Flooding in the United States has been increasing over the past century due to changing hydrological conditions as well as increased human manipulation of the waterways. People continue to live in these high hazard areas, even with increasing risk levels. Flood hazard mitigation has increasingly become a primary goal of floodplain managers with buyouts, insurance, and other nonstructural approaches becoming more prevalent over the past two decades. Whole town relocations have become one flood mitigation option. This study explores which community factors affect a town's decision to relocate. Three study areas in the Midwestern U.S. were analyzed: Valmeyer, IL, Rhineland, MO, and Pattonsburg, MO. Each of these three towns underwent a buyout and town relocation after the flood of 1993. Data was gathered using personal interviews with community members, specifically elected officials and relocation committee members. Analysis of interview responses identified community sense of place as the primary factor influencing relocation decisions including leadership, cost, people, and landscape. Leadership included town incorporation, relocation decision and committees, handling of legal issues, and site selection criteria. Cost involved the relocation cost, post-disaster development and tourism, and the business community of the study areas. People included the town heritage, community type, and the various community organizations. Landscape includes the types of relocation completed, the speed of the relocation event, and the amount of pre-disaster planning. Maps created show the pre and post-relocation municipal boundary of the study sites in relation to the 500-year floodplain boundary.

Conservation practices are needed to reduce nitrate loss across the Midwest. Different riparian wetland designs have been investigated, but the physical, chemical and biological processes controlling nutrient cycling in restored oxbows are not well understood. A restored oxbow’s influence on nutrient cycling was investigated by studying the hydrogeology and water quality at a recently reconstructed oxbow site adjacent to Morgan Creek in Linn County, Iowa. Over a one-year period, the lentic oxbow’s nitrate loading was found to be dominated by flood pulses. Nitrate concentrations in the stream ranged from 7.38 – 12.95 mg l-1, concentrations were consistently low in the oxbow ranging from < 0.10 – 5.35 mg l-1, and the lowest nitrate concentrations were detected in the groundwater ranging from 0.10 to 3.4 mg l-1. Following a spring flood event, an in-situ sensor measured the nitrate concentration in the oxbow. Nitrate retention efficiency was estimated to be 0.30 g N m-2 d-1 or a 74.2% reduction efficiency. The observed nitrate reduction was compared to a first order denitrification model. The observed nitrate reduction measured in the oxbow followed a linear decay rather than an exponential decay suggested by first order kinetics.

The global climate is changing and much of this is attributed to the greenhouse effect, which has been exacerbated by increased anthropogenic releases of greenhouse gases (GHGs). However, important GHGs, carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4), are produced naturally in the soil during the metabolism of many soil microbial and plant communities. The generation rate of GHGs depends on many factors, including soil community composition, nutrient availability, temperature, and soil moisture. Predicted climate variability is expected to alter temperature and rainfall patterns, which can impact the factors regulating natural generation of GHGs. With changing fluxes of GHGs, the natural feedback loops between GHG generation and climate may change. Increased emissions from natural sources would exacerbate climate change, whereas decreased emissions may mitigate its impacts. Floodplains may be particularly susceptible to climate change, as their biogeochemical processing is driven by hydrology. For this study, ten mesocosms were installed on the floodplain of Stroubles Creek in southwest Virginia. A flood event was simulated in half of these mesocosms in both early spring and mid-summer, which represent extremes in soil moisture and primary productivity on the floodplain. Headspace gases were monitored for CO, N2O, and CH4. Efflux of CO2 and N2O was higher in summer than spring, and also increased following wetting events. Methane production was greater in the spring, with no detectable change with wetting. Increases in summer rainfall events could increase the release of important GHGs to the atmosphere, potentially at levels significant to climate change. / Master of Science

