No description available.

Runion is a protohistoric Native American village located on the floodplain of the Nolichucky River in western Washington County. Previous archaeological excavations and radiocarbon dates suggest that the village was occupied during the mid-16th to mid-17th century. The Nolichucky River, in contrast, has been flowing through the area for millennia. Geophysical surveys are used to image the subsurface non-invasively, without disturbing protected land and/or organisms. Preliminary geophysical data collected at Runion include ground penetrating radar (GPR), electromagnetic induction (EMI), and magnetometry. These data show a linear feature surrounding the protohistoric village. Given its placement around the margins of the village, the feature could be interpreted as a fortification ditch, which is often paired with a palisade wall to defend a village from attack. The feature is also consistent with typical meandering floodplain stratigraphy, where sections of channel are often abandoned to form oxbow lakes. Over time these abandoned channels fill in and are called paleochannels. Each geophysical method measures the properties and characteristics of the linear feature, a presumed paleochannel. GPR sends electromagnetic radar waves into the ground, which reflect off different subsurface layers and are recorded as radargrams. Magnetometry measures subtle changes in earth magnetism, including the magnetization of rocks, soils, and/or ferrous objects. EMI systems transmit low frequency electromagnetic waves to measure both electrical conductivity (EC) and magnetic susceptibility (MS). Each of these instruments are used to collect data in transects and then processed to produce profiles, maps and, in the case of GPR, three-dimensional datasets of the subsurface. It is anticipated that GPR will reveal details about the stratigraphy of the linear feature. Magnetic, EC, and MS measurements will further help to interpret the GPR data by distinguishing between different types of sediments. These data may show if the feature is a paleochannel or a ditch excavated into older stratigraphic layers by village inhabitants for fortification. Ultimately, the feature will be tested with soil cores to study the sediments directly. At this preliminary stage the feature is interpreted to be a paleochannel. The stratigraphic layers revealed by GPR show a broad depression with stratigraphic layers characteristic of a paleochannel. In addition, magnetic readings are anomalously low on the eastern margin (closer to the modern river channel) and high on the western margin. This could indicate paired point bar sands and paleochannel fill, respectively. This interpretation is still tentative, however, because we have not yet integrated the EMI data, extracted soil cores, or dated the feature. Radiocarbon dates might help determine the relative age of the feature if organic carbon is present. In conclusion, preliminary data currently suggests that the structure is geological rather than archaeological. In the coming months we will collect more GPR data with different frequency GPR antennas, integrate the EMI data, and test the findings by extracting soil cores and reconstructing the stratigraphy.

Currently, our ability to predict the flux of fine sediment at the watershed scale is limited by the precision of erosion rate estimates for the many potential sources distributed throughout a landscape as well as our understanding of the connectivity of sediment pathways during transport. In absence of a robust predictive model which can be validated by measurements of sediment fluxes and use of geochemical tracers. Predicting fine sediment yield at the watershed scale requires multiple redundant lines of information. This thesis outlines the methods used, and the data sets collected in the Root River watershed in Southeastern Minnesota, all of which are multiple lines of evidence to the sediment dynamics in the Root River. The research indicates that the Root River is a very dynamic watershed. The hydrologic regime of the watershed has shifted over the last half century. Due to this shift sediment fluxes are very dependent of the magnitude and sequence of events. Geomorphic analysis of the landforms and the use of a developed tool, TerEx, indicate that many reaches of the river have easily accessible near-channel sources of sediment. Sediment fingerprinting results illustrate that source tracer concentrations are variable across the landscape, that as a whole, upland sources are still a major contributor to the suspended sediment load, and that in some sub-watersheds near-channel sources are dominate in the suspended load. Over all the channel-floodplain exchange exerts strong control on the flux of sediment through this river system.

