Browsing by Subject "fluvial geomorphology"

Now showing 1 - 4 of 4
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    Buried in bluff country: Stream and valley sedimentation in the Whitewater River Valley, Minnesota (USA)
    (2023) Wood, Jimmy
    Erosion and sedimentation are natural and beneficial surface processes but when accelerated by anthropogenic activities related to agriculture yield negative economic and ecologic consequences. European style agriculture spread through 16th to 19th century colonialism has had a profound effect on erosion and sedimentation rates across the globe. The Upper Mississippi River Valley (UMRV) region of the United States, where the Whitewater River Watershed is located, has been particularly affected by European style agriculture implemented in the mid-20th century. From the 1890s through 1920s, increased erosion, sedimentation, and flood frequency precluded land from agricultural production and damaged property and infrastructure in the Whitewater basin. Living and working conditions became untenable and most of the lower valley was abandoned by the 1960s. This geomorphic upheaval invited scrutiny by Soil Conservation Service geologist Stafford Coleman Happ who established a basin-wide sedimentation survey in 1939. He and assistant surveyors established 94 valley transects upon which the distribution and thickness of Euro-American Legacy Sediment (ELS) was measured through auger boring and surface elevation surveys. Repeat field surveys in the 1960s, 1970s, and 1990s were conducted along with an aerial lidar survey in 2008 yielding a robust, over 150-year, record of river valley changes and sedimentation throughout the basin. We use this historical transect sedimentation data to ask how sedimentation rates in the Whitewater watershed have changed since the implementation of soil conservation measures around 1940. Mean sedimentation rates are calculated per transect between floodplain cross-sections or from soil bore depth measurements and are then compared statistically with Welch’s ANOVA and the Games-Howell tests. Between 1939 and 1994, mean transect sedimentation rates for the basin decrease from 0.92 to 0.22 cm/yr. We speculate that this is due to improved soil conservation measures implemented in the basin around 1940. An analysis of land use and land cover change over this time should be completed to corroborate this assumption. The 1994 to 2008 time interval indicates that sedimentation has increased over the last 14 years of this record, but we lack the spatial data coverage to make conclusions about basin wide changes. Still, this change may likely be attributed to the effects of large floods to mobilize sediment, such as the record flood of 2007, as well as anecdotally reported land use intensification since the 1990s. Downstream spatial patterns of sedimentation from the uplands, through the middle gorges of the Whitewater River, to the bluff bordered lower valley appear to follow trends reported in other basins of the UMRV in relation to valley and channel geometry characteristics. These should be investigated in turn to understand how sediment is being routed throughout the river network.
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    Experimental alluvial-river and landsliding response to base-level fall
    (2020-04-24) Beaulieu, Olivia P; Wickert, Andrew D; Witte, Elizabeth D; Tofelde, Stefanie; awickert@umn.edu; Wickert, Andrew D; Saint Anthony Falls Laboratory; Department of Earth & Environmental Sciences; Universität Potsdam
    We observed the incisional response of an alluvial river to base-level fall. We conducted the experiment in a 3.9 × 2.4 × 0.4 m box that we filled with uniform 0.140±0.04 mm sand. We dropped base level by lowering the elevation of an "ocean" pool at the river outlet. As the initial condition, we cut a 10±2 cm wide channel to a steadily increasing depth, from 3±0.5 cm at the inlet, where we supplied water and sediment, to 10±1 cm at the outlet. Input water and sediment discharge were 0.1 L/s and 0.0022 L/s (including pore space), respectively. As base level fell, the river incised and migrated laterally, forming a valley with abandoned terrace surfaces and walls that failed in mass-wasting events as they were undercut. We include a control case with no base-level fall, as well as experiments with 25 mm/hr, 50 mm/hr, 200 mm/hr, 300 mm/hr, and 400 mm/hr of base-level fall. We supply georeferenced overhead photos (0.89 mm resolution, every 20 seconds), digital elevation models (DEMs, 1 mm horizontal resolution, every 15–30 minutes), videos generated from the overhead photos, mapped landslides in GIS vector area (polygon) format, and landslide attributes. Relevant code to process and plot the data, as well as further information on grain size, is available from GitHub and Zenodo.
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    The morphodynamic influence of cohesive sediment on coastal systems across scales
    (2016-07) Abeyta, Antoinette
    Cohesive sediment makes up a large portion of the rock record and much of the earth’s surface sediment. Despite how common cohesive sediments are, the focus of research on sedimentary systems has largely been on non-cohesive sediment. Consequently, there has been limited research on how cohesive sediment influences sediment transport and the implications this has for depositional systems. To increase our knowledge of cohesive sediment, it is important to understand the morphological impact of cohesive sediment on depositional systems. Physical experiments provide a powerful tool for approaching this problem as they will allow us to constrain and measure parameters which may be difficult to measure in the field. The overarching goal of this project is to expand our experimental framework to include the use of cohesive sediment, which allows us to investigate an important set of effects in the field. Presented here is a framework of physical experiments, which investigate quantitative aspects of how cohesive sediment influences morphodynamics across scales. The first experimental series investigates how mass failures form in cohesive sediment on delta fronts and what factors influence their occurrence and evolution. The second experimental series is a study on how cohesion influences deltaic processes and overall morphology. Finally, the last experimental series is on how cohesive and other fine sediment lead to changes in the gradient of sediment flux that in turn lead to upstream changes in the overall sediment mass balance in coastal systems.
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    Nature and Effects of County Drainage Ditches in South Central Minnesota
    (Water Resources Research Center, 1980-11) Quade, Henry W.; Boyum, Kent W.; Braaten, Duane O.; Gordon, Donald; Pierce, Clay L.; Silis, Ainars Z.; Smith, David R.; Thompson, Bill C.
    The extent of county drainage was determined for four counties in South Central Minnesota followed by a study of the geomorphic nature of man’s drainage in contrast to natural drainage. Selected drainage ditches and low order rivers were sampled for water quality and quantity in order to determine the contributions and timing of nutrient loads from each. Seventy-nine percent of the drainage ditches were found to terminate into rivers and they more than doubled the length of the surface fluvial systems. The closeness of fit of the drainage ditch systems to the low order Strahler classification scheme suggests that man has taken an immature lake-marsh environment and within 100 years created a geomorphically mature fluvial landscape. Nutrient loading by ditches into receiving bodies was found to vary by season, by individual ditch or river, and by stream order indicating that each ditch was unique. Water quality of one ditch during this wet study year was compared to a previous dry year study and the nutrient loading data was consistent and predictable. The most significant loading nutrient chemical parameter to the Minnesota River was found to be nitrate-nitrogen. Flow showed flashy response to storm events in some ditches and some were quite conservative. Sediment load was directly correlated to flow.