Les eaux souterraines des plaines alluviales agricoles sont particulièrement vulnérables à la contamination en nitrates en raison d’une fertilisation importante, et de la faible profondeur des aquifères. Au sein de ces plaines alluviales, les zones ripariennes, caractérisées par des échanges importants entre les eaux de surface et les eaux souterraines, constituent des environnements propices à l’atténuation des nitrates via le processus de dénitrification. Ce processus naturel dépend de nombreux facteurs et est caractérisé par une forte variabilité spatio-temporelle. La modélisation est une approche intéressante pour étudier la dénitrification au sein des zones ripariennes car elle permet d’intégrer les différents facteurs contrôlant le processus de manière dynamique. L’objectif de cette thèse est d’améliorer la caractérisation et la quantification du processus de dénitrification et d’identifier ses facteurs de contrôle dans les plaines alluviales à travers une approche de modélisation à l’échelle du tronçon de plaine alluviale. L’analyse d’un jeu de données collectées dans un réseau de 25 piézomètres installés dans un méandre de la Garonne (Monbéqui, 6,6 km²) lors de 12 campagnes mensuelles a permis, dans un premier temps, d’identifier les facteurs contrôlant la dynamique des nitrates et le processus de dénitrification. Les données ont ensuite servi à la mise en place et à la validation de l’application du modèle distribué MOHID Land pour simuler l’hydrologie de la zone d’étude. Puis, un module permettant de simuler la dénitrification et prenant en compte les facteurs identifiés au préalable, a été introduit dans le modèle. L’analyse des données récoltées sur le terrain a montré que la dénitrification dans la zone d’étude est contrôlée par la géomorphologie, l’hydrologie et la présence de carbone organique. L’application du modèle hydrologique distribué MOHID Land a permis de simuler correctement l’hydrologie du site étudié en prenant en compte la géomorphologie de la plaine alluviale, les échanges eaux de surface - eaux souterraines et les épisodes de crues. Un module de dénitrification incluant à la fois le carbone organique dissous apporté par la rivière et le carbone organique particulaire présent dans l’horizon supérieur des sols a été implémenté dans le modèle hydrologique. Les résultats indiquent une dénitrification moyenne de 28 kg-N.ha-1.an-1 sur la période simulée dans la zone riparienne de Monbéqui. La dénitrification est plus importante dans les zones ripariennes de basses altitudes et plus globalement dans la partie aval du méandre, caractérisée par de fortes concentrations en nitrates. Les facteurs contrôlant la dénitrification au sein des plaines alluviales ont été identifiés et sont i) la géomorphologie qui détermine la saturation des horizons supérieurs des sols et la disponibilité du carbone organique ; ii) les écoulements souterrains qui contrôlent la répartition spatiale des nitrates, et iii) l’intensité et la fréquence des épisodes de crues qui entrainent des périodes favorables à la dénitrification. Finalement, les résultats obtenus dans la zone d’étude ont été comparés avec des applications du modèle dans des plaines alluviales possédant des caractéristiques contrastées, validant ainsi l’utilisation du modèle dans les environnements de plaine alluviale variés. Les résultats ont mis en avant l’importance de la connectivité hydrologique entre la rivière et la nappe alluviale ainsi que la distribution spatiale des sources de nitrates et de carbone organique comme facteurs expliquant les différences de capacité de dénitrification entre les sites. Ces travaux ouvrent des perspectives pour évaluer l’impact des modifications induites par le changement global sur le processus de dénitrification ainsi que sur leur modélisation à plus large échelle. / Groundwater systems in cultivated floodplains are vulnerable to nitrate contamination due to extensive fertilisationand the shallow depth of the groundwater. Within the floodplain environment, riparian areas, characterised by significantexchanges between surface water and groundwater, are a favourable site for nitrate removal through denitrification.Denitrification is a natural process influenced by numerous factors and characterised by a high spatio-temporal variability.Modelling is an interesting approach for the study of denitrification within riparian areas because it means that floodplainspatial heterogeneity can be taken into account and many of its control factors integrated.The main objective of this thesis was to enhance knowledge of the denitrification process in floodplains and toidentify its control factors using a modelling approach at the scale of the floodplain reach. First, a dataset collected at amonthly time step over the course of a year within a 25-piezometer network of a meander area (Monbéqui, 6.6 km²) wasanalysed in order to identify factors controlling nitrate and denitrification patterns. The data were then used to set up andvalidate the MOHID Land model to simulate the hydrology in the study area. A module designed to simulate thedenitrification process, taking the main denitrification control factors into account, was then integrated into the MOHID Landmodel.The analysis of the dataset collected from the study area showed that denitrification was controlled bygeomorphology, hydrology and organic carbon presence. The application of the MOHID Land model allowed the hydrologyof the study area to be reproduced correctly, particularly the surface water – groundwater exchanges and the influence offlood events. A denitrification module integrating dissolved organic carbon borne by the river and particulate organic carbonfrom soil was added to the model. The results indicated that denitrification in the modelled riparian area was an average ofaround 28 kg-N.ha-1.yr-1 over the simulated period. High denitrification areas were located within the low elevation riparianarea and, more generally, in the downstream area of the meander where the nitrate concentrations were highest. The factors controlling denitrification that were identified in the study area were i) geomorphology, which controlled topsoil layersaturation and organic carbon availability; ii) groundwater flowpaths, which controlled the variability in nitrateconcentrations over the study area; and iii) flood event frequency and intensity, leading to high denitrification periods.Finally, the results were compared with other applications of the model in contrasting floodplains in order to assess themodel’s performance in various floodplain environment. The results indicated that hydrologic connectivity between the riverand groundwater and the spatial location of sources of nitrates and organic carbon were the major factors behind differencesin the denitrification process between floodplains. This study provides insight for an assessment of the impact ofmodifications that could be brought about by global changes to the denitrification process and for the modelling ofdenitrification at larger scales.

