Theses and Dissertations

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Open Access
Numerical modeling investigation of long-term hydrologic change due to surface water and groundwater withdrawals from a high Andean headwater basin, southern Peru
(Colorado State University. Libraries, 2024) Stansfield, William J., author; Ronayne, Michael J., advisor; Cooper, David, committee member; Sanford, William, committee member
Reliable surface water and groundwater resources are of critical importance in the arid central Andes of Southern Peru. Low elevation cities and towns in coastal regions are dependent on water derived from relatively humid mountains and high elevation basins on the Andean Altiplano. The Huaytire Basin, located on the Altiplano at approximately 4,450 meters above mean sea level, is a headwater basin that has experienced hydrologic change in recent years. Surface water diversions from the perennial Lake Suches began in the 1960s, followed by groundwater pumping starting in the 1980s. These water development activities have been accompanied by observations of declining surface water quantity in the downgradient Rio Callazas and deteriorating phreatophytic vegetation within the basin itself. A review of precipitation and pan evaporation data from weather stations in the region did not reveal any clear climate-related trends that would impact water resource availability. A numerical groundwater flow model was constructed using MODFLOW to estimate the impact of long-term pumping on local hydrology and to investigate the sustainability of the Huaytire Basin pumping regime. The model accounted for groundwater-surface water interaction, including lake-aquifer exchange and stream-aquifer exchange along three major streams that originate within the basin. Surface water levels and flow rates were computed as part of the numerical solution, dependent on the simulated hydraulic head in the aquifer, which controls the amount of groundwater-surface water exchange. Three different recharge scenarios were considered to acknowledge uncertainty associated with groundwater recharge rates on the Altiplano. All three scenarios resulted in the study area converting from an open basin with surface water outflow to a closed basin within 50 years of the start of development. Other simulated impacts of pumping include a reduction in the stage and areal extent of Lake Suches and significant reductions in head-dependent outflows for the aquifer system. Relative to predevelopment conditions, groundwater discharge to Lake Suches, groundwater discharge to gaining stream reaches, phreatophytic evapotranspiration, and underflow out of the basin were all lower at the end of the 63-year transient simulation (by ~ 9.5, 50, 18, and 51%, respectively, using base-case recharge rates). It was concluded that groundwater development in the Huaytire Basin is a key factor that explains the observed hydrologic changes and that current pumping rates may be unsustainable.
Embargo
Understanding the role of topography and air-mass mixing across the Dinaric Alps using stable isotope measurements
(Colorado State University. Libraries, 2024) Sanchez Ortiz, Gabriela, author; Rugenstein, Jeremy Caves, advisor; Gallen, Sean, committee member; Keys, Patrick, committee member
The collision of Eurasia with the Adria microplate within the Alpine-Himalayan orogenic belt resulted in the formation of the Dinaric Alps and the creation of basins that later evolved into the Dinaride Lake System (DLS). The topography of the Dinaric Alps during this period of formation remains poorly understood, contributing uncertainties about the geodynamic processes that shaped the range and the climatic conditions that supported the highly diverse DLS. The oxygen isotope composition (δ18O) of authigenic carbonates can be used as a paleo-altimeter to reconstruct past elevations of mountain ranges. However, changes in factors such as temperature and moisture sources can affect the composition of the waters that form these authigenic minerals. In an effort to constrain the Miocene δ18O pattern across the Dinaric Alps, we collected new stream and carbonate samples from seven basins ranging from the coast of Croatia to high-elevation basins in Bosnia and Herzegovina. In addition, we compiled published water samples to better constrain the modern δ18O pattern of the Dinaric Alps. Today, we find higher δ18O at the coast and lower δ18O near the crest of the modern range. We observe a different trend in the lacustrine carbonate δ18O; the highest Miocene δ18O values are near the crest of the range, with lower δ18O values at the coast. We attribute the modern δ18O pattern to the orographic uplift of air parcels containing moisture from the Mediterranean Sea. The Miocene-age δ18O pattern obtained from the lacustrine carbonates is likely a result of the evaporation of the lake waters that formed the carbonates at the crest of the range. Using these high δ18O values can lead to the underestimation of the Miocene topography of the Dinaric Alps, thus there is a need for a novel method to eliminate the effect of evaporation on lacustrine carbonates.
Open Access
Machine learning prediction of deepwater slope-channel facies using core-analogous outcrop observations
(Colorado State University. Libraries, 2024) Ronnau, Patrick, author; Stright, Lisa, advisor; Ronayne, Michael, committee member; Gallen, Sean, committee member; Krishnaswamy, Nikhil, committee member
Sedimentological (SED) data is often qualitative, making combining it with Machine Learning (ML) workflows challenging. SED data in subsurface exploration incorporates qualitative interpretations that remain valuable to subsequent exploration efforts. These exploration projects often have access to geologic core data that is limited spatially, making subsurface interpretation difficult and highly uncertain. Incorporating core-like data into ML workflows provides a framework to generate consistent interpretation over large datasets. ML, a technique already employed in well-log interpretation, represents an advantage over manual interpretation methods which are time intensive and introduce errors and bias. This research investigates methods to automate geologic interpretation (specifically of sedimentary facies) through ML techniques. Sedimentological observations (grain size, bed thickness) from outcrop measured sections in the deepwater slope strata of the Magallanes Basin provide training and testing features to make ML predictions (classifications) of human-interpreted geologic facies. The study employs seven ML techniques (K-Means, Least Squares Regression, Logistic Regression, Linear Discriminant Analysis, Quadratic Discriminant Analysis, Random Forest, and Neural Networks) to investigate the problem of facies prediction from multiple methodological angles. The results show that some ML methods are not suitable for this classification problem due to their architecture or the qualitative aspects of manually collected SED data. Supervised methods generally provide better results than unsupervised methods (PCA and K-Means). Supervised ML both produces better raw performance metrics (Accuracy, BedThickness Normalized, Accuracy, Recall) than K-Means, and generates qualitatively better predictions of measured sections (Fig. 48; Fig. 49). Among methods that are suitable, a random forest model generates the best facies prediction performance.
