Mountain Scholar :: Browsing by Author "Ronayne, Michael, committee member"

Browsing by Author "Ronayne, Michael, committee member"

Now showing 1 - 20 of 46

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
Assessing of performance of stormwater control measures under varying maintenance regimes
(Colorado State University. Libraries, 2020) Joseph George, Alfy, author; Arabi, Mazdak, advisor; Sharvelle, Sybil, committee member; Ronayne, Michael, committee member
Stormwater control measures (SCMs) are being installed worldwide to curb urbanization impacts such as flooding, stream degradation, nutrient pollution, and contaminant loading in receiving water bodies. Regular inspection and maintenance are important to ensure long term effective performance of SCMs over their design life. This study investigates the performance, reliability, and time to failure of permeable pavement, a filtration based SCM, as a function of the design life and different maintenance strategies. The Stormwater Management Model (SWMM) is used to simulate performance of infiltration based SCMs under different climate and operational conditions including different maintenance regimes. A probabilistic approach is developed to characterize the risk, reliability and vulnerability of the system. Performance data including the effects of clogging and maintenance was obtained from comprehensive literature review of numerous international studies on performance of SCMs under different maintenance activities and strategies. The method of Sobol' global sensitivity analysis is used to evaluate the predictive uncertainty in the estimated surface overflow/bypass flow, runoff, and infiltration to characterize uncertainty in the input parameters of SWMM. Risk-based evaluation metrics are defined and characterized to assess the performance and probability of failure of the systems. A hazard function approach is used to characterize the time to failure of the systems under full, partial, and no maintenance regimes. Results indicate that maintenance plays a significant role in the simulated flow budgets and the performance of infiltration based SCMs. The time to failure of the systems is substantially increased by partial maintenance, while full maintenance marginally increases the time to failure compared to the partial maintenance regime. The analysis can be used to develop effective maintenance strategies for SCMs to ensure longevity and reliability of SCMs over their design life.
Open Access
Assessment of the CLASIC urban hydrology model, in the Spring Creek Watershed, northern Colorado
(Colorado State University. Libraries, 2021) Mohammad Zadeh, Mahshid, author; Arabi, Mazdak, advisor; Bhaskar, Aditi, committee member; Ronayne, Michael, committee member
Urban development influences the quantity and quality of water at local to watershed scales. Urban hydrology models are commonly used to plan, design, and implement stormwater infrastructure systems to minimize water quality and flooding consequences of urban development. However, the applicability of existing models at municipal scales is hampered by extensive data and computational requirements. The Community-enabled Life-cycle Analysis of Stormwater Infrastructure Costs (CLASIC) tool is a cloud-computing web application that facilitates the simulation of hydrological and water quality responses at municipal scales. The tool also provides modules to assess the lifecycle costs of green stormwater infrastructure systems. CLASIC is a modified version of the EPA's SWMM model with direct linkages to disperse land use, climate, soils, and other data resources. This study aims to assess the performance validity of the CLASIC tool for the characterization of urban hydrologic processes and responses. Specifically, the objectives of the study are to: i) evaluate the performance of the model compared to the SWMM model and observed stream discharge at various spatial and temporal scales; and ii) identify the most influential model parameters to inform model parameterization. The study is conducted in the Spring Creek catchment within the Cache la Poudre River watershed in Colorado. Streamflow in Spring Creek is influenced by urban activities in the City of Fort Collins. Model evaluation is conducted at hourly, daily, and monthly time steps at two USGS gaging stations along the stream. Comparison of observed and simulated flow duration curves along with several goodness-of-fit measures, including Nash-Sutcliff coefficient of efficiency and percent bias are used to evaluate the model performance. The Sobol' Global Sensitivity Analysis method is used to assess the importance of model parameters for different model responses, including mean and peak stream discharge. The first and total order sensitivity indices are computed to evaluate the effects of parameters individually and in combination. Overall, hydrological budgets are simulated similarly between CLASIC and SWMM. The results indicate the performance validity of CLASIC stream discharge simulations at computational time steps greater than the time of concentration of the catchment. However, SWMM peak discharge simulations at smaller time steps are closer to the observed behavior of the system. Sensitivity analysis results underline the importance of the Horton infiltration parameters and the percent of imperviousness of the catchment.
