VTechWorks Repository :: Browsing by Author "Hester, Erich Todd"

Browsing by Author "Hester, Erich Todd"

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Analysis, Modeling, and Forecasting Of Urban Flooding
Brendel, Conrad (Virginia Tech, 2020-04-08)
As the world becomes more urbanized and heavy precipitation events increase in frequency and intensity, urban flooding is an emerging concern. Urban flooding is caused when heavy rainfall collects on the landscape, exceeding the capacity of drainage systems to effectively convey runoff. Unlike riverine and coastal flooding, urban flooding occurs frequently, and its risks and impacts are not restricted to areas within floodplains or near bodies of water. The objective of this dissertation is to improve our understanding of urban flooding and our capability to predict it through the development of tools and knowledge to assist with its analysis, modeling, and forecasting. To do this, three research objectives were fulfilled. First, the Stream Hydrology And Rainfall Knowledge System (SHARKS) app was developed to improve upon existing real-time hydrologic and meteorological data retrieval/visualization platforms through the integration of analysis tools to study the hydrologic processes influencing urban flooding. Next, the ability to simulate the hydrologic response of urban watersheds with large storm sewer networks was compared between the fully distributed Gridded Surface/Subsurface Hydrologic Analysis (GSSHA) model and the semi-distributed Storm Water Management Model (SWMM). Finally, the Probabilistic Urban Flash Flood Information Nexus (PUFFIN) application was created to help users evaluate the probability of urban flash flooding and to identify specific infrastructure components at risk through the integration of high-resolution quantitative precipitation forecasting, ensemble forecasting, and hydrologic and hydraulic modeling. The outcomes of this dissertation provide municipalities with tools and knowledge to assist them throughout the process of developing solutions to their site-specific urban flooding issues. Specifically, tools are provided to rapidly analyze and respond to rainfall and streamflow/depth information during intense rain events and to perform retrospective analysis of long-term hydrological processes. Evaluations are included to help guide the selection of hydrologic and hydraulic models for modeling urban flooding, and a new proactive paradigm of probabilistic flash flood guidance for urban areas is introduced. Finally, several potential directions for future work are recommended.
A Coupled Hydrologic-Economic Modeling Framework for Evaluating Alternative Options for Reducing Watershed Impacts in Response to Future Development Patterns
Amaya, Maria Teresa (Virginia Tech, 2022-04-28)
Economic input-output (I-O) and watershed models provide useful results but when seeking to integrate these systems, the structural, spatial, and temporal differences between these models must be carefully considered. To reconcile these differences, a hydrologic-economic modeling framework is designed to couple an economic model with a watershed model. A physically constrained, I-O model, RCOT, is used to represent the economic system in this framework because it provides sectoral detail for a regional economy and calculates physical resource quantities used by these sectors. Uniquely, it also allows for technology options for all sectors and minimizes the resource use based on environmental constraints imposed by the watershed, which adds complexity to the representation of the economic system and its interactions with the watershed system. To represent the watershed system in this framework, the Hydrological Simulation Program-Fortran (HSPF) is used. An HSPF model has been calibrated to represent the hydrological processes of Cedar Run Watershed by the Occoquan Watershed Monitoring Laboratory (OWML). Thus, the capabilities of this framework are demonstrated using strategic scenarios developed to examine future development patterns that may occur within Fauquier County, northern Virginia, and its local basin, Cedar Run Watershed. The scenarios evaluate both the downstream and seasonal impacts on water flow and nitrogen concentration within the watershed, and the changes made within the economic system in response to these impacts. For these scenarios, the most efficient solution is the one that minimizes the use of resource inputs within the economic sectors, including developed land, water withdrawn, and applied nitrogen, which in turn inform watershed health. The scenario results demonstrate that this coupled hydrologic-economic modeling framework can overcome the spatial differences of the individual models and can capture the interactions between watershed and economic systems at a temporal resolution that expands the types of questions one can address beyond those that can be analyzed using these models separately.
