VTechWorks Repository :: Browsing by Author "Irish, Jennifer L."

Browsing by Author "Irish, Jennifer L."

Now showing 1 - 20 of 46

Advancement of Using Portable Free Fall Penetrometers for Geotechnical Site Characterization of Energetic Sandy Nearshore Areas
Albatal, Ali Hefdhallah Ali (Virginia Tech, 2018-04-24)
Portable Free Fall Penetrometers (PFFPs) are lightweight tools used for rapid and economic characterization of surficial subaqueous sediments. PFFPs vary in weight, shape and size with options for using add-on units. The different configurations enable deployments in various environments and water depths, including the nearshore zone where conventional methods are challenged by energetic hydrodynamics and limited navigable depth. Moreover, PFFPs offer an opportunity to reduce the high site investigation costs associated with conventional offshore geotechnical site investigation methods. These costs are often a major obstacle for small projects serving remote communities or testing novel renewable energy harvesting machines. However, PFFPs still face issues regarding data analysis and interpretation, particularly in energetic sandy nearshore areas. This includes a lack of data and accepted analysis methods for such environments. Therefore, the goal of this research was to advance data interpretation and sediments characterization methods using PFFPs with emphasis on deployments in energetic nearshore environments. PFFP tests were conducted in the nearshore areas of: Yakutat Bay, AK; Cannon Beach, AK; and the U.S. Army Corps of Engineers' Field Research Facility's beach, Duck, NC. From the measurements, the research goal was addressed by: (1) introducing a methodology to create a regional sediment classification scheme utilizing the PFFP deceleration and pore pressure measurements, sediment traces on the probe upon retrieval, and previous literature; (2) investigating the effect of wave forcing on the sediments' behavior through correlating variations in sediment strength to wave climate, sandbar migration, and depth of closure, as well as identifying areas of significant sediment mobilization processes; and (3) estimating the relative density and friction angle of sand in energetic nearshore areas from PFFP measurements. For the latter, the field data was supported by vacuum triaxial tests and PFFP deployments under controlled laboratory conditions on sand samples prepared at different relative densities. The research outcomes address gaps in knowledge with regard to the limited studies available that investigate the sand geotechnical properties in energetic nearshore areas. More specifically, the research contributes to the understanding of surficial sediment geotechnical properties in energetic nearshore areas and the enhancement of sediment characterization and interpretation methods.
Advances in Morphodynamic Modeling of Coastal Barriers: A Review
Hoagland, Steven W. H.; Jeffries, Catherine R.; Irish, Jennifer L.; Weiss, Robert; Mandli, Kyle; Vitousek, Sean; Johnson, Catherine M.; Cialone, Mary A. (ASCE, 2023-05-30)
As scientific understanding of barrier morphodynamics has improved, so has the ability to reproduce observed phenomena and predict future barrier states using mathematical models. To use existing models effectively and improve them, it is important to understand the current state of morphodynamic modeling and the progress that has been made in the field. This manuscript offers a review of the literature regarding advancements in morphodynamic modeling of coastal barrier systems and summarizes current modeling abilities and limitations. Broadly, this review covers both event-scale and long-term morphodynamics. Each of these sections begins with an overview of commonly modeled phenomena and processes, followed by a review of modeling developments. After summarizing the advancements toward the stated modeling goals, we identify research gaps and suggestions for future research under the broad categories of improving our abilities to acquire and access data, furthering our scientific understanding of relevant processes, and advancing our modeling frameworks and approaches.
