Accurately measuring denitrification in stochastic floodplains, particularly the leveed and unleveed reaches of the Mississippi River basin, requires innovative experiments. To replicate hydraulic variability ranging from overland flooding to groundwater exfiltration in floodplain wetlands, I incubated sediment cores collected from four field sites across the Dogtooth Bend of the middle Mississippi River; pairing novel deep injection (Graphic Abstract Fig. A, left) with traditional surface delivery (Graphic Abstract Fig. A, right) of both oxic and anoxic Mississippi River water. In sandy sediments with unconstrained flux of nutrients, denitrification more than doubled across a range from 192 to 429 mg N m-2 day-1 in a linear anoxic-injection hierarchy of anoxic deep > anoxic surface > oxic deep > oxic surface treatments. In contrast, for incubations in diffusion-limited clay sediments, injection type made no difference; however, in anoxic conditions denitrification rates were as high as 435 mg N m-2 day-1 compared to oxic incubations at 187 mg N m-2 day-1. This methodology reveals the magnitude of diverse denitrification rates spanning different hydrologic conditions (Abstract Fig. B) and the mediation of denitrification by sediment type. These findings provide quantified bounds to inform resource management decisions regarding what areas should be selected for protection or hydrologic reconnection to best facilitate nutrient processing services like denitrification under varying hydrologic conditions.

The Lower Mississippi Alluvial Valley (LMAV) was once the largest floodplain in the United States. Flooding regimes in the LMAV have strong impacts on the soil biogeochemical processes, nutrient cycling, forest species distribution, agricultural production, and wildlife habitat. This study characterized the LMAV flooding regimes using the 8-day-composite Moderate Resolution Imaging Spectroradiometer (MODIS) surface reflectance product from 2001 - 2018. The results showed significant spatial variations in the annual flooding duration in the LMAV, and the flooding area showed remarkable seasonal variations in the northern and central LMAV with the peak flooding area in winter and early spring. Digital Elevation Model (DEM) and slope were identified as the two major factors in determining the spatial pattern of flooding regimes. The LMAV flooding regimes dataset provides a scientific basis for the governments to design forest, agriculture, and wildlife management policies to enhance ecosystem services. Landowners also can use this information to make decisions for cropland retirement and tree plantation.

No description available.

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. / Doctor of Philosophy / Climate change is causing significant changes in natural hazards, leading to more frequent and intense extreme weather events. These changes pose risks to vulnerable populations worldwide. To address these risks, it is crucial to adopt policies that mitigate the impacts of climate change on natural hazards and communities. This dissertation focuses on the adoption of such policies at the local level in the United States. The study examines the factors that influence the adoption of floodplain property buyout programs, which aim to protect communities and critical infrastructure from the impacts of floods. The research employs a combination of quantitative and qualitative methods to understand the adoption process and identify key factors that shape policy decisions. By studying case studies in North Carolina, New Jersey, and Virginia, the research provides insights into the motivations and obstacles surrounding the adoption of hazard mitigation policies. The findings emphasize the need for strong local leadership, considering community population size, addressing flood loss perceptions, building organizational capacity, and considering tax revenue implications. The research offers practical guidance for policymakers, practitioners, and researchers in enhancing flood risk management practices and promoting resilient and sustainable communities. By addressing the identified factors and adopting comprehensive approaches, communities can improve their resilience to natural hazards. The implications extend to policymakers, practitioners, and researchers, providing valuable insights into the adoption of hazard mitigation policies.

