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- Genre: Doctoral Dissertation
Description
An array of north-striking, left-stepping, active normal faults is situated along the southwestern margin of the Gulf of California. This normal fault system is the marginal fault system of the oblique-divergent plate boundary within the Gulf of California. To better understand the role of upper-crustal processes during development of an obliquely rifted plate margin, gravity surveys were conducted across the normal-fault-bounded basins within the gulf-margin array and, along with optically stimulated luminescence dating of offset surfaces, fault-slip rates were estimated and fault patterns across basins were assessed, providing insight into sedimentary basin evolution. Additionally, detailed geologic and geomorphic maps were constructed along two faults within the system, leading to a more complete understanding of the role of individual normal faults within a larger array. These faults slip at a low rate (0.1-1 mm/yr) and have relatively shallow hanging wall basins (~500-3000 m). Overall, the gulf-margin faults accommodate protracted, distributed deformation at a low rate and provide a minor contribution to overall rifting. Integrating figures with text can lead to greater science learning than when either medium is presented alone. Textbooks, composed of text and graphics, are a primary source of content in most geology classes. It is essential to understand how students approach learning from text and figures in textbook-style learning materials and how the arrangement of the text and figures influences their learning approach. Introductory geology students were eye tracked while learning from textbook-style materials composed of text and graphics. Eye fixation data showed that students spent less time examining the figure than the text, but the students who more frequently examined the figure tended to improve more from the pretest to the posttest. In general, students tended to examine the figure at natural breaks in the reading. Textbook-style materials should, therefore, be formatted to include a number of natural breaks so that learners can pause to inspect the figure without the risk of losing their place in the reading and to provide a chance to process the material in small chunks. Multimedia instructional materials should be designed to support the cognitive processes of the learner.
ContributorsBusch, Melanie M. D (Author) / Arrowsmith, Ramon (Thesis advisor) / Reynolds, Stephen (Thesis advisor) / Chi, Michelene (Committee member) / Semken, Steven (Committee member) / Tyburczy, James (Committee member) / Arizona State University (Publisher)
Created2011
Description
The focus of this study is statistical characterization of the significant duration of strong ground motion time histories. The significant duration is defined as the time needed to build up between five and seventy five (SD575) and ninety five percent (SD595) of the energy of a strong motion record. Energy is measured as the integral of the square of the acceleration time history and can be used to capture the potential destructiveness of an earthquake. Correlations of the geometric means of the two significant duration measures (SD575 and SD595) with source, path, and near surface site parameters have been investigated using the geometric mean of 2,690 pairs of recorded horizontal strong ground motion data from 129 earthquakes in active plate margins. These time histories correspond to moment magnitudes between 4.8 and 7.9, site to source distances up to 200 km, and near surface shear wave velocity ranging from 120 to 2250 m/s. Empirical relationships have been developed based upon the simple functional forms, and observed correlations. The coefficients of the independent variables in these empirical relationships have been determined through nonlinear regression analysis using a random effects model. It is found that significant duration measures correlate well with magnitude, site to source distance, and near surface shear wave velocity. The influence of the depth to top of rupture, depth to the shear wave velocity of 1000 m/s and the style of faulting were not found to be statistically significant. Comparison of the empirical relationship developed in this study with existing empirical relationships for the significant duration shows good agreement at intermediate magnitudes (M 6.5). However, at larger and smaller magnitude, the differences between the correlations developed in this study and those from previous studies are significant.