Open Access
Atoll island freshwater resources: modeling, analysis, and optimization
(Colorado State University. Libraries, 2015) Wallace, Corey David, author; Bailey, Ryan, advisor; Gates, Timothy, committee member; Niemann, Jeffrey, committee member; Ronayne, Michael, committee member
Atolls consist of ring-shaped structures of small islets of varying sizes that encircle a shallow central lagoon. Freshwater supply on atoll islands is very fragile, consisting exclusively of rainwater harvested from rainwater catchment systems and groundwater extracted from the freshwater lens. Optimal water management necessitates accurate estimation of the current and future quantity of available freshwater; of principle concern is the quantity of water to be expected in the coming decades under the influence of changing rainfall patterns. In this thesis, current and future quantities of daily captured rainwater and available groundwater are investigated using a modeling approach, with a daily water balance used for rainwater catchment systems and a numerical groundwater flow model used for the groundwater system. The conjunctive use of rainwater and groundwater in a sustainable framework is also explored. Models are tested against observed data, with sensitivity analysis then performed to investigate the governing system factors on available volume of rainwater and groundwater. Future quantities are estimated for the 2010-2050 time period using climate data obtained from general circulation models contributing to the CMIP5 framework. Rainwater catchment system sensitivity and optimization analyses are carried out for a specific atoll island in Micronesia (Nikahlap, Pakein Atoll, Pohnpei State) to not only isolate parameters influential to system performance but also to identify easily amendable system shortcomings. Results from the simulations show that daily per capita water demand, catchment area, and transmission efficiency govern the volume of stored rainwater. Using simulated future climate data, household-scale design curves are developed to assist island residents in sizing their rainwater catchment systems to satisfy specified rates of reliability. Using the design curves it was determined, for example, that an average household of 4 with a rooftop catchment area of 10 m² will require a storage cistern of approximately 250 L to ensure adequate water supply 90% of the time. The three-dimensional, density-dependent groundwater flow and transport model SEAWAT is used to simulate the dynamics of the freshwater lens within the atoll geologic system. Of the eight Micronesian atoll islands modeled, five are located in eastern Pohnpei State and three are in western Yap State. Using observed values of lens thickness available for four of the islands modeled, the geologic characteristics of the upper Holocene aquifer were calibrated for both leeward and windward islands. The orientation of the islands in relation to the direction of the prevailing winds has a significant influence on the quantity of available freshwater; islands located on the leeward and windward sides of atolls have a hydraulic conductivity of 25 m day⁻¹ and 200 m day⁻¹, respectively. Sensitivity analysis is performed to identify which geologic and climatic variables have the greatest effect on the available volume of extractable groundwater. Results from steady-state simulations show that hydraulic conductivity, the depth to contact between the upper and lower aquifers, and depth of annual recharge govern the volume of the lens. Using future simulated climate data, the size of the freshwater lens is modeled from 2010-2050. Results indicate that, with the exception of islands of extremely narrow width, lens depletion will be infrequent, occurring less than 10% of the time. When the volume of captured rainwater is depleted, extractable groundwater from the freshwater lens remains the only viable source of freshwater. It is during periods of low rainfall that conjunctive use of captured rainwater and groundwater can meet island community water demand. The concurrent use of rainwater catchment and the groundwater models allows for estimation of the total available volume of freshwater on islands of various size and atoll orientation for the 2010-2050 study period. Results indicate that when the supply of captured rainwater has been depleted, there will still be an available volume of extractable fresh groundwater nearly 99% of the time. The general nature of these methods makes them further applicable to regions outside of the FSM, and may provide water resources managers with information to more effectively manage community water supply.
Open Access
Beyond the case study: characterizing natural floodplain heterogeneity in the United States
(Colorado State University. Libraries, 2023) Iskin, Emily Paige, author; Wohl, Ellen, advisor; Morrison, Ryan, committee member; McGrath, Daniel, committee member; Ronayne, Michael, committee member
With human degradation of natural river corridors, the number of natural, functional floodplains is rapidly decreasing due to dams, diversions, artificial levees, draining, development, agriculture, and invasive species. At the same time, small- to large-scale interest in and implementation of river restoration is expanding, with floodplain restoration soon to take a starring role. To properly manage and restore processes to floodplains, we first need a broad understanding of what they look like and why. A key component of natural river-floodplain systems is heterogeneity, defined as the spatial variation of geomorphic and vegetation classes and patches across a floodplain. Heterogeneity of floodplains both reflects and influences the fluvial processes acting on floodplains and can help shape our understanding of the form and function of floodplains. To begin characterizing floodplain spatial heterogeneity, I present in this dissertation: 1) the development of a method to combine field measurements and remote sensing data products to calculate integrative landscape-scale metrics of floodplain spatial heterogeneity, and the demonstration of which metrics from landscape ecology are likely to be useful for identifying qualities of natural floodplains at four case study sites; 2) a sensitivity analysis to determine whether and how the values of the heterogeneity metrics change when spatial and spectral resolution of the input data are increased, and the extraction of underlying data from the classification results to determine whether using higher resolution data allows identification of the resulting unsupervised classes in relation to field and remote data at four case study sites; and 3) quantification of floodplain spatial heterogeneity, evaluation of whether statistically significant patterns are present, and interpretation of the statistical analyses with respect to the influence of channel lateral mobility and valley-floor space available using a complete dataset of 15 sites representing diverse floodplains across the continental United States. I found that "stacking" Sentinel-2A multispectral satellite imagery and digital elevation model topographic data allows for unsupervised classification of floodplains, and that metrics from landscape ecology can differentiate between different floodplain types. I also found via a sensitivity analysis that increasing the spatial resolution of the topographic data to finer than 10 m and including band ratios related to vegetation improves the classification results. Comparison of the field classes with the remote sensing classes allows for general interpretation of the results, but it is the heterogeneity within the broad classes that I expect is most important to these ecosystems. Lastly, through classification of 15 diverse river corridors across the United States, calculation of five heterogeneity metrics, and completion of a comparative analysis, I found that these natural floodplains have moderate aggregation of classes (median aggregation index = 58.8%), high evenness (median Shannon's evenness index = 0.934) and intermixing of classes (median interspersion and juxtaposition index = 74.9%), and a wide range of patch densities (range of patch density = 491–1866 patches/100 ha). I also found that the river corridor characteristics of drainage area, floodplain width ratio (space available), and elevation, precipitation, total sinuosity, large wood volume, planform, and flow regime (channel mobility) emerge as important variables to understanding floodplain heterogeneity.