Over the last century, the construction and management of large dams and stream-flow diversions, and periodic drought have resulted in significant declines in stream flow of the lower Rio Grande in the Big Bend region. Reductions in mean annual flow and peak discharge have resulted in channel narrowing by the formation of vertically accreting inset floodplains. Narrowing has been temporarily interrupted by infrequent large dam releases greater than 1000 m3/s that have temporarily widened the channel; however, after each of these events, narrowing has resumed. Prior to 1942, floods of this magnitude occurred approximately once every 4 years and maintained a wide sandy channel. Since 1942, they have occurred 4 times. The decline in frequency of these large floods has resulted in a channel approximately 50% narrower than in the 1940s. Since the most recent channel widening floods in 1991, the channel has narrowed between 35 and 50%. In two large floodplain trenches, we observed between 2.75 and 3.5 m of vertical accretion during the same period. Additionally, nearly 90% of bare active channel bars have been converted to vegetated floodplains. Since 1991, the cross section channel area at the Johnson Ranch gage has decreased by approximately 30%. The reduction in cross section area and the invasion of non-native vegetation have resulted in higher flood stages, flooding at lower discharges, and continued vertical accretion. Channel narrowing has negatively impacted the native and endemic aquatic ecosystem through the loss of ecologically important habitats such as backwaters, side channels, and low velocity portions of the channel. Reductions in cross section area and resultant increased flood stages have also endangered historic cultural sites within the Big Bend region. Restoration efforts are currently underway within the region without a clear understanding of these historical channel changes and why they occurred. Our reconstruction of historical channel changes shows that the most significant periods of channel narrowing occurred during drought and increased stream-flow management. Management practices also appear to have enabled the invasion of non-native riparian species, which promoted sedimentation, bank stabilization, and additional channel narrowing. In order to restore historical measures of channel width, management options include non-native vegetation removal, common low magnitude dam releases that provide flood disturbance and prevent vegetation establishment, and large dam releases in excess of 1000 m3/s that create and maintain a wide channel. Vegetation management is expensive; and time consuming, and managed dam releases are politically unpopular and expensive, however, without the management of non-native riparian species and reinstatement of portions of the historical flood regime, ecological restoration will be difficult.

No description available.

Active geomorphic features of rivers like sandbars provide habitat for endangered and threatened riparian plant and animal species. However, human development has altered flow and sediment regimes, thus impairing formation of sandbars and islands. Large scale mapping of the fluvial geomorphology in river ecosystems like the Connecticut River is are necessary to understand the dynamics of these features and preserve habitat. Orthophotographs from 2012 from United States Department of Agriculture's Farm Service Agency (FSA), National Agriculture Imagery Program (NAIP) were used to develop a model in ArcGIS Pro to identify fluvial geomorphic features in the Connecticut River and 12 of its major tributaries. This multi-stage image classification model identifies and ranks pixels of proximity and similar color to identify and map sandbars and islands. Locations of sandbars distribution were mapped and analyzed for each river. In the majority of rivers, sandbar area per reach decreases downstream. For the mainstem, sandbar area decreased towards the mouth but with three increases of sandbars due to meandering and major tributary confluences of the White and Deerfield rivers. Dams tend to decrease sandbars downstream but the effect of dams is context specific. Sandbars are stored upstream of the impoundment on the Black River as expected, sandbars appear downstream of a dam on the mainstem if a tributary confluence is present. Conservation of high sandbar area reaches and naturally eroding stream banks are necessary for preservation of endangered species. This spatial model for sandbar mapping can be applied in other river ecosystems across the region.

