Physical and Environmental Geography Commons^™

Timing And Formation Of Linear Dunes South Of The Niobrara River Valley, North-Central Nebraska Sand Hills, Ashley K. Larsen

Department of Geography: Dissertations, Theses, and Student Research

The Nebraska Sand Hills is a vast (7500 square kilometer) area of grass-stabilized sand dunes. Larger dunes in the Nebraska Sand Hills formed primarily during the Late Pleistocene, but many underwent widespread reactivation during the Holocene. Recent Optically Stimulated Luminescence (OSL) dating indicates that the last major phase of reactivation in the Sand Hills was during the Medieval Warm Period, approximately 800 years ago. Nevertheless, many questions about the evolution of the dunes remain unanswered, particularly regarding the formation of linear dunes in portions of the Sand Hills.

This study seeks to understand more about the formation of linear dunes …

Keeping Pace With Relative Sea Level Rise: Marsh Platform Monitoring Shows Minimal Sediment Deficit Along The Louisiana Coast, Kelly Marie Sanks

Graduate Theses and Dissertations

Recent reports estimate that the marshes of the Mississippi Delta receive just 30% of the sediment necessary to sustain current land area1. An extensive monitoring campaign by the USGS and LCPRA provides direct measurements of sediment accumulation, subsidence rates, and deposit characteristics along the coast over the past 10 years2, allowing us to directly evaluate this sediment balance. By interpolating bulk density, organic fraction, and vertical accretion rates from 273 sites, a direct measurement of organic and inorganic sediment accumulation can be made. Results show that a total of 82 MT/year of sediment is delivered to the coast. Using a …

Evolution Of Grain Size Distributions And Bed Mobility During Hydrographs In Gravel-Bed Braided Rivers, Sarah Peirce, Peter Ashmore, Pauline Leduc

Geography & Environment Publications

Evolution of bed material mobility and bedload grain size distributions under a range of discharges is rarely observed in braiding in gravel-bed rivers. Yet, the changing of bedload grain size distributions with discharge is expected to be different from laterally stable, threshold, channels on which most gravel bedload theory and observation are based. Here, simultaneous observations of flow, bedload transport rate, and morphological change were made in a physical model of a gravel-bed braided river to document the evolution of grain size distributions and bed mobility over three experimental event hydrographs. Bedload transport rate and grain size distributions were measured …

Forewarned Is Forearmed: Review Of Curbing Catastrophe: Natural Hazards And Risk Reduction In The Modern World By Timothy H. Dixon (2017), Jason Makansi

Numeracy

Timothy H. Dixon. 2017. Curbing Catastrophe: Natural Hazards and Risk Reduction in the Modern World. (New York, NY: Cambridge University Press) 300 pp. ISBN 978-1108113663.

Curbing Catastrophe for the most part lives up to what is claimed in the foreword: “…a compelling account of recent and historical disasters, both natural and human-caused, drawing on common themes and providing a holistic understanding of hazards, disasters, and mitigation for anyone interested in this important and topical subject.” This is a pretty thorough treatment of an extraordinarily complex subject, and the gaps identified in this review should be considered explications more than …

Changing Snow Seasonality In The Highlands Of Kyrgyzstan, Monika Tomaszewska, Geoffrey Henebry

NASA Land-Cover Land-Use Change Data Sets

Few studies have examined changing snow seasonality in Central Asia. Here, we analyzed changes in the seasonality of snow cover across Kyrgyzstan (KGZ) over 14 years from 2002/03–2015/16 using the most recent version (v006) of MODIS Terra and Aqua 8 day snow cover composites (MOD10A2/MYD10A2).We focused on three metrics of snow seasonality—first date of snow, last date of snow, and duration of snow season—and used nonparametric trends tests to assess the significance and direction of trends. We evaluated trends at three administration scales and across elevation. We used two techniques to assure that our identification of significant trends was not …

An Assessment Of Atmospheric And Meteorological Factors Regulating Red Sea Phytoplankton Growth, Wenzhao Li, Hesham El-Askary, Mohamed A. Qurban, Emmanouil Proestakis, Michael J. Garay, Olga V. Kalishnikova, Vassilis Amiridis, Antonis Gkikas, Eleni Marinou, Thomas Piechota, K. P. Manikandan