Open Access
Climate controls on ecosystem-atmosphere carbon exchange and hydrological dynamics in Rocky Mountain fens
(Colorado State University. Libraries, 2015) Millar, David, author; Cooper, David, advisor; Dwire, Kate, committee member; Hubbard, Robert, committee member; Ronayne, Michael, committee member; von Fischer, Joseph, committee member
Groundwater fed peatlands known as fens are among the most important ecosystems in the Rocky Mountains of North America. These wetlands have sequestered atmospheric carbon dioxide for several millennia, provide important habitat for wildlife, and serve as refugia for regionally-rare plant species typically found in boreal regions. Perennially high water tables are critical for ecosystem functioning in fens, and provide conditions that support the development and persistence of organic soils. It is unclear how Rocky Mountain fens will respond to a changing climate, and those found at lower elevations may be particularly susceptible, where changes in hydrological cycles that control water tables are likely to be greatest. Further, it is unclear how regionally variable monsoon rainfall influences water tables and carbon dynamics, late in the growing season. In this dissertation I addressed the following questions: 1) How does ecosystem-atmosphere CO₂ exchange vary with elevation and monsoon influence in Rocky Mountain fens? 2) How do snowmelt dynamics at high and low elevations and varying monsoon influence affect groundwater dynamics in fens of the Rocky Mountains? 3) How will mountain fen hydrological dynamics potentially change under a future climate, and what will be the subsequent impact on ecosystem-atmosphere C exchange? My results show that net ecosystem production was higher for fens located at high elevations compared to those found at lower elevations. This was reflected in the negative correlation of growing season net ecosystem production with air temperature, and positive correlation with water table position, as the high elevation sites had the lowest air temperatures and highest water tables. Study fens in the San Juan Mountains of southwest Colorado received almost twice as much late summer precipitation than those in the Medicine Bow Mountains of Wyoming, causing more frequent water table rises. However, differences in net ecosystem production associated directly with varying monsoon influence were less discernable. Peak snow water equivalent was lower for fens located at low elevations, and the snow-free season occurred approximately one month earlier at these sites compared to high elevation fens. The earlier onset of snow-free conditions led to steady declines in water table position early in the growing season at the low elevation fens, driven primarily by evapotranspiration. Under two future climate modeling scenarios at a low elevation fen, warmer air temperatures increased the proportions of winter precipitation that fell as rain, and peak snow water equivalent was reduced along with the number of days which snowpack persisted. Results from a coupled carbon exchange and hydrological model showed these changes in hydrological processes led to lower water tables that persisted through the growing season, and subsequently impacted ecosystem-atmosphere C exchange. Under the future climate scenarios, the overall global warming potential of gaseous C emissions increased as a result of increased ecosystem respiration, despite decreases in methane emissions. Further, the future climate scenarios suggest that the sustainability of low-elevation fens may be in jeopardy, as losses of C exceed inputs.
Open Access
Comparison of alternative estimators of deep percolation in full and deficit irrigation
(Colorado State University. Libraries, 2015) King, Jonathan, author; Sanford, William E., advisor; Butters, Gregory, committee member; Ronayne, Michael, committee member
Farmers are increasingly selling their water rights to growing municipalities and abandoning their farms (buy and dry). A loss of food production in the midst of a growing population is a recipe for food shortages. There is a need for municipalities to meet their water demand from the water rights held by farmers while farmers continue to produce crops. One solution to prevent a 'buy and dry' scenario is for farmers to lease a portion of their water rights to municipalities and continuing to farm under a deficit irrigation program. For this solution to work Colorado Water Law requires that return flows be maintained for down gradient water users. According to Colorado Water Law, deep percolation is any water in the unsaturated zone below the root zone (Colorado Foundation for Water Education, 2009). Deep percolation is also assumed to result in groundwater recharge. The first objective of this study is to quantify deep percolation. The second objective is to determine an optimal deficit irrigation technique. The third objective is to evaluate the methods used to estimate deep percolation. This study investigated three different cornfields (referred to as Blocks) in 2011 in Greeley, Colorado. Each block practices different flood irrigation techniques for the purpose of finding an optimal deficit irrigation plan. Block 2 practices traditional flood irrigation, Block 1 applies water at the same frequency as in Block 2 but uses half the volume of water, and Block 3 only irrigates twice during the growing season but applies large volumes of water per irrigation. Three methods were used to estimate deep percolation in each block: Lysimeters, Unsaturated Zone Water Balance (UZWB), and Darcy Flux. At the same time as this study, the United States Department of Agriculture - Agricultural Research Service (USDA-ARS) estimated deep percolation using a water balance method. The lysimeter method found an average deep percolation for Block 1 at 58mm, Block 2 at 334 mm, and Block 3 at 238 mm. The UZWB method found an average deep percolation for Block 1 at 291mm, Block 2 at 518 mm, and Block 3 at 516 mm. The Darcy flux method found an average deep percolation for Block 1 at 209 mm, Block 2 at 160 mm, and Block 3 at 1,246 mm. The USDA-ARS found an average deep percolation for Block 1 at 391 mm, Block 2 at 838 mm, and Block 3 at 635 mm. Corn was harvested by the USDA-ARS at the end of the season and yields were estimated. Block 1 produced 149 bushels/acre, Block 2 produced 196 bushels/acre, and Block 3 produced 84 bushels/acre. All methods found the irrigation strategy applied to Block 3, in relation to the other Blocks, resulted in the greatest percentage of deep percolation compared to water applied. The lysimeter method determined that the irrigation plan used in Block 1 was the least efficient in creating deep percolation while the UZWB and Darcy Flux method found that the irrigation applied to Block 2 was the least efficient. Although Block 3 was the most effective in producing deep percolation it produced the least amount of corn. The UZWB method was thought to be the most valuable method in this study. Installation of the neutron probe access tubes caused minimal disturbance to the soils and this method investigated the entire unsaturated zone below the zero flux plane, which accounted for most vertical heterogeneity. The lysimeter method was the most direct method, but installation caused extensive soil disturbances. However, once the soil settled over time the lysimeter method provided consistent and reliable results. In this study the Darcy Flux Method provided the greatest range in results compared to the other methods. The primary concern in using the estimates from this method was the quality of the data collected by the sensors.
