Evaluating Stream Restoration Techniques in the Mitchell Watershed
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A stream restoration initiative was implemented in the Mitchell River Watershed in the mid 1990’s. The Mitchell River is located in the Piedmont of North Carolina with its headwaters originating along the Blue Ridge escarpment. The watershed scale effort is led by the Natural Resources Conservation Service and a watershed coalition comprised of state and local agencies, private consultants, private industry, non-profits, and land owners. The number one water quality impairment to the Mitchell River is sediment pollution, primarily from streambank erosion along the South Fork Mitchell and Snow Creek, two major tributaries to the Mitchell. Stream restoration using natural channel design techniques has been the primary method used to decrease sediment inputs into the Mitchell River. The first project was implemented in 1996 and work continues today. Currently, over 30,000 feet of stream channels has been restored through the implementation of 14 projects. In 2002, the NC Clean Water Management Trust Fund provided a grant to the Surry Soil and Water Conservation District to study the effectiveness of using natural channel design techniques to improve water quality in the Mitchell River. Five projects were selected for the study ranging from small step pool channels with gravel/cobble beds to low gradient meandering channels with sand/small gravel beds. During the four year study period the project sites have experienced multiple bankfull events, including two hurricanes. Results show that the study sites remain dynamically stable with the majority of cross sections trending towards narrower bankfull widths and increased mean depths. Maximum riffle depths are generally unchanged, while maximum pool depths have increased. The longitudinal profile for the high gradient step pool channel showed an increase in the number of pools present, as well as a decrease in pool to pool spacing. Stream substrate data have shown a trend toward coarsening through reductions in fine sediments. Floodplain deposition was observed on all sites, particularly after the hurricanes on the sites with high sediment supply from upstream sources.