Mathematics, Physics, and Computer Science Faculty Articles and Research

This study considers the various factors that regulate nutrients supply in the Red Sea. Multi-sensor observation and reanalysis datasets are used to examine the relationships among dust deposition, sea surface temperature (SST), and wind speed, as they may contribute to anomalous phytoplankton blooms, through time-series and correlation analyses. A positive correlation was found at 0–3 months lag between chlorophyll-a (Chl-a) anomalies and dust anomalies over the Red Sea regions. Dust deposition process was further examined with dust aerosols’ vertical distribution using satellite lidar data. Conversely, a negative correlation was found at 0–3 months lag between SST anomalies …

The Variability In The Morphological Active Width: Results From Physical Models Of Gravel‐Bed Braided Rivers, Sarah Peirce, Pauline Leduc, Peter Ashmore

Geography & Environment Publications

The morphological active width, defined as the lateral extent of bed-material displacement over time, is a fundamental parameter in multi-threaded gravel-bed rivers, linking complex channel dynamics to bedload transport. Here, results are presented from 5 constant discharge experiments, and three event hydrographs, covering a range of flow strengths and channel configurations for which morphological change, bedload transport rates, and stream power were measured in a physical model. Changes in channel morphology were determined via differencing of photogrammetrically-derived digital elevation models (DEMs) of the model surface generated at regular intervals over the course of ~115 hours of experimental runs. Independent measures …

Expanding The "Active Layer", Peter Ashmore, Sarah Peirce, Pauline Leduc

Geography & Environment Publications

Church and Haschenburger (2017) make helpful distinctions around the issue of defining the active layer, with which we agree. We propose expanding discussion and definition of the ”active layer” in fluvial bedload transport to include the concept of the “morphological active layer”. This is particularly applicable to laterally unstable rivers (such as braided rivers) in which progressive morphological change over short time periods is the process by which much of the bedload transport occurs. The morphological active layer is also distinguished by variable lateral and longitudinal extent continuity over a range of flows and transport intensity. We suggest that the …

Paleoflood Hydrology And Basin Morphometric Characteristics Related To Flooding In The Colorado Front Range, Natalie Trivino

Electronic Theses and Dissertations

Flooding hazards are common in the Colorado Front Range due to the steep, complex terrain of the mountains where waters quickly spill out onto the most populated region of Colorado. This region has experienced numerous catastrophic floods, such as the 2013 Front Range Floods, the Fort Collins Flood of 1997, and the Big Thompson Canyon Flood of 1976 to name a few. The objective of this study was to analyze basin morphometric characteristics of several drainage basins throughout the Colorado Front Range South Platte River tributaries and determine how these characteristics relate to extreme flooding. This was done through three …

Accounting For Spatial Autocorrelation In Modeling The Distribution Of Water Quality Variables, Lorrayne Miralha

Theses and Dissertations--Geography

Several studies in hydrology have reported differences in outcomes between models in which spatial autocorrelation (SAC) is accounted for and those in which SAC is not. However, the capacity to predict the magnitude of such differences is still ambiguous. In this thesis, I hypothesized that SAC, inherently possessed by a response variable, influences spatial modeling outcomes. I selected ten watersheds in the USA and analyzed them to determine whether water quality variables with higher Moran’s I values undergo greater increases in the coefficient of determination (R²) and greater decreases in residual SAC (rSAC) after spatial modeling. I compared non-spatial ordinary …

Geomorphic Consequences Of Hydroelectricity And Transportation Development Near Celilo Falls, Lower Mid-Columbia River, Washington, Noah I. Oliver

All Master's Theses

Along the Columbia River, hundreds of miles of transportation infrastructure and over sixty hydroelectric dams have been constructed. This altered a rich cultural landscape with evidence of 10,000 years of continuous occupation. Researchers have attempted to understand the impacts of anthropogenic factors on the Columbia River, focusing on the riverine environment. However, the effect of transportation and hydroelectricity developments to eolian landforms on the floodplains and adjoining slopes have not been studied. Focusing on 2,800 acres near Celilo Falls, this study 1) establishes a baseline condition of eolian landforms from 1805 to 1900; 2) conducts an air photo increment analysis …

The Origin Of Dark Mats At The Sunrise Ridge Borrow Pit Site (45pi408) Mount Rainier National Park, Washington, Sean Stcherbinine

All Master's Theses

The Sunrise Ridge Borrow Pit Site is a precontact archaeological site located in the upland forest soils of Mount Rainier National Park. Site stratigraphy is complicated, consisting of tephra deposits from mostly known origins that are intercalated with dark sediments of unknown origin, referred to here as dark mats. Precontact occupation has been split previously into two components based on the ambiguous depositional history of the dark mats, notably their unknown parent material, depositional environment, and relationship with adjacent tephra strata. Stratigraphic samples from excavation units, features, and one off-site excavation unit was used to investigate these data gaps. Grain …