Open Access
Environmental effects of the 1978 Sunnyside Mine flood
(Colorado State University. Libraries, 2024) Arnold, Victoria S., author; Ridley, John, advisor; Wohl, Ellen, committee member; Bareither, Chris, committee member
In 1978, the pillar of rock and sediment between Lake Emma and the Sunnyside Mine collapsed, draining 5-25 M gallons (19-95 ML) of water and sediment through the mine and the American Tunnel within a few hours (Thompson, 2018). This caused a major flood in Cement Creek, a tributary of the Animas River north of Silverton, Colorado. Although work has been done on the geochemistry of mine outwash in the same drainage from the 2015 Gold King Mine spill, the material from the Sunnyside Mine flood has not been extensively studied previously. This study aims to determine whether the 1978 Sunnyside Mine flood had significant geochemical and geomorphic effects and continues to affect the environment today. Likely flood deposits were identified approximately fifteen centimeters above the typical spring flood level based on sediment characteristics, interviews with witnesses to the flood and community stakeholders, as well as newspaper articles and photographs from shortly after the flood. Cement Creek sediment samples from flood and non-flood deposits were analyzed with VNIR spectroscopy for mineralogy. Sediment samples from the Sunnyside flood contained vermiculite, iron smectite, zeolites, gypsum, and secondary copper minerals, while most stream sediment included ferrihydrite, K-illite, and vermiculite. Sediment samples were also analyzed for their bulk elemental geochemistry, which revealed that the Sunnyside flood sediments had lower concentrations of heavy metals than the other sediments in Cement Creek, but had 59% more iron and 518% more sulfur. It is not clear whether the increased iron and sulfur exist as unweathered sulfides or as sulfates, but if there are sulfides or secondary sulfate minerals present in the flood sediment, then the flood sediment has significantly more acid generation potential than the other sediment in Cement Creek. Additionally, the average Fe/Cu ratios of the flood sediment is higher than the non-flood sediment, which indicates that the material is either from a different source, or that the flood water had lower pH than the water in Cement Creek when the other sediments were deposited. The significant difference in the minerals present and the elemental geochemistry, as well the continued preservation of flood horizon sediments, indicate that the Sunnyside Mine flood impacted the Cement Creek watershed. Understanding the impact that a major disaster like the Sunnyside Mine flood had on the area is important to have a better picture of a region that continues to face environmental impacts from mining activities.
Embargo
Identifying seepage pathways through an embankment dam using electrical and electromagnetic geophysical methods
(Colorado State University. Libraries, 2024) Warden, Camilla, author; Sanford, William E., advisor; McGrath, Daniel, committee member; Bailey, Ryan T., committee member
In the 1950's, increased water supply demands resulted in a construction project at the earth and rockfill embankment Little Wood River Dam to increase the reservoir water capacity. After the enlargement of the structure from 1958 to 1960, seepage was observed in the auxiliary spillway channel, vicinity of the downstream toe, and downstream on river left. In earth and rockfill embankment dams, seepage can manifest as internal erosion, or "piping", which may compromise the structural integrity of the embankment over time. Though no symptoms of internal erosion were observed, seepage monitoring weirs reported a significant increase in seepage flow rate when the reservoir surpasses a particular "critical" elevation or was at high pool conditions. As a result, the United States Bureau of Reclamation, the operator of the dam, opted to do a comprehensive site review to identify potential seepage pathways and determine if remediation were necessary. This geophysical study was designed to compare survey results to see if there was a change in subsurface saturation from low to high pool, that may indicate the presence of a seepage pathway originating at the reservoir. Additionally, this investigation also explored the groundwater conditions at the study area to determine if regional groundwater flow was contributing to observed seepage. Electrical and electromagnetic near-surface geophysical surveys were conducted in September 2021 (low pool) and June 2023 (high pool) and compared as timelapse to show any changes in subsurface bulk electrical resistivity distribution that could be attributed to change in moisture content or a seepage pathway that becomes active due to the increased hydraulic gradient from high pool reservoir conditions. Repeated Electrical Resistivity Tomography and Frequency Domain Electromagnetic surveys were conducted during low and high pool, and a Streaming Potential survey and Saltwater Injection Tracer Test were conducted during high pool only. Findings revealed that seepage originating at the reservoir travels through the left abutment and main embankment through a discontinuity between the dam enlargement material and underlying unit. Seepage from the reservoir contributes to the seepage seen in the auxiliary spillway channel and in the vicinity of the downstream toe. Regional groundwater flow from outside the reservoir footprint also contributes to observed seepage in the auxiliary spillway channel, vicinity of the downstream toe, and downstream on river left. Results of this geophysical study allowed for the delineation of seepage pathways through the left abutment and main embankment, providing a valuable contribution to the larger comprehensive review that will determine if future work to the structure is necessary. Regional groundwater was found to be a contributor to all observed seepage which may result in the extension or installation of concrete cutoff walls designed to prevent flow. Locations of observed seepage pathways can be individually targeted for remediation such as trenching and backfilling with impervious materials, and other observed seepage zones can be strategically monitored and maintained. Increasing the timelapse survey coverage to include average water level conditions could further improve the results and delineate if seepage observed below the critical elevation were being contributed to solely by groundwater flow. This timelapse technique paired with multiple electrical and electromagnetic geophysical methods provided extensive data coverage and excellent data quality that could be utilized for similar seepage studies.
Open Access
Evaluating L-band radar for the future of snow remote sensing
(Colorado State University. Libraries, 2024) Bonnell, Randall, author; McGrath, Daniel, advisor; Fassnacht, Steven, committee member; Kampf, Stephanie, committee member; Marshall, Hans-Peter, committee member; Ronayne, Michael, committee member
Snowpack monitoring is essential because seasonal snowpacks provide water for billions of people, support streamflow and ecosystems, and are a fundamental component of the Earth's energy system. However, no current snowpack monitoring system is capable of measuring snow water equivalent (SWE), the most important snowpack hydrologic variable, accurately and at high spatiotemporal (<500 m, 20 km of nearly continuous relative permittivity estimates, and thereby bulk density, from combined near-coincident measurements of GPR two-way travel times and lidar snow depths at three different field sites and in both dry and wet snow conditions. Variogram analyses were conducted and revealed a 19 m median correlation length for relative permittivity and density in dry snow. For wet snow, the correlation length increased to >30 m. I then leveraged the derived densities to evaluate six snow density models to better understand the limitations of these models within lidar and radar remote sensing methods. Two models yielded densities that estimated SWE within ±10% when SWE exceeded 400 mm, but model uncertainty increased to >20% when SWE was less than 300 mm. Thus, the refinement of these density models and the development of future density models is a high priority to fully realize the potential of SWE remote sensing methods. The L-band (1–2 GHz) InSAR technique for measuring changes in SWE (ΔSWE) is a promising method for SWE retrievals because the longer wavelength (~0.25 m) has minimal interaction with the snowpack microstructure and has increased canopy penetrative capabilities. In Chapter 3, I evaluated 10 L-band InSAR pairs collected by NASA UAVSAR near Cameron Pass, Colorado with GPR and terrestrial lidar measurements of ΔSWE in open meadows and burned forests. For single InSAR pairs, UAVSAR ΔSWE retrievals yielded an overall Pearson's correlation coefficient of 0.72–0.79, with a RMSE of 19–22 mm. I expanded the analysis beyond the locations of GPR and lidar surveys to evaluate the time series of UAVSAR SWE retrievals by including measurements of SWE from seven automated stations and found a RMSE of 42 mm. These findings support the use of this technique in unforested areas with dry snow conditions for the upcoming L-band NISAR satellite mission Given the findings of Chapter 3 and the canopy penetration capabilities of L-band radar, I designed Chapter 4 to evaluate the influence of forest cover on the UAVSAR signal. In Chapter 4, I evaluated eight L-band InSAR pairs collected by UAVSAR over the montane forests of Fraser Experimental Forest, Colorado with manually surveyed snow depths and snow pits and a pair of airborne lidar surveys. Compared with in situ measurements, I found that forest cover fractions <40% yielded RMSEs of ~15 mm, whereas RMSE more than doubled for forest cover fractions >50%. Further, normalized cumulative UAVSAR SWE and normalized lidar snow depths yielded identical statistical distributions for forest cover fractions <50% across the full study area, but these distributions diverged as forest cover fraction increased. Thus, forest cover fraction is a significant source of uncertainty for L-band InSAR retrievals of SWE, but this technique may be the first space-borne technique capable of retrieving SWE below non-dense forest canopy without any a priori information.