ContributorsGhanat, Simon T (Author) / Kavazanjian, Jr., Edward (Thesis advisor) / Houston, Sandra (Committee member) / Arrowsmith, Ramon (Committee member) / Arizona State University (Publisher)
Created2011
Description
Geoscience educators commonly teach geology by projecting a photograph in front of the class. Geologic photographs often contain animals, people, and inanimate objects that help convey the scale of features in the photograph. Although scale items seem innocuous to instructors and other experts, the presence of such items is distracting and has a profound effect on student learning behavior. To evaluate how students visually interact with distracting scale items in photographs and to determine if cueing or signaling is an effective means to direct students to pertinent information, students were eye tracked while looking at geologically-rich photographs. Eye-tracking data revealed that learners primarily looked at the center of an image, focused on faces of both humans and animals if they were present, and repeatedly returned to looking at the scale item (distractor) for the duration an image was displayed. The presence of a distractor caused learners to look at less of an image than when a distractor was not present. Learners who received signaling tended to look at the distractor less, look at the geology more, and surveyed more of the photograph than learners who did not receive signaling. The San Antonio area in the southern part of the Baja California Peninsula is host to hydrothermal gold deposits. A field study, including drill-core analysis and detailed geologic mapping, was conducted to determine the types of mineralization present, the types of structures present, and the relationship between the two. This investigation revealed that two phases of mineralization have occurred in the area; the first is hydrothermal deposition of gold associated with sulfide deposits and the second is oxidation of sulfides to hematite, goethite, and jarosite. Mineralization varies as a function of depth, whereas sulfides occurring at depth, while minerals indicative of oxidation are limited to shallow depths. A structural analysis revealed that the oldest structures in the study area include low-grade to medium-grade metamorphic foliation and ductile mylonitic shear zones overprinted by brittle-ductile mylonitic fabrics, which were later overprinted by brittle deformation. Both primary and secondary mineralization in the area is restricted to the later brittle features. Alteration-bearing structures have an average NNW strike consistent with northeast-southwest-directed extension, whereas unaltered structures have an average NNE strike consistent with more recent northwest-southeast-directed extension.
ContributorsCoyan, Joshua (Author) / Reynolds, Stephen (Thesis advisor) / Arrowsmith, Ramon (Committee member) / Chi, Michelene (Committee member) / Piburn, Michael (Committee member) / Semken, Steven (Committee member) / Arizona State University (Publisher)
Created2011
Description
The tectonic significance of the physiographic transition from the low-relief Tibetan plateau to the high peaks, rugged topography and deep gorges of the Himalaya is the source of much controversy. Some workers have suggested the transition may be structurally controlled (e.g. Hodges et al., 2001), and indeed, the sharp change in geomorphic character across the transition strongly suggests differential uplift between the Himalayan realm and the southernmost Tibetan Plateau. Most Himalayan researchers credit the South Tibetan fault system (STFS), a family of predominantly east-west trending, low-angle normal faults with a known trace of over 2,000 km along the Himalayan crest (e.g. Burchfiel et al., 1992), with defining the southern margin of the Tibetan Plateau in the Early Miocene. Inasmuch as most mapped strands of the STFS have not been active since the Middle Miocene (e.g., Searle & Godin, 2003), modern-day control of the physiographic transition by this fault system seems unlikely. However, several workers have documented Quaternary slip on east-west striking, N-directed extensional faults, of a similar structural nature but typically at a different tectonostratigraphic level than the principal STFS strand, in several locations across the range (Nakata, 1989; Wu et al., 1998; Hurtado et al., 2001). In order to explore the nature of the physiographic transition and determine its relationship to potential Quaternary faulting, I examined three field sites: the Kali Gandaki valley in central Nepal (~28˚39'54"N; 83˚35'06"E), the Nyalam region of south-central Tibet (28°03'23.3"N, 86°03'54.08"E), and the Ama Drime Range in southernmost Tibet (87º15'-87º50'E; 27º45'-28º30'N). Research in each of these areas yielded evidence of young faulting on structures with normal-sense displacement in various forms: the structural truncation of lithostratigraphic units, distinctive fault scarps, or abrupt changes in bedrock cooling age patterns. These structures are accompanied by geomorphic changes implying structural control, particularly sharp knickpoints in rivers that drain from the Tibetan Plateau, across the range crest, and down through the southern flank of the Himalaya. Collectively, my structural, geomorphic, and thermochronometric studies confirm the existence of extensional structures near the physiographic transition that have been active more recently than 1.5 Ma in central Nepal, and over the last 3.5 Ma in south-central Tibet. The structural history of the Ama Drime Range is complex and new thermochronologic data suggest multiple phases of E-W extension from the Middle Miocene to the Holocene. Mapping in the accessible portions of the range did not yield evidence for young N-S extension, although my observations do not preclude such deformation on structures south of the study area. In contrast, the two other study areas yielded direct evidence that Quaternary faulting may be controlling the position and nature of the physiographic transition across the central Tibetan Plateau-Himalaya orogenic system.
