A Comparative Study of Stream Restoration Projects in the Upstate, Piedmont of South Carolina
Abstract
Two Rosgen priority level two stream restoration projects in the upstate, Piedmont ecoregion of South Carolina were the focus of this research. Approximately 324 linear feet of Hunnicutt Creek was restored in 2013 as part of a compensatory mitigation project. This stream is located on Clemson University's campus in Pickens County. Hunnicutt Creek's watershed consists of primarily urban land cover, with over 50% impervious surface cover. Approximately 984 linear feet of Little Garvin Creek was restored in 2002. This stream is located on Clemson University's Simpson Research Farm and Experiment Station in Anderson County. Little Garvin Creek's watershed is primarily agricultural land cover, with less than 10% impervious surface cover. Geomorphic and biological stability are key indicators of success for restoration purposes. Geomorphology of these streams was assessed by cross-sectional surveys, longitudinal profile surveys, wetted perimeter cross-sectional pebble count surveys, and Bank Erodibility Hazard Index (BEHI) surveys (for Hunnicutt Creek). Biology of these streams was assessed by analyzing the composition and abundance of Ephemeroptera, Plecoptera, and Trichoptera (EPT) species. These geomorphic and biological measurements collected (observed conditions) were compared to as-built or immediately following restoration (existing) conditions to evaluate the empirical success of these restoration projects. Hunnicutt Creek has experienced floodplain aggradation, channel aggradation in some areas, and channel migration. Modest streambed habitat variation with limited riffle-pool sequencing is also evident and high bank erosion is probable. Little Garvin Creek has experienced floodplain aggradation, channel aggradation, and channel shifting. A loss in riffle-pool sequence is also shown. For both streams, observed changes in EPT composition by order in relation to each other is occurring through time. Also, observed low abundance and diversity of EPT taxa is present. Poor water quality and sedimentation issues are likely present within these stream systems. This geomorphological and biological assessment of Hunnicutt Creek and Little Garvin Creek evaluated the processes and underlying causes of current channel conditions following Rosgen priority level two stream restoration. Hunnicutt Creek is still undergoing channel adjustment, while Little Garvin Creek has reached a quasi-equilibrium state but measurable change from existing conditions has occurred. Stable stream channels have yet to be achieved. Surrounding land use can significantly alter critical watershed processes that control rates and amounts of water transport, sediment transport, and nutrient availability to stream systems (Vitousek et al., 1997; Jackson et al., 2001; Poff et al., 2006). These geomorphic changes and biological changes are likely explained by the surrounding land use in these stream drainage areas having significant continuous effects on these stream systems. Designing streams as Natural Channel Designs (NCD) for restoration purposes is not favorable in highly disturbed watersheds when land use continues to alter the natural hydrology of stream channels; failure of restoration efforts is likely. The downstream location of these stream restoration reaches may also increase the likelihood of unsuccessful restoration efforts. Choosing a better reach upstream, more suitable for restoration, and a better design could have been potentially more successful, increased stability, and more ecologically beneficial. The need for post-restoration monitoring is key in improving methodology of stream restoration efforts, determining meaningful success criteria for restoration efforts, and justifying a restoration project as a success or failure (Palmer et al., 2005). This research is intended to provide academic, regulatory, and design communities with a local dataset that identifies and quantifies stream restoration projects from fourteen years and three years of completion for a variety of geomorphic and biological parameters in evaluation of empirical success of these restorations. Data availability of this nature is rare and time consuming to collect. Locally conducted studies such as these are useful in the development of future restoration projects and to help make future restoration projects more effective.