• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 52
  • 3
  • 2
  • 1
  • 1
  • Tagged with
  • 95
  • 95
  • 22
  • 18
  • 17
  • 16
  • 12
  • 11
  • 11
  • 10
  • 9
  • 9
  • 8
  • 8
  • 8
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Evaluating the Long-Term Morphological Response of a Headwater Stream to Three Restoration Techniques

Hendrix, Coral Elise 23 August 2022 (has links)
The stream restoration industry has been growing since the addition and modification of Section 404 to the Clean Water Act. Many projects follow the guidelines of Natural Channel Design and use in-stream structures to stabilize stream channels. Post-project monitoring rarely exceeds 3-5 years, and the lack of guidance, funding, and pre-restoration data prevents meaningful post-project assessment of the design techniques. The Virginia Tech Stream Research, Education, and Management (StREAM) Lab is a research facility where a stream restoration project was completed along 1.3 km of Stroubles Creek in 2010. The study site provides a unique opportunity to compare the use of three restoration treatments with different intensities of restoration actions. Following exclusion of cattle from all three sites, the first treatment reach was left to naturally revegetate (Treatment 1) and along Treatment 2 the streambanks were re-graded to a 3:1 slope and replanted. An additional inset floodplain was constructed within the active channel of Treatment 3. Pre-restoration data, including topographic surveys and erosion pin measurements, provided a baseline for quantification of morphological response 11 years post-restoration. This project utilized as-built survey data from 2010 and a follow-up survey in 2021. The spatial data were analyzed to quantify important stream metrics: cross-sectional area, width, maximum depth, hydraulic depth, and width-to-depth ratio. Overall, the percent change per year of each metric decreased substantially following the restoration, indicating an increase in stability. While Treatment 3 continues to show minor erosion on average (+3.3% in area, +3.2% in width, and +11.2% in maximum depth), Treatments 1 (excluding cross section 5) and 2 decreased on average in area (-3.4% and -18.6%) and hydraulic depth (-13.3% and -10.8%). Treatment 1 eroded by an average of 11.7% in width compared to a decrease of -13.4% in Treatment 2 and an increase in 3.2% in Treatment 3. Comparisons of each treatment to Virginia Mitigation Banking Standards indicated Treatment 1 met the fewest number of criteria, followed by Treatment 2 and then Treatment 3, indicating that hard structures are not necessary to meet mitigation bank standards, even in urban watersheds. In an urban, incised channel with cattle impacts, re-grading the streambanks, actively planting woody riparian vegetation, and incorporating an inset floodplain will accelerate the establishment of channel stability, as compared to the more passive approach of simply removing cattle access to the channel. / Master of Science / The stream restoration industry has been growing since the addition and modification of Section 404 to the Clean Water Act. Specific design models, such as Natural Channel Design which focuses heavily on preventing the stream from moving using stone and wood structures, guide many projects. Post-project monitoring rarely exceeds 3-5 years, and the lack of guidance, funding, and pre-restoration data prevents meaningful post-project assessment of the design techniques. The Virginia Tech Stream Research, Education, and Management (StREAM) Lab is a research facility in which human interactions in the Stroubles Creek Watershed can be evaluated. A stream restoration project was completed on Stroubles Creek at the StREAM Lab property in 2010. This project provides a unique opportunity to compare three different intensities of restoration actions. Following exclusion of cattle from all three sites, plants were left to naturally regrow in the first treatment reach and Treatment 2 re-shaped the banks to a gentler slope and replanted. Like Treatment 2, an additional inset floodplain was constructed within the active channel of Treatment 3. Pre-restoration data, including topographic surveys and bank erosion measurements provided a baseline for quantification of physical response 11 years post-restoration. This project utilized survey data from immediately post-restoration in 2010, and a follow-up survey in 2021. The surveys were analyzed using AutoCAD Civil3D and cross-sectional area, width, maximum depth, hydraulic depth (area/top width), and width-to-depth ratio were calculated. Overall, the percent change per year of each metric decreased substantially following the restoration, indicating an increase in stability. While Treatment 3 continues to show minor erosion (+3.3% in area, +3.2% in width, and +11.2% in maximum depth), Treatments 1 (excluding cross section 5) and 2 decreased on average in area (-3.4% and -18.6%) and hydraulic depth (-13.3% and -10.8%). Treatment 1 eroded by an average of 11.7% in width compared to a decrease of -13.4% in Treatment 2 and an increase in 3.2% in Treatment 3. Comparisons of each treatment to Virginia Mitigation Banking Standards indicated Treatment 3 met the highest number of criteria, followed by Treatment 2 and then Treatment 1, indicating that hard structures are not necessary to meet mitigation bank standards, even in urban watersheds. In an urban, incised channel with cattle impacts, regrading the streambanks, actively planting woody riparian vegetation, and incorporating an inset floodplain will accelerate the establishment of channel stability, as compared to the more passive approach of simply removing cattle access to the channel.
22