Development and Evaluation of System Dynamics Education Modules for Complex Socioenvironmental Systems
Costello, Ryan Patrick (Virginia Tech, 2023-05-30)
Complex socioenvironmental problems such as food, energy and water shortages, health impacts from environmental contamination and global climate change present significant challenges to the global community. Addressing these problems will require an interdisciplinary systems-thinking approach that coordinates problem-solving between practitioners of varied disciplines including engineers, physical scientists, economists and other social scientists. Civil and environmental engineers have distinct technical skills necessary to help address these challenges as part of coordinated multidisciplinary efforts towards the achievement of comprehensive and sustainable resolutions to these problems. Ensuring civil and environmental engineers are trained to think and work in this multidisciplinary exchange requires incorporation of systems-thinking into engineering academic curricula. Attempts have been made to incorporate these skill sets into civil and environmental engineering (CEE) coursework. These efforts, as well as evaluation of their effectiveness in training CEE students to think systemically, have lacked in coordination to integrate them as part of the overarching academic curricula. This research advances the current body of knowledge regarding incorporation of systems-thinking into CEE coursework by examining the impacts of system dynamics model based educational tools on systems-thinking learning outcomes of CEE students in a one-semester CEE elective course. The findings suggest that system dynamics modeling can be an effective tool in educating future systems thinkers in the CEE disciplines.
The Exchange of Fine Muddy Sediment in Gravel-Bed Fluvial Systems
Schiller, Brayden Jeffery (Virginia Tech, 2024-05-31)
The presence of fine muddy sediment (grain size < 0.1 mm) in streams has many impacts on the fluvial system and those relying on it, both humans and aquatic biota. Previously, fine sediment was considered a washload and has been ignored in transport models. More recently, it has been treated as being transported once the surface gravel layer that stores it is able to be mobilized. We propose that the surface layer need not be mobilized in order for muddy sediment to travel through the fluvial system in a series of erosive and depositional events. Our first study uses a new in situ device to show how mud entrainment from immobile gravel beds behaves cohesionlessly and can be modeled using the framework of classic sand-based models modified to account for hiding effects present in the stream bed. It also provides a method to predict how deep into the surface layer of gravel entrainment of fine sediment will occur given flow and stream bed characteristics. The second study investigates the primary pathway that fine sediment is traveling to get captured within bluehead chub fish nests. It was determined that more deposition of mud occurred in the upstream half of the nest concluding that the primary pathway was hyporheic pumping through the nest. Capture efficiencies of the nests were also found to increase as the length of nests increased. Both of these studies provide supporting evidence in the need to transition modeling fine sediment transport as a series of deposition and resuspension.
Impact of Stream Restoration on Flood Attenuation and Channel-Floodplain Exchange During Small Recurrence Interval Storms
Federman, Carly Elizabeth (Virginia Tech, 2022-01-18)
Extreme flooding and excess nutrient pollution have been detrimental to river health under increased environmental stress from human activities (e.g., agriculture, urbanization). Riverine flooding can be detrimental to human life and infrastructure yet provides important habitat and ecosystem services. Traditional flood control approaches (e.g., levees, dams) negatively impact habitat and ecosystem services, and cause flooding elsewhere along the river. Prior studies have shown that stream restoration can enhance flood attenuation, and increased exchange of water between the channel and floodplain can improve water quality. However, the effects of floodplain restoration during small and sub annual recurrence interval storms have not been thoroughly studied, nor have cumulative impacts of floodplain restoration on water quality at watershed scales. We used HEC-RAS to perform 1D unsteady simulations on a 2nd-order generic stream from the Chesapeake Bay Watershed to study flood attenuation under small and sub-annual recurrence interval storms (i.e., 2-year, 1-year, 0.5-year, and monthly). In HEC-RAS we varied percent of channel restored, location of restoration, bank height of restoration, floodplain width, and floodplain Manning's n. Overall, stream restoration reduced peak flow (up to 37%) and decreased time to peak (up to 93%). We found the timing of tributary inflows could obscure the attenuation achieved, and even reverse the trends with certain parameters in the sensitivity analysis. The greatest exchange with the floodplains (greater volume and exchange under more recurrence interval storms) was observed from Stage 0 restoration, which reduces bank height more than other approaches. We also conducted a quantitative literature synthesis of nitrate removal rates from stream restoration projects. We focused on how removal rates varied with properties relevant at watershed scales, such as effects of stream order. The resulting database will aid in determining which stream restoration parameters better reduce nutrient loads and in simulating the effects of stream restoration on water quality at watershed scales. Floodplain restoration practices, and particularly Stage 0 approaches, enhance flood attenuation which can help to counteract urban hydrologic effects.
