- 223 Veihmeyer Hall, LAWR
University of California at Davis
1 Shields Avenue
Davis, CA 95616 - 530-302-5658
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Keli Mutu is a stratovolcano that has three crater lakes containing exotic fluids. This study presents the analytical results describing the chemistry of each lake, interprets the chemistries in terms of water-rock interactions and... more
Keli Mutu is a stratovolcano that has three crater lakes containing exotic fluids. This study presents the analytical results describing the chemistry of each lake, interprets the chemistries in terms of water-rock interactions and volcanic fluxes, and derives a physical lake model that delineates the parameter-window for volcanic crater lake existence. Geochemical investigation of the vertical and lateral compositions of the lakes on Keli Mutu required the use of a remote sampling system. Lake temperature, pH, and dissolved oxygen content were determined in the field, while the analytical chemistries of lake fluids and sediments were determined in the months after the expedition to Keli Mutu. To reconstruct the in situ chemistries of the lakes' aqueous systems, a solution equilibrium modeling program (SOLVEQ) was applied. The energy flux model that was developed assumes thermal steady state conditions to gain insight into the physical dynamics of volcanic crater lakes. This model leads to graphs of lake temperature versus volcanic gas input for lakes of different radii. Assessment of the growth and shrinking of lake volume as a function of the relative influences of endogene versus exogene forces was provided by using the additional requirement of hydrological steady state. In general, for a crater of a given radius, the temperature of the lake that exists at thermal steady state within it is a function of sulfur dioxide influx and evaporative cooling. The primary conclusion of this thesis is that the three Keli Mutu lakes are all fed by a similar volcanic gas source, but as a result of the mediated transport of that gas it yields different chemical "expressions" in each crater lake. Comparison of the individual lakes with their respective historic chemistries demonstrates that they are all approaching chemical steady state. Future studies of Keli Mutu should include a thorough investigation of volcano flank seepage outlets, as at least one such spring-fed river bears a crater lake signature and could be used to calculate element fluxes through the volcanic edifice.
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Scientists and engineers design river topography for a wide variety of uses, such as experimentation, site remediation, dam mitigation, flood management, and river restoration. A recent advancement has been the notion of topographical... more
Scientists and engineers design river topography for a wide variety of uses, such as experimentation, site remediation, dam mitigation, flood management, and river restoration. A recent advancement has been the notion of topographical design to yield specific fluvial mechanisms in conjunction with natural or environmental flow releases. For example, the flow convergence routing mechanism, whereby shear stress and spatially convergent flow migrate or jump from the topographic high (riffle) to the low point (pool) from low to high discharge, is thought to be a key process able to maintain undular relief in gravel bedded rivers. This paper develops an approach to creating riffle-pool topography with a form-process linkage to the flow convergence routing mechanism using an adjustable, quasi equilibrium synthetic channel model. The link from form to process is made through conceptualizing form-process relationships for riffle-pool couplets into geomorphic covariance structures (GCSs) tha...
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Alongshore sediment bypassing rocky headlands remains understudied despite the importance of characterizing littoral processes for erosion abatement, beach management, and climate change adaptation. To address this gap, a numerical model... more
Alongshore sediment bypassing rocky headlands remains understudied despite the importance of characterizing littoral processes for erosion abatement, beach management, and climate change adaptation. To address this gap, a numerical model sediment transport study was developed to identify controlling factors and mechanisms for sediment headland bypassing potential. Four idealized headlands were designed to investigate sediment flux around the headlands using the process-based hydrodynamic model Delft-3D and spectral wave model SWAN. The 120 simulations explored morphologies, substrate compositions, sediment grain sizes, and physical forcings (i.e., tides, currents, and waves) commonly observed in natural settings. A generalized analytical framework based on flow disruption and sediment volume was used to refine which factors and conditions were more useful to address sediment bypassing. A bypassing parameter was developed for alongshore sediment flux between upstream and downstream c...
