<p> The role of bed shear stress in bed surface grain size sorting was investigated on a reconstructed reach of the Merced River in the Central Valley of California. Pebble count data were collected at the inside, middle, and outside of ten bends in April 2015 and compared to data from pebble counts conducted in previous years. Output from a previously developed 2D flow model (FaSTMECH) was compared to critical shear stresses calculated from median grain-size data. Comparison of pebble count results from 2002 through 2015 showed that there was no temporally consistent pattern of coarsening or fining along the study reach; however, the bed surface coarsened between 2002 and 2015. Pebble count data from April 2015 revealed a distinct spatial distribution of grain sizes with a larger median grain size (D₅₀) at the outside of bends and a smaller D₅₀ at the inside of bends. Regression analyses performed on pebble count data from point bars revealed statistically significant downstream changes in surface grain size on two of the seven bars. Analysis of shear stress data showed a weak relationship between the modeled bed shear stress (&tau;_b) and the calculated critical shear stress (&tau;_cr). The weak relationship between &tau;_b and &tau;_cr indicated that bed shear stress was not solely responsible for the grain size sorting in the study reach. It is likely that the observed grain size sorting patterns resulted from helical secondary flows at the bends. </p>

abstract: Western Utopia Planitia, located in the northern plains of Mars, is home to a myriad of possible periglacial landforms. One of these is scalloped depressions, defined primarily by their oval-shape and north-south asymmetry, including both pole-facing “steps” and an equator-facing slope. Scalloped depressions are thought to have formed through sublimation of ground ice in the Late Amazonian, consistent with the hypothesis that Mars is presently in an interglacial period marked by the poleward retreat of mid-latitudinal ice. The directional growth of scalloped depressions was mapped within the region and present a correlation between topography and scalloped depression development. It was determined that topography appears to play a role in scallop development, as noted by the most-densely scalloped region residing among a lower spatial density of craters previously mapped by Harrison et al. (2019). Within this region, scallops were also observed to be absent atop crater ejecta, but present atop crater ejecta in other regions of the study area. A large majority of scallops maintain a north-south asymmetry and observed changes in geomorphology that range from predominantly smoother terrain in the northern latitudes to very hummocky terrain dominated by possible periglacial features as latitude decreases. Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) images were primarily used, with a few images coming from the MRO High Resolution Imaging Science Experiment (HiRISE). Observations are consistent with previous studies showing the overall density of scalloped depressions decreases with increasing latitude, with the majority exhibiting steps facing in a poleward direction. The majority of scallops observed to have steps in a non-poleward direction occur within in ice-rich regions mapped by Stuurman et al. (2016). It was ultimately concluded that scallops demonstrating poleward-facing steps likely formed during periods of high obliquity on Mars in the Late Amazonian, while scallops within the ice-rich regions potentially formed at a greater range of obliquities. / Dissertation/Thesis / Masters Thesis Geological Sciences 2019

No description available.

No description available.

Thèse--Paris. / Includes bibliographical references.

Thesis (Ph. D.)--İstanbul Üniversitesi, Edebiyat Fakültesi, 1977. / Summary in French. Includes bibliographical references (p. [195]-204).

<p> Beginning in the early 20th century and continuing into the 21st century, the lower 87 km of the San Rafael River in central Utah underwent rapid geomorphic changes. Extensive water development in the headwaters, invasion of the non-native tamarisk shrub, and man-made perturbations to the channel-floodplain system have been responsible for the changes that we documented in this study. We used a combination of spatially robust and temporally precise methods to reconstruct the modern history of channel change and identify the processes responsible for those changes. These methods include analysis of historic aerial photographs, analysis of USGS gage data, dendrogeomorphic analysis of floodplain stratigraphy, and comparison of historic and modern longitudinal profiles. </p><p> The San Rafael River changed from a wide, shallow, heterogeneous channel to a narrow, deep, homogeneous channel. Specifically, between 1938 and 2009, the San Rafael River along the length of the entire study area narrowed 83%. Additionally, the floodplain vertically accreted between 1.0 and 2.5 m. The majority of the channel narrowing occurred during two distinct time periods - 1952 to 1979 and 1987 to the present - when low, mean annual stream flow was low. Channel narrowing is primarily due to the reduction in transport capacity, but when coupled with tamarisk establishment, channel narrowing and floodplain aggradation has been rapid. </p><p> We documented the spatial extent of channel bed changes over the course of the 20th century. We found that the channel bed aggraded in five segments, lowered in one segment, and remained the same in the other portions of the study area. Analysis of historic, precise measurements of bed elevation at the USGS gage 09328500 revealed that the channel bed incised between Hatt&rsquo;s Ranch and MacMillan Lower Ranch Dam during two time periods: from 1952-1965 and 1983 to the present. Both episodes of incision were caused by unequal amounts of scour and fill. This imbalance in bed fluctuation was induced by human modification of the channel during the first episode and lowering of the local base control during the second episode of incision. </p><p> The changes to the physical template of the San Rafael River have implications for the management of three endemic fish &ndash; the roundtail chub (Gila robusta robusta), the bluehead sucker (<i>Catostomus discobolus</i>), and the flannelmouth sucker (<i>Catostomus Latipinnis</i>) &ndash; which currently utilize the study area. Future management of the river will benefit from the results of our study, which reveal the physical processes that are responsible for the historic and current condition of the river. </p>

Thesis (Ph. D.)--University of Adelaide, Dept. of Geology and Geophysics, 1998? / Includes bibliographical references (leaves 291-315).

Thesis (B.A.Hons.) from the Department of Geography, University of Adelaide, 1977. / Includes bibliographical references (p. 44-45).

Thesis (B.A.Hons.1971) - Dept. of Geography, University of Adelaide, 1969.