Streams and rivers are a vital part of our ecosystem. They are imperiled by human ecological activities such as urbanization, industrialization, and agriculture which discharge excess nitrate and other pollutants into our waterways. Here, this dissertation seeks to understand the physical and biogeochemical processes which attenuate pollutants in stream corridors. The focus is hyporheic zones which form the interface between surface water and groundwater below and adjacent to stream channels, and riparian zones which form the interface between channels and adjacent uplands, both of which can attenuate pollutants. In this context, soil-pipes can dominate subsurface hydraulics. This research first employed MODFLOW and MT3D-USGS to model transient hyporheic hydraulics and nitrate transport in a length of riparian/riverbank soil to probe the effects of soil pipes on hydraulics and denitrification due to peak flow events in the channel. Findings showed that inserting just one soil pipe 1.5 m in length caused a ~75% increase in both hyporheic exchange and denitrification. A rough upscaling showed soil pipes could remove up to ~3% of nitrate along a 1-km reach. Next, the ability of soil pipes to bypass the often championed ability of riparian buffers to remove nitrate migrating from uplands to the channel was evaluated. This effort also employed MODFLOW and MT3D-USGS to simulated hydraulics and nitrate removal along a length of riparian soil. Findings showed that soil pipes increased flow of nitrate to the banks by five orders of magnitude in some cases. We posited a non-dimension parameter which governs when nitrate bypass is significant. In addition to soil pipes, dune bedforms can also enhance hyporheic exchange, primarily in the stream/riverbed. Again employing MODFLOW but now pairing with the transport code SEAM3D to simulate microbially-mediated aerobic metabolism of dissolved organic carbon and dissolved oxygen, the combined effects of dune translation and microbial growth and death were explored. Major findings include that neglecting microbial growth can lead to inaccurate modeling of biogeochemistry, and that aerobic metabolism increased with celerity. The results herein bolster knowledge of natural pollutant attenuation in stream and river corridors, and have implications for pollutant mitigation strategy and stream credit allocation. / Doctor of Philosophy / Streams are a vital part of our ecosystem. They are imperiled by human ecological activities such as urbanization, industrialization, and agriculture which discharge nitrate and other pollutants into our waterways. Here, this dissertation seeks to understand the physical and biological processes which attenuate pollutants. The hyporheic zone is the interface between surface water and groundwater below the bed and adjacent to stream banks, and can attenuate pollutants. Transient peak flow events such as a storm or snow melt raise the stream water levels, causing the water pressure in the stream channel to temporarily outweigh the water pressure in the soil pore spaces adjacent to the stream channel. This drives water into the banks subjecting it to pollutant attenuation processes. Soil pipes (long cylindrical void spaces created by decayed plant roots) are prevalent along stream banks, and they dominate subsurface hydraulics. This dissertation implemented a numerical study on a chunk of riparian soil to probe the effects of soil pipes on hydraulics and denitrification. Findings showed that inserting just one – 1.5 m soil pipe caused a ~75% increase in both water flow volume into the bank and nitrate removal. Riparian buffers are the vegetated strips adjacent to stream channels and have long been championed as stalwarts of pollutant removal. Soil pipes undermine this by acting as a bypass mechanism. A numerical study was again performed on a chunk of riparian soil to quantify the effects soil pipes on riparian bypass of nitrate. Findings showed that soil pipes increased flow of nitrate to the banks by five orders of magnitude in some cases. This means that a buffer enhancement strip with fine roots that prevent the formation of soil pipes should be installed along riparian buffers. In addition to soil pipes, dune bedforms can increase flowrate of water into the hyporheic zone. This dissertation modeled the combined effects of dune translation and microbial growth and death. Major findings include that neglecting microbial growth can lead to inaccurate modeling of biogeochemistry, and that biodegradation increases with increased dune velocity. The results herein bolster knowledge on natural pollutant attenuation in streams, and have implications in terms of pollutant mitigation strategy and stream credit allocation.