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Balancing ecological and human water needs often requires characterizing key aspects of the natural flow regime and then predicting ecological response to flow alterations. Flow metrics are generally relied upon to characterize long-term... more
Balancing ecological and human water needs often requires characterizing key aspects of the natural flow regime and then predicting ecological response to flow alterations. Flow metrics are generally relied upon to characterize long-term average statistical properties of the natural flow regime (hydrologic baseline conditions). However, some key aspects of hydrologic baseline conditions may be better understood through more complete consideration of continuous patterns of daily, seasonal, and inter-annual variability than through summary metrics. Here we propose the additional use of high-resolution dimensionless archetypes of regional stream classes to improve understanding of baseline hydrologic conditions and inform regional environmental flows assessments. In an application to California, we describe the development and analysis of hydrologic baseline archetypes to characterize patterns of flow variability within and between stream classes. We then assess the utility of archetyp...
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UMI. ProQuest® Dissertations & Theses The world's most comprehensive collection of dissertations and theses. Learn more... ProQuest. Large wood aids Chinook salmon (Oncorhynchus tshawytscha ) spawning in marginal habitat on a... more
UMI. ProQuest® Dissertations & Theses The world's most comprehensive collection of dissertations and theses. Learn more... ProQuest. Large wood aids Chinook salmon (Oncorhynchus tshawytscha ) spawning in marginal habitat on a regulated river in California. ...
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To date, subreach-scale variations in flow width and bed elevation have rarely been included in channel classifications. Variability in topographic features of rivers, however, in conjunction with sediment supply and discharge produces a... more
To date, subreach-scale variations in flow width and bed elevation have rarely been included in channel classifications. Variability in topographic features of rivers, however, in conjunction with sediment supply and discharge produces a mosaic of channel forms that provides unique habitats for sensitive aquatic species. In this study we investigated the utility of topographic variability attributes (TVAs) in distinguishing channel types and dominant channel formation and maintenance processes in montane and lowland streams of the Sacramento River basin, California, USA. A stratified random survey of 161 stream sites was performed to ensure balanced sampling across groups of stream reaches with expected similar geomorphic settings. For each site surveyed, width and depth variability were measured at baseflow and bankfull stages, and then incorporated in a channel classification framework alongside traditional reach-averaged geomorphic attributes (e.g., channel slope, width-to-depth,...
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Understanding the spatial organization of river systems in light of natural and anthropogenic change is extremely important because it can provide information to assess, manage, and restore them to ameliorate worldwide freshwater fauna... more
Understanding the spatial organization of river systems in light of natural and anthropogenic change is extremely important because it can provide information to assess, manage, and restore them to ameliorate worldwide freshwater fauna declines. For gravel- and cobble-bedded alluvial rivers studies spanning analytical, empirical and numerical domains suggest that at channel-forming flows there is a tendency towards covarying bankfull bed and width undulations amongst morphologic units such as pools and riffles, whereby relatively wide areas have relatively higher minimum bed elevations and relatively narrow areas have relatively lower minimum bed elevations. The goal of this study was to determine whether minimum bed elevation and flow-dependent channel top width are organized in a partially confined, incising gravel–cobbled bed river with multiple spatial scales of anthropogenic and natural landform heterogeneity across a range of discharges. A key result is that the test river exh...
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Pretreatment of sediment with hydrogen peroxide to remove organic constituents and aid deflocculation is a common component of particle size analyses of terrestrial and marine sediments. This study quantitatively determined the effect of... more
Pretreatment of sediment with hydrogen peroxide to remove organic constituents and aid deflocculation is a common component of particle size analyses of terrestrial and marine sediments. This study quantitatively determined the effect of a range of treatment levels on particle size distribution among four sediment types representing a range of mineral/organic particle size distributions, organic content and particle characterisation (charcoal or detrital plant material). The hypothesis was that complete removal of organic particles would lead to improved repeatability of results for a given sample and treatment level. Repeatability was assessed with a coefficient of variance calculation and a comparison of particle size distribution patterns within and across treatments. The effect of treatment levels on commonly used distribution descriptors (e.g. texture ratios and measures of central tendency) were then examined for each sample. Samples characterised primarily by detrital materia...