Cumulative Impacts of Watershed-Scale Hyporheic Stream Restoration on Nitrate Loading to Downstream Waterbodies

Calfe, Michael Louis 23 January 2020 (has links)
Excess nutrient pollution and eutrophication are widespread problems that must be solved at watershed scales, and stream restoration is increasingly implemented as a solution. Yet few studies evaluate the cumulative effects of multiple individual restoration projects on watershed-scale nutrient loading. We constructed a HEC-RAS model of stream restoration implemented throughout a generic 4th order watershed typical of the Piedmont physiographic province of the eastern USA. We simulated restoration of hyporheic exchange as one increasingly popular technique that receives dissolved nitrate-nitrogen (NO3--N) mitigation credit under the Chesapeake Bay TMDL. We populated the model with hyporheic exchange (0.3% of surface flow per hyporheic-exchange inducing in-stream restoration structure) and NO3--N removal (supply-limited denitrification removes all NO3--N that enters the hyporheic zone) values from prior literature on in-stream structures and related restoration techniques. We then varied the percentage of stream channels in the watershed in which restoration occurred. For watersheds with less than 100% of stream channels restored, we also varied where in the watershed (i.e. stream order) that restoration occurred. We found that hyporheic restoration in our 4th order watersheds has the potential to reduce NO3--N loading to downstream waterbodies by up to 83%, but that a maximum of <100% reduction exists given certain watershed characteristics. Model results revealed a nonlinear relationship between percent of stream channels restored and percent NO3--N loading reduction that occurred at the watershed outlet. This indicates that the effects of individual projects are not linearly additive, and must be evaluated in the context of how much of the watershed has already been restored. We also found that restoration was more effective at reducing NO3--N loading when it occurred in higher order streams (e.g., 3rd and 4th order), yielding load reductions upward of 30% compared to < 10% in lower order streams (e.g., 1st and 2nd order). Thus, the location of an individual restoration project within a watershed is important in determining its effect on NO3--N. Overall, our results indicate that hyporheic restoration can have significant effects on watershed NO3--N loading to downstream waterbodies, yet the watershed must be viewed as a whole to understand the potential impacts of any particular project under consideration. / Master of Science / Nutrient pollution and harmful algal blooms are widespread problems that must be solved at watershed scales, and stream restoration is increasingly implemented as a solution. Yet few studies evaluate the cumulative effects of multiple individual restoration projects on watershed-scale nutrient loading. We constructed a HEC-RAS model of stream restoration implemented throughout a generic watershed typical of the mid-Atlantic USA. We simulated restoration of nutrient-reducing groundwater flow cells along a stream corridor (hyporheic exchange) as one increasingly popular technique that is emphasized under the Chesapeake Bay TMDL. We populated the model with hyporheic exchange and nitrate-nitrogen (NO3--N) removal values from prior literature on in-stream structures and related restoration techniques. We then varied the percentage of stream channels in the watershed in which restoration occurred. For watersheds with less than 100% of stream channels restored, we also varied where in the watershed (i.e. stream order) that restoration occurred. We found that hyporheic restoration in our watershed has the potential to reduce NO3--N loading to downstream waterbodies by up to 83%, but that a maximum of less than 100% reduction exists given certain watershed characteristics. Model results revealed a nonlinear relationship between percent of stream channels restored and percent NO3--N load reduction that occurred at the watershed outlet. This indicates that the effects of individual projects are not linearly additive, and must be evaluated in the context of how much of the watershed has already been restored. We also found that restoration was more effective at reducing NO3--N loading when it occurred in larger streams, yielding load reductions upward of 30% compared to less than 10% in smaller streams. Thus, the location of an individual restoration project within a watershed is important in determining its effect on NO3--N. Understanding the maximum possible degree of NO3--N reducing hyporheic exchange is an important step for practitioners and policy-makers in choosing the most effective location for a stream restoration based on a project's goals, and cannot be done without analyzing the watershed as a whole. With more watershed-scale planning and a better understanding of certain physical characteristics, we can choose restoration locations and strategies that will ultimately work more efficiently toward reaching a nutrient reduction goal.
23