Throughout history floods have been part of the human experience. They are recurring phenomena that form a necessary and enduring feature of all river basin and lowland coastal systems. In an average year, they benefit millions of people who depend on them. In the more developed countries, major floods can be the largest cause of economic losses from natural disasters, and are also a major cause of disaster-related deaths in the less developed countries. Flood disaster mitigation research was conducted to determine how remotely sensed data can effectively be used to produce accurate flood plain maps (FPMs), and to identify/quantify the sources of error associated with such data. Differences were analyzed between flood maps produced by an automated remote sensing analysis tailored to the available satellite remote sensing datasets (rFPM), the 100-year flooded areas "predicted" by the Flood Insurance Rate Maps, and FPMs based on DEM and hydrological data (aFPM). Landuse/landcover was also examined to determine its influence on rFPM errors. These errors were identified and the results were integrated in a GIS to minimize landuse / landcover effects. Two substantial flood events were analyzed. These events were selected because of their similar characteristics (i.e., the existence of FIRM or Q3 data; flood data which included flood peaks, rating curves, and flood profiles; and DEM and remote sensing imagery.) Automatic feature extraction was determined to be an important component for successful flood analysis. A process network, in conjunction with domain specific information, was used to map raw remotely sensed data onto a representation that is more compatible with a GIS data model. From a practical point of view, rFPM provides a way to automatically match existing data models to the type of remote sensing data available for each event under investigation. Overall, results showed how remote sensing could contribute to the complex problem of flood management by providing an efficient way to revise the National Flood Insurance Program maps.

Die Untersuchungsschwerpunkte der vorliegenden Promotion, die von 1996-1999 im Rahmen des BMBF-Projektes "Auenregeneration nach Deichrückverlegung" im Biosphärenreservat Flusslandschaft Elbe - Brandenburg durchgeführt wurde, waren: - Lage und räumliche Verteilung der Vegetationstypen des Auengrünlandes in einem geplanten Rückdeichungsgebiet bei Lenzen (Elbe-km 476-484) im jetzigen Deichvor- und Deichhinterland - Erforschung der kausalen Zusammenhänge zwischen der jetzigen Vegetationszonierung im überflutungsgeprägten Deichvorland und den abiotischen und biotischen Standortsfaktoren vor Ort - aus den zwei erstgenannten Untersuchungen ableitend die Erstellung einer verbindlichen Prognose zur Zonierung der Grünlandvegetation nach der Deichrückverlegung (Übertragung der standortsbezogenen Untersuchungsergebnisse auf das Rückdeichungsgebiet im Geografischen Informationssystem GIS) - Auswirkung verschiedener Weide- und/oder Mahd-Nutzungsformen auf die jetzige Grünlandvegetation und Prognose der landwirtschaftlichen und naturschutzfachlichen Nutzungsmöglichkeiten nach einer Rückdeichung - Landschaftpflegerische Möglichkeiten zur Wiederansiedlung gefährdeter Stromtal-Arten nach einer Deichrückverlegung Anhand multivariater Verfahren (Kanonische Korrespondenzanalyse CCA, Hauptkomponentenanalyse DCA) konnte festgestellt werden, daß die mittlere jährliche Überflutungsdauer sich dazu eignet, die rezente Vegetationszonierung im Auengrünland zu beschreiben und zukünftige Vegetationsverteilung im Rückdeichungsgebiet zu prognostizieren. Die Überprüfung der Prognosergebnisse an Hand des rezenten, bereits überflutungsgeprägten Vordeichgrünlandes ergibt hohe bis sehr hohe Übereinstimmungen zwischen vorhergesagter und Ist-Vegetation bei wechselfrischen bis wechselfeuchten Grünlandbeständen der Typen Leucanthemo-Rumicetum thyrsiflori und Elytrigia repens-Alopecurus pratensis-Gesellschaft. Bei den wechselfeuchten bis wechselfrischen Flutrasen (Alopecuretum