Open Access
Understanding the daily to decadal evolution of mountain glaciers in Alaska and high mountain Asia from satellite remote sensing
(Colorado State University. Libraries, 2024) Zeller, Lucas R., author; McGrath, Daniel, advisor; Gallen, Sean, committee member; Ross, Matthew, committee member; Florentine, Caitlyn, committee member
Glaciers are important components of mountain ecosystems, mountain hydrological systems, and the global water cycle. Improving our scientific understanding of the spatial and temporal variability in glacier changes and the physical processes that drive those changes will allow better prediction of future glacier evolution. In this dissertation, I explore ways in which satellite-based remote sensing products can be used to study mountain glaciers across a wide range of spatial and temporal scales, with a specific focus on Alaska and High Mountain Asia. The accumulation area ratio (AAR) of a glacier reflects its current state of equilibrium, or disequilibrium, with climate and its vulnerability to future climate change. In Chapter 1, I present an inventory of glacier-specific annual accumulation areas and equilibrium line altitudes (ELAs) for over 3,000 glaciers in Alaska and northwest Canada (88% of the regional glacier area) over the 2018–2022 period derived from Sentinel-2 satellite imagery. I find that the five-year average AAR of the entire study area is 0.41, with an inter-annual range of 0.25–0.49. More than 1,000 glaciers, representing 8% of the investigated glacier area, were found to have effectively no accumulation area. Summer temperature and winter precipitation from ERA5-Land were found to be effective predictors of inter-annual ELA variability across the entire study area (R2=0.47). An analysis of future climate projections (SSP2-4.5) shows that ELAs will rise by 170 m on average by the end of the 21st century. Such changes would result in a loss of 25% of the modern accumulation area, leaving more than 1,900 glaciers (22% of the investigated area) with no accumulation area. These results highlight the current state of Alaska glacier disequilibrium with modern climate, as well as their vulnerability to projected future warming. In High Mountain Asia, many glaciers have thick debris cover over the majority of their ablation zones, earning them the name 'debris-covered glaciers'. Supraglacial lakes (SGLs) play an important role in debris-covered glacier (DCG) systems by enabling efficient interactions between the supraglacial, englacial, and subglacial environments. Developing a better understanding of the short-term and long-term development of these features is needed to constrain DCG evolution and the hazards posed to downstream communities, ecosystems, and infrastructure from rapid drainage. In Chapter 2, I present an analysis of supraglacial lakes on eight DCGs in the Khumbu region of Nepal by automating SGL identification in PlanetScope, Sentinel-2, and Landsat 5–9 satellite images. I identify a regular annual cycle in SGL area, with lakes covering approximately twice as much area during their maximum annual extent (in the pre-monsoon season) than their minimum annual extent (in the post-monsoon season). The high spatiotemporal resolution of PlanetScope imagery (∼ daily, 3 m) shows that this cycle is driven by the appearance and expansion of small lakes in the upper debris-covered regions of these glaciers throughout the winter. Decadal-scale expansion of large, near-terminus lakes was identified on four of the glaciers (Khumbu, Lhotse, Nuptse, and Ambulapcha), while the remaining four showed no significant increases over the study period. The seasonal variation in SGL area is of comparable or greater magnitude as decadal-scale changes, highlighting the importance of accounting for this seasonality when interpreting long-term records of SGL changes from sparse observations. The complex spatiotemporal patterns revealed in this analysis are not captured in existing regional-scale glacial lake databases, suggesting that more targeted efforts are needed to capture the true variability of SGLs on large scales. In Chapter 3, I expand these methods across a wider spatial extent by using the Landsat 5, 7, 8, and 9 archive to delineate SGLs on debris-covered glaciers across all of High Mountain Asia at near-annual cadence from 1988–2023. I find that SGL area has increased throughout the study period, rising to 17.2 km2 (0.7% of the investigated debris-covered area) in 2023, compared to ~8 km2 (0.3% of debris-covered area) in 1988. SGL growth is most concentrated in the Himalaya and Nyainqêntanglha regions, which have also experienced the greatest rates of 20th and 21st century mass loss. The 21st century SGL growth is concentrated almost entirely near the termini of these glaciers, indicating the possibility of continued growth and coalescence into large proglacial lakes. Areas of high SGL concentration are predominantly found in areas with lower surface gradients, low velocity, and thicker debris cover. Glaciers with high SGL concentrations are found to have steeper longitudinal gradients of thinning, with greater thinning rates further from the terminus resulting in lower surface slopes and more concave geometries throughout their entire debris-covered extents. However, the representative longitudinal thinning pattern of glaciers without substantial SGL formation have become more similar to this pattern in recent years, suggesting that more of these glaciers may be primed for SGL formation in the future.
Open Access
Vegetation and lithologic influences on channel morphology in the southwestern U.S.