The Development of a Stream Restoration Decision Support Tool for the County of Henrico Stream Assessment and Watershed Management Program

Sweet, Dan I. 18 November 2003 (has links)
Several Municipalities in Virginia are currently developing and implementing watershed programs. While programmatic goals and objectives vary, all seek to incorporate stream restoration project work. Decision support tools exist for many aspects of watershed and water resources management, however, there are currently no such tools to aid municipalities in their stream restoration efforts. This study details the development of such a decision support tool for the Henrico County Stream Assessment/Watershed Management Program based on the assessment of stream restoration opportunities and feasibility constraints. A framework for the development of future municipal watershed programs is presented and related issues are discussed. / Master of Landscape Architecture
24

Long-term implications of dam removal for mesohabitat and macroinvertebrate communities in Michigan and Wisconsin rivers

Hansen, Jonathan Ford. January 2008 (has links)
Thesis (M.S.)--Michigan State University. Dept. of Fisheries and Wildlife, 2008. / Title from PDF t.p. (viewed on Aug. 10, 2009) Includes bibliographical references (p. 64-68). Also issued in print.
25

Responses of fishes and salamanders to instream restoration efforts in western Oregon and Washington

Roni, Philip. January 1900 (has links)
"Project completion report." / "January 2001." "Funded by Bureau of Land Management, Oregon State Office ... (Interagency Agreement No. 1422H952-A98-3007) and Environmental Conservation Division, Northwest Fisheries Science Center, National Marine Fisheries Service ..." Originally issued as the author's thesis (Ph. D.)--University of Washington, 2000. Includes bibliographical references (p. 119-132). Also issued in print.
26

Restoring Our Urban Streams: A Study Plan for Restoring/Rehabilitating Stroubles Creek in Blacksburg, Virginia

Zhou, Daquan 01 June 2004 (has links)
As the Americans have become more aware of the impact to the environment from the human induced disturbances which includes physical, chemical and biological disturbances to the degradation of streams and rivers, many studies and experiments have been done in an attempt to restore streams and rivers to more natural conditions. At the same time, success in public education and community involvement has encouraged grass-root movements that engage people in stream restoration efforts. Stroubles Creek is a freshwater stream located in Blacksburg, Virginia. The creek has experienced considerable disturbance due to land use changes over the past 100 years. The Stroubles Creek Water Initiative (SCWI), originated by the Virginia Water Resources Research Center at Virginia Tech, has been monitoring the creek for a number of years. This paper develops a planning framework for restoring and/or rehabilitating Stroubles Creek within the Town of Blacksburg. The results of stream monitoring and other research by SCWI are used to inform the recommended planning process, while a literature review and discussion of “urban stream restoration case studies” are used to guide future decision-making related to Stroubles Creek restoration/rehabilitation. / Master of Urban and Regional Planning
27

Characterizing water quality and hydrologic properties of urban streams in central Virginia