geniculati) und Rohrglanzgras-Röhrichten (Phalaridetum arundinaceae) weichen die Prognoseergebnisse in Flächenausdehnung und Kongruenz weiter von der rezenzten Vegetationsverteilung ab. Ursächlich sind hierfür vor allem das Mikrorelief des Deichvorlandes und seine Auswirkungen auf den Wasserzu- und abfluss während und nach Hochwässern verantwortlich. In der Diskussion werden die standortbezogenen Untersuchungesergebnisse mit ökologischen Modellen zur Sukzession und Überflutungstoleranz in Beziehung gesetzt. Das verwendete Prognosemodell wird anhand aktueller Literatur bewertet. Vor dem Hintergrund der weitreichenden hydrologischen Eingriffe in die Flussaue wird deutlich, dass nur solche Grünlandarten und -gesellschaften wieder angesiedelt werden können, die dynamische Grundwasserverhältnisse tolerieren. Eine Wiederbesiedlung kann mit Hilfe verschiedener Techniken aus nahegelegenen Restpopulationen im rezenten Deichvorland gelingen. / The investigations described in this study have been carried out between 1996 and 1999 as a part of the research project "Auenregeneration durch Deichrückverlegung" promoted by the German Federal Ministry of Education and Research (BMBF) in the "Mankind and the Biosphere" (MAB) reserve "Flusslandschaft Elbe - Brandenburg". The main objectives of the study were - to map the spatial distribution of different types of riparian grassland within a prospective re-inundation area near the town of Lenzen on the river Elbe (river kilometer 476-484) comprising the current grassland in front of the river dike and in its hinterland, - to quantify the influence of non-biotic and biotic site factors on temporarily inundated areas by thorough investigation of the present/current vegetation zonation of the dike's foreland, - to integrate the results of vegetation mapping and environmental research using a Geographical Information System (GIS) in order to predict the future vegetation zonation after the re-flooding of the proposed area, - to predict the impact of different types of land use on characteristic riparian grassland communities (extensive types of land use with hay harvest(ing) and grazing vs. hay harvest(ing) twice a year) with respect to nature preservation aspects and economic aspects of agricultural land use, and - to propose measures suitable to recover characteristic and endangered plant species and communities of riparian grassland after the setting back of the dike. By means of multivariate statistics (Canonical Correspondence Analysis CCA, Detrended Correspondence Analysis DCA) the mean annual duration of the inundation period was identified as a parameter suitable to describe the current grassland zonation and to predict the future zonation of the prospective re-inundation area. The results of the prediction were evaluated by comparing the predicted areas with the mapped areas of the present grassland types: The spatial distribution of the rarely flooded Leucanthemo-Rumicetum thyrsiflori and Elytrigia repens-Alopecurus pratensis grassland communities were highly congruent and matched well while the predicted and the mapped areas differed widely in more frequently flooded grassland types such as Alopecuretum geniculati and Phalaridetum arundinaceae These differences, however, were due to the microtopography of the dike's foreland (e. g. enbankments) governing the access and reflux of flooding water during inundation periods (site factor "isolation"). Furthermore the results of the evironmental studies were compared with current models of vegetation dynamics and inundation tolerance. The thus developed prediction model was evaluated. Taking the profound alterations in the hydrological characteristics of the flood plain into account it became evident that only those grassland species and communities that are able to tolerate highly dynamic ground water movements can be rehabilitated. Their restitution can be achieved by different techniques making use of left-over plant populations that can be found in the nearby grasslands of the dike's foreland.

