CHATTOOGA RIVER WATERSHED ECOLOGICAL/SEDIMENTATION PROJECT

As an integral part of the comprehensive water quality investigation of the Chattooga River watershed, an ecological and sedimentological study was conducted on selected stream reaches within the study area. The objective of this study was to conduct a sediment yield study and determine if sediment was a primary cause of physical and biological impairment to streams within the watershed. As result of this study, accelerated sedimentation has been identified to be the leading determinant in loss of habitat and reduction in bedform diversity within the study area. Good correlation was observed between aquatic ecology and normalized total suspended solids (TSS) data. Based on overlaying the biological index on TSS normalized to discharge/mean discharge, TSS concentrations greater than 284 mg/l adversely affected aquatic macroinvertebrate community structure. However, based on historic regional suspended-sediment concentrations, a normalized TSS concentration of 58 mg/l or less during storm flow provides an adequate margin of safety and is protective of aquatic macroinvertebrates in the Blue Ridge physiography. Corresponding turbidity limits of 69 and 22 NTU established the threshold of biological impairment and margin of safety, respectively. Previously, a similar turbidity of 25 NTU has been recommended for stream restoration management plans. Relative to reference streams, impaired streams yielded higher bedload and suspended load. The results of this study showed that road density and associated sediment sources accounted for 51% of the total sediment loading. Sedimentation has been reported to be the leading determinant in loss of habitat and reduction in bedform diversity within the study area. The State of Georgia is initiating a statewide effort and geographic calibration of reference conditions for assessing the ecological status of its water resources using biological assessment. However, the effort has not been completed. As an interim solution, it was necessary to develop reference conditions at the scale of the Chattooga Basin. The objective of this study was to conduct a sediment yield study and determine if sediment was a primary cause of physical and biological impairment to streams within the watershed. The results were correlated with aquatic ecological data to develop an overall condition of the watershed. Setting The Chattooga River watershed, located in northeast Georgia, northwest South Carolina, and southwest North Carolina, has a total drainage area of approximately 180,000 acres, and is entirely within the Blue Ridge Ecoregion. Land cover within the watershed is primarily forested, with some areas of commercial development, urban and residential use, and agriculture. Although the average "forested" land cover within the watershed is greater than 96%, there has been concern that gradual increases in sediment inputs to streams may be causing ecological impairment. Consequently, EPA Region 4 began an evaluation of water quality conditions within the Chattooga River watershed, and how they may have changed due to forestry or forestry-related practices. To accomplish this, sampling and analysis was undertaken in 1997-2000 by U.S. EPA Region 4 for biological and habitat quality, channel morphology, selected water chemistry, and sediment yield.