Browsing by Subject "River"

Now showing 1 - 7 of 7
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    Field, experimental and numerical investigations into the mechanisms and drivers of lateral erosion in bedrock channels
    (2014-01) Fuller, Theodore Kent
    The process of lateral erosion in bedrock channels is poorly understood. This thesis sheds light on the mechanisms of lateral bedrock erosion as well as the larger scale drivers of lateral erosion. Contained in this thesis are three distinct studies: a field-based study that investigates the drivers of lateral planation of strath surfaces; an experimental study that seeks to identify specific mechanisms of lateral erosion; and a numerical modeling study that seeks to corroborate the findings of the experimental study and permit exploration of parameter space. The field study (Chapter 1) concludes that lateral planation of strath surfaces in the dominant channel erosion process during periods of elevated sediment supply. This study further concludes that the elevated sediment supply conditions were driven by changes in climate. The experimental study (Chapter 2) concludes that the deflection of saltating bedload particles by fixed roughness elements into the wall is an effective mechanism of erosion. In addition, the experimental study identifies a minimum roughness threshold that must be crossed before significant lateral erosion can occur. Finally, the experimental study suggests that once the roughness threshold is crossed (i.e. moving from a smooth bed devoid of roughness elements to a bed with roughness elements), further increases in bed roughness do not produce ever increasing rates of lateral erosion. Rather, an erosion rate plateau is reached shortly after the roughness threshold is crossed. The numerical modeling study (Chapter 3) corroborates the findings of the experimental study and demonstrates, from first principles, that lateral erosion by deflected bed load particles is an effective mechanism of lateral bedrock erosion. In addition, this study identifies an important trade-off between increased deflection surface area from larger roughness elements and the increased form drag associated with the larger roughness elements. Here, the increase in the number of particle deflections is offset by the decrease in particle kinetic energy on impact, resulting in the erosion rate plateau observed in the physical experiments.
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    Habitat Quality in the Floodplain Following a Channel Reconfiguration Project: Stewart River, MN
    (2021-02) Scott, Larissa
    Low flows and elevated temperatures threaten many cold-water habitats. Restoration work is commonly implemented to improve a variety of habitat degradations like elevated temperatures and lack of deep pool habitat. However, the influence of restoration work on groundwater storage and connectivity in systems with low human impacts is not well understood, especially restoration projects that involve the installation of off-channel ponds. This study looks at the connectivity and habitat quality of seven floodplain ponds with very different morphology and connectivity with the channel. The ponds were constructed as part of a large channel reconfiguration project to decrease width-to depth ratios, and improve/create coldwater fish habitat in the Stewart River, a trout stream near Two Harbors, Minnesota. During May-September of 2016 and 2017 (one year and two years following the realignment work), I studied the constructed ponds influence on water storage and water temperatures by installing water level and temperature sensors in the ponds, in shallow groundwater wells, and in the main channel. I also measured dissolved oxygen in the channel and ponds and surveyed the locations of thermal refuges between 2016 and 2018. Only one of seven floodplain ponds had suitable low-flow habitat for coldwater fish. This pond (P761) was directly connected to the channel at all flows. Three of six ponds in which temperature was measured throughout the summer were warmer than the channel, and six of seven ponds exhibited low dissolved oxygen levels (≤ 7 mg/L) in summer. Habitat quality in ponds, as measured by temperature and dissolved oxygen, was related to shading, pond morphology, and connectivity with the channel. Sunny locations displayed warmer water temperatures than shaded locations (p = 0.0001). Dissolved oxygen levels increased with pond surface area and connectivity with the channel. This study illustrates that pond geometry, connectivity with the channel, and canopy cover primarily drive temperature and dissolved oxygen levels in constructed ponds. Water elevations in five ponds and several channel locations showed that water levels in the channel peaked earlier and receded slightly quicker than ponds following precipitation events. It took about a day for the channel to reach its peak water elevation following summer precipitation events and two days for constructed ponds to peak. Pond water elevations receded to half their elevation ~3-6 days slower than the channel, but not gradually enough to augment low flows long term. During storm events, channel water elevations peaked earlier and were higher than nearby pond water elevations making the upper part of the realignment behave like a losing reach. Overall, the Stewart River reconfiguration project did not generate substantial long-term water storage or lasting high-quality floodplain fish habitats. This study illustrates the challenges and risks of channel re-meandering in flashy, relatively healthy river systems.
