Stream Assessment and Constructed Stormwater Wetland Research in the North Creek Watershed

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Title: Stream Assessment and Constructed Stormwater Wetland Research in the North Creek Watershed
Author: Carter, Melanie Dawn
Advisors: Dr. Robert Borden, Committee Member
Dr. William Hunt, Committee Member
Dr. Garry Grabow, Committee Member
Dr. Robert Evans, Committee Co-Chair
Dr. Jean Spooner, Committee Co-Chair
Dr. Samuel Mozley, Committee Member
Abstract: North Creek is a small urban stream flowing through Centennial Campus, NCSU, Raleigh, NC. The watershed (0.5 mi2) is 40% impervious, with campus development in progress. The purpose of this study was to measure channel morphology, sediment load, water quality, and biological integrity over two years. Streambank erosion rates (0.3-1.7 ft/yr) and streambed erosion in the lower reach (1-3 ft) indicated that channel erosion was occurring. Streambed substrate was evaluated using four methods that suggested fine sediment was accumulating in the gravel substrate. Suspended sediment and turbidity were measured during storm events using single-stage samplers, and were found to significantly increase moving downstream and as the stage height increased. Suspended sediment yields were estimated using a single-stage sampler (229 tons/yr) and an automated sampler (94 tons/yr). Biological integrity of the stream was evaluated through benthic macroinvertebrate sampling, which showed reduced taxa richness and relative abundance, with a chironomid majority. Preliminary water quality measurements suggested that metals, and organic PAHs were high during stormflows. Habitat availability was reduced, based on detailed stream feature maps, organic matter amounts, and substrate characteristics. Based on stormwater runoff concerns, two constructed stormwater wetlands (0.3 ac) were designed and installed on the North Creek floodplain. The purpose of this study was to measure stormwater treatment of sediment and nutrients during initial stabilization (three months). Suspended sediment was generated in both wetlands (W1 and W2) during the first two weeks. Total suspended sediment loads were reduced in W2 but not in W1 by the end of the study. Nutrients (TKN, NH4, NO3, TP) were all reduced in W1 throughout the study. Ammonium and total phosphorus were generated in W2 throughout the study. Differences between the two wetlands were due to several variables, including the larger sediment and nutrient concentrations entering W2. Polyacrylamide (PAM) was applied to W1 only (15 lb/ac) during hydromulching after construction. The influence of PAM was not clear, however, due to the numerous different variables between the two wetlands.
Date: 2005-03-17
Degree: PhD
Discipline: Biological and Agricultural Engineering

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