River-floodplain connectivity is the degree of water-driven transport of matter, energy, and organisms between rivers and their floodplains. Recent advancement of high-resolution lidar data and numerical modeling is helpful to explore river-floodplain connectivity precisely to improve our predictions of sediment transport and deposition on floodplains. In the present work, we studied floodplain sediment transport and deposition, and juvenile mussel settling in three river systems in the US. A two-dimensional hydrodynamic model was developed and simulated model results were coupled with field measurements to study river-floodplain systems of the East Fork White River in Indiana, South River in Virginia, and Dan River in North Carolina. Results show that the East Fork White River in Indiana is capable of supplying sand to the channels on the floodplain and these floodplain channels can transport sand in suspension and gravel as bedload. These floodplain channels are supply limited under the current hydrologic regime and identified as net erosional. On the South River floodplain in Virginia, incorporating hydrologic flowpaths as an explicit measure of river-floodplain connectivity can improve predictions of floodplain sediment deposition. Three regression models were developed incorporating flow pathways and the best model was applied to hydrodynamic model results to create a spatial map of floodplain sedimentation rate. The deposition map highlights how floodplain topography and river-floodplain connectivity affect sedimentation rates and can help inform the development of floodplain sediment budgets. Lastly, streamflow conditions were investigated in the Dan River, North Carolina as they affect juvenile freshwater mussel settling. Two uplooking velocity sensors on the river bed were deployed and hydraulic parameters were measured for a 7-mo period in May-November 2019 to estimate the juvenile mussel settling. Results show that juvenile freshwater mussels as large as 280-508 µm could always be suspended during our study period and not be able to settle onto the river bed at the location of our velocity sensors. Therefore, the flow and shear velocity during our study period was high enough to prohibit the recruitment of juvenile freshwater mussels from settling out of suspension at the sensor locations. Modest flow obstructions such as large boulders, downed trees, or large wood that create downstream wakes may be important features that provide suitable conditions for the settling of juvenile freshwater mussels onto the river bed. Furthermore, low flows have been increasing since the year 2000 which may be exacerbating the decline in freshwater mussel populations. / Doctor of Philosophy / Human civilization has developed near rivers due to the wide range of benefits provided by rivers. Rivers provide food, water, and energy to more than 2.7 billion people around the world. However, the health of the rivers is degrading rapidly to meet the increasing demand of the growing population. We studied water, sediment, and mussel transport in the three rivers in the US: East Fork White River in Indiana, South River in Virginia, and Dan River in North Carolina. These rivers play an important role in agriculture, water supply, sediment, and nutrient transport of the surrounding environment. Our research work on East Fork White River in Indiana, USA shows that the area directly adjacent to the river is eroding, which is important information for river managers and policymakers. As part of that work, we identified the potential of various sizes of sediment to move over this area at different flows and developed a method to predict the largest sediment size that could be moved in water and hopping along the ground. This method is also applicable to other areas along rivers and the coast. We estimated the sediment deposition rate, deposition volume, and prepared a spatial map of the sediment deposition pattern for the South River floodplain in Virginia. From this map, deposition hot spots could be identified. We estimated that 66% of the sediment deposited adjacent to the South River was located in 32% of the area. This information will be helpful for understanding how sediment and sediment-associated pollutants deposit around rivers. Our work on the Dan River in North Carolina was focused on freshwater mussels. Our results showed that juvenile freshwater mussels could not have settled onto the river bed at the location of our measurements. Historical data reveal that freshwater mussels are declining at an alarming rate in that river, posing a threat to the river environment. We identified that streamflow has been increasing over the last two decades, which could be a potential cause of declining freshwater mussels.