ContributorsMcDermott, Jeni Amber (Author) / Hodges, Kip V (Thesis advisor) / Whipple, Kelin X (Thesis advisor) / Van Soest, Matthijs C (Committee member) / Arrowsmith, Ramon (Committee member) / Semkin, Steven (Committee member) / Arizona State University (Publisher)
Created2012
Description
How is knowledge created at the intersections between basic science, biotechnology, and industry? Gene drives are an interesting example, as they combine a long-standing interest with a recent technological breakthrough and a new set of commercial applications. Gene drives are genes engineered such that they are preferentially inherited at a frequency greater than the typical Mendelian fifty percent ratio. During the historical and conceptual evolution of gene drives beginning in the 1960s, there have been many innovations and publications. Along with that, gene drive science developed considerable public attention, explosion of new scientists, and variation in the way the topic is discussed. It is now time to look at this new organization of science using a systematic approach to characterize the system that has enabled knowledge to grow in this scientific field. This project breaks new ground in how knowledge advances in genetic engineering science, and how scientists understand what a “gene drive” is through analysis of language, communities, and other social factors. In effect, this research will advance multiple fields and enable a deeper understanding of knowledge and complexity. This project documents patterns of publication, collaborative relationships, linguistic variation, innovation, and knowledge expansion. The results of computational analysis provide an in-depth and complete characterization of the structure, dynamics, and evolution of scientific knowledge found in the gene drive technology. Further, time series analysis of the multiple layers of discourse enabled a diachronic connective mapping of collaborative relationships and tracked linguistic variation and change, highlighting where ambiguous language may appear, improving and creating more cohesive scientific language.
Overall, depicting the structure, dynamics, and evolution of scientific knowledge during a novel eruption of scientific complexity can shed light on the factors that can lead to: (1) improved scientific communication, (2) reduction of scientific progress, (3) new knowledge, and (4) novel collaborative relationships. Therefore, characterizing the current technological, methodological, and social contexts that can influence scientific knowledge.
ContributorsOToole, Cody Lane (Author) / Laubichler, Manfred (Thesis advisor) / Collins, James P (Committee member) / Simeone, Michael (Committee member) / Evans, James (Committee member) / Arizona State University (Publisher)
Created2021
Description
Rivers in steep mountainous landscapes control how, where, and when signals of base-level fall are transmitted to the surrounding topography. In doing so rivers play an important role in determining landscape evolution in response to external controls of tectonics and climate. However, tectonics and climate often covary and understanding how they influence landscape evolution remains a significant challenge. The Hawaiian Islands, where tectonics are minimized but climate signals are amplified, provide an opportunity to better understand how signals of climate are recorded by landscapes. Focusing on the Hawaiian Islands, I examine (1) how variability in rock mass properties and thresholds in sediment mobility determine where waterfalls form or stall along the Nāpali coast of Kauaʻi, (2) I then extend these findings to other volcanoes to test if observed physical limits in flood size, climate, and volcano gradient can determine where waterfalls form, and (3) I explore how thresholds in river incision below waterfalls limit information about the influence of climate on river incision rates. Findings from this analysis show that waterfalls form or stall where the maximum unit stream power is at or below a critical unit stream power for bedrock river incision. Climate appears to have little effect in determining where these conditions are met but where waterfalls stall or form does record information about discharge-area scaling for global maximum observed floods. Below waterfalls the maximum incision depth for rivers on the island of Kauaʻi (which formed ~ 4-5 million years ago) is approximately proportional to the inverse square root of mean annual rainfall. Though maximum river incision depths for some of the younger volcanoes do not exhibit the same dependency on mean annual rainfall rates they are comparable to the maximum incision depths observed on Kauaʻi even though they are a quarter to one-tenth the age of Kauaʻi. Importantly, these patterns of incision can be explained by thresholds in sediment mobility as recorded by river longitudinal profiles and indicate that the Hawaiian Islands are dominated by threshold conditions where signals of climate are recorded in the topography through controls on incision depth but not incision rates.
