Browsing by Author "Lindow, Nicholas L."

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    Channel Evolution of a Restored Low Gradient, Sand Bed Stream
    (2007-10-30) Lindow, Nicholas L.; Robert O. Evans, Committee Chair; Michael R. Burchell, II, Committee Member; Gregory D. Jennings, Committee Member; Richard A. McLaughlin, Committee Member
    Stream restoration design and construction relies on an accurate prediction of stable dimension, pattern, and profile within the bounds of expected dynamic equilibrium. This study charts the morphologic evolution of a small, restored headwater stream in response to hydrologic, hydraulic, and geologic conditions in a low gradient, coastal plain system. The goal of the project was to define an expected dynamic equilibrium for constructed streams in the geomorphic regime and equate changes in stream form to fluvial and geotechnical parameters for predictive analysis. The restored stream reach was a previously straightened stream near Cove City, NC in the Lower Coastal Plain. The channelized stream was degraded due to direct cattle access and lack of features for aquatic habitat. Restoration involved removing the cattle, constructing a new floodplain, and re-meandering the channel. Log sill and rootwad structures were used to protect the stream bed and banks. The floodplain and banks were planted with a mixture of hydrophytic, herbaceous, and woody vegetation. The constructed stream was a low gradient, sand bed channel with an equilibrium bed slope of 0.001 m⁄m, cross sectional area of 1.9 m2, top width of 4.8 m, maximum depth of 0.7 m, and W⁄D of 12. The stream and riparian zone were instrumented for monitoring hydrology and surveying permanent cross sections. Rapid development of channel morphology occurred in the first year of monitoring. No significant changes in channel dimension or profile were recorded after the first year post construction. Significant deviations within the stream features were related to structures. Cross sections with root wads had a 12% steeper median side slope than non-structured stream sections. The channel downstream of log sills was 20% deeper than the median cross sectional depth. The dimensional response to fluvial hydraulics and geotechnical parameters was a complex interaction between stream power, shear stress, inundation, water table gradient, and discharge. The survey information was treated as a longitudinal data set, and multivariate statistical analysis was used to relate changes in stream dimension to stream power, shear stress, inundation, shallow groundwater seepage, and discharge processes. Inundation was directly related to increases in stream bank side slopes. Shallow groundwater gradient measured within the stream banks was a significant explanatory variable of direct changes in channel width, while the hydraulic gradient measured in the floodplain and discharge were inversely proportional. Maximum depth was directly related to discharge, but shear stress and stream power were not significant. In order to study in detail the response in bank side slope to shallow groundwater seepage, a soil lysimeter experiment was conducted using soil from the stream site. Banks were constructed in the lab and a high water table gradient was used to induce seepage at the bank face. Bank side slope was varied between experiments, and each test was run until failure. The observed failure mechanism was due to small, pop-out failures and liquefaction of the underlying sandy soil. Positive pore water pressure in the upper loam horizon reduced apparent cohesion and promoted bank collapse. Bank failures occurred along linear failure planes that were similar to the initial bank slope. An increase in bank slope was observed to increase slope stability. Scour pools that developed downstream of the log sills at the restored stream were modeled using River2D. The survey data and information on roughness and hydrology was used to model the two-dimensional, depth-averaged velocity profile upstream of the logs and within the pools. The maximum depth of scour was modeled using empirical relationships based on the morphologic jump, headloss over the sill, meander radius of curvature, median bed particle size, and flow turbulence. The predicted and measured scour depths were significantly correlated in a mixed linear⁄interactive multivariate model. The model parameters included a morphologic jump term, turbulence, and median bed material size. The scour pool depth was dependent on downstream conditions and tailwater depth. An empirical relationship was derived relating headloss over the weir for prediction of downstream energy condition. Stream restoration design and construction techniques are specific to geomorphologic regime. This study provides scientific knowledge related to stream evolution under fluvial and geotechnical processes in the Lower Coastal Plain of North Carolina. The results can be used to evaluate channel equilibrium conditions, improve construction practices, and predict the implications of designed channel form and structures.