(Colorado State University. Libraries, 2024) Wieting, Celeste, author; Rathburn, Sara, advisor; Wohl, Ellen, committee member; McGrath, Dan, committee member; Morrison, Ryan, committee member; Friedman, Jonathan, committee member
Vegetation and lithology play critical roles in shaping landscapes, creating diverse river and gully morphologies. Vegetation stabilizes banks and alters flow dynamics. In the Southwestern United States, non-native, invasive plant species contributed to regional trends of river channel narrowing and simplification and degraded diverse riparian habitats throughout the 20th century. More recently, efforts to remove invasive riparian vegetation (IRV) have been widespread, especially since 1990. Restoration practitioners who perform IRV treatments often focus on wildlife or vegetation response; however, geomorphic processes should be considered in restoration planning because they drive flow, sediment transport, and aquatic habitat and vegetation dynamics, and because of the potential for damage to downstream people and infrastructure. Depending on the restoration goal, management practices can be used to enhance or minimize the increase in channel dynamism caused by IRV removal. At the river reach scale, I investigated biogeomorphic feedbacks at one of the 15 previously analyzed study sites, the Rio Grande in Texas. Along the Rio Grande in Big Bend National Park (BIBE), restoration goals to remove invasive giant cane (Arundo donax) include decreasing channel narrowing and increasing water and sediment conveyance. Recent work has indicated that removal of giant cane has successfully reduced its extent, but the geomorphic effects of giant cane treatment and subsequent revegetation are still not well understood. A general lack of reach-scale studies of riparian plant pronation during flow inundation and the biogeomorphic feedbacks between plants, flow, and sediment transport contribute to this knowledge gap. I quantified morphological-effect plant traits for three common riparian plant species: invasive giant cane, native baccharis (Baccharis salicifolia), and native phragmites (Phragmites australis). I collected data at the plant, plot, and reach scales and created upright and flexible frontal area and vegetation roughness curves using photographs of plants and stem counts of plots. Then, I used these data in a reach-scale 2D hydraulic model to simulate species-specific effects and the effects of giant cane removal on channel hydraulics. Results indicate that the mean vegetation roughness is similar for all three species at the plant scale, but at the plot scale, vegetation roughness is higher for giant cane and phragmites due to higher stem densities. Hydraulic modeling results suggest that vegetation increased velocities in the center of the channel and decreased velocities on the channel margins. When all the vegetation was represented as giant cane, reach-scale water surface elevations were the highest and reach-scale velocities the lowest. Removing giant cane decreased water surface elevations, indicating increased conveyance. To determine the effects of IRV removal on a regional scale across the Southwest U.S., treated and untreated reaches at 15 sites along 13 rivers were compared before and after IRV treatment using repeat aerial imagery to assess long-term (~10 year) channel change. Resolving observations of channel change into separate measures of floodplain destruction and formation provided more information on underlying processes than simple measurements of channel width and centerline migration rate. IRV treatment significantly increased channel width and floodplain destruction. Treated reaches had higher floodplain destruction than untreated reaches at 14 of 15 sites, and IRV treatment increased floodplain destruction by a median factor of 1.9. The effect of treatment increased with the stream power of the largest flow over the study period. From the results, I suggest that restoration managers consider the system's susceptibility to change, downstream threats, and desired process changes when defining their geomorphic restoration goal because treatment of a dominant species over a large area can be expected to have major fluvial geomorphic consequences. In addition to vegetation, the lithology and surficial sediment properties influence hydrological processes, sediment transport, and gully and channel morphology. In semi-arid environments where vegetation is lacking, and precipitation is sufficient to drive erosion, sediment yields tend to be greatest. Increased landscape erosion is predicted as more extreme weather causes frequent or intense rainfall, and flooding. In Wupatki National Monument (WUPA), heavy rainstorms over the past decade, lack of vegetation, and presence of unconsolidated volcanic-derived cinders expose archaeological sites to erosion, a concern to cultural resource managers. To identify archaeological sites of highest vulnerability to erosion, I analyzed gully morphologic change over a 5-year period. I found that 35 measured gullies are actively eroding, with statistically significant changes in gully depth from 2016 to 2021. Up to 0.5 m of incision was documented over a five-year period. A structure-from-motion analysis at the hillslope scale confirmed gully morphological changes and supports the applicability of conducting similar analyses on a larger scale. More erosion occurred in gullies with catchments predominantly covered with cinders because of cinder mobility. A weak relationship was noted between gully catchment area and gully head slope, likely related to runoff processes from outcrops of resistant sedimentary rocks forming cliffs and characteristics of cinders that maximize infiltration and transport. Based on assessment of gully morphologic change and substrate characteristics, 22 archaeological sites along Wupatki Wash were identified as having a high vulnerability to erosion.
Open Access
Islands in the stream: spatial and temporal patterns of logjam-induced river corridor dynamics
(Colorado State University. Libraries, 2024) Marshall, Anna E., author; Wohl, Ellen, advisor; McGrath, Dan, committee member; Morrison, Ryan, committee member; Rathburn, Sara, committee member
Spatial and temporal variations in water and sediment fluxes moving within the river corridor drive changes in the three-dimensional geometry of channels and floodplains. In forested river corridors, pieces of large wood (> 10 cm diameter and 1 m length) and logjams (≥ 3 pieces of large wood) become an integral part of the interactions among water, sediment, and the resulting river corridor form and function. The net effect of logjams stored at least temporarily in the river corridor is to increase spatial heterogeneity, or patchiness, via processes such as channel avulsion and formation/abandonment of secondary channels, increased channel-floodplain connectivity, and greater instream aggradation. The importance of spatial heterogeneity, logjams, and secondary channels/islands to river corridor function has been well documented, but a lack of existing quantitative underpinning creates knowledge gaps in the processes driving island formation and persistence, the role of wood in facilitating these processes, and the complex interactions between flow, sediment, and wood in dynamic river corridors. This dissertation addresses some of the existing knowledge gaps around how logjams interact in a river corridor to create heterogeneity at different spatial and temporal scales by characterizing the patterns, processes, and interactions occurring in a naturally dynamic system. The topics explored here focus on research primarily conducted along the Swan River in the Northern Rocky Mountains of Montana with mention of sites in the Southern Rocky Mountains of Colorado. These locations represent some of the few remaining river corridors in the contiguous U.S. with natural flow, sediment, and wood regimes, but represent former widespread conditions. In the work that follows, Chapter 2 explores the processes driving spatial patterns in bifurcations induced by logjams. I find that logjam-induced bifurcations exist as a continuum of different patterns and the position of a river segment along this continuum correlates with the ratio of erosive force to erosional resistance. Chapter 3 builds on this by investigating how accretionary and avulsive processes shape bifurcations over time, emphasizing a temporal progression of logjam-induced features using 14C and tree ring data. I find that islands tend to grow through upstream migration – the presence of buried logs with contemporary trees growing on them indicates this process – and lateral accretion. Chapter 4 dives deeper into the interactions between process and form, demonstrating the relationship between channel dynamism, logjam presence, and spatial heterogeneity at larger temporal and spatial scales. I find that logjams and channel movement through time interact in a cascade of processes and feedbacks that foster increased spatial heterogeneity. Wood preferentially accumulates in more geomorphically heterogeneous portions of the river corridor that provide sites capable of trapping and retaining wood. Logjams can then drive greater total sinuosity and the formation of secondary channels that result in further wood trapping, greater heterogeneity of floodplain vegetation, and ideal habitat for beaver that further modify river corridor heterogeneity. I also find that bifurcations and spatial heterogeneity persist even after logjam is no longer present. These results have implications for river management. If sections of the river corridor with more logjams and more beaver meadows display higher spatial heterogeneity, creating and protecting wood-rich heterogeneous retention zones within a river corridor is an important component to emphasize for river resilience. If physical effects persist even after a logjam is no longer present, than wood reintroduced to the river corridor as individual pieces or engineered logjams does not have to be anchored in place to facilitate formation of geomorphic heterogeneity within the river corridor. By dissecting the complexities of processes governing naturally dynamic river corridors, this work adds quantitative insight to the diverse functionality of heterogenous river systems in forested or historically forested regions and provides a launching point for future river management aimed at fostering river corridor function and resilience.