In the Zone: the Effects of Soil Pipes and Dunes on Hyporheic and Riparian Zone Hydraulics and Biogeochemistry
Lotts, William Seth (Virginia Tech, 2022-06-10)
Streams and rivers are a vital part of our ecosystem. They are imperiled by human ecological activities such as urbanization, industrialization, and agriculture which discharge excess nitrate and other pollutants into our waterways. Here, this dissertation seeks to understand the physical and biogeochemical processes which attenuate pollutants in stream corridors. The focus is hyporheic zones which form the interface between surface water and groundwater below and adjacent to stream channels, and riparian zones which form the interface between channels and adjacent uplands, both of which can attenuate pollutants. In this context, soil-pipes can dominate subsurface hydraulics. This research first employed MODFLOW and MT3D-USGS to model transient hyporheic hydraulics and nitrate transport in a length of riparian/riverbank soil to probe the effects of soil pipes on hydraulics and denitrification due to peak flow events in the channel. Findings showed that inserting just one soil pipe 1.5 m in length caused a ~75% increase in both hyporheic exchange and denitrification. A rough upscaling showed soil pipes could remove up to ~3% of nitrate along a 1-km reach. Next, the ability of soil pipes to bypass the often championed ability of riparian buffers to remove nitrate migrating from uplands to the channel was evaluated. This effort also employed MODFLOW and MT3D-USGS to simulated hydraulics and nitrate removal along a length of riparian soil. Findings showed that soil pipes increased flow of nitrate to the banks by five orders of magnitude in some cases. We posited a non-dimension parameter which governs when nitrate bypass is significant. In addition to soil pipes, dune bedforms can also enhance hyporheic exchange, primarily in the stream/riverbed. Again employing MODFLOW but now pairing with the transport code SEAM3D to simulate microbially-mediated aerobic metabolism of dissolved organic carbon and dissolved oxygen, the combined effects of dune translation and microbial growth and death were explored. Major findings include that neglecting microbial growth can lead to inaccurate modeling of biogeochemistry, and that aerobic metabolism increased with celerity. The results herein bolster knowledge of natural pollutant attenuation in stream and river corridors, and have implications for pollutant mitigation strategy and stream credit allocation.
Laboratory Experiments on Mud Flocculation Dynamics in the Fluvial and Estuarine Environments
Abolfazli, Ehsan (Virginia Tech, 2023-06-06)
Due to the flocculation process, suspended mud aggregates carried by rivers and streams can undergo changes in their size, shape, and settling velocity in response to environmental drivers such as turbulence, sediment concentration, organic matter (OM), and salinity. Some have assumed that salt is necessary for floc formation, and that mud, therefore, reaches the estuary unflocculated. Yet mud flocs exist in freshwater systems long before the estuarine zone, likely due to the presence of OM and ions in the water that facilitate binding and aggregation of mud particles. This research aimed to examine the flocculation state of mud over the fluvial as well as fluvial to marine transition (FtMT) zones of the Mississippi River basin and how salinity, or the ion concentration of water, and organic matter independently and together affect flocculation. Suspended mud was found to be mostly flocculated in the headwaters of the Mississippi River in southwest Virginia, USA. However, increasing the ion concentration of water samples to levels measured following winter storms changed the size distribution of suspended particles, led to more of the mud existing in large flocs, and resulted in an overall increase in average size by about 40%, thereby increasing the settling rate of the mud relative to the suspensions without salt. These results suggested that potential negative effects of road salts on mud deposition should be investigated further. Additional experiments were used to examine the flocculation of a natural mud sample with and without OM showed that the rate of floc growth and equilibrium size both increase with salinity regardless of the presence or absence of OM. However, the response of both to salinity was stronger when OM was present. In deionized water, natural sediment with OM was seen to produce large flocs. However, the size distribution of the suspension tended to be bimodal. With the addition of salt, increasing amounts of unflocculated material became bound within flocs, producing a more unimodal size distribution. Here, the enhancing effects of salt were noticeable at even 0.5 ppt, and increases in salinity past 3 to 5 ppt only marginally increased the floc growth rate and final size. A salinity-dependent model to account for changes in floc growth rate and equilibrium size was presented. Laboratory experiments on the sediment suspended in the lower reaches of the Mississippi River were used to provide further insight on the mud flocs behavior in the FtMT. Turbulence shear rate, a proxy for the river hydrodynamics, was found to be the most influential factor in mud floc size. While artificial increase in salinity by adding of salts did not lead to considerable increase in floc size, addition of water collected from the Gulf of Mexico enhanced the flocculation. These effects were speculated to originate from the biomatter composition of the Gulf water, particularly where the nutrient-rich Mississippi River water reaches the marine water.
