall simulation
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Recent decisions by the United States Supreme Court and United States Environmental Protection Agency (EPA) have re-emphasized the importance of forestry best management practices (BMPs) at stream crossings. Stream crossings are potential major sources of sediment due to their direct connectivity between the potential erosion source and the stream, which eliminates potential sediment reduction provided by filter/buffer strips and stream side management zones. The effectiveness of stream crossing BMPs for sediment control were tested for a permanent bridge crossing, culvert crossing, and improved ford crossing on three first-order streams in the Virginia Piedmont using rainfall simulation. The three crossings were located on a low standard legacy road having unimproved ford crossings before experimentation. All legacy fords received three levels of rainfall intensity via simulation prior to crossing installation. Following crossing installation, rainfall simulations were performed at each of the crossings under the following three treatments: (1) minimal levels of BMP erosion control (Low); followed by (2) installation of BMPs recommended by the Virginia BMP Manual (Medium); and (3) erosion control measures beyond the Virginia BMP Manual (High). Stream sediment (TSS) was monitored upstream and downstream during rainfall simulations to determine total sediment contribution from each individual crossing. The comparison of minimal BMPs, recommended BMPs, and extensive protection provides insight into the erosion associated with the crossing types and the effectiveness of current BMPs for nonpoint source pollution (NPSP) reduction. The Culvert crossing produced a sediment concentration (2.9 g/L) that was double the concentration produced by the Ford crossing (1.4 g/L) and over 10 times the concentration of the Bridge crossing (0.2 g/L).