Assessments of Restored, Undisturbed, and Gaged Streams in the Southern Appalachian Mountains.

摘要

Stream restoration practitioners rely on a combination of tools, including an understanding of reference reaches, hydraulics and sediment transport, and hydraulic geometry of stream channels. These tools are supplemented by professional experience, often gained through long-term monitoring of existing stream restoration projects. Long-term monitoring and interpretation of stream restoration projects is widely considered to be essential to the advancement of the field. This dissertation provides reviews of water quality impacts of stream restoration and geomorphic monitoring methodologies for streams. Additionally, three studies are presented to enhance the body of knowledge used by restoration professionals. The first regards channel roughness coefficients (e.g., Manning's n), which are an integral part of estimating velocity and discharge in streams. Values for n were calculated from the historical flow record for five gaged streams in western North Carolina. Roughness coefficients were found to vary both among sites and with stage in a specific channel. Values for n at bankfull flow ranged from 0.039 to 0.064, with n at low-flow conditions between 0.069 and 0.179. The second study explores geomorphic characteristics of streams with minimal anthropogenic impacts in the Joyce Kilmer/Slickrock Wilderness of North Carolina and Tennessee. Morphological information, including channel dimensions and longitudinal profiles, was gathered from fourteen alluvial stream reaches. The study sites had drainage areas from 0.25 to 41.6 km 2 and stream slopes from 0.014 m/m to 0.104 m/m. Bankfull cross-section dimensions of the study stream reaches were strongly correlated to drainage area across the observed range of slopes and bed morphology. Cross-section area and width relationships for the streams in this study did not differ significantly from regional curves for the mountain physiographic region of North Carolina. Observations of these reaches did not suggest a definitive rule regarding the proportion of steps and riffles in streams. Pools occupied greater than 50% of the length in all stream reaches with slopes less than 0.07 m/m. Significant correlation existed between step height ratio and slope, suggesting that step height can be approximated as the product of channel width and slope. Riffle length and riffle slope ratios were also significantly correlated with slope, though pool spacing was not. The third study reports findings from the monitoring of four stream restoration projects on Little Brasstown Creek in western North Carolina. These projects, monitored between 2005 and 2011, represented different design approaches, and ranged in age from zero to four years old at the beginning of the monitoring period. Morphological monitoring assessed dimensional changes in 22 cross-sections and profile changes along 3,000 linear meters of stream. The biological component of the monitoring evaluated changes in the benthic fauna in the four restoration projects. Changes in net cross-section area were generally minimal and varied by project, though riffle cross-sections generally became wider and shallower at all projects. Large changes in riffle lengths and slopes occurred, though trends differed by project. Pool spacings remained constant over time, and were lower than typical values suggested in the literature; likely a result of the in-stream structures installed as part of the stream restoration. Benthic macroinvertebrate indices peaked in 2005 and 2006, when the restoration projects were young, and declined by 2011.