Open Access
Geological control on aquifer storage and recovery (ASR) feasibility and efficiency in carbonate aquifers (Edwards aquifer and Floridan aquifer)
(Colorado State University. Libraries, 2024) Simbo, Christophe Wakamya, author; Sutton, Sally, advisor; Sale, Tom, committee member; Ronayne, Michael, committee member; Ridley, John, committee member
Aquifer storage and recovery (ASR) is increasingly being used to enhance freshwater security and sustainability. Though proven technology, ASR implementation and efficiency are mainly controlled by the aquifer system's geological characteristics. Aquifer or reservoir quality, aquifer geochemistry and heterogeneity, and ASR-induced stress exerted on aquifer systems affect the operation of ASR and, hence, ASR recovery feasibility and efficiency. This dissertation evaluates the feasibility of ASR operations in two major carbonate aquifers in the USA: the brackish portion of the Edwards aquifer and the Floridan aquifer. Aquifer matrix petrology and geochemistry, groundwater geochemistry, surface water geochemistry, and time series water chemistry coupled with numerical modeling with PHAST and Geochemists' Workbench (GWB), and analytical modeling were used to understand the aquifers and evaluate ASR optimization strategies. The Edwards Aquifer petrography provides insights into the aquifer texture, fabric, and aquifer/reservoir quality controlled by depositional and post-depositional processes. Though the development of porosity and permeability are likely controlled by the precursor texture of the aquifer matrix, diagenetic processes, mainly dolomitization together with fracturing and dissolution, may be the main agents affecting aquifer quality for ASR operation. Suitable aquifer zones for water storage are characterized by permeability likely controlled by intercrystalline, fracture, and vuggy porosity in dolomitic zones. Bulk aquifer geochemistry documents major and trace elements, with high MgO/CaO revealing extensive dolomitization preferentially located towards the middle of the Person and Kainer Formations, aquifer units within the Edwards aquifer system. The relatively higher content of SiO2, Al2O3, and, to some extent, K2O and TiO2 in confining layers points to a modest increase in clay minerals compared to aquifer sections. Clay minerals, together with compaction features observed in confining layer thin sections, potentially reduce confining layer permeability and porosity. However, high fracture porosity within the Regional Dense Member (RDM) confining layer separating both Edwards aquifer zones offers potential pathways connecting both zones. That these fractures may, in fact, be pathways is supported by changes in groundwater hydrochemistry in the non-targeted aquifer zone (Kainer) during the initial ASR recharge cycle. Based on injectant and groundwater chemistry and time series water chemistry of recovered water samples during the first ASR operation cycle, initial and evolved hydrochemical facies were evaluated in the Edwards aquifer ASR operation (in New Braunfels). Forward GWB water-water and water-rock interaction modeling revealed the mixing of the injectant and the native groundwater to be the main contributing factor in the hydrochemical facies evolution of groundwater during the first ASR recharge cycle. Estimated hydraulic conductivity values using the numerical PHAST model and corroborated by the Hemker analytical model support the combined effect of lateral flow and vertically-induced flow of high total dissolved solids (TDS) groundwater from the Kainer Formation into the Person Formation via the RDM confining layer during ASR recovery. Estimated hydraulic property values (hydraulic conductivity and porosity) of these three aquifer layers aided in predicting the recovery rate to optimize ASR operations. Implementation of two ASR wells, respectively screened in the Person and Kainer Formations, presents a potential long-term ASR optimization strategy at the Edwards aquifer study site. Induced arsenic releases to concentrations higher than their maximum contaminant level (MCL) of 10 μg/L hinder aquifer storage and recovery (ASR) operations worldwide. Statistical data and time series analyses of the recovered water hydrochemical data were used to assess the operational methodology maintaining the buffer zone for arsenic attenuation during ASR operations in the Floridan aquifer. Additionally, based on Injectant and groundwater hydrochemical data with geochemical data of the aquifer matrix , 1D GWB reactive transport model was used to assess the buffer zone operation methodology that holds promise in managing arsenic releases during ASR operations in the Floridan aquifer. Time series data from the Tampa ASR operations show a positive correlation between percent recovery and arsenic concentration in the recovered water, with high recovery percentages inducing mobilization of arsenic up to 38 μg/L, a value roughly four times the arsenic maximum contaminant level of 10 μg/L. Further, the developed 1D forward reactive transport model suggests underlying processes that control arsenic behavior upon injection of oxygenated source water into a reducing carbonate storage zone. Two model scenarios were used in this study. Model scenario 2 developed such that a larger oxygen front expanded up to 565 m away from the ASR well, three times further than in scenario 1, and promoted the production of Fe(III) oxides/oxyhydroxides with abundances up to 18,700 µg/Kg formed at 555 m away from the ASR well. These Fe(III) oxides/oxyhydroxides may provide sorbing sites that attenuate arsenic concentrations in the groundwater.
Open Access
Shifting sands: drivers and mobilization of fine sediment on the Cache la Poudre River following a wildfire
(Colorado State University. Libraries, 2024) Katz, Aaron, author; Wohl, Ellen, advisor; Bestgen, Kevin, committee member; McGrath, Dan, committee member
The Cameron Peak wildfire (840 km2) of 2020 led to widespread but varied detrimental effects throughout the Poudre River watershed (4,895 km2). The Poudre River flows through a high gradient canyon section with a somewhat unimpaired flow regime before it reaches a low gradient transition zone with several human impacts including channel modifications and flow reduction. Burned tributaries contributed elevated levels of fine sediment (< 2 mm) to the mainstem Poudre within the canyon, and in 2021 a large debris flow in Black Hollow Creek, a canyon tributary, delivered substantial amounts of material, including fine sediment, directly into the mainstem Poudre River. This led to a major fish kill and the transportation and deposition of fine sediment for at least 100 km downstream. In the transition zone, extensive fine sediment deposits either partially blocked or filled several channel margin backwaters and side channels, which are important habitats for native fish, and fine sediment filled interstices of coarse substrate grains in the mainstem river, which impacts benthic macroinvertebrate and fish spawning habitat. I quantify the degree of fine sediment retention along 100 km of the Poudre River by measuring reach-averaged fine sediment volumes and embeddedness and use model selection of multiple linear regression models to determine whether distance downstream from the sediment source or reach-scale geometric variables are the primary drivers of fine sediment retention. I also conduct a flushing flows study using 2-dimensional hydraulic modelling to determine the discharge required to mobilize the substrate at four sites along the longitudinal gradient of the study area representing different geomorphic settings and hydrologic regimes. Results from model selection using Akaike's Information Criterion corrected for small sample size (AICc) show that for both metrics of fine sediment retention, reach location (canyon vs. transition zone) is the primary driver of sediment retention, but some reach-scale variables are significant predictors of fine sediment retention. Both fine sediment retention metrics (site-averaged volumes and embeddedness) are greater in the transition zone. At the reach scale, gradient and cross-sectional area are both significant predictors of embeddedness, and models with gradient as a predictor variable have substantial support in explaining site-averaged fine sediment volumes. A mixed model of embeddedness at the transect level with bedform as the fixed effect nested with site as the random effect indicates that fine sediment is preferentially retained in pools and that all backwaters are 100% embedded. Although there are only three sites upstream of Black Hollow, fine sediment retention is either greater or not statistically different than canyon sites downstream of Black Hollow. Hydraulic modelling of the 2-, 5-, and 10-year recurrence interval flows at four sites indicates major differences in the magnitude and frequency of bed substrate mobilization between the canyon and transition zone. At a high gradient canyon site, the 2-year flow mobilizes a substantial portion of the bed, while at transition zone sites, bed mobilization occurs only at the 5- or 10-year flow level. I posit that artificially reduced flows in the transition zone are responsible for the lack of bed mobilization and will lead to longer residence times of fine sediment and prolonged impacts to aquatic ecosystems. This study adds to the literature by investigating post-fire fluvial responses at a greater spatial scale than most previous studies of the matter. By quantifying spatial distribution, physical drivers, and mobilization potential of fine sediment following a large wildfire on a major river, we can better understand how large rivers with varied human impacts respond to major disturbances and make informed management and restoration decisions going forward.