ContributorsRaming, Logan Wren (Author) / Whipple, Kelin X (Thesis advisor) / Arrowsmith, Ramon (Committee member) / Heimsath, Arjun M. (Committee member) / DeVecchio, Duane E. (Committee member) / Schmeeckle, Mark (Committee member) / Arizona State University (Publisher)
Created2022
Description
Despite the rapid adoption of robotics and machine learning in industry, their application to scientific studies remains under-explored. Combining industry-driven advances with scientific exploration provides new perspectives and a greater understanding of the planet and its environmental processes. Focusing on rock detection, mapping, and dynamics analysis, I present technical approaches and scientific results of developing robotics and machine learning technologies for geomorphology and seismic hazard analysis. I demonstrate an interdisciplinary research direction to push the frontiers of both robotics and geosciences, with potential translational contributions to commercial applications for hazard monitoring and prospecting. To understand the effects of rocky fault scarp development on rock trait distributions, I present a data-processing pipeline that utilizes unpiloted aerial vehicles (UAVs) and deep learning to segment densely distributed rocks in several orders of magnitude. Quantification and correlation analysis of rock trait distributions demonstrate a statistical approach for geomorphology studies. Fragile geological features such as precariously balanced rocks (PBRs) provide upper-bound ground motion constraints for hazard analysis. I develop an offboard method and onboard method as complementary to each other for PBR searching and mapping. Using deep learning, the offboard method segments PBRs in point clouds reconstructed from UAV surveys. The onboard method equips a UAV with edge-computing devices and stereo cameras, enabling onboard machine learning for real-time PBR search, detection, and mapping during surveillance. The offboard method provides an efficient solution to find PBR candidates in existing point clouds, which is useful for field reconnaissance. The onboard method emphasizes mapping individual PBRs for their complete visible surface features, such as basal contacts with pedestals–critical geometry to analyze fragility. After PBRs are mapped, I investigate PBR dynamics by building a virtual shake robot (VSR) that simulates ground motions to test PBR overturning. The VSR demonstrates that ground motion directions and niches are important factors determining PBR fragility, which were rarely considered in previous studies. The VSR also enables PBR large-displacement studies by tracking a toppled-PBR trajectory, presenting novel methods of rockfall hazard zoning. I build a real mini shake robot providing a reverse method to validate simulation experiments in the VSR.
