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Browsing by Author "Hodges, Clayton Christopher"

Now showing 1 - 14 of 14
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    Assessment of Mansionization and Residential Infill Development on Stormwater Runoff
    Hekl, Meghan Louise (Virginia Tech, 2018-06-19)
    Residential infill development and the associated increases in impervious cover and stormwater runoff have the potential to overwhelm aging infrastructure causing erosion, flooding, and ecological degradation of waterways. The lack of greenfield sites available for new development around urban centers coupled with a desire for maintaining a traditional neighborhood aesthetic drives residential infill and replacement of existing smaller homes by significantly larger structures, minimizing open space available for stormwater mitigation. An analysis of residential infill development trends in Fairfax County was performed to characterize the effects of intensified development. Development patterns were identified and assessed using digitized impervious cover data extracted from aerial imagery of the study area for six selected years from 2002 to 2015. The average annual increase in percent impervious area was computed to be 0.3%. Redevelopment was found to be mainly occurring in areas zoned as lower-density residential. The spatial distribution of redevelopment showed trends of clustered increases as opposed to isolated events. The hydrologic analysis performed revealed that from 2002 to 2015, there was an 8,930 m3 (7.2 acre-ft) increase in stormwater runoff volume, 38% of which is contributed to by runoff generated from development that is considered exempted from regulation in Fairfax County. Additionally, there was a 28 kg/year (62 lb/year) increase in total phosphorus loads attributable to the change in impervious cover due to residential development throughout the study area. The results of this study provide a quantitative basis for municipalities to amend policies regulating residential development and its associated stormwater management.
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    Assessment of Predictive Real-Time Control Retrofits on Stormwater Basin Performance in an Urban Watershed
    Honardoust, Dylan Russell (Virginia Tech, 2020-06-04)
    The potential real-time control (RTC) has to improve the performance of existing stormwater management systems is a topic of increasing interest as hydraulic and hydrologic modeling capabilities proliferate. The benefits of incorporating precipitation forecast data into a RTC algorithm to allow for prediction-based control of an urban watershed is explored using an EPA SWMM 5.1 watershed model. One reactive and two predictive RTC algorithms are simulated in various configurations across seven dry detention ponds located in the 162 hectare urbanized watershed. The hydraulic benefits they provide at the site and watershed outlet in regards to peak flow and the flow duration curve are compared to conventional, static control. The ponds retrofit with the novel predictive RTC algorithm had lower peak flows during 24-hour design storms more consistently than when retrofit with reactive RTC. The duration of erosive flows at the site level was decreased by the novel predictive RTC in most cases. Improvements at the watershed outlet depended on where RTC was applied as hydrograph compounding was observed during some RTC implementations.
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    Cost Trends and Estimates for Dam Rehabilitation in the Commonwealth of Virginia
    Baron, Stefany A. (Virginia Tech, 2020-06-08)
    In recent years, the United States has seen a high demand for dam rehabilitation projects as most dam infrastructure has started to reach or exceed the expected life span of 50-70 years. Rehabilitation projects can be very expensive, however, and the funding options for dam owners are limited. To raise awareness, organizations such as ASDSO and the Virginia DCR release cost estimates every few years to encourage more investment in dam infrastructure. Unfortunately, many cost estimates have been made with limited data and outdated methodologies. This research collects a new sample of cost data for Virginia dam rehabilitation projects and uses it to assess key factors for cost estimating. Factors such as height, drainage area, hazard classification, and ownership type were used to make regression models that predict the cost of addressing Virginia's non-compliant dams. This study estimates that approximately $300 million is needed to address Virginia's 98 deficient high hazard, local government owned dams and that $122 million of that estimate is need for SWCD dams alone.
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    Development of Effective Procedures for Stormwater Thermal Pollution Potential Risk Mapping
    Martin, Clinton James (Virginia Tech, 2017-02-02)
    Thermal pollution of waterbodies occurring from heated stormwater runoff in urban catchments is a growing concern among municipalities in the United States. The U.S. Environmental Protection Agency (EPA) maintains regulatory criteria for temperature of waters of the U.S. as many species of aquatic life depend on an environment that maintains water temperatures below a certain threshold. Thermal pollution from urban stormwater runoff threatens the livelihoods of cold-water fish species, like trout, among other species of wildlife. In order to reduce thermal pollution loading to its streams, a municipality or regulatory authority must first identify the sources of thermal pollution in its waterbodies. This study predicts areas within an urban watershed in the Town of Blacksburg, VA that may be sources of thermal pollution in stormwater runoff by investigating indicators of thermal pollution potential (TPP) through and analysis of land cover types and runoff flow patterns in a geographic information system (GIS) environment. Results of the study provide a theoretical foundation for TPP risk mapping with recommendations for authorities interested in pursuing TPP risk mapping as a tool to guide and focus efforts toward reduction of thermal pollution and land planning.