Open Access
DC electrical resistivity constraints on hydrostratigraphy in the lower South Platte River alluvial aquifer in northeastern Colorado
(Colorado State University. Libraries, 2013) Lonsert, Reece, author; Harry, Dennis, advisor; Stednick, John, committee member; Ronayne, Michael, committee member
This study uses DC Electrical Resistivity Tomography (ERT) to delineate hydrostratigraphic units within the lower South Platte River alluvial aquifer. The geophysical investigation was conducted at Tamarack Ranch State Wildlife Area in northeastern Colorado, where the South Platte River is artificially recharged via pumping to surface recharge ponds and groundwater flow through the underlying unconfined alluvial aquifer system. Twenty-seven ERT profiles collected within a 4.2 km2 study area on the south bank of the South Platte River define 3 different electrostratigraphic units. The ERT data was correlated with drilling logs and laboratory resistivity measurements to develop a hydrostratigraphic model and confining bedrock surface map. Results indicate 7-25 m thick eolian sand deposits (50-800 ohm-m) serve as infiltration zones and do not readily store groundwater. These eolian deposits form up to 15 m high sand hills in the southern half of the study area, and underlie recharge ponds that are used as water sources for artificial recharge of the river. The underlying alluvium (20-3890 ohm-m) varies from 10-70 m thick and functions as the primary groundwater storage unit. A 10-20 m thick intermittent conductive zone (25-80 ohm-m) occurs within the upper part of the alluvial layer that underlies the sand hills, and is interpreted to be caused by clay deposits that potentially influence initial groundwater flow paths emanating from the recharge ponds. The alluvium is underlain by highly conductive siltstone and claystone bedrock formations (1-60 ohm-m) that confine the aquifer system. The bedrock surface is complexly eroded (1055-1110 m.a.s.l.) and is characterized by prominent large-scale paleo-topographic lows (at typical scales of 700 m wide, 35-40 m deep and 700 m wide, 20-25 m deep) that occur on the northern bank of an incised paleo-channel. These features are interpreted to represent a paleo-topographic surface formed by groundwater outflow in the form of piping and sapping networks. The rugged bedrock topography establishes a previously unrecognized first order control on groundwater flowpaths within the unconfined alluvial aquifer.
Open Access
Diagenesis, composition and porosity of the upper Three Forks Formation, Williston basin, North Dakota and Montana
(Colorado State University. Libraries, 2014) Kolte, Ketki, author; Egenhoff, Sven, advisor; Ronayne, Michael, committee member; Paschke, Mark, committee member
The upper part of the Three Forks Formation in the Williston basin of North Dakota and Montana is one of the prime targets for oil exploration in the onshore part of the US today. The unit is mainly composed of dolomite, yet the details of dolomite formation and its relative timing are unknown. This study is the first that combines an analysis of cement generations and porosity to develop a diagenetic scheme based on detailed microscopical observations. The upper Three Forks Formation shows a total of seven dolomite generations along with some anhydrite and pyrite. Most of the rock consists of an inclusion-rich dolomite, likely dolomite II, that forms mm- to sub-mm-size rhombic crystals showing overgrowth of five more alternating clear and inclusion-rich dolomite generations, and in places a core of iron-rich dolomite I. Porosity types in the upper Three Forks Formation are intercrystalline, intracrystaline, and "moldic" which here stands for the dissolution of entire dolomite crystals. Detrital components are quartz, feldspars, mica, and clay particles. The Three Forks Formation was most likely deposited on a mixed carbonate-siliciclastic ramp as a limestone unit with varying amounts of detrital input. Initial replacement of limestone into dolomite probably occurred early entirely changing the texture of this unit. Several dolomite phases occurred during burial post-dating early dolomitization. The effective porosity, characterized by intercrystalline and "moldic" pores, is linked to the dolomitization, most likely originally to an early event as no late dolomite is seen filing these pores. Up to centimeter-size voids, though, representing mostly non-effective porosity is generally partly filled with several generations of dolomite and leaving some part of the vugs open. This indicates that most likely the voids were formed before the last few generations of dolomite cement, and also that not all open space was easily occluded by these dolomitizations but left some of the porosity untouched. Based on a limited data set, porosity distribution in the upper Three Forks Formation does not show a clear link to the distribution of dolomite. However, it does show a trend to overall increased values from the east (less than 1%) to the west (around 5%) with a north-south extending zone of maximum porosities (about 10-12%) around 103.5°. It is therefore likely that potential hot spots in this basin are rather located in western ND while towards the east porosities are lower.