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    Use of Soybean Oil and Soybean Products for Groundwater Bioremediation
    (2004-07-07) Lindow, Nicholas L.; Joel Ducoste, PhD, Committee Member; Wei Shi, PhD, Committee Member; Robert Borden, PhD, Committee Chair
    Recent laboratory and field studies have shown that injection of soybean oil and related materials into the subsurface can provide an effective, low-cost alternative for enhanced anaerobic bioremediation. The purpose of this laboratory study is to further evaluate the effectiveness of emulsified soybean products for the reduction and immobilization of nitrate, chromate, and acid mine drainage. Batch microcosm screening studies were first conducted to evaluate the potential of several different substrates to enhance in-situ anaerobic biodegradation of nitrate. The substrates evaluated were food-grade materials, including molasses, liquid soybean oil, fully hydrogenated soybean wax, blown soybean oil, soy methyl ester, and mineral oil. With the exception of mineral oil, the tested substrates were all able to support nitrate degradation with the slowest degradation rates occurring for fully hydrogenated soybean wax. Intermittent flow through soil column studies were also conducted to evaluate the substrate degradation rate, nitrate removal efficiency, and lifespan of different soybean treatments. The soybean oil treatment stimulated denitrification removed nitrate and nitrite concentrations below detection in the liquid and fully hydrogenated soybean wax treated columns without the addition of a denitrifying bacterial inoculum. No apparent benefits or disadvantages were observed for either treatment. An identical study was conducted for chromate. Microcosm results were favorable, showing aqueous chromium (VI) removal even in no added carbon control microcosms. However, soil column experiments yielded mixed results. No removal of influent chromium was observed in columns treated with liquid or fully hydrogenated soybean oil at high influent chromate concentrations. A second set of columns were tested with lower concentrations of chromate, and resulted in complete removal of effluent chromium to below detection. Batch microcosms were also constructed with acid mine drainage (AMD) generating spoils from a former coal mine in Sequatchie Valley, TN. The bottles were amended with simulated acid mine drainage and a small liquid inoculum from an anaerobic treatment wetland. Several combinations of treatments were evaluated including easily degradable sugars (molasses), more slowly degradable oils (soybean), yeast extract, and partially neutralized with sodium bicarbonate buffer. Despite the low pH and presence of toxic metals, in-situ reduction of AMD was significantly enhanced with a soybean oil substrate. Sulfate declined from 1,800 mg/L to 10 mg/L, pH increased from 2.6 to 6.4 and iron was precipitated in a 2:1 molar ratio with sulfate removal. Lesser removal of some iron and sulfate also occurred in bottles amended with only molasses and yeast extract. These results demonstrate that soybean oil addition can be very effective in treating AMD and the initial pH of the AMD is not a significant problem if an appropriate microbial inoculum is provided. Laboratory soil columns packed with mine spoils were also studied for AMD degradation. Treated columns received a one time amendment of the commercially available soybean emulsion EOS® (Edible Oil Substrate) and were bioaugmented with the bacterial consortia developed from the microcosm studies. Simulated AMD was then pumped through the columns with a six to seven-day hydraulic retention time (HRT). During passage through the EOS® treated columns, pH increased from <3 to ~6, SO₄ was reduced by 75%, and aluminum, copper and zinc were reduced to below the analytical detection limit. Amendments were later made to the influents to include greater concentrations of manganese, zinc, aluminum, copper, and sulfate with less iron. The effect of the added sulfate increased electron donor usage and effectively shortened the potential lifespan of the treatment. Changes in permeability were monitored for all the column experiments to evaluate the potential for fouling of an edible oil barrier with biomass and/or inorganic precipitates. Significant loss in permeability was observed in most of the treated columns. A mass balance of the carbon added through soybean treatment and potential carbon use due to biological redox reactions is also evaluated for all columns. The rate of carbon use appears heavily reliant on the electron acceptor loading rate, but only gross estimates of treatment lifespan are possible due to high mass balance error.