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    Identifying erosional hotspots in streams along the North Shore of Lake Superior, Minnesota using high-resolution elevation and soils data
    (2013-09) Wick, Molly Jane
    Many streams on the North Shore of Lake Superior, Minnesota, USA, are impaired for turbidity driven by excess fine sediment loading. The goal of this project was to develop a GIS-based model using new, openly-available, high-resolution remote datasets to predict erosional hotspots at a reach scale, based on three study watersheds: Amity Creek, the Talmadge River, and the French River. The ability to identify erosional hotspots, or locations that are highly susceptible to erosion, using remote data would be helpful for watershed managers in implementing practices to reduce turbidity in these streams. Erosion in streams is a balance between driving forces, largely controlled by topography; and resisting forces, controlled by the materials that make up a channel's bed and banks. New high-resolution topography and soils datasets for the North Shore provide the opportunity to extract these driving and resisting forces from remote datasets and possibly predict erosion potential and identify erosional hotspots. We used 3-meter LiDAR-derived DEMs to calculate a stream power-based erosion index, to identify stream reaches with high radius of curvature, and to identify stream reaches proximal to high bluffs. We used the Soil Survey Geographic (SSURGO) Database to investigate changes in erodibility along the channel. Because bedrock exposure significantly limits erodibility, we investigated bedrock exposure using bedrock outcrop maps made available by the Minnesota Geological Survey (MGS, Hobbs, 2002; Hobbs, 2009), and by using a feature extraction tool to remotely map bedrock exposure using high-resolution air photos and LiDAR data. Predictions based on remote data were compared with two datasets. Bank Erosion Hazard Index surveys, which are surveys designed to evaluate erosion susceptibility of banks, were collected along the three streams. In addition, a 500-year flood event during our field season gave us the opportunity to collect erosion data after a major event and validate our erosion hotspot predictions. Regressions between predictors and field datasets indicate that the most significant variables are bedrock exposure, the stream power-based erosion index, and bluff proximity. A logistic model developed using the three successful predictors for Amity Creek watershed was largely unsuccessful. A threshold-based model including the three successful predictors (stream power-based erosion index, bluff proximity, and bedrock exposure) was 70% accurate for predicting erosion hotspots along Amity Creek. The limited predictive power of the models stemmed in part from differences in locations of erosion hotspots in a single large-scale flood event and long-term erosion hotspots. The inability to predict site-specific characteristics like large woody debris or vegetation patterns makes predicting erosion hotspots in a given event very difficult. A field dataset including long-term erosion data may improve the model significantly. This model also requires high resolution bedrock exposure data which may limit its application to other North Shore streams.
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    Living with the Mississippi
    (River Life, University of Minnesota, 2014) Hines, Rachel; Nunnally, Patrick D.
    “Living with the Mississippi” is a blog series that examines the history of the river flats communities and what it means to almost literally live on the Mississippi River. Follow along to learn more about life on the Mississippi prior to luxury condos and clean river water, before the riverfront was considered a desirable place to live.
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    Paddling-with the Mississippi River: An Exploration of Building Relationships With Place
    (2023-04) Warren, Natalie
    It is not guaranteed that we will notice or care when life-supporting relationships between humans and more-than-humans are severed or imbalanced. In this dissertation, I argue that moving with a landscape—rooted in place-based ways of knowing—can make visible the complex interconnectedness of relationships with all others that often go ignored or unseen. Through personal narratives and theoretical reflections, I explore how paddling-with the length of the Mississippi River encouraged me to know, feel, and care for the river; to build perspective that, like the river, is capable of holding many tensions and contradictions. Embodied encounters with human, nonhuman, and more-than-human others along the 2,300-mile river directed my attention toward the water and its many uses and identities in ways that challenged the discursive binary of human-nature. I reflect on the transformative power of paddling-with the river to learn from place, reveal histories and practices that are often hidden from the public eye, and expose the vast interconnectedness of living and nonliving entities. I argue that emotionally-charged encounters with different others were vital to my experience building a relationship with the river. Feelings like shame and grief revealed my care and love for the water and propelled me to take action toward more reciprocal, balanced, and life-supporting relationships. Rooted in subjective storytelling and rhetorical analysis, this work explores one of the myriad ways we might be moved to care for earthly coexistence.
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    Topography and flow model files for the Platte River, Nebraska, 2016-2017
    (2017-10-13) Limaye, Ajay B; aslimaye@umn.edu; Limaye, Ajay B
    Automated techniques for extracting channels from topography are well developed for convergent channel networks, and identify flow paths based on land-surface gradients. These techniques—even when they allow multiple flow paths—do not consistently capture channel networks with frequent bifurcations (e.g., in rivers, deltas, and alluvial fans). The project uses multithread rivers as a template to develop a new approach for channel extraction suitable for channel networks with divergences. This data set includes topography and flow model data used to demonstrate this new approach for automated identification of channels on planetary surfaces. The data set accompanies a 2017 publication in the Journal of Geophysical Research: Earth Surface.
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    Water quality trading on the Minnesota River: lessons learned from the Jordan trading program
    (2013-08) Zajicek, Michael Nathan
    Water quality permit trading in an attractive option lower the costs of pollution cleanup in lakes and rivers, and while similar programs for air pollution have been successful, most attempts at Water Quality Trading have failed. The Jordan Trading Program, based on the Minnesota River, is one of the few exceptions. This paper examines the program to discover how the program succeeds where others have failed. The Jordan Trading has averaged 17 trades a year, and with some assumptions has resulted in cost savings. The river is modeled using a Farrow et. al. (2005) model to show that savings are theoretically possible, even if the program does not act in the same fashion. It was found that while cost savings occur, the facilities in the program are not profit maximizers due to their status as government wastewater treatment facilities, and thus the maximum potential cost savings are not achieve. The program has still been successful, and several suggestions are made for future water quality trading programs.