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    Evaluation of Green Stormwater Infrastructure Monitoring Protocols
    Cetin, Lauren Marie (Virginia Tech, 2018-06-21)
    Due to development of once natural landscapes, also referred to as urbanization, stormwater management has evolved in an effort to address and counteract impairment of waterways in the United States by extensively implementing best management practices (BMPs) or Green Stormwater Infrastructure (GSI). Facilities are installed without any requirement of long-term monitoring; instead relying on lab-tested or assumed pollutant removal efficiencies that often do not translate into field implementation and do not perform as intended and required by regulatory agencies. Monitoring studies have often been applied with variable standards, which lead to inconsistent results and inconclusive data. This study aims to synthesize essential components of a GSI monitoring program based on a review of existing programs (Technology Assessment Protocol – Ecology [TAPE], Technology Assessment Reciprocity Partnership [TARP], etc.). Data from past protocols was used in tandem with historic precipitation data to develop a methodology for creating a local or small region-specific protocol. This methodology was applied to the case study area of Fairfax, Virginia. Results from the study indicate that historic precipitation data and past protocol recommendations can be effectively applied in a local setting to create a more suitable protocol adapted for GSI monitoring in order to confirm designed efficiency.
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    Evolution and Application of Urban Watershed Management Planning
    Mika, Melissa Lynn (Virginia Tech, 2018-01-11)
    The development of Watershed Management Plans (WMPs) in urban areas aids municipalities in allocating resources, engaging the public and stakeholders, addressing water quality regulations, and mitigating issues related to stormwater runoff and flooding. In this study, 63 urban WMPs across the nation were reviewed to characterize historical approaches and identify emerging trends in watershed planning. Planning methods and tools were qualitatively evaluated, followed by statistical analyses to identify correlations between planning factors. Plans developed by a municipality or consultant were correlated to higher occurrences of hydrologic modeling and site-specific recommendations, and lower occurrences of characterizing social watershed factors. Trends in the use and selection of hydrologic, hydraulic, and pollutant load models were identified, specifically in the past decade. Project prioritization was found to increasingly focus on feasibility in implementation. Additional qualitative trends identified include an increased focus on water quality and interdisciplinary studies, public participation, responsiveness to water quality regulations, and risk aversion. The study concludes by envisioning future watershed planning trends. This state of the practice review of planning efforts, innovation in implementation, and the adoption of emergent technologies will aid future planners in employing current tools and strategies in the development of new WMPs.
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    Identifying Key Factors for the Implementation and Maintenance of Green Stormwater Infrastructure
    Delgrosso, Zack Lee (Virginia Tech, 2018-05-25)
    Construction and maintenance can have huge implications on the long-term functioning of GSI facilities. GSI facilities investigated were bioretention, permeable pavement, sand filters, infiltration trenches, and vegetated swales. This study first highlights the most important construction and maintenance items based on relevant studies and state stormwater manuals. Fairfax County, VA was used as a case study to evaluate the County's current stormwater program and illuminate common maintenance issues found for each GSI type. Data analysis of 3141 inspection records illustrated particular deficiencies for each GSI type and that there are differences between public and private facilities, most likely depending on site conditions and frequency of routine maintenance. Sediment accumulation was found to be the most common maintenance issue (27.8% of inspections), supporting the importance of adequate pretreatment and good housekeeping when implementing GSI. The Northern Virginia Soil and Water Conservation District (NVSWCD) performed a study surveying 63 public bioretention facilities in which they measured ponding depth, filter media depth, ponding area, and infiltration rates. The NVSWCD concluded that deficiencies found in facilities could mostly be attributed to inadequacies during construction. By comparing current post-construction inspections performed by the County to the NVSWCD data, it was found that these County inspections are failing to detect these inadequacies in bioretention facilities from improper construction. It is recommended that MS4s thoroughly record and track construction and post-construction inspection items to improve the longevity of its facilities and better inform future decision making regarding GSI.