Open Access
A characterization of Colorado Front Range and Denver basin aquifer system water stable isotope signatures
(Colorado State University. Libraries, 2024) Ulate, Isabella, author; Rugenstein, Jeremy K. C., advisor; Ronayne, Michael, committee member; Ross, Matthew, committee member
The Denver Basin Aquifer System (DBAS) is an important groundwater resource for Front Range communities and is currently experiencing increasing demand as populations grow and surface water supplies remain limited. It is necessary to better constrain aquifer recharge mechanisms to enable sustainable use of this resource. In other sedimentary basin aquifer systems, mountain front recharge has been shown to be a significant contributor to local basin groundwater recharge. In the DBAS, inputs from the mountain block are poorly understood, and previous numerical models have treated large segments of the mountain-front boundary as impermeable. However, there exist potential connections between the mountain block and the DBAS, either by direct contact of permeable units, which would facilitate underflow recharge into the basin, or by surface water infiltration to the aquifer units where they outcrop near the mountain front. To observe spatial and temporal relationships between mountain block water and DBAS water, we use water stable isotopes and characterize the δ2H and δ18O of monthly precipitation, seasonal surface waters, and groundwaters in and around the Front Range and Denver Basin. The goal of this study is to determine if differences in the isotopic composition of waters across the Front Range permit the use of δ18O and δ2H as tracers of water flow between Front Range streams and groundwater and the DBAS. We analyzed the unique signature of mountain-block water to compare with DBAS water stable isotope data collected from Castle Rock Water municipal wells. Stable isotope ratios varied spatially and temporally, with the greatest temporal variance observed in precipitation. Streams showed great spatial variance, and less significant seasonal variance between the three seasonal sampling events conducted. Groundwaters showed very little temporal variance but had great spatial variance both between the aquifer units of the DBAS and between different locations within the mountain block crystalline aquifer. The lowest δ2H and δ18O ratios were measured in winter precipitation, winter streams, and groundwater samples collected from the high-elevation Front Range. Samples of DBAS groundwaters with the lowest δ2H and δ18O ratios indicate potential hydrogeologic connection to the mountain block. Interpreted mixing lines on a d-excess versus δ18O plot support the potential DBAS-mountain block connection. The deepest aquifer units of the DBAS (Arapahoe and Laramie-Fox Hills) show the least relationship with meteoric or surface waters on both a δ2H and δ18O plot and the d-excess versus δ18O plot and have higher δ18O values than would be predicted based on their previously measured recharge ages and paleoclimate data from the region. Characterizing the spatial and temporal variations in water stable isotope signatures of the Front Range and DBAS region enhances understanding of the region's hydrology and hydrogeology. Additionally, these results help to better inform models of aquifer recharge and promote sustainable use of the DBAS resource.
Open Access
A catchment is more than the sum of its reaches: post-fire resilience at multiple spatial scales
(Colorado State University. Libraries, 2024) Triantafillou, Shayla P., author; Wohl, Ellen, advisor; Rathburn, Sara, committee member; Morrison, Ryan, committee member
As wildfires are projected to increase in frequency and severity, there is a growing interest in understanding river resilience to the wildfire disturbance cascade. Numerous 3rd-order mountain catchments within the Cache la Poudre (Poudre) River basin in the Colorado Front Range, USA burned severely and extensively during the 2020 Cameron Peak fire. Many of these catchments experienced debris flows and flash floods triggered by convective storms after the fire. The downstream effects of the debris flow sediment varied along a continuum from attenuated and largely contained within the catchment, through contributing to a pre-existing debris fan at the catchment outlet, to releasing substantial volumes of water and sediment to the Poudre River. I conceptualize these catchments as exhibiting decreasing resilience to post-fire disturbance along the continuum described above based on the geomorphic evidence of relative sediment export. The characteristics affecting resilience and magnitude of response to disturbance span multiple spatial scales from the catchment to stream corridor reaches hundreds of meters in length. I conceptualize characteristics on different spatial scales as driving or resisting response to disturbance and therefore impacting the resilience outcome of the catchment. As the magnitude of resisting characteristics increases at the catchment, inter- and intra- reach scales, I hypothesize that a catchment will be more resilient to the wildfire disturbance cascade. At the catchment scale I consider geomorphic, burn, vegetation, and precipitation characteristics. I conducted longitudinally continuous surveys to measure reach-scale characteristics within each study catchment. I focus on the reach-scale geomorphic, vegetation, and burn characteristics, with a particular focus on elements that introduce inter- and intra-reach spatial heterogeneity including channel planform, beaver-modified topography, the distribution of channel and floodplain logjam distribution density, and the floodplain width/channel width ratio for the population of reaches within each catchment. The floods observed at the study catchments illustrate fire lifting the elevation above which rainfall-induced flooding occurs due to the efficient conveyance of water from hillslopes to channels after wildfire. Results suggest that inter- and intra-reach spatial heterogeneity are better descriptors of resilience than catchment-scale characteristics: resilience is associated with greater longitudinal variations in floodplain/channel width and more reaches with wide floodplains, low channel gradients, beaver-modified topography, and multi-stem deciduous vegetation.
