Browsing by Subject "Geomorphology"

Now showing 1 - 8 of 8
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    Experimental Studies of the Influence of the Properties of the Matrix of a Debris Flow on Its Erosional Behavior
    (2018-03) Mullenbach, Jared
    Debris flows – massive flows of fluid and particles – create significant hazard for communities established in or near mountainous regions. There is evidence that the frequency of debris flows and hazards associated with them are increasing associated with changes in macro and micro climate and subsequent changes in rainfall patterns, soil moisture, and local sediment supply. Thus there is an increasing need for a mechanistic understanding of the manner in which physical parameters give rise to certain debris flow behaviors. Recent field and laboratory observations have indicated that the nature of the matrix of rocky debris flows – the muddy or watery interstitial fluid among the gravel and boulders – can have a significant influence on the flow behaviors of a debris flow, from local sorting behaviors to entrainment and depositional behaviors, to associated avulsion behaviors. In this presentation, we report on our experimental investigations of the influence of the rheology and relative density of the matrix of a debris flow on its behaviors using laboratory experiments of particle-fluid flows and their erosive behaviors. To do so, we perform laboratory experiments of erosive debris flows where we systematically vary the interstitial fluid in our debris flow and the erodible bed over which it flows. We track the particles throughout the experiment along with pore fluid pressure which enables us to determine the instantaneous flow dynamics and correlations in the flow and erosion behavior. We find that entrainment rate varies substantially with interstitial fluid viscosity, essentially increasing with decreasing interstitial fluid viscosity, yet this relationship is not strictly monotonic and varies in time. We use these variations as a basis to investigate three specific mechanisms previously suggested responsible for entrainment by debris flows: (1) bed shear stress, (2) granular temperature (essentially, correlated velocity fluctuations), and (3) excess pore fluid pressure (measured pore pressure that exceeds that associated with the weight of the interstitial fluid). We find that both average and instantaneous bed shear stresses and granular temperatures are poorly correlated with associated entrainment rates. Rather, the excess pore pressure is well correlated with entrainment rates, particularly under conditions when the entrainment rate is the greatest. We investigate the source of the excess pore pressure and find that through the majority of the experiment it is likely due to the suspension of the particles in the sparsest most energetic part of the flow, effectively fluidizing them and increasing the effective density of the interstitial fluid in that region. We conclude with a brief discussion of preliminary field work we performed to extend this understanding to field scale debris flows to provide a stepping stone to prevention and avoidance of loss to property and communities due to these dangerous phenomena.
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    An Experimental Study of Drainage Network Development by Surface and Subsurface Flow in Low-Gradient Landscapes Raster Datasets
    (2021-09-28) Sockness, Brian G; Gran, Karen B; kgran@d.umn.edu; Gran, Karen B; University of Minnesota - Duluth Earth and Environmental Sciences Department
    The data include raster format elevation measurements and other derived parameters captured from small-scale drainage network development experiments conducted at the University of Minnesota - Duluth. Elevation data were captured as point elevation measurements using a terrestrial lidar unit and converted to raster format digital elevation models at four millimeter resolution via interpolation. The digital elevation models are provided here as 1.) ArcGIS Map Package, 2.) TIFF files, and 3.) JPEG images.
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    Factors influencing roadside erosion and in-stream geomorphic stability at road-stream crossings for selected watersheds, North Shore, Minnesota, USA.
    (2012-07) Dutton, Patricia Danielle
    Currently, 10 major watersheds in Minnesota's North Shore exceed state water quality standards for turbidity (10 NTU) a surrogate for total suspended solids. In this region, recent anthropogenic disturbances can be attributed to roadway construction and maintenance. The presence of roadways can pose a serious threat to ecosystem functions, altering local and landscape hydrology, fragmenting riparian areas, and delivering chemical pollutants and suspended sediments to nearby waterways via surface runoff and seepage. This study examined the current extent of hydrologic connectivity between roads and streams, by investigating roadside erosion for select sub-watersheds within the North Shore watershed of Minnesota, USA. Surveys were conducted at 54 road-stream crossings along 12.2 km of roadways in the summer of 2010. A Road-stream connectivity analysis found roads increase the drainage density of North Shore watersheds by approx. 1.45-9.47%. Measureable erosion was observed at 64.8% of survey sites (gully, or rill) totaling 93.26 m3, with an average loss per site of 1.73 m3, or 7.64 m3/km. Traffic intensity, road construction, parent material, stream order, soil k factor, hillslope gradient best predicted erosion for this dataset using logistic regression at local and watershed wide scales. The effect road-stream crossings as a localized stress on stream stability was also examined at seven sites, using Rosgen level I classification and Pfankuch stability metrics. This qualitative analysis of stream stability upstream and downstream of road-stream crossing structures indicated study road-stream crossings are causing localized instability. Assessments indicated stream segments are negatively impacted both upstream and downstream of crossing structures.