Anticipating and adapting to the future impacts of climate change on the health, security and welfare of low elevation coastal zone (LECZ) communities in Southeastern USA
Allen, Thomas; Behr, Joshua; Bukvic, Anamaria; Calder, Ryan S. D.; Caruson, Kiki; Connor, Charles; D'Elia, Christopher; Dismukes, David; Ersing, Robin; Franklin, Rima; Goldstein, Jesse; Goodall, Jonathon; Hemmerling, Scott; Irish, Jennifer L.; Lazarus, Steven; Loftis, Derek; Luther, Mark; McCallister, Leigh; McGlathery, Karen; Mitchell, Molly; Moore, William B.; Nichols, C. Reid; Nunez, Karinna; Reidenbach, Matthew; Shortridge, Julie; Weisberg, Robert; Weiss, Robert; Donelson Wright, Lynn; Xia, Meng; Xu, Kehui; Young, Donald; Zarillo, Gary; Zinnert, Julie C. (MDPI, 2021-10-29)
Low elevation coastal zones (LECZ) are extensive throughout the southeastern United States. LECZ communities are threatened by inundation from sea level rise, storm surge, wetland degradation, land subsidence, and hydrological flooding. Communication among scientists, stakeholders, policy makers and minority and poor residents must improve. We must predict processes spanning the ecological, physical, social, and health sciences. Communities need to address linkages of (1) human and socioeconomic vulnerabilities; (2) public health and safety; (3) economic concerns; (4) land loss; (5) wetland threats; and (6) coastal inundation. Essential capabilities must include a network to assemble and distribute data and model code to assess risk and its causes, support adaptive management, and improve the resiliency of communities. Better communication of information and understanding among residents and officials is essential. Here we review recent background literature on these matters and offer recommendations for integrating natural and social sciences. We advocate for a cyber-network of scientists, modelers, engineers, educators, and stakeholders from academia, federal state and local agencies, non-governmental organizations, residents, and the private sector. Our vision is to enhance future resilience of LECZ communities by offering approaches to mitigate hazards to human health, safety and welfare and reduce impacts to coastal residents and industries.
Barrier Island Morphodynamic Insights from Applied Global Sensitivity Analysis and Decadal Exploratory Modeling
Hoagland, Steven William Harvey (Virginia Tech, 2024-10-02)
Barrier islands serve as valuable resources for coastal communities by reducing backbarrier flooding, providing wildlife habitat, and creating local economic activity through opportunities for recreation and tourism. Because the benefits of these islands are linked to their morphology, coastal resource planners must consider what management alternatives will maximize these benefits, considering both short- and long-term goals. Recent advances in long-term computational modeling of barrier island, marsh, and lagoon systems have created opportunities for gaining additional insights into the morphodynamics of these systems, which may help planners make better-informed coastal management decisions. In this series of studies, a recently developed long-term barrier-marsh-lagoon model is evaluated to better understand system morphodynamics and applied to a real barrier island system in the mid-Atlantic to understand its vulnerabilities and the potential impacts of management alternatives. In the first study, a comprehensive review of advances in barrier island morphodynamic modeling was presented. In the second study, a global sensitivity analysis method, the Sobol method, was used to explore the parameter space of the barrier-marsh-lagoon model. The significant influence of initial barrier geometry, the combination of parameters required for short-term drowning to occur, and the significant role of tidal dispersion on backbarrier sediment dynamics were morphodynamic insights drawn from this study. In the third study, five global sensitivity analysis methods were evaluated based on their ability to rank parameters, converge to stable results, and their reliability. Groups of the most significant parameters were generally identified by all methods; however, the Morris method exceeded all others in terms of performance, especially its ability to converge and its reliability. VARS performed second best, on average, with better convergence and reliability results than the Sobol method, and with lower simulation counts. In the fourth study, the long-term model was applied to a mid-Atlantic barrier island and used to assess the island's vulnerabilities to sea level rise, overwash, and the impact of coastal management alternatives. Thin-layer placement and beach nourishment were found to be effective at sustaining the marsh and minimizing island retreat, respectively.