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    Modeling Watershed-Wide Bioretention Stormwater Retrofits to Achieve Thermal Pollution Mitigation Goals
    Chen, Helen Yuen (Virginia Tech, 2020-04-08)
    Stream ecosystems are increasingly at risk for thermal impairment as urbanization intensifies, resulting in more heated runoff from impervious cover that is less likely to be cooled naturally. While several best management practices, including bioretention filters, have been able to reduce thermal pollution, success has been limited. The extent of thermal mitigation required to prevent ecological damage is unknown. A calibrated runoff temperature model of a case study watershed in Blacksburg, VA was developed to determine the cumulative treatment volume of bioretention filters required to reduce thermal impacts caused by runoff from development in the watershed to biologically acceptable levels. A future build out scenario of the study watershed was also analyzed. Results from this study established that runoff thermal pollution cannot be fully reduced to goal thresholds during all storms using bioretention filter retrofits. While retrofitting significantly decreased temperatures and heat exports relative to the controls, increasing treatment volumes did not really enhance mitigation. Alternate thermal mitigation methods which actively remove runoff volume should be considered where more thermal mitigation is required.
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    Optimization of BMP Selection for Distributed Stormwater Treatment Networks
    Hodges, Clayton Christopher (Virginia Tech, 2016-07-19)
    Current site scale stormwater management designs typically include multiple distributed stormwater best management practices (BMPs), necessary to meet regulatory objectives for nutrient removal and groundwater recharge. Selection of the appropriate BMPs for a particular site requires consideration of contributing drainage area characteristics, such as soil type, area, and land cover. Other physical constraints such as karst topography, areas of highly concentrated pollutant runoff, etc. as well as economics, such as installation and operation and maintenance cost must be considered. Due to these multiple competing selection criteria and regulatory requirements, selection of optimal configurations of BMPs by manual iteration using conventional design tools is not tenable, and the resulting sub-optimal solutions are often biased. This dissertation addresses the need for an objective BMP selection optimization tool through definition of an objective function, selection of an optimization algorithm based on defined selection criteria, development of cost functions related to installation cost and operation and maintenance cost, and ultimately creation and evaluation of a new software tool that enables multi-objective user weighted selection of optimal BMP configurations. A software tool is developed using the nutrient and pollutant removal logic found in the Virginia Runoff Reduction Method (VRRM) spreadsheets. The resulting tool is tested by a group of stormwater professionals from the Commonwealth of Virginia for two case studies. Responses from case study participants indicate that use of the tool has a significant impact on the current engineering design process for selection of stormwater BMPs. They further indicate that resulting selection of stormwater BMPs through use of the optimization tool is more objective than conventional methods of design, and allows designers to spend more time evaluating solutions, rather than attempting to meet regulatory objectives.
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    Precipitation Estimation Methods in Continuous, Distributed Urban Hydrologic Modeling
    Woodson, David (Virginia Tech, 2019-06-19)
    Quantitative precipitation estimation (QPE) remains a key area of uncertainty in hydrological modeling, particularly in small, urban watersheds which respond rapidly to precipitation and can experience significant spatial variability in rainfall fields. Few studies have compared QPE methods in small, urban watersheds, and studies which have examined this topic only compared model results on an event basis using a small number of storms. This study sought to compare the efficacy of multiple QPE methods when simulating discharge in a small, urban watershed on a continuous basis using an operational hydrologic model and QPE forcings. The Research Distributed Hydrologic Model (RDHM) was used to model a basin in Roanoke, Virginia, USA forced with QPEs from four methods: mean field bias (MFB) correction of radar data, kriging of rain gauge data, uncorrected radar data, and a basin-uniform estimate from a single gauge inside the watershed. Based on comparisons between simulated and observed discharge at the basin outlet for a 6-month period in 2018, simulations forced with the uncorrected radar QPE had the highest accuracy, as measured by root mean square error (RMSE) and peak flow relative error, despite systematic underprediction of the mean areal precipitation (MAP). Simulations forced with MFB corrected radar data consistently and significantly overpredicted discharge but had the highest accuracy in predicting the timing of peak flows.
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    Resistance to Flow Through Riprian Wetlands
    Hodges, Clayton Christopher (Virginia Tech, 1997-05-16)
    Increasing interest in the role of wetlands in pollutant removal, flood plain management, and sedimentation in recent years has prompted research into hydraulic processes inherent to these systems. The research described in this thesis focuses on flow processes within ecosystems known as riparian wetlands. An attempt has been made to summarize existing research in this field to ensure that a contribution will be made to the field of hydraulics. Included in this thesis are results from laboratory models investigating flow through vegetation in riparian wetlands. Particular emphasis in this research has been placed on velocity profile measurement of flow within vegetation. Measurements were taken within various density configuration of rigid simulated vegetation for emergent and submerged cases. In addition, many of the experiments tested the effect on the velocity profile when two distinct layers of vegetation are present. The results described herein should aid in visualization of flow processes within riparian wetlands.
