Watershed study of BMP effectiveness in Georgia

John D. Hewlett (University of Georgia) started a field study of forestry Best Management Practices (BMPs) in the early 1970s in two watersheds at the B.F. Grant Memorial Forest. A recent study in the same watersheds has produced strong evidence that contemporary BMPs are effective in controlling water quality impacts of forestry operations. Results of the recent study are presented in paper titled “A paired watershed investigation of silvicultural best management practices revisited: B.F. Grant Memorial Forest, Georgia” (Forest Science 58 (6): 652-662). The abstract follows. 

“During the 1970s, a paired watershed study was conducted on adjacent first-order Georgia Piedmont streams. Forestry Best Management Practices (BMP) of that period, including thinned 6-m stream buffers, did not prevent large increases in maximum daily water temperatures and sediment inputs due to clearcut harvest and regeneration. After harvest, peak flows in the clearcut watershed increased substantially relative to reference watershed peaks. This study repeated the earlier study on the same watersheds using 1999 Georgia BMP guidelines after 34 years of loblolly pine regrowth on the treatment watershed. Relative to the original study, the new treatment featured wider streamside management zones, 12–21 m, and better road runoff management. In the original study, much of the increase in treatment sediment load was attributed to soil and brush road crossings on the treatment stream, but these crossings were eliminated after the first study. Implementation of modern BMP eliminated daily maximum water temperature effects. In addition, suspended sediment concentrations appeared unaffected by treatment. However, sediment loads relative to the reference tripled after treatment apparently because changes in treatment watershed hydrology accelerated bank slumping. Suspended sediment yields (560 –1,070 kg/ha/year) were small relative to Natural Resources Conservation Service tolerable erosion (1,800–4,400 kg/ha/year) rates.”


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