Bayesian Methods for Intensity Measure and Ground Motion Selection in Performance-Based Earthquake Engineering
Dhulipala, Lakshmi Narasimha Somayajulu (Virginia Tech, 2019-03-19)
The objective of quantitative Performance-Based Earthquake Engineering (PBEE) is designing buildings that meet the specified performance objectives when subjected to an earthquake. One challenge to completely relying upon a PBEE approach in design practice is the open-ended nature of characterizing the earthquake ground motion by selecting appropriate ground motions and Intensity Measures (IM) for seismic analysis. This open-ended nature changes the quantified building performance depending upon the ground motions and IMs selected. So, improper ground motion and IM selection can lead to errors in structural performance prediction and thus to poor designs. Hence, the goal of this dissertation is to propose methods and tools that enable an informed selection of earthquake IMs and ground motions, with the broader goal of contributing toward a robust PBEE analysis. In doing so, the change of perspective and the mechanism to incorporate additional information provided by Bayesian methods will be utilized. Evaluation of the ability of IMs towards predicting the response of a building with precision and accuracy for a future, unknown earthquake is a fundamental problem in PBEE analysis. Whereas current methods for IM quality assessment are subjective and have multiple criteria (hence making IM selection challenging), a unified method is proposed that enables rating the numerous IMs. This is done by proposing the first quantitative metric for assessing IM accuracy in predicting the building response to a future earthquake, and then by investigating the relationship between precision and accuracy. This unified metric is further expected to provide a pathway toward improving PBEE analysis by allowing the consideration of multiple IMs. Similar to IM selection, ground motion selection is important for PBEE analysis. Consensus on the "right" input motions for conducting seismic response analyses is often varied and dependent on the analyst. Hence, a general and flexible tool is proposed to aid ground motion selection. General here means the tool encompasses several structural types by considering their sensitivities to different ground motion characteristics. Flexible here means the tool can consider additional information about the earthquake process when available with the analyst. Additionally, in support of this ground motion selection tool, a simplified method for seismic hazard analysis for a vector of IMs is developed. This dissertation addresses four critical issues in IM and ground motion selection for PBEE by proposing: (1) a simplified method for performing vector hazard analysis given multiple IMs; (2) a Bayesian framework to aid ground motion selection which is flexible and general to incorporate preferences of the analyst; (3) a unified metric to aid IM quality assessment for seismic fragility and demand hazard assessment; (4) Bayesian models for capturing heteroscedasticity (non-constant standard deviation) in seismic response analyses which may further influence IM selection.
Boulder dislodgement during coastal storms and tsunamis: Insights from a new ensemble model
Weiss, Robert; Irish, Jennifer L.; Goodman Tchernov, Beverly (American Geophysical Union, 2022-03-01)
Boulders are excellent candidate deposits to study coastal inundation events by storms and tsunamis due to their significant preservation potential. However, it is difficult to infer how and what forcing dislodged the boulder. We present a new model that enables ensemble and Monte-Carlo-type simulations to study the sensitivity of boulder, the fluid flow, and environmental parameters. Our examples show that boulder transport is complex and nonlinear, and to acknowledge the uncertainties of the boulder's preexisting transport conditions, a range of velocities and environmental parameters should be used to quantify the flow that caused boulder dislodgement.
Characterization and prediction of tropical cyclone forerunner surge
Liu, Yi; Irish, Jennifer L. (Elsevier, 2019)
Forerunner surge, a water level rise ahead of tropical cyclone landfall, often strikes coastal communities unexpectedly, stranding people and increasing loss of life. Surge forecasting systems and emergency managers almost exclusively focus on peak surge, while much less attention is given to forerunner surge. To address the need for fast and accurate forecasting of forerunner surge, we analyze high-fidelity surge simulations in Virginia, New York/New Jersey and Texas and extract physical scaling laws between readily available storm track information and forerunner surge magnitude and timing. We demonstrate that a dimensionless relationship between central-pressure scaled surge and wind-duration scaled time may effectively be used for rapid forerunner surge forecasting, where uncertainty is considered. We use our method to predict forerunner surge for Hurricanes Ike (2008)—a significant forerunner surge event—and Harvey (2017). The predicted forerunner surge 24 to 6 hours before Hurricane Ike’s landfall ranged from 0.4 to 2.8 m, where the observed forerunner surge ranged from 0.4 to 2.6 m. This new method has the potential to be incorporated into real-time surge forecasting systems to aid emergency management and evacuation decisions.
Development and Uncertainty Quantification of Hurricane Surge Response Functions and Sea-Level Rise Adjustments for Coastal Bays
Taylor, Nicholas Ramsey (Virginia Tech, 2014-06-16)
Reliable and robust methods of extreme value based hurricane surge prediction, such as the Joint Probability Method (JPM), are critical in the coastal engineering profession. The JPM has become the preferred surge hazard assessment method in the United States; however, it has a high computational cost: one location can require hundreds of simulated storms, and more than ten thousand computational hours to complete. Optimal sampling methods that use physics based surge response functions (SRFs), can reduce the required number of simulations. This study extends the development of SRFs to bay interior locations at Panama City, Florida. Mean SRF root-mean-square (RMS) errors for open coast and bay interior locations were 0.34 m and 0.37 m, respectively; comparable to expected ADCIRC model errors (~0.3 m—0.5 m). Average uncertainty increases from open coast and bay SRFs were 10% and 12%, respectively. Long-term climate trends, such as rising sea levels, introduce nonstationarity into the simulated and historical surge datasets. A common approach to estimating total flood elevations is to take the sum of projected sea-level rise (SLR) and present day surge (static approach); however, this does not account for dynamic SLR effects on surge generation. This study demonstrates that SLR has a significant dynamic effect on surge in the Panama City area, and that total flood elevations, with respect to changes in SLR, are poorly characterized as static increases. A simple adjustment relating total flood elevation to present day conditions is proposed. Uncertainty contributions from these SLR adjustments are shown to be reasonable for surge hazard assessments.