ContributorsChen, Zhiang (Author) / Arrowsmith, Ramon (Thesis advisor) / Das, Jnaneshwar (Thesis advisor) / Bell, James (Committee member) / Berman, Spring (Committee member) / Christensen, Philip (Committee member) / Whipple, Kelin (Committee member) / Arizona State University (Publisher)
Created2022
Description
Mountain landscapes reflect competition between tectonic processes acting to build topography and erosive processes acting to wear it down. In temperate mountain landscapes, bedrock rivers are the primary erosional agent, setting both the pace of landscape evolution and form of the surrounding topography. Theory predicts that river steepness is sensitive to climatic, tectonic, and lithologic factors, which dictate the rates and mechanics of erosional processes. Thus, encoded into topography is an archive of information about forces driving landscape evolution. Decoding this archive, however, is fraught and climate presents a particularly challenging conundrum: despite decades of research describing theoretically how climate should affect topography, unambiguous natural examples from tectonically active landscapes where variations in climate demonstrably influence topography are elusive. In this dissertation, I first present a theoretical framework describing how the spatially varied nature of orographic rainfall patterns, which are ubiquitous features of mountain climates, complicate expectations about how climate should influence river steepness and erosion. I then apply some of these ideas to the northern-central Andes. By analyzing river profiles spanning more than 1500 km across Peru and Bolivia, I show that the regional orographic rainfall pattern this landscape experiences systematically influences fluvial erosional efficiency and thus topography. I also show how common simplifying assumptions built into conventional topographic analysis techniques may introduce biases that undermine detection of climatic signatures in landscapes where climate, tectonics, and lithology all covary – a common condition in mountain landscapes where these techniques are often used. I continue by coupling this analysis with published erosion rates and a new dataset of 25 cosmogenic 10Be catchment average erosion rates. Once the influence of climate is accounted for, functional relationships emerge among channel steepness, erosion rate, and lithology. I then use these functional relationships to produce a calibrated erosion rate map that spans over 300 km of the southern Peruvian Andes. These results demonstrate that accounting for the effects of climate significantly enhances the ability to decode channel steepness patterns. Along with this comes the potential to better understand rates and patterns of tectonic processes, and identify seismic hazards associated with tectonic activity using topography.
ContributorsLeonard, Joel Scott (Author) / Whipple, Kelin (Thesis advisor) / Arrowsmith, Ramon (Committee member) / Christensen, Philip (Committee member) / Forte, Adam (Committee member) / Heimsath, Arjun (Committee member) / Hodges, Kip (Committee member) / Arizona State University (Publisher)
Created2022
Description
The movement between tectonic plates is accommodated through brittle (elastic) displacement on the plate boundary faults and ductile permanent deformation on the fault borderland. The elastic displacement along the fault can occur in the form of either large seismic events or aseismic slip, known as fault creep. Fault creep mainly occurs at the deep ductile portion of the crust, where the temperature is high. Nonetheless, aseismic creep can also occur on the shallow brittle portion of the fault segments that are characterized by frictionally weak material, elevated pore fluid pressure, or geometrical complexity. Creeping segments are assumed to safely release the accumulated strain(Kodaira et al., 2004; Rice, 1992)(Kodaira et al., 2004; Rice, 1992)(Kodaira et al., 2004; Rice, 1992)(Kodaira et al., 2004; Rice, 1992)(Kodaira et al., 2004; Rice, 1992) on the fault and also impede propagation of the seismic rupture. The rate of aseismic slip on creeping faults, however, might not be steady in time and instead consist of successive periods of acceleration and deceleration, known as slow slip events (SSEs). SSEs, which aseismically release the strain energy over a period of days to months, rather than the seconds to minutes characteristic of a typical earthquake, have been interpreted as earthquake precursors and as possible triggering factor for major earthquakes. Therefore, understanding the partitioning of seismic and aseismic fault slip and evolution of creep is fundamental to constraining the fault earthquake potential and improving operational seismic hazard models. Thanks to advances in tectonic geodesy, it is now possible to detect the fault movement in high spatiotemporal resolution and develop kinematic models of the creep evolution on the fault to determine the budget of seismic and aseismic slip.
In this dissertation, I measure the decades-long time evolution of fault-related crustal deformation along the San Andrea Fault in California and the northeast Japan subduction zone using space-borne geodetic techniques, such as Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar (InSAR). The surface observation of deformation combined with seismic data set allow constraining the time series of creep distribution on the fault surface at seismogenic depth. The obtained time-dependent kinematic models reveal that creep in both study areas evolves through a series of SSEs, each lasting for several months. Using physics-based models informed by laboratory experiments, I show that the transient elevation of pore fluid pressure is the driving mechanism of SSEs. I further investigate the link between SSEs and evolution of seismicity on neighboring locked segments, which has implications for seismic hazard models and also provides insights into the pattern of microstructure on the fault surface. I conclude that while creeping segments act as seismic rupture barriers, SSEs on these zones might promote seismicity on adjacent seismogenic segments, thus change the short-term earthquake forecast.