Open Access
Effects of conjunctive use on streamflow at the Tamarack State Wildlife Area, northeastern Colorado
(Colorado State University. Libraries, 2012) Donnelly, Erin, author; Stednick, John, advisor; Ronayne, Michael, committee member; Sale, Thomas, committee member; Kampf, Stephanie, committee member
The Tamarack Recharge Project in northeastern Colorado is intended to augment the streamflow of the South Platte River by 10,000 acre-feet between April and September to increase aquatic habitat for four federally threatened or endangered bird and fish species in Nebraska. The project goal is to retime surface water flows by pumping unappropriated alluvial groundwater into a recharge pond where it infiltrates and returns to the river at critical low flow periods. Retimed surface water flow will help maintain critical habitat for native aquatic species by increasing streamflow without harming water rights holders. To evaluate the effects of this managed groundwater recharge on streamflow in the South Platte River, the hydrologic environment was characterized and quantified through streamflow monitoring, water table elevation mapping, and a groundwater tracer study. Stream discharge measurements were taken at 4 cross sections on the South Platte River. Two cross sections were considered upgradient of the recharge pond and two were downgradient of the recharge pond. The mean flow of the upstream cross sections was 2.64 cubic meters per second (cms) compared to 2.66 cms at the downstream cross sections, which was not a significant difference. A fluorescein tracer study was used to estimate groundwater travel times and hydraulic conductivity. Based on the arrival time of the breakthrough curve at different piezometers, the mean hydraulic conductivity was estimated to be 331 m/d. Using this value, the estimated return time to the South Platte River at 4 cross sections ranged from 92 to 534 days. Measurements of discharge and water table elevations suggesting that Tamarack Project did not produce a measureable increase in streamflow in the South Platte River during the target period are not indicative of project functionality. The annual volume of water pumped into the recharge pond was less than 1% of the annual yield of the South Platte River. While the volume of return flows did not produce measureable results in the river, data from the tracer study and in-stream vertical hydraulic gradient data indicate a gaining stream condition during the fall and a losing stream during the winter and early spring. Potential source(s) of groundwater discharging to the stream include the recharge pond and irrigation return flows and warrant further study.
Open Access
Effects of mountain pine beetle caused tree mortality on streamflow and streamflow generation mechanisms in Colorado
(Colorado State University. Libraries, 2014) Maggart, Ariann Lenore, author; Stednick, John D., advisor; Fassnacht, Steven, committee member; Ronayne, Michael, committee member
The mountain pine beetle (Dendroctonus ponderosae Hopkins) (MPB), an endemic beetle in Colorado forests, saw dramatic population growth in the 1990's. As a result of this epidemic, the mountain pine beetle killed large tracts of forest as it spread. To evaluate the effects of MPB caused tree mortality on streamflow and streamflow generation mechanisms multiple investigative approaches were taken. In north-central Colorado, 21 watersheds representing minimally to highly affected watershed areas were chosen. Physical watershed characteristics were determined through a geographic information system. Long-term streamflow records for each watershed were assessed for data stationarity and change-points in peak flow, date of peak flow and annual water yield. Peak streamflow, date of peak streamflow and annual water yield all had stationarity. Since data were stationary, change-point analyses were not conducted. Streamflow, groundwater and precipitation samples were collected and analyzed for stable isotope concentrations. Isotopes of 2H and 18O partition source water contributions to streamflow from precipitation as snow or rain and groundwater (as a surrogate for groundwater). Annual δ2H and δ18O isotopic signatures for streamflow and streamflow source waters, as snow, groundwater and rain, were determined and used to partition source water contributions to streamflow for each watershed. In general, during the 2012 water year, source water contributions to streamflow were as follows: snow 60%, groundwater 20% and rain 20%. The correlations between snow, groundwater and rain contributions to streamflow and MPB killed area were not statistically significant at α ≤ 0.05 (psnow = 0.582, pgroundwater = 0.543 and p;rain = 0.897). While Colorado has suffered extensive forest kill since the onset of the MPB epidemic, the results of this study suggest that MPB killed watershed area has little to no effect on peak streamflow, date of peak streamflow, annual water yield or streamflow generation mechanisms.