Effects of future sea level rise on coastal habitat
Von Holle, Betsy; Irish, Jennifer L.; Spivy, Annette; Weishampel, John F.; Meylan, Anne; Godfrey, Matthew H.; Dodd, Mark; Schweitzer, Sara H.; Keyes, Tim; Sanders, Felicia; Chaplin, Melissa K.; Taylor, Nick R. (2019-04)
Sea level rise (SLR) and disturbances from increased storm activity are expected to diminish coastal ecosystems available to nesting species by removing habitat and inundating nests during incubation. We updated the United States Geological Survey's (USGS) Coastal Vulnerability Index, which provides a qualitative and relative assessment of a coastal area's vulnerability to erosion and shoreline retreat as a function of SLR and other factors, for the South Atlantic Bight. We considered a eustatic SLR projection of 14 cm by 2030. We linked long-term survey data for 3 sea turtle species, 3 shorebird species, and 5 seabird species to future coastal erosion vulnerability to SLR to understand effects of future SLR on nesting habitats. Over 2,000 km (43%) of the South Atlantic Bight coastline is projected to have an increase in coastal erosion vulnerability by the 2030s, with respect to its present vulnerability. Future vulnerability of SLR-induced erosion along the South Atlantic Bight is spatially variable, and the 11 coastal study species also varied in their use of coastal habitats with high future coastal vulnerability to SLR. For example, only 23% of high-density nesting habitat for the brown pelican (Pelecanus occidentalis) is expected to be at increased vulnerability to SLR, whereas >70% of the high-nesting density habitat for 2 seabird species (gull-billed tern [Gelochelidon nilotica], sandwich tern [Thalasseus sandvicensis]) is predicted to have higher future coastal erosion vulnerability by 2030. We provide predictions for the level of susceptibility of the study species to erosion from future SLR, which is the first step in managing coastal species for the changing environmental conditions associated with climate change and SLR. (c) 2019 The Authors. Journal of Wildlife Management Published by Wiley Periodicals, Inc. on behalf of The Wildlife Society.
The effects of natural structure on estimated tropical cyclone surge extremes
Resio, Donald T.; Asher, Taylor G.; Irish, Jennifer L. (2017-09)
The past 12 years have seen significant steps forward in the science and practice of coastal flood analysis. This paper aims to recount and critically assess these advances, while helping identify next steps for the field. This paper then focuses on a key problem, connecting the probabilistic characterization of flood hazards to their physical mechanisms. Our investigation into the effects of natural structure on the probabilities of storm surges shows that several different types of spatial-, temporal-, and process-related organizations affect key assumptions made in many of the methods used to estimate these probabilities. Following a brief introduction to general historical methods, we analyze the two joint probability methods used in most tropical cyclone hazard and risk studies today: the surface response function and Bayesian quadrature. A major difference between these two methods is that the response function creates continuous surfaces, which can be interpolated or extrapolated on a fine scale if necessary, and the Bayesian quadrature optimizes a set of probability masses, which cannot be directly interpolated or extrapolated. Several examples are given here showing significant impacts related to natural structure that should not be neglected in hazard and risk assessment for tropical cyclones including: (1) differences between omnidirectional sampling and directional-dependent sampling of storms in near coastal areas; (2) the impact of surge probability discontinuities on the treatment of epistemic uncertainty; (3) the ability to reduce aleatory uncertainty when sampling over larger spatial domains; and (4) the need to quantify trade-offs between aleatory and epistemic uncertainties in long-term stochastic sampling.