Mixing and Attenuation of Upwelling Groundwater Contaminants in the Hyporheic Zone
Santizo, Katherine Yoana (Virginia Tech, 2021-06-16)
The hyporheic zone is the reactive interface between surface water and groundwater found beneath streams and rivers, where chemical gradients and an abundant biological presence allow beneficial attenuation of contaminants. Such attenuation often requires reactants from surface water and groundwater to mix, but few studies have explored the controls on mixing of upwelling groundwater water in the hyporheic zone and its potential to foster mixing-dependent reactions. The goals of this dissertation are therefore to evaluate the effects of (1) hydraulic controls and (2) reaction kinetic controls on hyporheic mixing and mixing-dependent reactions, and (3) use two-dimensional visualization techniques to quantify patterns of hyporheic mixing and mixing-dependent reactions. These objectives were addressed by hyporheic zone simulations using a laboratory sediment mesocosm and numerical models. In the laboratory, a hyporheic flow cell was created to observe both conservative dye mixing and abiotic mixing-dependent reaction. The numerical models MODFLOW and SEAM3D were then used to simulate the experimental data to better understand hydraulic and transport processes underlying laboratory observations and provide sensitivity analysis on hydraulic and reaction kinetic parameters. Visualization techniques showed a distinct mixing zone developing over time for both conservative and reactive conditions. Mixing zone thickness in both conditions depended on surface water head drop and the ratio of boundary inflows of surface water and groundwater (inflow ratios). The abiotic reaction caused the mixing zone to shift even under steady-state hydraulics indicating that hyporheic zone mixing-dependent reactions affect the location of mixing as chemical transformations take place. The numerical model further showed the production zone to be thicker than the mixing zone and located where reactants had already been depleted. Finally, mapping of two-dimensional microbial respiration (i.e., electron acceptor utilization) patterns in streambed sediments using dissolved oxygen and carbon dioxide planar optodes showed that coupling multiple such 2D chemical profiles can enhance understanding of microbial processes in the hyporheic zone. Temporal dynamics for these chemical species revealed development of spatial heterogeneity in microbial respiration and hence microbial activity. Our results show key hydrologic and biogeochemical controls on hyporheic mixing and mixing-dependent reactions. These reactions represent a last opportunity for attenuation of groundwater borne contaminants prior to entering surface water.