Open Access
Enhanced watershed modeling and data analysis with a fully coupled hydrologic model and cloud-based flow analysis
(Colorado State University. Libraries, 2014) Wible, Tyler, author; Arabi, Mazdak, advisor; Bailey, Ryan, advisor; Baù, Domenico, committee member; Ronayne, Michael, committee member
In today's world of increased water demand in the face of population growth and climate change, there are no simple answers. For this reason many municipalities, water resource engineers, and federal analyses turn to modeling watersheds for a better understanding of the possible outcomes of their water management actions. The physical processes that govern movement and transport of water and constituents are typically highly nonlinear. Therefore, improper characterization of a complex, integrated, processes like surface-subsurface water interaction can substantially impact water management decisions that are made based on existing models. Historically there have been numerous tools and watershed models developed to analyze watersheds or their constituent components of rainfall, run-off, irrigation, nutrients, and stream flow. However, due to the complexity of real watershed systems, many models have specialized at analyzing only a portion of watershed processes like surface flow, subsurface flow, or simply analyzing local monitoring data rather than modeling the system. As a result many models are unable to accurately represent complex systems in which surface and subsurface processes are both important. Two popular watershed models have been used extensively to represent surface processes, SWAT (Arnold et al, 1998), and subsurface processes, MODFLOW (Harbaugh, 2005). The lack of comprehensive watershed simulation has led to a rise in uncertainty for managing water resources in complex surface-subsurface driven watersheds. For this reason, there have been multiple attempts to couple the SWAT and MODFLOW models for a more comprehensive watershed simulation (Perkins and Sophocleous, 1999; Menking, 2003; Galbiati et al., 2006; Kim et al., 2008); however, the previous couplings are typically monthly couplings with spatial restrictions for the two models. Additionally, most of these coupled SWAT-MODFLOW models are unavailable to the general public, unlike the constituent SWAT and MODFLOW models which are available. Furthermore, many of these couplings depend on a forced equal spatial discretization for computational units. This requires that one MODFLOW grid cell is the same size and location of one SWAT hydrologic response unit (HRU). Additionally, many of the previous couplings are based on a loose monthly average coupling which might be insufficient in natural spring and irrigated agricultural driven groundwater systems which can fluctuate on a sub-monthly time scale. The primary goal of this work is to enhance the capacity for modeling watershed processes by fully coupling surface and subsurface hydrologic processes at a daily time step. The specific objectives of this work are 1) to examine and create a general spatial linkage between SWAT and MODFLOW allowing the use of spatially-different existing models for coupling; 2) to examine existing practices and address current weaknesses for coupling of the SWAT and MODFLOW models to develop an integrated modeling system; 3) to demonstrate the capacity of the enhanced model compared to the original SWAT and MODFLOW models on the North Fork of the Sprague River in the Upper Klamath Basin in Oregon. The resulting generalized daily coupling between a spatially dis-similar SWAT and MODFLOW model on the North Fork of the Sprague River has resulted in a slightly more lower representation of monthly stream flow (monthly R2 = 0.66, NS = 0.38) than the original SWAT model (monthly R2 = 0.60, NS = 0.57) with no additional calibration. The Log10 results of stream flow illustrate an even greater improvement between SWAT-MODFLOW correlation (R2) but not the overall simulation (NS) (monthly R2 = 0.74, NS = -0.29) compared to the original SWAT (monthly R2 = 0.63, NS = 0.63) correlation (R2). With an improved water table representation, these SWAT-MODFLOW simulation results illustrate a more in depth representation of overall stream flows on a groundwater influenced tributary of the Sprague River than the original SWAT model. Additionally, with the increased complexity of environmental models there is a need to design and implement tools that are more accessible and computationally scalable; otherwise their use will remain limited to those that developed them. In light of advancements in cloud-computing technology a better implementation of modern desktop software packages would be the use of scalable cloud-based cyberinfrastructure, or cloud-based environmental modeling services. Cloud-based deployment of water data and modeling tools assist in a scalable as well as platform independent analysis; meaning a desktop, laptop, tablet, or smart phone can perform the same analyses. To utilize recent advancements in computer technology, a further focus of this work is to develop and demonstrate a scalable cloud-computing web-tool that facilitates access and analysis of stream flow data. The specific objectives are to 1) unify the various stream flow analysis topics into a single tool; 2) to assist in the access to data and inputs for current flow analysis methods; 3) to examine the scalability benefits of a cloud-based flow analysis tool. Furthermore, the new Comprehensive Flow Analysis tool successfully combined time-series statistics, flood analysis, base-flow separation, drought analysis, duration curve analysis, and load estimation into a single web-based tool. Preliminary and secondary scalability testing has revealed that the CFA analyses are scalable in a cloud-based cyberinfrastructure environment to a request rate that is likely unrealistic for web tools.
Open Access
Evaluating covariance-based geostatistical methods with bed-scale outcrop statistics conditioning for reproduction of intra-point bar facies architecture, Cretaceous Horseshoe Canyon Formation, Alberta, Canada
(Colorado State University. Libraries, 2022) McCarthy, Andrew Louis, author; Stright, Lisa, advisor; Ronayne, Michael, committee member; Bailey, Ryan, committee member
Geostatistical characterization of petroleum reservoirs typically suffers from problems of sparse data, and modelers often draw key parameters from analogous outcrop, numerical, and experimental studies to improve predictions. While quantitative information (bed-scale statistical distributions) from outcrop studies is available, translating the data from outcrop to models and generating geologically-realistic realizations with available geostatistical algorithms is often problematic. The overarching goal of this thesis is to test the capacity of covariance-based geostatistical methods to reproduce intra-point bar facies architecture while guiding those algorithms with bed-scale outcrop statistics from the Late Cretaceous Horseshoe Canyon Formation in southeastern Alberta. First, general facies architecture reproduction is tested with 2- and 3-facies synthetic and outcrop-based experiments with variable hard data, soft data weight, and soft data reliability. Next, 3-D sector models compare performance of different geostatistical simulation methods: sequential / co-sequential indicator, plurigaussian, and nested truncated gaussian. Findings show that despite integration of outcrop statistics, all conventional covariance-based geostatistical algorithms struggle to reproduce complex facies architecture that is observed in outcrop. Specifically, problems arise with: 1) low-proportion facies and 2) a weak statistical relationship between hard data (measured sections) and soft data (probability models). Nested modeling partially mitigates low-proportion issues and performs better as a result.