The Sacramento River watershed provides important rearing habitat for key aquatic species, including juvenile Chinook salmon (Oncorhynchus tshawytscha). Salmon rearing in the watershed may inhabit the mainstem river channel or a corresponding floodplain, the Yolo Bypass, before migrating to the ocean. Studies of juvenile salmon have indicated that floodplain rearing may be beneficial in terms of growth and survival, likely related to different trophic pathways of the river and floodplain. However, fish also encounter many anthropogenic stressors in these habitats, such as pesticides, which have well-documented use and environmental presence in the region. Rearing individuals are potentially exposed to pesticides via trophic transfer, which may vary based on utilized food webs due to hydrophobic pesticide fate and transport. To examine the food web structure of each system and the potential for pesticide exposure through dietary routes, a two-year field study was completed. First, to characterize dietary contributions, a three-tiered approach incorporating stable isotopes (δ13C, δ15N and δ34S), essential fatty acids and gut content analyses was employed. Subsequently, pesticides were extracted from prey items and salmon and analyzed to determine contaminant residues. Stable isotope analyses indicated that critically important components of juvenile Chinook diet were amphipoda and adult diptera in 2019 and 2020, respectively. Amphipoda groups had higher concentrations of the fatty acid docosahexaenoic acid (DHA), an important component for fish development, than juvenile diptera or oligochaeta. Diptera (larvae and adults) were frequently found in juvenile Chinook stomachs from both areas and years. Throughout the pesticide examination, organochlorines including the DDT group (p,p’-DDT, p,p’-DDD and p,p’-DDE) were prevalent in all examined biota. There were a significantly greater number of pyrethroid and phenylpyrazole detections and concentrations in zooplankton as compared to macroinvertebrates (Poisson regression, p < 0.05) across regions and years. Additionally, significantly higher concentrations of organochlorines were exhibited in floodplain rearing fish as compared to the Sacramento River (ANOVA, p < 0.05). These findings suggest that juvenile Chinook feeding primarily on zooplankton may be exposed to a greater range of pesticides than those exhibiting benthic feeding, but these pelagic prey were not demonstrated as a major dietary item during the two-year study. Additionally, the previously inferred benefits of floodplain rearing may come at a cost of increased organochlorine exposure. This research has allowed for a robust assessment of potential trophic transfer of pesticides to juvenile salmon, which may help inform future floodplain restoration efforts.