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Traditionally it is has been thought that rivers possess the capability of adjusting their attributes to accommodate varying flow and sediment transport regimes so that sediment in- and out-fluxes are balanced and landform conditions are... more
Traditionally it is has been thought that rivers possess the capability of adjusting their attributes to accommodate varying flow and sediment transport regimes so that sediment in- and out-fluxes are balanced and landform conditions are ``stable''. In reality, however, geomorphic drivers and boundary conditions are much more independently dynamic than classically envisioned, such that landforms may always be in a
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ABSTRACT Two-dimensional (depth-averaged) hydrodynamic models have existed for decades and are used to study a variety of hydrogeomorphic processes as well as to design river rehabilitation projects. Rapid computer and coding advances are... more
ABSTRACT Two-dimensional (depth-averaged) hydrodynamic models have existed for decades and are used to study a variety of hydrogeomorphic processes as well as to design river rehabilitation projects. Rapid computer and coding advances are revolutionizing the size and detail of 2D models. Meanwhile, advances in topo mapping and environmental informatics are providing the data inputs to drive large, detailed simulations. Million-element computational meshes are in hand. With simulations of this size and detail, the primary challenge has shifted to finding rapid and inexpensive means for testing model predictions against observations. Standard methods for collecting velocity data include boat-mounted ADCP and point-based sensors on boats or wading rods. These methods are labor intensive and often limited to a narrow flow range. Also, they generate small datasets at a few cross-sections, which is inadequate to characterize the statistical structure of the relation between predictions and observations. Drawing on the long-standing oceanographic method of using drogues to track water currents, previous studies have demonstrated the potential of small dGPS units to obtain surface velocity in rivers. However, dGPS is too inaccurate to test 2D models. Also, there is financial risk in losing drogues in rough currents. In this study, an RTK GPS unit was mounted onto a manned whitewater kayak. The boater positioned himself into the current and used floating debris to maintain a speed and heading consistent with the ambient surface flow field. RTK GPS measurements were taken ever 5 sec. From these positions, a 2D velocity vector was obtained. The method was tested over ~20 km of the lower Yuba River in California in flows ranging from 500-5000 cfs, yielding 5816 observations. To compare velocity magnitude against the 2D model-predicted depth-averaged value, kayak-based surface values were scaled down by an optimized constant (0.72), which had no negative effect on regression analysis. The r2 value for speed was 0.78 by this method, compared with 0.57 based on 199 points from traditional measurements. The r2 value for velocity direction was 0.77. Although it is not ideal to rely on observed surface velocity to evaluate depth-average velocity predictions, all available velocity-measurement methods have a suite of assumptions and complications. Using this method, the availability of 10-100x more data was so beneficial that the outcome was among the highest model performance outcomes reported in the literature.
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ABSTRACT A consensus is emerging that multiple scales of landform heterogeneity exert a first-order control on fluvial processes and system resilience in gravel-bed rivers. The key question now is to understand exactly how features at... more
ABSTRACT A consensus is emerging that multiple scales of landform heterogeneity exert a first-order control on fluvial processes and system resilience in gravel-bed rivers. The key question now is to understand exactly how features at each scale express themselves and interact with each other during flows ranging from baseflow to megaflood. In this study, repeated decadal, high-resolution digital elevation models of ~30-km of the gravel-bed Lower Yuba River corridor were analyzed for geomorphic change with uncertainty and a comparable-resolution 2D hydrodynamic model of flows spanning 0.2-20 times bankfull discharge with spatially distributed vegetation roughness was used to infer physical processes. Decadal topographic change was found to vary by geomorphic unit, with pools scouring more than riffles, indicating resilience. Spectral analysis of landforms showed correlations between bed and width undulations, a key characteristic of resilient landforms. The 2D model revealed that stage-dependent flow-convergence routing was ubiquitous, except in a few forced constrictions where peak velocities never shifted as discharge increased. Because the lower Yuba River corridor is lightly vegetated, stage-dependent roughness patterns yielded only a second-order effect on hydrodynamics responsible for channel resilience.
