Browsing by Subject "Stream restoration"

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    Humans are Earth too: Hydrology, stream restoration, and the human side of Earth science
    (2023-06) Jones, Jabari
    Human beings (Homo sapiens) influence the Earth in profound and multifaceted ways. Humans directly alter geologic processes, including sediment transport, altered hydrologic pathways, and more. Humans also benefit and suffer from geologic processes – access to water, greenspace, and hazards. And human processes, including discrimination and power dynamics affect where and how science is done. My dissertation addresses each of these dimensions of human/Earth interaction. I begin with a human → Earth interaction by analyzing the influence of climate change and land-use change on streamflow in Minnesota and Wisconsin. We find that precipitation change has been consistent across the region, but streamflow response has been variable. Watersheds in (geologically) recently glaciated central and western Minnesota had greater streamflow increases than watersheds in eastern Minnesota and the western Wisconsin Driftless Area. This streamflow response also maps onto land-use change, as watersheds with glacial till have more agriculture drainage. Information-theory metrics reveal inconsistent patterns in the relationship between precipitation and streamflow, underscoring the hydrologic complexity of the upper Midwest. I then explore an interrelated human ↔ Earth system by developing a new stream restoration database for the state of Minnesota and exploring the environmental justice implications of restoration siting. We find that restoration projects are systematically located in whiter and more affluent locations compared to the overall population of the state. Restoration projects are also responsive to environmental degradation, as restored streams are more likely to be impaired than average streams in the state. Finally, I explore human aspects of the geosciences through three chapters: I present reflections and recommendations from my time balancing life as a geoscientist and a black resident of South Minneapolis following the murder of George Floyd in summer 2020, with a focus on how greater institutional risk is needed to truly advance visions of diversity equity and justice. I describe the pedagogical underpinnings of field learning via a literature review in geoscience, environmental science, and ecology. We find that active learning, co-creation of knowledge, rapid feedback, and place-based learning are key reasons that students learn during field trips. Finally, I offer reflections from a community science event hosted between local organizations and the Department of Earth & Environmental Sciences. Attendees considered the event a success and there were many positive and negative lessons to implement in future attempts to bridge the divide between university and non-university partners. These diverse projects illustrate a multitude of ways that humans influence and interact with the Earth, and underscore the need to consider human processes as a key element of the Earth system.
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    Numerical modeling of turbulent flows in arbitrarily complex natural streams.
    (2010-08) Kang, Seok Koo
    An efficient and versatile numerical model is developed for carrying out high-resolution simulations of turbulent flows in natural meandering streams with arbitrarily complex, albeit fixed, bathymetry and instream hydraulic structures. The numerical model solves the three-dimensional, unsteady, incompressible Navier-Stokes and continuity equations in generalized curvilinear coordinates. This model can handle the arbitrary geometric complexity of natural streams by using the sharp-interface curvilinear immersed boundary (CURVIB) method. To enable efficient simulations on grids with tens of millions of nodes in long and shallow domains typical of natural streams, the algebraic multigrid method (AMG) is used to solve the Poisson equation for pressure. Free-surface is treated either with the rigid-lid approach or modeled using a two-phase flow approach implemented using level-sets. Depending on the desired level of resolution and available computational resources, the numerical model can either simulate turbulence via direct numerical simulation (DNS), large-eddy simulation (LES) or unsteady Reynolds-averaged Navier-Stokes (URANS) simulation. The numerical model is validated by simulating several test cases for which good quality laboratory data or benchmark simulations are available in the literature. The potential of the model as a powerful tool for simulating energetic coherent structures in turbulent flows in natural river reaches is demonstrated by applying it to carry out LES and URANS simulations in a field scale natural-like meandering stream, Outdoor StreamLab, at resolution sufficiently fine to capture vortex shedding from cm-scale roughness elements on the bed. Comparisons between the simulated mean velocity and turbulence kinetic energy fields with field-scale measurements are reported and show that the numerical model can capture all features of the measured flow with high accuracy. Furthermore, the simulated flowfields are analyzed to elucidate the multi-faceted physics of the flow in a natural stream with pool-riffle sequences and to uncover the underlying physical mechanisms. The simulations provide new insights into the role of large-scale roughness in flow through riffles and elucidate the three-dimensional structure, interactions and governing mechanisms of the inner and outer bank secondary flow cells and recirculation zones in the pools. Moreover, the simulations underscore the role of turbulence anisotropy throughout the stream and suggest important links between stream hydrodynamics and morphodynamics. Calculations are also carried out for the same meandering stream with an instream structure installed along its outer bank to demonstrate the utility of the model as a powerful tool for developing science-based design guidelines for stream restoration.