Elevation based classification of streams and establishment of regime equations for predicting bankfull channel geometry
Jha, Rajan (Virginia Tech, 2013-09-06)
Since past more than hundred years, fluvial geomorphologists all across the globe have been trying to understand the basic phenomena and processes that control the behavioral patterns of streams. A large number of stream classification systems has been proposed till date, but none of them have been accepted universally. Lately, a large amount of efforts have been made to develop bankfull relations for estimating channel geometry that can be employed for stream restoration practices. Focusing on these two objectives, in this study a new stream classification system based on elevation above mean sea level has been developed and later using elevation as one of the independent and nondimensionalising parameters, universal and regional regime equations in dimensionless forms have been developed for predicting channel geometry at bankfull conditions. To accomplish the first objective, 873 field measurement values describing the hydraulic geometry and morphology of streams mainly from Canada, UK and USA were compiled and statistically analyzed. Based on similar mode values of three dimensionless channel variables (aspect ratio, sinuosity and channel slope), several fine elevations ranges were merged to produce the final five elevation ranges. These final five zones formed the basis of the new elevation based classification system and were identified with their unique modal values of dimensionless variables. Performing joint probability distributions on each of these zones, trends in the behavior of channel variables while moving from lowland to upland were observed. For the completion of second objective, 405 data points out of initial 873 points were selected and employed for the development of bankfull relations by using bankfull discharge and watershed variables as the input variables. Regression equations developed for width and depth established bankfull discharge as the only required input variable whereas all other watershed variables were proved out to be relatively insignificant. Channel slope equation did not show any dependence on bankfull discharge and was observed to be influenced only by drainage area and valley slope factors. Later when bankfull discharge was replaced by annual average rainfall as the new input variable, watershed parameters (drainage area, forest cover, urban cover etc.) became significant in bankfull width and depth regression equations. This suggested that bankfull discharge in itself encompasses the effects of all the watershed variables and associated processes and thus is sufficient for estimating channel dimensions. Indeed, bankfull discharge based regression equation demonstrated its strong dependence on watershed and rainfall variables.
Experiments on the Transformation of Mud Flocs in Turbulent Suspensions
Tran, Duc Anh (Virginia Tech, 2018-06-21)
This dissertation aims to better understand how floc aggregate characteristics and behaviors are modified under different local conditions and how such alterations impact the floc settling velocity, which is one of the most crucial parameters influencing sediment transport modeling. A series of laboratory experiments were conducted to examine the impact of suspended sediment concentration, mixes of clay and silt, and resuspension process to equilibrium floc size and floc settling velocity. In order to observe floc size evolution, a new floc imaging acquisition was first developed. This new method allows flocs in suspended sediment concentration up to C = 400 mg/L can be imaged non intrusively. This new method was applied in all three individual studies, which are composed of this dissertation. The first chapter investigates the behaviors of flocs under constant and decay suspended sediment concentrations within a steady turbulent suspension. In the constant-concentration set of experiments, floc size time series were measured for 12 h for each of the concentration C = 15, 25, 50, 100, 200, 300, and 400 mg/L. In the decay-concentration experiments, clear water was introduced to the mixing tank, simultaneously the suspension was drained out of the mixing tank at the same rate to make the suspended sediment concentration reduce while the turbulent shear was remained unchanged. The data shows that the equilibrium floc size is a weak, positive function of concentration. For example, in order to increase 20% of floc size (approximate 22 um) the concentration needs to be increased by 700% (going from 50 to 400 mg/L). The data also illustrates that during the decrease of concentration from C = 400 to 50 mg/L, the floc size responses to the changes of concentration in the order of 10 min or less. The second chapter examines how silt particles and clay aggregates interact in a turbulent suspension. Floc sizes and settling velocity of three different suspensions, i.e., pure clay, pure silt, and a mixture of clay and silt, were monitored. The floc size data show that the presence of silt particles does not have significant impacts on clay aggregate sizes. Silt particles, however, get bound up within floc aggregates, which in turn increase the settling velocity of the floc by at least 50%. The third chapter examines whether any changes in floc properties during the deposition and resuspension processes. The floc sizes and shapes in a set of experiments with different consolidation times, concentrations, and shear patterns were measured. The conditions at which the flocs deposited or resuspended were maintained the same. The data reveal that floc size and shape of freshly deposited and after resuspended are unchanged. The erosion rate and concentration is a function of consolidation time and the applied shear stress during the deposition phase. Hence, there is a small reduction in resuspended concentration resulting in a slight decrease in resuspension floc size since floc size is also a function of concentration.