Modeling the Impact of Flood Pulses on Disease Outbreaks in Large Water Basins with Scarce Data
Abu-Saymeh, Riham Khraiwish (Virginia Tech, 2023-05-30)
Large river water basins play a critical role in the economic, health, and biodiversity conditions of a region. In some basins, such as the Zambezi River Basin, extreme weather events introduce cycles of drought and heavy rainfall that can have extreme impacts on local communities vulnerable to environmental shifts. Annual flood pulse dynamics drive ecological dynamics in the system. In the dry season, water dependent wildlife in northern Botswana concentrates along the Chobe River- Floodplains. Elephant concentration, in particular, is matched to surface water quality declines. These flood pulse events have been linked to diarrheal disease outbreaks in the local population, the magnitude of which is associated positively with flood height. Modeling these interactions can advance our ability to predict events and develop mitigation and prevention actions. However, many challenges hinder this development including availability of data in regions that lack resources and the difficulties in create models for such large basins that account for overland water movement. This thesis presents work focused on addressing these challenges. Chapter 2 reports the development of a freely available Large Basin Data Portal (LBDP) that can be used to identify and create critical inputs for hydrodynamic models. This portal was used to create a hydrological model of the Upper Zambezi River Basin model (Chapter 3), a hydrodynamic model of the one of the three subbasins of the Zambezi River. The model was used to calculate downstream river discharges entering the Chobe-Zambezi Floodplains based on upstream rain events. The Upper Zambezi River Basin model was integrated with another more detailed model of the Chobe- Zambezi Floodplains (Chapter 4) that is designed to model the Chobe River and flood water movement in the floodplains. The models were created using the set of MIKE modeling software. The models were used to study various scenarios including water reductions that might occur due to climate change or drought and water increase that might be associated with extreme weather events.
Moving beyond the stream reach: Assessing how confluences alter ecosystem function and water quality in freshwater networks
Plont, Stephen James (Virginia Tech, 2023-05-22)
In freshwater networks, the sources, movement, and cycling of carbon and nutrients are shaped both by in-stream processes and the surrounding landscape. Streams receive and transport materials from upstream and terrestrial sources that support in-stream ecosystem processes and regulate downstream water quality. Understanding how these processes within a stream alter downstream carbon and nutrient fluxes is needed to assess the functional role of lotic ecosystems on the landscape. Further, predictions of how materials cycle and move throughout freshwater networks are derived from measurements at the stream reach scale which deliberately avoid complex geomorphology such as stream confluences. As a result, the impact of stream confluences on in-stream ecosystem processes and the fate of carbon and nutrients in freshwater networks has been overlooked. In this dissertation, I seek to address the following questions: (1) How are coupled carbon and nitrogen cycles altered by land use? (2) To what extent can rates of in-stream organic carbon removal inform our understanding of the role of streams in landscape carbon fluxes? (3) How are carbon metabolism and nutrient uptake altered downstream of a stream confluence? (4) How do confluences alter the transport and fate of carbon and nutrients within a freshwater network? In Chapter 2, I showed that the fate of organic carbon and nitrate are similar in headwater streams across the United States. Organic carbon travels longer distances before being respired in agricultural and urban streams compared to reference streams, suggesting that human modifications to landscapes impact carbon cycling and transport in streams. In Chapter 3, I demonstrated how rates of in-stream organic carbon removal can be used to quantify terrestrial-aquatic linkages and showed that laboratory bioassays systematically underestimate ecosystem organic carbon fluxes compared to whole-stream metabolism measurements. In Chapter 4, I conducted whole-ecosystem manipulation experiments to assess how ecosystem processes are altered by a confluence. I found that carbon metabolism and phosphorus uptake are suppressed downstream of a confluence and that rates of organic carbon uptake are spatially variable throughout a confluence mixing zone. In Chapter 5, I examined potential reach-scale and watershed-scale drivers to explain patterns of organic matter and nutrient chemistry downstream of confluences throughout a stream network. Reaches downstream of confluences were geomorphically and biogeochemically distinct from upstream reaches, and differences in upstream and tributary reach chemistry or drainage area did not explain patterns of biologically reactive parameters at confluences. My dissertation highlights the importance of in-stream ecosystem processes in driving the cycling and downstream fate of carbon and nutrients. I show how rates of whole-stream carbon metabolism can be used to better constrain terrestrial-aquatic organic carbon fluxes. I investigate the potentially disproportionate role of ecosystem interfaces, namely stream confluences, in determining the cycling and fate of carbon and nutrients in freshwater networks. This work challenges assumptions around controls over water quality in freshwater networks and asserts that by ignoring (1) contributions of all in-stream processes to whole-ecosystem function and (2) how confluences alter those processes, we risk misrepresenting the role of running waters in determining the fluxes and fate of carbon and nutrients from the reach- to the network-scale.