Planícies de inundação são áreas sujeitas a fluxo episódico de água, que devido a disponibilidade de água, nutrientes e substrato estável, foram largamente afetadas desde o surgimento e subsequente evolução de plantas vasculares terrestres. Neste contexto, a escassez de exemplos documentados de planícies de inundação formadas anteriormente ao período Siluriano contrasta com décadas de debate acerca dos efeitos da evolução de plantas terrestres em estilos de canais fluviais. Dada a importância de planícies de inundação como sítios de acumulação de partículas sedimentares, intemperismo de minerais silicáticos e desenvolvimento de perfis de solo, esta falta de dados sobre planícies de inundação antigas tem importante impacto na forma como entendemos sistemas transporte de sedimento, o registro climático e ciclos geoquímicos globais do Precambriano e início do Paleozoico. Com o objetivo de aprimorar os modelos existentes de planícies de inundação pré-vegetação, desenvolvidos antes da evolução de plantas vasculares no continente, três exemplos de ambientes aluviais foram investigados com o emprego de análise de fácies e de elementos arquiteturais. Os exemplos escolhidos oferecem a oportunidade de avaliar não apenas a existência destes depósitos sedimentares, mas também de propor um modelo para a deposição deste ambiente sedimentar particular. A Formação Tombador (Supergrupo Espinhaço, BA) é parte de espessa sucessão sedimentar de idade Mesoproterozoica, que inclui depósitos aluviais e costeiros; O Grupo Santa Bárbara e o Grupo Guaritas (Supergrupo Camaquã, RS), que se estendem do fim do Neoproterozoico ao início do Cambriano, representam sucessões aluvias depositadas em rift continental. O estudo destes três exemplos permitiu a determinação de possíveis feições comuns a planícies de inundação pré-vegetação, como depósitos de granulação relativamente mais grossa em comparação a exemplos modernos, melhor preservação de estruturas sedimentares e abundância de facies arenosas representativas de condições de fluxo e sedimentação desconfinadas. Os exemplos de planícies de inundação pré-vegetação utilizadas para compor este modelo simplificado compartilham de semelhanças marcantes a depósitos de rios efêmeros, que são frequentemente citados como explicação para a formação de espessos depósitos de arenitos-em-lençól. A reavaliação de depósitos fluviais pré-vegetação, considerando a possibilidade de que planícies de inundação de granulação grossa, sugere que este ambiente deposicional tem sido bastante negligenciado, e que inferências climáticas obtidas da alternância de estilos fluviais contrastantes pode ser equivocada, uma vez que a alternância de registro de rios perenes e efêmeros podem ser parte de um mesmo sistema deposicional. / Floodplains are areas of unconfined and episodic water flow that, given the generalized availability of water, nutrients and stable substrate, have been extensively affected by the first appearance and subsequent evolution of land plants. In this respect, the scarcity of documented examples of pre-Silurian floodplain deposits contrasts with the continuous and decades-long debate on the effects of land plants evolution on fluvial channel styles. Given the importance of floodplains as sites of sediment storage, silicate minerals weathering and development of soil profiles, this lack of data on ancient floodplains has great implications for our understanding of the source-to-sink systems, the climate record and the global geochemical cycles of the Precambrian and the Early Paleozoic. Aiming at the improvement of the current models regarding pre-vegetation floodplains, which were developed prior to the evolution of vascular land plants, three examples of alluvial environments were investigated trough facies and architectural elements analysis. The used examples offer the opportunity to assess not only the existence of such deposits, but also to propose a model for the deposition of those particular sedimentary environments. The Mesoproterozoic Tombador Formation (Espinhaço Supergroup, Northeastern Brazil) is part of thick sedimentary deposits, which includes alluvial and coastal environments; the Neoproterozoic Santa Bárbara Group and the Cambrian Guaritas Group (Camaquã Basin, Southern Brazil) represents alluvial successions deposited in a continental rift system. The study of the three examples allowed the determination of some common features to pre-vegetation floodplain deposits, like relatively coarser grained deposits in comparison to modern examples, better preservation of sedimentary structures and abundance of sandstone facies representative of sedimentation in unconfined flow settings. The pre-vegetation floodplain deposits used to draw this simplified model share characteristics remarkably similar to ephemeral river deposits, which are frequently evoked to explain the formation of thick successions of sheet-like sandstone deposits. The re-evaluation of pre-vegetation fluvial deposits considering the possibility of coarse grained floodplains suggests that this environment have been greatly overlooked, and that climate inferred from the alternation of contrasting fluvial styles might be misleading, since alternation of deposits representing perennial and ephemeral fluvial deposits can be part of the same depositional system.