Open Access
Rhenium-osmium geochronology and geochemistry of the Upper Jurassic marine black shales, Agardhfjellet Formation, Central Spitsbergen, Svalbard and mercury degradation of Upper Permian shales, East Greenland and mid-Norwegian shelf
(Colorado State University. Libraries, 2024) Park, Junhee, author; Hannah, Judith, advisor; Harry, Dennis, committee member; Borch, Thomas, committee member; Georgiev, Svetoslav, committee member; Hammer, Øyvind, committee member; Olaussen, Snorre, committee member
Every rock has its own story. Rocks are categorized as igneous, metamorphic, and sedimentary types based on their origins and overprinting processes. The human species is confronting the crisis of climate change and some rocks hold a climate story from the past, permitting speculation on the future. On the geological time scale, Earth has experienced both scorching and freezing environments, the latter referred to as Snowball Earth. A critical key to resolving the problems we are facing lies in geology, which deconvolutes environments where specific rocks have formed. This dissertation addresses Boreal sedimentary sections during the Late Jurassic period by conducting three projects; Project I pinpoints depositional ages for black shales from the Agardhfjellet Formation and discusses Os isotopic ratios in the Boreal ocean during the Late Jurassic. Project II evaluates the depositional environments of the Agardhfjellet Formation, which was deposited during a shelf dysoxic-anoxic event. Project III focuses on Hg degradation incurred during incipient weathering and calls attention to interpreting Hg signals of sedimentary rocks, which have been used as an indicator of ancient volcanism. This dissertation provides new radiometric ages and detailed geochemical discussions of the Late Jurassic Agardhfjellet Formation and cautions the use of Hg concentrations when interpreting from outcrop sections. The findings herein significantly enhance our understanding of shelf dysoxic-anoxic events compared with oceanic anoxic events and Hg behavior during the early stage of weathering.
Open Access
Land use influences on adjacent ecological systems: implications for conservation planning
(Colorado State University. Libraries, 2009) Wade, Alisa Ann, author; Laituri, Melinda J., advisor; Theobald, David M., advisor; Hoeting, Jennifer A., advisor
This research investigated the spatial relationships between land uses, primarily urbanization, and adjacent ecological systems. As anthropogenic stressors encroach on protected areas and aquatic systems, the ecological functioning of those systems is reduced, and this has implications for natural resource management and conservation. I conducted three separate studies to address different research questions relating to land use and land cover-ecological system linkages. I assessed the vulnerability of conservation lands throughout the U.S. to adjacent anthropogenic threats and identified protected lands that are likely threatened by human activities as well as unprotected lands that offer opportunities for future conservation action. I also quantified the amount of residential development encroachment surrounding protected lands in the U.S., and I quantified how encroachment has altered the landscape structure around conservation lands nationally from 1970 through 2000, and forecast changes for years 2000 through 2030. Results from these two studies showed that there are a number of protected areas that are vulnerable to neighboring threats and that development has both reduced the buffer surrounding and the connectedness between protected areas. However, results also suggested that there are a number of options for future conservation action, although continued urbanization will limit these options. These studies indicate that conservation planning must consider adjacent land uses. However, the final study presented in this dissertation illustrated that conservation scientists and land managers must recognize the limitations of their approach when modeling the relationships between ecological systems and adjacent land use. I used a conceptual model of how land cover at different upslope scales influences aquatic integrity to show how different modeling approaches can substantially alter resulting inference. Results suggest that a modeling approach that incorporates ecological knowledge may provide more relevant inference for management decisions. A finding applicable to all three studies is that a key conservation strategy will be to work cooperatively with adjacent land owners and mangers to successfully manage both protected areas and aquatic systems.
Open Access
Predicting cumulative watershed effects in small forested watersheds
(Colorado State University. Libraries, 2009) Litschert, Sandra E., author; MacDonald, Lee H., advisor
Cumulative watershed effects (CWEs), such as the hydrologic and sedimentary changes due to management activities, are a critical concern for many land managers. The goal was to develop a suite of GIS-based models for assessing CWEs in forested watersheds. The models need to be easy-to-use, spatially and temporally explicit, and scientifically based. Delta-Q and FOREST (FORest Erosion Simulation Tools) are a series of empirical and conceptual models that calculate the annual changes in discharge (Delta-Q) and annual sediment production, delivery and yield (FOREST) from roads, fires, and forest management. Given the paucity of data on hillslope sediment delivery, a field study also was conducted to assess the connectivity of sediment pathways from timber harvest units. Delta-Q and FOREST were verified using data from the Eldorado National Forest in California. The models were evaluated using measured data from three experimental watersheds. The predicted and measured 50th percentile flows were closer than the 1st and 99th percentiles, as extreme flows are more sensitive to climatic fluctuations. While predicted bedload sediment yields usually fell within the range of measured values, suspended sediment yields were generally overpredicted. FOREST results were most sensitive to changes in mean annual precipitation and GIS data scale. FOREST generates GIS layers to show the hillslopes, roads, and stream reaches with the greatest risk for altering runoff and erosion, and inducing sedimentation. Both models can be used to compare management scenarios within a watershed or among watersheds. By design the models take a middle approach between commonly used, unvalidated empirical models, and complex physically based models that are rarely used by land managers. During the field study in the Sierra Nevada mountains of California, the downslope edges of nearly 200 timber harvest units were traversed. Only 19 rills or sediment plumes were found that originated from harvest units. Five of the six features that extended through the stream-side management zone to a stream channel were generated by runoff from skid trails. The results indicate that harvest units rarely deliver sediment to streams, but post-harvest skid trail treatments may be needed to reduce surface runoff and sediment delivery to streams.
Open Access
Enhanced recovery from ancient carbonate ramps: lessons and analogs from Paleozoic successions and the Persian Gulf
(Colorado State University. Libraries, 2009) Jaffri, Ali R., author; Egenhoff, Sven, advisor
Satellite imagery of the Persian Gulf, fieldwork in Kuwait and Abu Dhabi, and data from published sources are integrated to develop a thorough understanding of large-scale stratal architecture in carbonate ramps. A section of this study deals with the identification of key-surfaces in homogeneous successions. An Ordovician carbonate ramp from Sweden is selected to illustrate the importance of trace fossils in identification of maximum regression surfaces. By comparing Ordovician trace fossils from Sweden with modern crab burrows in Kuwait, a sequence stratigraphic model that shows strata architecture is presented. Oolitic facies in ancient carbonate ramps in the Devonian-Mississippian Bakken Formation that have been previously ignored or considered subtidal sheet-like deposits have been reinterpreted as coastal embayment, eolian dunes on barrier islands, and tidal channel deposits. Geometric analyses of similar environments in the modern Persian Gulf reveal that none of the oolitic facies in the Bakken Formation would be conducive to a sheet-like morphology. This paper highlights the diversity in shapes and dimensions of modern oolitic tidal channels in the Persian Gulf. Tidal channels documented in satellite imagery are oriented parallel, perpendicular or oblique to the shoreline. Planforms are remarkably similar to terrestrial fluvial systems, and transitions between straight, meandering, anastomosing, and braided patterns occur. Wide, straight channels form where bank materials consist of non-cohesive oolitic-skeletal sands, whereas those with prolific cyanobacterial growth along banks are prone to sinuous channels. A section investigates the challenges that oil and gas companies face when attempting to strike a balance between appeasing authorities and exploiting hydrocarbons while maintaining sustainable development. It also recommends policies that include amendments regarding oil fields in Kurdish territory and healthy alternatives to Production Sharing Agreements which ensure the flow of oil from Iraq while maintaining sustainable development. These include exclusion of oil fields in the Kurdish territory, which constitute only 3 percent of Iraq's oil reserves, from article 5a of the Iraqi Oil and Gas Law. This study recommends the use of contracts, such as Technical Service Agreements, that satisfy both the foreign oil companies and the Iraqi populace.