Seasonal Variation of Mud Floc Sizes in Two Small Freshwater Streams
Delay, Lailee Alena (Virginia Tech, 2024-06-05)
Flocculation is not only an important part of sediment dynamics within coastal marine waters, but is also a factor of sediment transport within small freshwater streams in Blacksburg, Virginia. The goal of this project was to develop a relationship between floc sizes and stream characteristics (temperature, salinity, chlorophyll-a, organic content, TSS, pH) and to compare how that relationship varies seasonally and spatially across two streams in the same watershed with a similar drainage area but different land uses within these areas. Microscopic images of flocs and water samples were taken within two local streams every two to four weeks throughout the span of one year. The images were analyzed to obtain the floc sizes and the water samples were tested in a lab for various stream properties. The compiled data from the entire year were analyzed to determine if there was a seasonal relationship between floc sizes and the various properties of the water. The process was also repeated at multiple locations along the entire length of both of the streams once in the summer and once in the winter to see if there was a spatial relationship within a single stream. Our study found that significant rainfall events tend to have the greatest effect on floc size in the small headwater streams. However, many of the individual variables alone do not correlate strongly with floc size and a combination of variables may be the best way to analyze the floc size.
Watershed Scale Impacts of Floodplain Restoration on Nitrate Removal and the Practical Applications of Modeling Cumulative Floodplain Restoration Hydraulics
Oehler, Morgan Ashleigh (Virginia Tech, 2024-06-14)
Human land use practices such as urbanization and agriculture contribute excess nutrients (nitrogen and phosphorus) and runoff volumes to rivers that degrade aquatic ecosystems and cause a loss of river functions such as nutrient processing and flood attenuation. Floodplain restoration increases floodplain exchange and is commonly implemented to improve water quality and reduce flood impacts at watershed scales. However, the effect of multiple restoration projects at the watershed scale is not well studied. We addressed this knowledge gap by two studies. The first study evaluated the impact of cumulative and spatially varying Stage-0 and bankfull floodplain restoration on nitrate removal in a generic 4th-order Virginia Piedmont watershed for small and sub-annual storm sizes (i.e. 2-year, 1-year, half-year, and monthly recurrence intervals). We used HEC-RAS hydraulics results from a prior study together with a nitrate removal model coded in R. Results indicated that watershed nitrate removal varied depending on the location of restoration in the watershed and where removal was evaluated. The greatest reductions in nitrate loads were observed in the same part of the river network where restoration occurred, with diminished impacts downstream. Removal also increased with increasing stream order/river size. However, removal was generally of small magnitude, with up to 1% or 19% of the watershed load removed for median or 90th-percentile removal rates, respectively. We estimated removal for our restoration scenarios under the Chesapeake Bay Program Protocols and found the removal rate to also be a critical factor in determining the efficiency of restoration project. Other controlling factors for nitrate removal were the amount of restoration and storm size. The second study entailed modeling cumulative restoration in a case study watershed to assess the impacts on nutrient removal and flood attenuation. We built a 1D HEC-RAS model of the 4th-order Gwynns Falls watershed near Baltimore MD using georeferenced HEC-RAS model geometries from the Maryland Department of the Environment and simulated unsteady stormflow hydraulics due to cumulative Stage-0 floodplain restoration for small and sub-annual storms. Restoration actually increased peak flow on the main channel (up to 0.9%) due to slowing of the flood wave on the main channel which was then better synchronized with tributary inflows. Restoration increased nitrate removal but at low levels (up to 0.12% or 2.6% removal for a median and 90th-percentile removal rate respectively) due to the small footprint of restoration in the watershed (up to 21.4% of the main channel was restored). These small and sometimes adverse outcomes occurred in response to what would be expensive restoration. Therefore, we argue for large-scale solutions to address watershed-scale water quality and flooding issues yet acknowledge re-evaluation of restoration goals against other societal priorities may be necessary. Overall, our results highlight the potential value and limitations of floodplain restoration in reducing flooding and nitrate exports at the channel network scale and provide practical insight for application of floodplain modeling at the watershed scale.

Browsing by Author "Hester, Erich Todd"

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