Rivers and their surrounding riparian and subsurface ecosystems, known as river corridors, are important landscape features that provide a myriad of ecological and societal benefits. While the importance of riverine flooding has been widely acknowledged and extensively studied, very little research has been conducted on the interactions between river channels and their adjacent floodplains. The importance of this hydrologic connectivity between rivers and floodplains has been emphasized in recent decades and now ecological engineering techniques such as stream restoration are often utilized to restore connectivity between streams and their riparian ecosystems. Despite its ubiquity in practice, there are still many basic components of river-floodplain connectivity that are not well understood. Furthermore, a lack of cost-effective monitoring techniques makes sustainable management of river corridors quite challenging. Thus, the overall goals of my dissertation were: 1) develop user-friendly river corridor monitoring techniques utilizing cost-effective approaches such as time-lapse digital imagery and satellite remote sensing and 2) identify the effects of anthropogenic activities on river corridor hydrologic and biogeochemical processes that occur at varying spatial and temporal scales during flood events. These goals were addressed through five independent studies that span spatiotemporal scales. The five studies utilized a combination of novel remote sensing, hydrologic/hydraulic modeling, and high frequency spatial sampling techniques to analyze river corridor dynamics. Results highlight that digital imagery and satellite remote sensing can be effective tools for monitoring river corridors in data scare regions. Additionally, impounding streams and river corridors alters floodplain connectivity and biogeochemical processing of reactive solutes such as nitrogen and phosphorus. Findings from this work highlight the important role that spatial and temporal scale plays in river corridor dynamics. Overall, this research provides new analytical techniques and findings that can be used to effectively monitor and manage river corridors. / PHD / Rivers are important landscape features that provide basic societal needs such as drinking water, water for agricultural irrigation, and hydroelectric energy. Engineers have traditionally sought to manage rivers for these purposes while also minimizing flooding. However, flooding actually provides a number of environmental benefits such as increased aquatic biodiversity and removal of excess sediment and pollutants from rivers. This notion of environmentally friendly flooding is a relatively new concept and much is still unknown about how these processes differ at varying scales. Additionally, there is currently a lack of techniques for monitoring such processes primarily due to the cost required for equipment and labor. Therefore, the goals of this dissertation were twofold: 1) develop cost-effective and user-friendly monitoring techniques that can be used to study river flooding dynamics and 2) examine the impacts of river flooding dynamics at three different spatial scales ranging from a small stream to a large watershed. This was accomplished through five separate case studies that examine rivers and watersheds of varying sizes at varying time scales. The studies utilized several emerging technologies that required a combination of field monitoring, computer simulations of flood dynamics, and satellite imagery to gain a better understanding of river flood hydrology and water quality. A key finding was the important role that scale plays in both spatial and temporal domains. Utilizing varying spatial and temporal scales allowed for identification of different processes that occur across a range of river and watershed sizes. Overall, this work can be used to better inform future river management and restoration decisions.

Seasonally fluctuating water levels, known as flood pulses, influence the population dynamics and catches of fishes from river-floodplains. Although different measures of flood pulses, here called flood pulse variables, have been correlated to changes in catches of river-floodplain fishes, the flood pulse variables that have the strongest relationships to catches have not been identified. Furthermore, it is unclear if flood pulses influence catches of river-floodplain fishes with different life history strategies in different ways. Catches of 21 taxa from approximately 18,000 fishing trips were modeled as a function of fishing effort, gear type, seasonal flood pulse variables, and interannual flood pulse variables. These models were analyzed to understand which flood pulse variables had the strongest relationships to catches, and evaluate different flood pulse influences among taxa with different life history strategies. High water flood pulse variables generally had positive influences on catches in future years, while low water flood pulse variables generally had negative influences on catches in future years. Flood pulses generally had stronger influences on the catches of fishes with high fecundities and smaller eggs than on catches of fishes with low fecundities and larger eggs. Variation was observed in strengths and directions of flood pulse influences on catches of fishes with similar and different life history strategies. While my results were generally consistent with prevailing knowledge of how flood pulses influence catches of fishes, other biological factors of specific fish populations may further explain population responses to flood pulses. / Master of Science / Seasonally fluctuating water levels, known as flood pulses, influence the population dynamics and catches of fishes from river-floodplains. Although different measures of flood pulses, here called flood pulse variables, have been related to changes in catches of riverfloodplain fishes, the flood pulse variables that have the strongest relationships to catches have not been identified. Furthermore, it is unclear if flood pulses influence catches of riverfloodplain fishes with different life history strategies in different ways. Catches of 21 taxa from approximately 18,000 fishing trips were modeled as a function of fishing effort, gear type, seasonal flood pulse variables, and interannual flood pulse variables. These models were analyzed to understand which flood pulse variables had the strongest relationships to catches, and evaluate different flood pulse influences among taxa with different life history strategies. High water flood pulse variables generally had positive influences on catches in future years, while low water flood pulse variables generally had negative influences on catches in future years. Flood pulses generally had stronger influences on the catches of fishes that produce many smaller eggs than on catches of fishes that produce fewer and larger eggs. Variation was observed in strengths and types of flood pulse influences on catches of fishes with similar and different life history strategies. While my results were generally consistent with prevailing knowledge of how flood pulses influence catches of fishes, other biological factors of specific fish populations may further explain population responses to flood pulses.