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
Evaluating the impact of hierarchical deep-water slope channel architecture on fluid flow behavior, Cretaceous Tres Pasos Formation, Chile
(Colorado State University. Libraries, 2021) Ruetten, Andrew, author; Stright, Lisa, advisor; Ronayne, Michael, committee member; Bailey, Ryan, committee member
Channelized deep-water reservoirs inherently contain sub-seismic scale heterogeneity, resulting in uncertainty when evaluating reservoir connectivity and flow patterns. Stratigraphic architectural features, including stacked channel elements, channel element fill, mass transport deposits (MTDs), and channel base drapes, can have a complex and significant impact on fluid flow pathways. While this detailed stratigraphic architecture can be difficult to capture at the development scale, it can be effectively modeled at the sector scale using high-resolution outcrop data. The characterization of flow behaviors and reservoir performance at this finer scale can then be used in the construction of lower-resolution development-scale simulations. This study uses a three-part sensitivity analysis to test how fluid flow behavior responds to channel element stacking patterns, net to gross ratio, channel base drape coverage, and MTD properties. First, simplified models are used to isolate key flow behaviors. Then, field data is incorporated from the seismic-scale Laguna Figueroa outcrop of the Cretaceous Tres Pasos Formation, Magallanes Basin, Chile to construct a deterministic outcrop model that incorporates realistic stacking patterns and architectural features, including MTDs. Finally, stochastic object-based methods are used to try to replicate the flow characteristics of the outcrop model using established geostatistical methods and limited data input. Fluid flow was simulated using a constant flux aquifer at the base of the model and three producing wells at the top, and the results of the three modeling methods were compared in an effort to elucidate key flow behaviors.
Open Access
Geochemical modeling-based prediction of water-rock interaction during aquifer storage and recovery utilizing selected Colorado Front Range aquifers
(Colorado State University. Libraries, 2023) Doherty, Amanda, author; Sutton, Sally, advisor; Sale, Thomas, committee member; Ronayne, Michael, committee member
This study characterizes the Fountain Formation, Ingleside Formation, and sandstones of the Dakota Group and considers the potential of these three formations as hypothetical Aquifer Storage and Recovery (ASR) targets. Compositional data from surface rock samples, including major, minor and trace elements from bulk rock geochemical analysis and mineral identification from petrography are used to infer a generalized mineral suite to represent each of the formations of interest. Similarly, compositional analyses from domestic water well samples, including major anions and cations and selected metals, were used as generalized representations of native water from each formation of interest. Finally, compositional data from treated city water was obtained and used as a generalized representation of injection water. The generalized rock data along with the generalized native water data represent a hypothetical injection environment while the treated water composition represents a hypothetical injection water. All water and rock data were used to populate a Single Pass Mixing equilibria Model that simulated an ASR system using the USGS geochemical modeling computer program PHREEQC (PH REdox EQuilibrium). Model results include mixed solution compositions, mineral saturation indices and estimates of mineral mass precipitation during simulated injection. Results of modeling suggest there is limited geochemical water-rock interaction during ASR in the hypothetical environment in this study. Model results indicate that the mixed solution composition is controlled more by the injected solution than by reactions occurring between the injection fluid and aquifer host material. Specifically, as greater volumes of hypothetical injection water are introduced with each model step, the compositions of the resulting mixed solutions increasingly resemble those of the injected water. The model predicted the precipitation of hematite, kaolinite and quartz during injection of the hypothetical injection water. Because aluminum was below detection in the water analyses and an arbitrary value less than the detection limit was used in the model, the prediction of kaolinite precipitation is not meaningful. Further, the model was constrained to not permit mineral dissolution, limiting the applicability of the model only to the consideration of mineral precipitation. In addition, benchtop leaching experiments were performed on rock samples to provide additional information about potential water-rock interaction. Benchtop experiment results are presented, but the focus of the study is primarily on geochemical modeling results. Water analysis results presented here suggest that the formations of interest currently contain good quality water. Modeling results suggest that injection of treated water would likely not lead to volumetrically important precipitation of minerals in the formations.