Forward and Inverse Modeling of Tsunami Sediment Transport
Tang, Hui (Virginia Tech, 2017-04-21)
Tsunami is one of the most dangerous natural hazards in the coastal zone worldwide. Large tsunamis are relatively infrequent. Deposits are the only concrete evidence in the geological record with which we can determine both tsunami frequency and magnitude. Numerical modeling of sediment transport during a tsunami is important interdisciplinary research to estimate the frequency and magnitude of past events and quantitative prediction of future events. The goal of this dissertation is to develop robust, accurate, and computationally efficient models for sediment transport during a tsunami. There are two different modeling approaches (forward and inverse) to investigate sediment transport. A forward model consists of tsunami source, hydrodynamics, and sediment transport model. In this dissertation, we present one state-of-the-art forward model for Sediment TRansport In Coastal Hazard Events (STRICHE), which couples with GeoClaw and is referred to as GeoClaw-STRICHE. In an inverse model, deposit characteristics, such as grain-size distribution and thickness, are inputs to the model, and flow characteristics are outputs. We also depict one trial-and-error inverse model (TSUFLIND) and one data assimilation inverse model (TSUFLIND-EnKF) in this dissertation. All three models were validated and verified against several theoretical, experimental, and field cases.
From Ideas to Actions: Hazard Mitigation Policy Adoption—Analysis of Floodplain Property Buyout Program
Wang, Qiong (Virginia Tech, 2023-08-23)
Climate change is exerting a profound influence on natural hazards, resulting in increased frequency, intensity, and altered patterns of extreme weather events. These changes pose significant risks to vulnerable populations worldwide. Consequently, it is imperative to adopt hazard mitigation policies to address the impacts of climate change on natural hazards and communities. The adoption of such policies is a complex and dynamic process that requires a thorough understanding of the key factors influencing policy adoption. The United States has experienced a rise in the severity and frequency of floods, necessitating the implementation of comprehensive flood mitigation policies. These policies aim to protect vulnerable communities, safeguard critical infrastructure, and reduce the economic and human costs associated with these natural disasters. Among the various flood mitigation strategies, floodplain property buyout programs have garnered attention. However, there is limited research that examines the factors influencing the adoption of buyout programs at the local government level from a government perspective. This dissertation provides a comprehensive analysis of the adoption process of floodplain property buyout programs at the local level in the United States. The study employs a mixed methods approach to examine the mechanism behind policy adoption and identify the key factors that influence this process. Chapter 1 lays the foundation for the research by defining relevant terms and outlining the characteristics of floodplain property buyout programs in the U.S. Chapter 2 presents a theoretical framework that enhances our understanding of hazard mitigation policy adoption at the local level. The framework is exemplified through case studies of property buyout programs in North Carolina and New Jersey. The case studies conducted in these states offer compelling evidence that supports the proposed framework, which encompasses five-factor categories: hazard problem, social context, institutional capacity, cross-sector collaboration, and policy diffusion. Notably, institutional capacity plays a crucial role in buyout adoption, encompassing individual, organizational, and system capacity. These factors influence the uptake of buyouts and contribute to their success or failure. This exercise gives us valuable insights into the buyout decision making process and suggests avenues for research in the subsequent chapters. Chapter 3 conducts a quantitative analysis to validate the hazard mitigation policy adoption framework. Specifically, it focuses on investigating the factors that influence the adoption of Federal Emergency Management Agency (FEMA) property buyout programs by local governments in Virginia counties. Utilizing logistic regression models and a survey dataset collected from local floodplain managers in the Commonwealth of Virginia, the study reveals that floodplain managers' perception of repetitive flood loss and economic spillovers in neighboring areas significantly impact the adoption of buyout programs. In Chapter 4, we conduct a qualitative approach to delve into the decision-making dynamics in the adoption of floodplain property buyout programs from a government perspective in Virginia. Through semi-structured interviews with 12 experts representing various stakeholders involved in floodplain management, this study demonstrates the variations in the adoption processes among different local governments. The findings underscore the importance of leadership, community population size, floodplain managers' perception of repetitive flood loss, organizational staff capacity, and tax revenue considerations in shaping buyout decisions. It highlights the need for local leadership commitment, empowerment of floodplain managers, and comprehensive approaches to address challenges faced by small communities. The research provides practical guidance to enhance flood risk management practices and promote resilient and sustainable communities. In conclusion, this dissertation contributes to the understanding of hazard mitigation policy adoption at the local level by proposing a theoretical framework and providing empirical evidence through case studies, surveys, and interviews. The findings emphasize the importance of various factors, such as hazard problem, social context, institutional capacity, and policy diffusion, in shaping buyout policy adoption. The implications of this research extend to policymakers, practitioners, and researchers, providing insights into the motivations, obstacles, and strategies surrounding the adoption and implementation of hazard mitigation policies. By considering these factors and employing comprehensive approaches, communities can enhance their resilience and effectively mitigate the impacts of natural hazards.