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    Geomorphological and Archaeoastronomical Analysis of a Neolithic Landscape, Cranborne Chase, Southern Britain
    (2024-01) Burley, Paul
    Cranborne Chase in southwest England is a well-known area of Neolithic archaeology where a nexus of population growth, cultural evolution and resource extraction during the 4th millennium led to development of one of the highest densities of earthen monuments, including numerous long barrows, the largest and longest cursus in Britain, and many other structures. Natural physiographic characteristics of the study area in tandem with anthropomorphic modification of local vegetation patterns on the downs since the Mesolithic provided a distinctive setting where the Early- to Middle-Neolithic cultural landscape developed. However, reasons for siting monuments at certain locations within the complex chalkland landscape, the purpose of specific and unique architectural forms and features of the earthen structures, and spatial relationships between the pattern of monuments and elements of the surrounding environment as a whole remain largely enigmatic. Are there special features of the natural landscape that the Neolithic population valued for earthen monument development, and why was such a high density of earthen monuments developed there? This thesis describes geological and paleo-environmental characteristics and cultural features of the study area c. 4th millennium, evaluates similarities and differences associated with Neolithic and Bronze Age earthen and chambered burial sites located across Britain, and presents methods and results of an astrometric analysis of topographic position, monument orientation, and viewscape from earthen monuments at Cranborne Chase. Results of this study demonstrate that spatial and temporal relationships between the earthen structures and elements of the surrounding landscape, seascape, and skyscape are key to recognizing and understanding the symbolism and signification expressed by the monumental architecture. The cultural landscape – including the pattern of both natural features and earthen monuments at Cranborne Chase, the South Hampshire Lowlands, and surrounding region – expresses spatial and temporal unification by alignment between Earth and sky, and the living and the dead. In that way, the cultural landscape is related to a Neolithic cosmology emphasizing features of the landscape and skyscape.
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    Interpretable Machine Learning to Improve Predictions of Fluvial Sediment Transport
    (2021-08) Lund, J.
    Fluvial sediment-transport contributes to many environmental concerns including flooding, nutrient loading, aquatic habitat degradation, reservoir sedimentation impacting dam operation, filling in of navigable waterways, and degrading of streams requiring costly restorations. However, there is a general lack of fluvial sediment-transport predictive power as it is difficult to comprehensively understand due to its complex process controlled by many factors such as hydrology, geology, land-use, and sediment supply. Field data can be used to better understand fluvial sediment-transport but is often limited due to it being expensive, technical, and labor intensive to collect. Minnesota provides a unique opportunity to study sediment-transport due to a complex glacial history that produced diverse landforms which combine with varying land uses and land covers to yield surface water conditions. Fortunately, Minnesota has a large sediment-transport dataset available with which to build and test a statewide predictive model in order to increase the knowledge of sediment-transport and help solve environmental concerns. XGBoost machine learning models were developed and trained to predict suspended-sediment concentration (SSC) and bedload transport rates at unsampled rivers and streams by using SSC samples collected from 56 sites and bedload samples collected from 43 sites by the U.S. Geological Survey from 2007-2019. Basin (full upstream area), catchment (nearby landscape), near-channel, and in-channel feature variables were compiled from available state and national datasets (NHDPlusV2, StreamCat, U.S. Stream Classification System, and StreamStats). The 2-year recurrence interval statistic for each site was used to normalize streamflow. The slope of the dimensionless hydrograph was calculated to teach the model the rate of rising or falling streamflow conditions before and after each sample was collected. Models for both bedload and SSC transport explained roughly 70% of the variance in the dataset. Shapley additive explanation values (SHAP) facilitated model interpretation and connected important model features to their roles with the sediment-transport process. Cumulative suspended sediment loads were calculated from model output and compared to in-situ surrogate loads from four sites in the study area to show model utility, and test model improvements. Results show that these models can inform sediment loads and stream-restoration activities across Minnesota by providing estimates of suspended-sediment concentrations and bedload rates where samples have not been collected.