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    Roanoke Urban Stormwater Research: Phase 1 - Discovery Final Report
    Dymond, Randel L.; Aguilar, Marcus F.; Bender, Paul; Hodges, Clayton Christopher (2014-12-01)
    This report is the final product of an 8 month long collaboration between the City of Roanoke’s Environmental, Engineering, Public Works, GIS, and Planning staff, and researchers in the Via Department of Civil and Environmental Engineering at Virginia Tech. This relationship was borne out of a mutual desire for improved urban stormwater science, with an anticipation that a long-term municipal-academic partnership would bring innovation to municipal stormwater management while providing opportunities to further the body of knowledge in this field. This report illustrates the City of Roanoke’s present political and environmental climate with respect to stormwater management by historical account and geographic context. It is descriptive and observational, providing both a foundation to proceed with future work, and a benchmark to measure success. The objective of this report is to characterize the regulations, people, and information that constitute stormwater management in the City of Roanoke. The Introduction is a summary of the City of Roanoke/Virginia Tech Urban Stormwater Research collaboration, and introduces the City as a densely urbanized political entity in the Upper Roanoke River watershed. The Introduction leads into Section I, a review of the Federal and State regulations that compel the City to prevent and treat stormwater runoff pollution, and a description of the City’s compliance strategies. Conversations with City staff and other stakeholders characterized these programs and helped contextualize stormwater management in the City and regionally; these conversations are recorded in Section II. City staff also supported the synopsis of City Geographic Information System data found in Section III by providing the necessary access. Section IV relates the quality and relevance of geographic datasets from external sources, and Section V does the same for water quality and quantity data. Section VI describes the pathways for general public engagement in stormwater in the City and regionally. The report body is bookended by Tables of Contents, Figures, and Tables at the front, and Index of Terms, References, and alphabetized Bibliography in the back. Supplemental information, including additional tables, figures, and text is found in the Appendices, organized using the same structure as the report. The submission of this report marks the end of the initial Discovery Phase of this research relationship; the resources have been discovered, collected, and organized. This also marks the commencement of the second phase, which focuses on a single City watershed as a precedent for future watershed planning. The completion of this first Phase, and even the anticipated completion of the next, do not bring finality to this work, but represent benchmarks along the way to the now unified objective of improving water quality in the City’s waterways – the terminal measure of success in this research project.
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    Simulation and Assessment of Long-Term Stormwater Basin Performance under Real-Time Control Retrofits
    Schmitt, Zoe Kendall (Virginia Tech, 2019-06-18)
    The use of real-time control (RTC) as an adaptation technique for improving existing stormwater systems has been gaining attention in recent years for its ability to enhance water quality and quantity treatment. A case study RTC retrofit of seven existing detention basins was simulated for a small (162 ha), urbanized watershed in Blacksburg, VA. Two heuristic, reactive control algorithms were tested and compared for their ability to improve hydraulic conditions at each detention basin and the watershed outlet through manipulation of an actuated valve, under various permutations of RTC retrofitting (single facility, multiple facilities, etc.). Change in peak flow during 24-hour design storms was assessed. RTC only reduced peak flows at some of the facilities for storms with a return period of 2 years or less. For larger storms, RTC maintained or increased peak flow rates. During a 15-year simulation with historic precipitation data, total duration of erosive flows was reduced for most facility retrofit simulations; however, the duration of high intensity flows increased, or remained unchanged. This result was also reflected at the watershed outlet.
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    Urban Erosion Potential Risk Mapping with GIS
    Weikmann, Amanda Maria (Virginia Tech, 2018-01-19)
    Federal, state and local governments are increasingly focused on the effects of development on water quality and quantity. With waterbodies being especially sensitive to certain pollutants, such as sediment and nutrients, regulations have been put in place to control the amount of pollutant that gets discharged. Sediment is a cause for concern as it originates during both rural and urban activities, and often carries other pollutants (metals, nutrients, etc.) with it. Existing erosion models focus primarily on estimating erosion from agricultural watersheds. Methods are needed to predict areas with high erosive potential (EP) in urban watersheds. Highlighting highly erosive areas in urbanized watersheds allows for the prioritization of maintenance and installation of Stormwater Control Measures (SCMs), and monitoring of sediment by municipal planners and engineers. This study utilizes commonly available geospatial layers in conjunction with a computational procedure to compute relative EP risk throughout a target urban watershed. A case study of the developed methodology was performed on a watershed in Blacksburg, VA, to generate EP risk maps. Results of the study indicate areas of erosive potential within the target watershed and provide a methodology for creating erosion potential risk maps for use by municipal planners and engineers