High-Fidelity Numerical Simulation of Shallow Water Waves
Zainali, Amir (Virginia Tech, 2016-12-09)
Tsunamis impose significant threat to human life and coastal infrastructure. The goal of my dissertation is to develop a robust, accurate, and computationally efficient numerical model for quantitative hazard assessment of tsunamis. The length scale of the physical domain of interest ranges from hundreds of kilometers, in the case of landslide-generated tsunamis, to thousands of kilometers, in the case of far-field tsunamis, while the water depth varies from couple of kilometers, in deep ocean, to few centimeters, in the vicinity of shoreline. The large multi-scale computational domain leads to challenging and expensive numerical simulations. I present and compare the numerical results for different important problems --- such as tsunami hazard mitigation due to presence of coastal vegetation, boulder dislodgement and displacement by long waves, and tsunamis generated by an asteroid impact --- in risk assessment of tsunamis. I employ depth-integrated shallow water equations and Serre-Green-Naghdi equations for solving the problems and compare them to available three-dimensional results obtained by mesh-free smoothed particle hydrodynamics and volume of fluid methods. My results suggest that depth-integrated equations, given the current hardware computational capacities and the large scales of the problems in hand, can produce results as accurate as three-dimensional schemes while being computationally more efficient by at least an order of a magnitude.
Impact of Patchy Vegetation on Wave and Runup Dynamics
Yang, Yongqian (Virginia Tech, 2016-08-18)
Coastal regions are vulnerable to various natural processes, ranging from normal waves to extreme events. Given the flourishing development and large population along coastlines, various measures have been taken to mitigate the water-induced damage. Nature-based coastal protection, especially vegetation, has attracted unprecedented studies over the past two decades. To enhance understanding of this subject, this dissertation evaluates the impact of patchy vegetation on wave and runup dynamics along coastlines. Selecting from a prototype in Dalehite Cove, Galveston Bay, TX, results from a Boussinesq model (COULWAVE) showed patchy vegetation reduced up to 75% mean shoreward current in the mound-channel wetland systems. These vegetation patches also reduced the primary circulation around mounds, with a power-form relation between circulation size and various parameters (i.e., bathymetry, incident wave and vegetated roughness). Substituting spectral waves for regular waves in the similar wetlands, more energy was transferred into the higher frequencies. The impact of patchy vegetation on wave energy was frequency- and space-dependent, with increased energy observed in specific harmonics and locations. Comparison with unvegetated horizontal bathymetry demonstrated that mound-channel bathymetry was the dominant factor in transferring and dissipating wave energy, while vegetation patches added a fair contribution. As for extreme events, such as tsunamis, laboratory experiments and numerical simulations were conducted to assess the effectiveness of patchy vegetation with various roughness levels, spacings and sizes. Overall, vegetation patches reduced the most destructive loads onshore by up to 80%. Within-patch roughness variation only caused uncertainty on the hydrodynamics around the seaward patches, while the mitigation of extreme loads was not undermined. A logarithmic relation was observed between the protected area from extreme loads and the vegetated coverage. These findings will fill the knowledge gap of hydrodynamics in the presence patchy vegetation, and improve the engineering practice of coastal protection using nature-based infrastructure.