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    Local and Non-local Geomorphic Effects of Hydrokinetic Turbines: Bridging Renewable Energy and River Morphodynamics
    (2019-06) Musa, Mirko
    Marine and Hydrokinetic (MHK) energy is an emerging renewable and sustainable technology which harnesses kinetic energy of natural water flows such as tides, rivers and ocean currents. In particular, rivers are currently an overlooked source of local and continuous kinetic energy that can be exploited using the available in-stream converters technology. The uncertainties regarding the interaction between these devices and the surrounding environment complicate the regulatory permitting processes, slowing down the expansion of MHK industry. A crucial issue that needs further attention is the interaction between these devices and the physical fluvial environment such as the bathymetry, sediment transport, and the associated morphodynamic processes. Analytical and experimental research conducted at Saint Anthony Falls Laboratory (SAFL) addressed this topic, unveiling the local and non-local (far from the device location) effects of hydrokinetic turbines on channel bathymetry and morphology. A theoretical model framework based on the phenomenology of turbulence was derived to predict the scour at the base of MHK device. Asymmetric installations of turbine array models within multi-scale laboratory channels were observed to trigger river instabilities known as forced-bars. Results suggest that the amplitude of these instabilities might be reduced by limiting the power plant lateral obstruction within the channel cross-section. A 12-turbine staggered array also proved to be resilient to intense flooding conditions, encouraging the expansion of this technology to large sandy rivers. Current research is investigating how hydrokinetic technology can be synergistically integrated in rivers, not only minimizing the environmental costs but also providing a positive feedback on the channel. Experiments suggest that turbines strategically installed in the river (i.e. at the side bank in yawed condition or in a vane-shaped array) could be used as stream bank protection systems and, eventually, be integrated in stream restoration projects.
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    Minnesota Guide for Stream Connectivity and Aquatic Organism Passage through Culverts
    (Minnesota Department of Transportation, 2019-01) Hernick, Matthew; Lenhart, Christian; Kozarek, Jessica; Nieber, John
    This guide assists Minnesota culvert designers in identifying, selecting, and implementing appropriate designs for maintaining aquatic organism passage (AOP) and stream connectivity at road-stream intersections. It was synthesized from existing literature and culvert design documents, a survey of Minnesota practitioners, research, and input from local, regional, and national experts. Culvert designs that create excessive velocity, physical barriers, or shallow depth can disrupt AOP and may be detrimental to the continuity of water flow, sediment, and debris transport vital to stream health. Conversely, the recommended culvert designs in this guide account for stream parameters such as slope and substrate that vary across Minnesota landscapes. A set of best practices captures critical design elements based on stream characteristics, which can be summarized as follows: 1.) Design the culvert to be similar to the stream channel (reference reach) by matching its slope, alignment, bankfull width, and flow depth to maximize AOP; 2.) Provide a continuous sediment bed with roughness similar to the channel, while maintaining continuity of sediment transport and debris passage, and; 3.) Design for public safety, longevity, and resilience. Culvert design that improves AOP and accounts for sediment transport is expected to reduce long-term maintenance costs and increase culvert life span.
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    Ravine alluvial fans as records of landscape change in the Le Sueur River Basin, southern Minnesota
    (2017-10) Treat, Ian
    Ravine alluvial fans in the Le Sueur River Basin (LSRB) of south-central Minnesota record post-glacial Holocene changes and modern anthropogenic disturbances to land cover and hydrology in high-latitude watersheds. Seventy meters of base-level drop at the end of the last glaciation initiated millennia of incision that continues on the LSRB today. Onto this template of on-going incision, Euro-American land clearing and drainage of previously stable upland prairie and wetlands in the mid-1800s further increased erosion rates in the basin. Ravines, first-order channels that link low-gradient uplands with the deeply-incised channel network, experienced changes in erosion rates over time from both impacts, with the erosional history preserved in alluvial fans at the mouths of ravines where they terminate on fluvial terraces. Establishing a post-settlement chronology is difficult in the highly erosive knickzone of the Le Sueur. We take advantage of six fan deposits spread throughout the LSRB to determine the fluvial response of upland agricultural land conversion on steep first-order drainages. Ravines respond quickly to sediment and hydrology fluxes in the basin that are reflected in their alluvial fans as packages of post-settlement alluvium (PSA) and incision through fan surfaces. Bulk soil samples collected at 10-, 20-, 40-, 100-, and 200-centimeter depths on the selected fans as well as samples from the incised channel were analyzed for fly ash, spherical silt-sized grains that are a byproduct of coal combustion. The presence of fly ash as an in-situ stratigraphic marker at depth was used to calculate conservative post-settlement deposition rates of 0.93 and 1.67 cm/yr using observation techniques from high-powered transmitted and reflected light microscopes as well as scanning electron microscopy, respectively. These rates are a three-fold increase over generous Holocene deposition rates of 0.27 cm/yr. Incision through fan surfaces also marks post-settlement changes. Trenching and tile drainage on the uplands allowed for greater transport of water down ravines and onto fans. These results confirm land use change triggered an increase in upstream erosion and fan deposition followed by incision on short time scales.