Flood plain mapping has become an increasingly important part of flood plain management. Flood plain mapping employs mapping software and hydraulic calculation packages to efficiently map flood plains. Modelers often utilize automation software to develop the complex geometries required to reduce the time to develop hydraulic models. The Utah Inundation Mapping System (UTIMS) is designed to reduce the time required to develop complex geometries for use in flood plain mapping studies. The automated geometries developed by UTIMS include: flood specific river centerlines, bank lines, flow path lines, cross sections and areal averaged n-value polygons. UTIMS thus facilitates developing automated input to US Army Corps of Engineer's HEC-RAS software. Results from HEC-RAS can be imported back to UTIMS for display and mapping. The user can also specify convergence criteria for water surface profile at selected locations along the river and thus run UTIMS and HEC-RAS iteratively till the convergence criterion is met. UTIMS develops a new flood specific geometry file for each iteration, enabling an accurate modeling of flood-plain. Utilizing this robust and easy to operate software within the GIS environment modelers can significantly reduce the time required to develop accurate flood plain maps. The time thus saved in developing the geometries allows modelers to spend more time doing the actual modeling and analyzing results. The time thus saved can also result in faster turn around and potential cost cutting in flood-plain modeling work. In this paper the authors describe UTIMS capabilities, compare them with other available software, and demonstrate the UTIMS flood plain automation process using a case study.

This thesis examined the relationships among ecology, economy, and society in the history of Longview, Washington, a planned timber settlement on the Columbia and Cowlitz Rivers. It compared the environmental, economic, and social histories of the Cowlitz Indians, American farmers, and urban industrialists that lived there over the past four hundred years. The central argument of the thesis is that human society cannot separate its economic and social organization from its ecology, nor can it reorder the environment without restructuring its economic and social institutions. Three different groups lived in the same physical space, but since they conceived and used the land differently, their societies developed distinct social and economic frameworks. The narrative of the thesis is chronological, tracing environmental, economic, and social change from about 1790 to 1934. During that time, humans gradually transformed a flood plain once dominated by vegetation and wildlife into a paved, sculpted, and densely populated industrial city. This study outlines the major causes and consequences of that transformation for both the land and its inhabitants. A wide range of source material provided the evidence upon which my conclusions were based. In addition to the more conventional historical sources such as diaries, letters, newspapers, memoirs, maps, and census data, I consulted anthropological studies, geological and geographical surveys, ecological reports, agricultural bulletins, and sociological analyses. My findings are presented in Chapters 2 through 5, with chapter 6 summarizing and drawing final conclusions.

Master of Science in Engineering - Engineering / There have been various threats from upstream catchment developments to the water supply of the ecologically important Nylsvlei floodplain in South Africa. Hydrological modelling of the catchments and unsteady hydraulic modelling of the floodplain (including measured losses to evapotranspiration and infiltration) with biotic links to Oryza longistaminata revealed that existing developments within the catchments have decreased areas suitable for growth of this plant in the Nylsvley Reserve by 9% on average from 1973/74 to 2000/01 compared to the catchment in a virgin state. Construction of the proposed Olifantspruit Dam with environmental flow releases would have reduced these suitable areas by a further 9% on average. Catchment developments were found to have the greatest impact on floodplain inundation in average to dry years and would also reduce the frequency of occurrence of suitable conditions for growth of Oryza longistaminata.

No description available.

<p> The stratigraphy of the Pleistocene sediments of the Credit Valley of Ontario embraces two large fining-upwards sequences which correspond to the deposition of glacial debris during the retreat of the last two glacial periods in south central Ontario. The fining-upwards sequences have a basal gravel unit, a middle cross-stratified sand unit, and an upper unit containing small coarsening-upward sequences. All three of these sedimentary units are the result of deposition of sediment in a braided fluvial system. The basal gravel unit displays mid-channel gravel bars and side channel deposits. The cross-bedded sand unit exhibits incised bed-form deposits such as linguoid bars, dunes and ripples. The upper unit of coarsening-upwards sequences (which in places are interbedded with the cross-stratified sand facies) represents the deposits of bank overflow and consequent reactivation of unused channels on the braided river floodplain.</p> <p> During the Halton and Wentworth ice advances, till was deposited on the surrounding plain. With retreat of the ice masses, meltwater and outwash debris built up an alluvial plain in the lower and wider reaches of the Credit Valley near Glen Williams. These alluvial plains or sandurs were built up by deposition from braided streams. Outwash from the Halton Ice built a sandur plain on top of one constructed in Wentworth time. Post glacial drainage has incised these glaciofluvial deposits and leaves them exposed along the banks of the present Credit River. </p> / Thesis / Master of Science (MSc)