Influence of Geotechnical Properties on Sediment Dynamics, Erodibility, and Geomorphodynamics in Coastal Environments Based on Field Measurements
Brilli, Nicola Carmine (Virginia Tech, 2023-06-06)
Geotechnical sediment properties such as moisture content, relative density, bearing capacity, and undrained shear strength have been discussed in the context of coastal sediment dynamics. However, these properties have rarely been assessed in their respective relevance or quantitatively related to sediment transport and erodibility. Also, to date there is no framework available for collecting direct measurements of these properties for estimating initiation of motion and erosion rates. Here, it is postulated that improving the ability to measure geotechnical sediment properties in energetic foreshore environments can improve our ability to predict coastal response to climate change. Through a series of field measurements, the research presented here (1) provides a framework for conducting geotechnical measurements of beaches, (2) advances portable free fall penetrometer (PFFP) data analysis in intertidal environments through the introduction of an impact velocity dependent strain-rate correction factor, (3) relates textural and sediment strength properties derived from PFFP measurements to an erosion rate parameter and hydrodynamically driven bed-level change, and (4) uses PFFP measurements to develop a sediment classification scheme in terms of soil behavior and erosion behavior for a mixed sediment type Arctic environment. Relationships between sediment properties other than grain size, most significantly void ratio, and erodibility parameters highlight the relevance of these measurements in geomorphodynamically active sandy beach environments. For the cohesive sediments in the Arctic, undrained shear strength was also related to an erosion rate parameter, allowing for a categorical framework for erodibility classification to be developed. The cohesive framework was combined with the relationships developed for sandy sediments and used to highlight areas of active sediment transport in the context of local morphodynamic and ice gouging processes. Finally, a simple case study showed how implementing in-situ erodibility parameters was important for long-term morphological modelling. The results represent a step forward in our ability to predict and mitigate climate change related issues from coastal erosion.
An investigation of compound riverine flooding and the influence of anthropogenic drivers within large-scale catchments.
Chilton, William Paul (Virginia Tech, 2023-12-21)
Water has always been an essential part of human life. It is necessary for every human activity and process. However, this life-sustaining resource can also cause mass destruction and loss of life. As populations grow and floods occur more frequently and at a larger scale, it becomes increasingly crucial to comprehend the variables and processes that surround flood events. Understanding these factors can help us mitigate the risks associated with floods and minimize their impact on communities. This dissertation consists of six chapters which cover two aspects of flooding. The first aspect deals with the sources of flooding events in a multi-regional basin. The second aspect concerns the impact of anthropogenic activity on flooding processes. In the first two chapters, the research motivation is presented, accompanied by a general review of the concepts that govern the research performed. Chapter three provides a statistical analysis of flood incidents based on their location and the prevailing weather conditions. The results of this chapter indicate that there has been a 6% annual increase in flooding each year across the basin of interest, with a staggering 770% increase in the last four years of the study. The main source of this increase is the lower level flood events, which are often the result of human development. Another notable observation in this chapter is that the majority of weather events that led to flooding were non-tropical in nature. Chapter four examines the relationship between land use and flooding by utilizing various statistical and machine learning techniques to identify the types of land use that contribute the most to flooding within the basin. Findings from this chapter include the loss of croplands across the entire basin, with an almost 1:1 replacement with open water surface and urban area, two land uses that produce the most runoff in precipitation events. In chapter five, we present a numerical model of the lower James River Basin in Virginia, which serves as a tool to assess the impact of land use modifications on flooding in the area. From 2004 to 2021, the basin lost over 13-million cubic meters of storage. Finally, chapter six provides an overview of future work and guidance in this area.
Investigation of the Spatiotemporal Evolution of Tropical Cyclone Storm Surge under Sea Level Rise
Liu, Yi (Virginia Tech, 2018-07-31)
Storm surges induced by tropical cyclones have been ravaging coastal communities worldwide, where a growing number of people reside. Tremendous life and economic losses are caused by tropical cyclones, contributing to more than half of the damages induced by natural hazards. To improve the resilience of coastal communities to surge hazards, it is of great importance to provide reliable and efficient real time forecasts of the spatiotemporal evolution of storm surge, as well as reliable predictions of the probabilistic surge hazards under future conditions. Three specific goals are addressed in this work. Studies on characterization and prediction of surge before a hurricane landfall show that a dimensionless relationship between intensity scaled surge magnitude and wind-duration scaled surge timing may effectively be used for rapid and reliable forerunner surge forecasting. Investigation of how probabilistic surge hazard changes with sea level rise (SLR) shows that the probabilistic surge with SLR can be 1.0 m larger, while different individual storm's surge with the same magnitude can be 1.5 m larger or 0.1 m smaller, indicating the importance of not relying on results from a limited number of storm surge events to assess the probabilistic surge hazard change to SLR. Finally, studying the temporal evolution of coastal flooding changes with SLR shows forerunner surge responds differently to SLR than peak surge, and that storm forward speed is a key factor determining the forerunner-SLR response.
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.

Browsing by Author "Irish, Jennifer L."

Results Per Page

Sort Options