Lucas, Rikki 01 January 2019 (has links)
The objective of this study was to characterize water quality and hydrologic properties of urban streams in the Richmond metropolitan area. Water quality data were analyzed for six urban sites and two non-urban sites. Geomorphological surveys and conservative tracer studies were performed at four urban sites and one non-urban site to describe intra- and inter- site variability in transient storage, channel geomorphology, and related hydrologic parameters. Urban sites showed elevated concentrations of nitrogen and more variable TSS concentrations relative to reference sites. Urban channels were deeply incised with unstable banks and low sinuosity. Little Westham Creek exhibited the greatest transient storage. This site was characterized by large, deep pools and therefore it is likely that transient storage was associated with surface water storage. Transient storage was low at all other sites, particularly for the study reach at Reedy Creek, which flowed through a concrete channel. Lowest transient storage was observed at this site in spring, though higher values were measured in summer corresponding to the presence of biofilms, A lower, more naturalized section of the concrete channel was found to have greater transient storage suggesting the possibility of passive restoration of concrete channels in urban environments. This study documents variability in the structure and function of urban streams. Restoration projects should work to improve impairments that are specific to each site at both the reach and watershed scale to maximize the efficacy of restoration.
28

A comparison of hyporheic transport at a constructed stream restoration structure and natural riffle feature, West Branch Owego Creek, New York, USA

Smidt, Samuel J. 01 May 2014 (has links)
While restoring hyporheic flowpaths has been cited as a benefit to stream restoration structures, little documentation exists confirming that constructed restoration structures induce hyporheic exchange comparable to natural stream features. This study compares a stream restoration structure (cross-vane) to a natural feature (riffle) concurrently in the same stream reach using time-lapsed electrical resistivity (ER) tomography. Using this hydrogeophysical approach, I am able to quantify hyporheic extent and transport beneath the cross-vane structure and riffle. I interpret from the geophysical data that the cross-vane and natural riffle induced spatially and temporally unique hyporheic extent and transport, and the cross-vane created both spatially larger and temporally longer hyporheic flowpaths than the natural riffle. Tracer from the 4.67-hr injection was detected along flowpaths for 4.6-hrs at the cross-vane and 4.2-hrs at the riffle. The spatial extent of the hyporheic zone at the cross-vane was 12% larger than at the riffle. I compare ER results of this study to vertical fluxes calculated from temperature profiles and conclude significant differences in the interpretation of hyporheic transport from these different field techniques. Results of this study demonstrate a high degree of heterogeneity in transport metrics at both the cross-vane and riffle and significant differences between the hyporheic flowpath networks at the two different features. Our results suggest that restoration structures may be capable of creating sufficient exchange flux and residence times to achieve the same ecological functions as natural features, but engineering of the physical and biogeochemical environment may be necessary to realize those benefits.
29

Quantifying the geomorphic recovery of disturbed streams : using migrating sediment slugs as a model

Bartley, Rebecca January 2001 (has links)
Abstract not available
30

Beneficial Assessment of Water Quality Purification for Constructed Wetland

Fu, Yu-Ting 13 September 2012 (has links)
A constructed wetland was built in southern Taiwan in 2007 for local stream water purification and ecosystem improvement. The inflow rate was approximately 1,350 m3/day. The wetland influents were mainly from the local streams containing secondary wastewater from hog farms located in the upper catchment of the wetland and drainage water from the farmlands. The influent water contained organic contaminants and nutrients, which needed to be removed. The mean measured hydraulic loading rate, hydraulic retention time, water depth, and total volume of wetland system were 0.1 m/day, 5.5 days, 0.7 m, and 7,800 m3, respectively. In this study, water, sediment, and plant samples were collected and analyzed quarterly for each wetland basin during the two-year investigation period. Results show that more than 77% of total coliforms (TC), 78% of biochemical oxygen demand (BOD), 88% of total nitrogen (TN), and 96% of ammonia nitrogen were removed via the constructed wetland system. Thus, the wetland system has a significant effect on water quality improvement and is able to remove most of the pollutants from the local stream through natural attenuation mechanisms. Results from the ecological investigation show that more than 50 different plant species and 45 different animal species were observed in the wetland system although this wetland had been created for less than four years. Except for stream water quality improvement and rehabilitating the natural ecosystem, this wetland also offered more water assessable eco-ponds and eco-gardens for public. This constructed wetland has become one of the most successful multi-function constructed wetlands in Taiwan.

Page generated in 0.1105 seconds