Open Access
The thermophysical and microstructural effects of an artificial ice layer in natural snow under kinetic growth metamorphism
(Colorado State University. Libraries, 2007) Greene, Ethan M., author; Smith, Freeman, advisor; Elder, Kevin, advisor
The macrostructure of a seasonal snow cover evolves with each new weather event. With wind and precipitation, layers of snow coat the old snow surface and the microstructure within these layers develops as a function of the environmental conditions. The thermal, mechanical and optical properties of snow are highly dependent on its microstructure. Many researchers have investigated metamorphism in homogenous snow, but little is known of snow metamorphism at the interface of two layers. In this study I observe the thermal and microstructural evolution of layered and non-layered samples of natural snow in kinetic growth metamorphism. The layered samples contain a 4 mm thick ice layer, which creates a large gradient in thermal conductivity and porosity. I collected samples of natural snow with a density range of 150-290 kg m-3 from the mountains of northern Colorado. In a cold laboratory, I subjected paired, treatment (layered) and control (non-layered), samples to a vertical temperature gradient of 60-110 K m-1 for a period of 5 days. During the experiment I measured the heat flux at the boundaries and the temperature profile within the sample. At the end of each experiment I cast the snow samples and performed serial sectioning and three-dimensional reconstruction of the snow microstructure. I also used the thermophysical data and microstructural data to simulate the evolution of the microstructure and the thermal state at the end of the experiment. The temperature profiles show snow in a steady-state thermal environment. There is no consistent signal from the ice layer in the temperature data. The microstructure within the snow samples undergoes a dramatic change during the experiments. In the control samples vertical chains of faceted and hollow particles develop and are responsible for transporting most of the thermal energy in the sample. Faceted structures grow off the bottom of the ice layer, while the upper surface erodes and becomes smooth and round. The presence of the ice layer affects thermal, mechanical and optical properties of the snow, these effects occur within several particles of the interface and would be difficult to detect with standard field techniques.
Open Access
Substrate controlled interactions between hydraulics, sediment transport, and erosional forms in bedrock rivers
(Colorado State University. Libraries, 2009) Goode, Jaime Ruth, author; Wohl, Ellen, advisor
Bedrock rivers are important components of the landscape that are distinguished from alluvial rivers by high sediment transport capacity relative to supply, and a direct link between the underlying geology and forms and processes. This dissertation examines how independent substrate controls influence the interactions among bedrock channel morphology, hydraulics, sediment transport, and incision processes at inter-reach and intra-reach scales. The majority of this research was conducted on the Ocoee River, Tennessee, which flows through the Blue Ridge province of the southern Appalachians. Substrate differences correlate with variation in reach morphology (i.e., gradient, bedform orientation and amplitude), such that less erodible substrates are associated with steeper reach gradient and with transversely oriented ribs of greater amplitude. Increased hydraulic roughness in reaches having steeper bed slopes, greater rib amplitude, and less erodible substrate, points to the importance of positive and negative feedbacks in these systems: Greater substrate erosional resistance limits profile lowering, which likely creates steeper bed slopes and greater stream power, creating a self-enhancing feedback. This local increase in stream power is balanced by increased roughness resulting from the erosional processes that produce bedrock ribs, which represents a self-regulating feedback. The overall result reflects quantifiable adjustments between substrate resistance and hydraulic driving forces in bedrock channels. Transport distance for coarse sediment is not a significant function of grain size, as has been reported for alluvial channels. Instead, the highly complex bed topography in this system leads to widely varying coarse sediment transport dynamics. Reach-scale differences in channel morphology correlate with transport distance. Local topographic controls exert the strongest influence on coarse sediment transport dynamics. Complex interactions among gradient and bed roughness appear to govern reach-scale differences in the degree of alluvial cover. In reaches with more resistant rock and heterogeneous bed topography, pothole dimensions are larger and follow an aggregated spatial pattern. Intermediate bed elevations show the highest likelihood of pothole formation, suggesting that local hydraulics and tools versus cover relationships govern pothole formation and maintenance. At different spatial scales, substrate characteristics play a key role in controlling the forms and processes of the bedrock channels examined in this study.
Open Access
Trends and processes of land cover change in the western High Plains ecoregion
(Colorado State University. Libraries, 2007) Drummond, Mark A., author; Laituri, Melinda J., advisor
The goal of this study was to better understand the agricultural land use processes and land cover changes affecting the semi-arid Western High Plains ecoregion in the United States Great Plains. Globally, the processes of agricultural expansion and loss have had widespread effects on land cover and ecosystems that are an ongoing concern of land change research. To improve the understanding of regional land change, three main topics were addressed: (1) the contemporary patterns and key processes of agricultural change in the conterminous United States; (2) the rates, causes, and processes of land cover change in the Western High Plains ecoregion between 1973 and 2000; and (3) the primary driving forces of contemporary land cover change in the Western High Plains, including the dynamics of water resource access. Land cover change estimates for the ecoregion were derived using a stratified random sample of 10 x 10 km blocks and remote sensing change detection. Land use was examined using the Census of Agriculture. Results of the study indicate that patterns of land change vary by region and time period depending on socioeconomic driving forces and environmental context. In the Western High Plains ecoregion, net grassland loss occurred from 1973 to 1986 as agricultural land expanded in response to market opportunities. Agricultural expansion affected 1.9% of the ecoregion. Processes of land change became substantially different after 1986. Between 1986 and 1992, grassland expanded and became the dominant land cover, driven in large part by the cropland retirement policies of the Conservation Reserve Program (CRP). Agricultural declines affected 7.3% of the ecoregion, primarily as cropland was converted to grassland cover. Between 1992 and 2000, net grassland expansion was less than 1%, although there was a high rate of gross change in the location of grassland and agriculture that had only a limited effect on net change. The primary driving forces of land cover change were enabled by water resource access, which had a substantial influence on grassland extent and pattern.