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ABSTRACT The description of fluvial form has evolved from anecdotal descriptions to artistic renderings to 2D plots of cross section or longitudinal profiles and more recently 3D digital models. Synthetic river valleys, artificial 3D... more
ABSTRACT The description of fluvial form has evolved from anecdotal descriptions to artistic renderings to 2D plots of cross section or longitudinal profiles and more recently 3D digital models. Synthetic river valleys, artificial 3D topographic models of river topography, have a plethora of potential applications in fluvial geomorphology, and the earth sciences in general, as well as in computer science and ecology. Synthetic river channels have existed implicitly since approximately the 1970s and can be simulated from a variety of approaches spanning the artistic and numerical. An objective method of synthesizing 3D stream topography based on reach scale attributes would be valuable for sizing 3D flumes in the physical and numerical realms, as initial input topography for morphodynamic models, stream restoration design, historical reconstruction, and mechanistic testing of interactions of channel geometric elements. Quite simply - simulation of synthetic channel geometry of prescribed conditions can allow systematic evaluation of the dominant relationships between river flow and geometry. A new model, the control curve method, is presented that uses hierarchically scaled parametric curves in over-lapping 2D planes to create synthetic river valleys. The approach is able to simulate 3D stream geometry from paired 2D descriptions and can allow experimental insight into form-process relationships in addition to visualizing past measurements of channel form that are limited to two dimension descriptions. Results are presented that illustrate the models ability to simulate fluvial topography representative of real world rivers as well as how channel geometric elements can be adjusted. The testing of synthetic river valleys would open up a wealth of knowledge as to why some 3D attributes of river channels are more prevalent than others as well as bridging the gap between the 2D descriptions that have dominated fluvial geomorphology the past century and modern, more complete, 3D treatments.
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Rehabilitation of salmonid spawning habitat in regulated rivers through spawning bed enhancement is commonly used to mitigate altered sediment and flow regimes and associated declines in salmonid communities. Partial design-phase... more
Rehabilitation of salmonid spawning habitat in regulated rivers through spawning bed enhancement is commonly used to mitigate altered sediment and flow regimes and associated declines in salmonid communities. Partial design-phase predictive results are reported from the application of SHIRA (Spawning Habitat Integrated Rehabilitation Approach) on the lower Mokelumne River, California. The primary management goal of the project was to improve habitat for spawning and incubation life stages of fall-run chinook salmon (Oncorhynchus tshawytscha). In the summer of 2001, we conducted a pre-project appraisal followed by development and testing of 12 design scenarios. A subsample of eight design hypotheses, used in three of the design scenarios, is presented. Hydrodynamic, habitat suitability and sediment entrainment model results were used to test five of the eight design hypotheses. Two of the three hypotheses not tested were due to inadequate data on flow boundary conditions at high disc...
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Morphological control of river hydraulics, or 'topographic steering', influences the spatial patterning and persistence of aquatic habitats and channel-change processes. While imperative to addressing questions or problems in... more
Morphological control of river hydraulics, or 'topographic steering', influences the spatial patterning and persistence of aquatic habitats and channel-change processes. While imperative to addressing questions or problems in river engineering, fluvial geomorphology, and aquatic ecology the study of topographic steering in natural rivers is still limited, particularly amidst the landform complexity of mountain rivers. This study presents new theory, methods, and findings for investigating landform structure, hydraulics, and mechanisms by which topographic steering asserts control in mountain rivers. Using a novel combination of point-cloud processing and topographic differencing 52,926 individual boulders and bedrock outcrops were mapped within a 13.2-km segment of the mountainous Yuba River (Northern California). Employing a 15% cover threshold these large bed elements (LBEs) were identified as an important source of landform non-uniformity. Coupled with outputs from two-di...