In this dissertation, I measure the decades-long time evolution of fault-related crustal deformation along the San Andrea Fault in California and the northeast Japan subduction zone using space-borne geodetic techniques, such as Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar (InSAR). The surface observation of deformation combined with seismic data set allow constraining the time series of creep distribution on the fault surface at seismogenic depth. The obtained time-dependent kinematic models reveal that creep in both study areas evolves through a series of SSEs, each lasting for several months. Using physics-based models informed by laboratory experiments, I show that the transient elevation of pore fluid pressure is the driving mechanism of SSEs. I further investigate the link between SSEs and evolution of seismicity on neighboring locked segments, which has implications for seismic hazard models and also provides insights into the pattern of microstructure on the fault surface. I conclude that while creeping segments act as seismic rupture barriers, SSEs on these zones might promote seismicity on adjacent seismogenic segments, thus change the short-term earthquake forecast.
ContributorsKhoshmanesh, Mostafa (Author) / Shirzaei, Manoochehr (Thesis advisor) / Arrowsmith, Ramon (Committee member) / Garnero, Edward (Committee member) / Tyburczy, James (Committee member) / Whipple, Kelin (Committee member) / Arizona State University (Publisher)
Created2018
Description
Worldwide, rivers and streams make up dense, interconnected conveyor belts of sediment– removing carved away earth and transporting it downstream. The propensity of alluvial river beds to self-organize into complex trains of bedforms (i.e. ripples and dunes) suggests that the associated fluid and sediment dynamics over individual bedforms are an integral component of bedload transport (sediment rolled or bounced along the river bed) over larger scales. Generally speaking, asymmetric bedforms (such as alluvial ripples and dunes) migrate downstream via erosion on the stoss side of the bedform and deposition on the lee side of the bedform. Thus, the migration of bedforms is intrinsically linked to the downstream flux of bedload sediment. Accurate quantification of bedload transport is important for the management of waters, civil engineering, and river restoration efforts. Although important, accurate qualification of bedload transport is a difficult task that continues t elude researchers. This dissertation focuses on improving our understanding and quantification of bedload transport on the two spatial scales: the bedform scale and the reach (~100m) scale.
Despite a breadth of work investigating the spatiotemporal details of fluid dynamics over bedforms and bedload transport dynamics over flat beds, there remains a relative dearth of investigations into the spatiotemporal details of bedload transport over bedforms and on a sub-bedform scale. To address this, we conducted two sets of flume experiments focused on the two fundamental regions of flow associated with bedforms: flow separation/reattachment on the lee side of the bedform (Chapter 1; backward facing-step) and flow reacceleration up the stoss side of the next bedform (Chapter 2; two-dimensional bedform). Using Laser and Acoustic Doppler Velocimetry to record fluid turbulent events and manual particle tracking of high-speed imagery to record bedload transport dynamics, we identified the existence and importance of “permeable splat events” in the region proximal to flow reattachment.
These coupled turbulent and sediment transport events are integral to the spatiotemporal pattern of bedload transport over bedforms. Splat events are localized, high magnitude, intermittent flow features in which fluid impinges on the bed, infiltrates the top portion of bed, and then exfiltrates in all directions surrounding the point of impingement. This initiates bedload transport in a radial pattern. These turbulent structures are primarily associated with quadrant 1 and 4 turbulent structures (i.e. instantaneous fluid fluctuations in the streamwise direction that bring fluid down into the bed in the case of quadrant 1 events, or up away from the bed in the case of quadrant 4 events) and generate a distinct pattern of bedload transport compared to transport dynamics distal to flow reattachment. Distal to flow reattachment, bedload transport is characterized by relatively unidirectional transport. The dynamics of splat events, specifically their potential for inducing significant magnitudes of cross-stream transport, has important implications for the evolution of bedforms from simple, two dimensional features to complex, three-dimensional features.