Understanding the factors influencing the abundance and distribution of tropical floodplain fishes is an important component of fisheries management plans to support future sustainable resource use. This thesis uses a multi-scale approach to understand the habitat factors controlling the distribution and abundance of arapaima (Arapaima spp.) in river floodplains of the lower Amazon River, near the municipality of Santarém, Para State, Brazil. In chapter 1, a study of eight environmental variables in 13 dry season floodplain lakes demonstrates that lake depth, relative depth, conductivity, and transparency were significantly related to the probability of arapaima presence at individual locations within lakes. Further, the study revealed that smaller arapaima were more likely to be found near macrophyte coverage than in open water locations. In chapter 2, a landscape scale approach was used to examine the interactions between management systems, landscape habitat coverage, and spatial arrangement on arapaima population sizes in 73 floodplain lakes. Results showed that all three influences were important in explaining variability in arapaima abundances. Management and habitat variables contributed equally in controlling arapaima abundances. Both had strong patterns of spatial arrangement and overlapped significantly, suggesting that analysis of either management systems or landscape habitats without the other would lead to overestimations of the strength of their influence. Findings from both chapters support the notion that future sustainable use of arapaima populations requires a dualistic approach combining habitat conservation with fisheries management techniques enacted at a local scale. / Master of Science / Understanding where fishes choose to live within aquatic habitats, and why they do so, is important for their long-term protection habitat destruction and overfishing. This thesis looks at fish habitats at both small and large scales to understand the variables affecting populations of the megafish arapaima (<i>Arapaima spp.</i>) in lakes of the lower Amazon River, near the municipality of Santarém, Pará State, Brazil. In chapter 1, a study of eight environmental variables in 13 lakes shows that for each lake, deeper, muddier (less clear), and more electricallyconductive waters were more likely placed to find arapaima. Further, the study revealed that young arapaima were more likely to be found near aquatic plants than in open water areas near the middle of the lake. In chapter 2, a larger-scale approach was used to examine the interactions between humans, habitats, and spatial groupings for arapaima population sizes in 73 lakes. Results showed that all three factors were important in explaining how many arapaima were found in each lake. Human and habitat variables were equally important variables affecting arapaima. Both were strongly related to spatial groupings and overlapped significantly, suggesting that analysis of either human systems or habitats without the other would lead researchers to overestimate how important they are for arapaima. Findings from both chapters support the notion that future sustainable use of arapaima populations requires an approach combining habitat conservation with fisheries management techniques enacted at a local scale.

Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 208-223). Also available on the World Wide Web.

Utilizing survey data gathered from local local level floodplain administrators (FPAs) operating within Federal Emergency Management Agency Region 6, this study provides a more nuanced understanding of perceived competency among FPAs across key floodplain management topics through the use of a principal component analysis (PCA). PCA identified six distinct components related to perceived competency among FPAs including; Modification and Update Process, General Knowledge, Grants and Programs, Analysis, Development and Real Estate, and Administration and Outreach. The study then employed regression analyses to identify organizational and individual level characteristics that predict perceived competency. Data analyses identified several organizational variables as significant positive predictors of perceived competency including working within an urban community, full-time job status and overall workload percentage dedicated to floodplain management. Additionally, several individual characteristics such as educational attainment, professional certification, previous disaster experience, and years of experience working as an FPA were also identified as significant positive predictors of perceived competency. Based on these findings the study makes several recommendations about improvements to training and educational materials for practitioners and students.