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ABSTRACT Channel conditions below dams are degraded by bed armoring, channel narrowing, and channel incision. The last process yields a long-term decrease in slope, as a river's base level is fixed at sea level. Thus, hydrodynamic... more
ABSTRACT Channel conditions below dams are degraded by bed armoring, channel narrowing, and channel incision. The last process yields a long-term decrease in slope, as a river's base level is fixed at sea level. Thus, hydrodynamic habitat conditions controlled by slope degrade over time, impacting populations naturally selected for pre-dam dynamics. In this experimental river rehabilitation, it was hypothesized that channel slope below the dam could be increased incrementally, and this increase could then be spread downstream in subsequent years, eventually yielding a reconstruction of the pre-dam longitudinal profile and increasing overall habitat quality. To test the hypothesis, competing experimental designs for the first stage of this plan were created and evaluated for the gravel-bed Mokelumne River in central CA below Camanche Dam using the Spawning Habitat Integrated Rehabilitation Approach. Gravel fill depth was constrained by the monitored 3 ft of incision over 40 years. Alternative designs aimed to maximize bed elevation gain, spawning habitat quality, and habitat heterogeneity, while avoiding bed scour at the test flow of 500 cfs. Using a 2D hydrodynamic model designs with a 3 ft fill were predicted to cause excessive scour regardless of design elements. Iteration yielded the key result that a maximum fill of 1.5 ft could be sustained by notching the upstream riffle to enable excess flow to bypass the spawning area thereby protecting it from scour and providing desirable habitat heterogeneity. Upon placing 2000 cu yds of gravel, riffle-to-riffle slope was raised from 0.001 to 0.0025. Due to project phasing the created slope yielded scour at the end of the site where the bed elevation dropped back to the original level, as predicted. Lower flows than originally expected resulted in gravel exposure. The second phase added another 2000 cu yds of gravel effectively spreading the slope downstream and backing water up to the first site to increase depth and decrease velocity to the desired levels. On-going post project monitoring and analysis is being used to assess slope creation as a spawning habitat rehabilitation tool.
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Keli Mutu is a stratovolcano that has three crater lakes containing exotic fluids. This study presents the analytical results describing the chemistry of each lake, interprets the chemistries in terms of water-rock interactions and... more
Keli Mutu is a stratovolcano that has three crater lakes containing exotic fluids. This study presents the analytical results describing the chemistry of each lake, interprets the chemistries in terms of water-rock interactions and volcanic fluxes, and derives a physical lake model that delineates the parameter-window for volcanic crater lake existence. Geochemical investigation of the vertical and lateral compositions of the lakes on Keli Mutu required the use of a remote sampling system. Lake temperature, pH, and dissolved oxygen content were determined in the field, while the analytical chemistries of lake fluids and sediments were determined in the months after the expedition to Keli Mutu. To reconstruct the in situ chemistries of the lakes' aqueous systems, a solution equilibrium modeling program (SOLVEQ) was applied. The energy flux model that was developed assumes thermal steady state conditions to gain insight into the physical dynamics of volcanic crater lakes. This model leads to graphs of lake temperature versus volcanic gas input for lakes of different radii. Assessment of the growth and shrinking of lake volume as a function of the relative influences of endogene versus exogene forces was provided by using the additional requirement of hydrological steady state. In general, for a crater of a given radius, the temperature of the lake that exists at thermal steady state within it is a function of sulfur dioxide influx and evaporative cooling. The primary conclusion of this thesis is that the three Keli Mutu lakes are all fed by a similar volcanic gas source, but as a result of the mediated transport of that gas it yields different chemical "expressions" in each crater lake. Comparison of the individual lakes with their respective historic chemistries demonstrates that they are all approaching chemical steady state. Future studies of Keli Mutu should include a thorough investigation of volcano flank seepage outlets, as at least one such spring-fed river bears a crater lake signature and could be used to calculate element fluxes through the volcanic edifice.