New advancements in sonar technology have enabled more detailed quantification of bedload transport on the reach scale, a process paramount to the effective management of rivers with sand or gravel-dominated bed material. However, a practical and scalable field methodology for reliably estimating bedload remains elusive. A popular approach involves calculating transport from the geometry and celerity of migrating bedforms, extracted from time-series of bed elevation profiles (BEPs) acquired using echosounders. Using two sets of repeat multibeam sonar surveys from the Diamond Creek USGS gage station in Grand Canyon National Park with large spatio-temporal resolution and coverage, we compute bedload using three field techniques for acquiring BEPs: repeat multi-, single-, and multiple single-beam sonar. Significant differences in flux arise between repeat multibeam and single beam sonar. Mulitbeam and multiple single beam sonar systems can potentially yield comparable results, but the latter relies on knowledge of bedform geometries and flow that collectively inform optimal beam spacing and sampling rate. These results serve to guide design of optimal sampling, and for comparing transport estimates from different sonar configurations.
Despite a breadth of work investigating the spatiotemporal details of fluid dynamics over bedforms and bedload transport dynamics over flat beds, there remains a relative dearth of investigations into the spatiotemporal details of bedload transport over bedforms and on a sub-bedform scale. To address this, we conducted two sets of flume experiments focused on the two fundamental regions of flow associated with bedforms: flow separation/reattachment on the lee side of the bedform (Chapter 1; backward facing-step) and flow reacceleration up the stoss side of the next bedform (Chapter 2; two-dimensional bedform). Using Laser and Acoustic Doppler Velocimetry to record fluid turbulent events and manual particle tracking of high-speed imagery to record bedload transport dynamics, we identified the existence and importance of “permeable splat events” in the region proximal to flow reattachment.
These coupled turbulent and sediment transport events are integral to the spatiotemporal pattern of bedload transport over bedforms. Splat events are localized, high magnitude, intermittent flow features in which fluid impinges on the bed, infiltrates the top portion of bed, and then exfiltrates in all directions surrounding the point of impingement. This initiates bedload transport in a radial pattern. These turbulent structures are primarily associated with quadrant 1 and 4 turbulent structures (i.e. instantaneous fluid fluctuations in the streamwise direction that bring fluid down into the bed in the case of quadrant 1 events, or up away from the bed in the case of quadrant 4 events) and generate a distinct pattern of bedload transport compared to transport dynamics distal to flow reattachment. Distal to flow reattachment, bedload transport is characterized by relatively unidirectional transport. The dynamics of splat events, specifically their potential for inducing significant magnitudes of cross-stream transport, has important implications for the evolution of bedforms from simple, two dimensional features to complex, three-dimensional features.
New advancements in sonar technology have enabled more detailed quantification of bedload transport on the reach scale, a process paramount to the effective management of rivers with sand or gravel-dominated bed material. However, a practical and scalable field methodology for reliably estimating bedload remains elusive. A popular approach involves calculating transport from the geometry and celerity of migrating bedforms, extracted from time-series of bed elevation profiles (BEPs) acquired using echosounders. Using two sets of repeat multibeam sonar surveys from the Diamond Creek USGS gage station in Grand Canyon National Park with large spatio-temporal resolution and coverage, we compute bedload using three field techniques for acquiring BEPs: repeat multi-, single-, and multiple single-beam sonar. Significant differences in flux arise between repeat multibeam and single beam sonar. Mulitbeam and multiple single beam sonar systems can potentially yield comparable results, but the latter relies on knowledge of bedform geometries and flow that collectively inform optimal beam spacing and sampling rate. These results serve to guide design of optimal sampling, and for comparing transport estimates from different sonar configurations.
ContributorsLeary, Kate (Author) / Schmeeckle, Mark W (Thesis advisor) / Whipple, Kelin X (Thesis advisor) / Heimsath, Arjun (Committee member) / Walker, Ian (Committee member) / Arrowsmith, Ramon (Committee member) / Arizona State University (Publisher)
Created2018