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
Hydrogeologic characterization of the Fountain Formation: prospective aquifer storage and recovery targets in Front Range Colorado
(Colorado State University. Libraries, 2018) Collazo, Daniel, author; Sutton, Sally, advisor; Sale, Thomas, committee member; Ronayne, Michael, committee member
Aquifer storage and recovery (ASR) is a method of water storage that typically involves using the same well to inject water into and recover water from an aquifer. Benefits of ASR include lower capital costs than surface storage methods, negligible losses due to evaporation or potential contamination, and a much smaller land use footprint. This method of storing water is of interest for northern Colorado because of the location of existing water supply infrastructure and bedrock aquifers along the Front Range and the need for additional water storage. A potential storage zone for ASR in northern Colorado is the Fountain Formation. The Fountain is a Pennsylvanian-Permian arkosic conglomeratic sandstone with interbedded siltstone and shale that outcrops in a narrow, north-south trending belt from southern Wyoming to central Colorado. Within the outcrop belt, the Fountain is about 500 to 4500 feet thick and dips steeply to the east. The Fountain Formation was formed from sediments shed off the Ancestral Rocky Mountains, an uplift associated with the Ouachita-Marathon Orogeny, and deposited mainly in alluvial fans and braided streams. The composition of the formation is heterogeneous with permeable facies such as coarse sandstones adjacent to impermeable facies such as mudstones. This study characterizes the hydrogeology of the Fountain Formation to assess the feasibility of the Fountain as a storage zone for ASR, and in particular in northern Colorado. Data from 1262 wells in the Fountain were collected from the Colorado Division of Water Resources AquaMap database to characterize the hydraulic properties of the formation. The data were used to calculate specific capacity for each well and plotted on maps to help identify areas of interest for ASR. Within the formation there are wells with high yields and specific capacities which suggests that the Fountain can host high yield wells suitable for ASR. Water level elevation maps were also made for selected quadrangles and provide an approximation of the water level surface within the aquifer as well as the direction of water flow. Well-cemented outcrop samples were collected and tested for permeability using an air permeameter. The samples all have relatively low permeabilities, but it is likely that the less cemented lithologies have much higher permeabilities. The heterogenous lithology of the formation is likely able to store large volumes of water while preventing the water from migrating away from an ASR well. The results of this study suggest that the Fountain Formation is a feasible target for ASR implementation.
Open Access
Hypothesis-based machine learning for deep-water channel systems
(Colorado State University. Libraries, 2020) Vento, Noah Francis Ryoichi, author; Stright, Lisa, advisor; Ronayne, Michael, committee member; Anderson, Charles, committee member
Machine learning algorithms are readily being incorporated into petroleum industry workflows for use in well-log correlation, prediction of rock properties, and seismic data interpretation. However, there is a clear disconnect between sedimentology and data analytics in these workflows because sedimentologic data is largely qualitative and descriptive. Sedimentology defines stratigraphic architecture and heterogeneity, which can greatly impact reservoir quality and connectivity and thus hydrocarbon recovery. Deep-water channel systems are an example where predicting reservoir architecture is critical to mitigating risk in hydrocarbon exploration. Deep-water reservoirs are characterized by spatial and temporal variations in channel body stacking patterns, which are difficult to predict with the paucity of borehole data and low quality seismic available in these remote locations. These stacking patterns have been shown to be a key variable that controls reservoir connectivity. In this study, the gap between sedimentology and data analytics is bridged using machine learning algorithms to predict stratigraphic architecture and heterogeneity in a deep-water slope channel system. The algorithms classify variables that capture channel stacking patterns (i.e., channel positions: axis, off-axis, and margin) from a database of outcrop statistics sourced from 68 stratigraphic measured sections from outcrops of the Upper Cretaceous Tres Pasos Formation at Laguna Figueroa in the Magallanes Basin, Chile. An initial hypothesis that channel position could be predicted from 1D descriptive sedimentologic data was tested with a series of machine learning algorithms and classification schemes. The results confirmed this hypothesis as complex algorithms (i.e., random forest, XGBoost, and neural networks) achieved accuracies above 80% while less complex algorithms (i.e., decision trees) achieved lower accuracies between 60%-70%. However, certain classes were difficult for the machine learning algorithms to classify, such as the transitional off-axis class. Additionally, an interpretive classification scheme performed better (by around 10%-20% in some cases) than a geometric scheme that was devised to remove interpretation bias. However, outcrop observations reveal that the interpretive classification scheme may be an over-simplified approach and that more heterogeneity likely exists in each class as revealed by the geometric scheme. A refined hypothesis was developed that a hierarchical machine learning approach could lend deeper insight into the heterogeneity within sedimentologic classes that are difficult for an interpreter to discern by observation alone. This hierarchical analysis revealed distinct sub-classes in the margin channel position that highlight variations in margin depositional style. The conceptual impact of these varying margin styles on fluid flow and connectivity is shown.
Embargo
Inter-daily temperature variability in the southern Rocky Mountains of Colorado
(Colorado State University. Libraries, 2024) Steen, Brian, author; Fassnacht, Steven, advisor; Barnard, David, committee member; Ronayne, Michael, committee member
While daily temperature variability has decreased in northern latitudes, variability across the western United States has increased. Changes in temperature variability can influence hydrological and earth system processes that could have severe ecological impacts. Mountainous areas are more sensitive to warming trends, but daily temperature variability in the Rocky Mountains is unknown. We investigated daily temperature trends across the Yampa and Rio Grande watersheds of the Southern Rocky Mountains in Colorado using 23 Snow Telemetry (SNOTEL) stations at high elevation, snow-covered regions (2521-3536m) and ten Cooperative Observer Program (COOP) stations at lower elevations (1961-2840m). SNOTEL data were homogenized to account for temperature sensor changes in 2003-2006, with five possible bias correction combinations compared. Daily data were detrended using the long-term and annual means, so that the day-to-day variability could be quantified. Trends were analyzed from the mid-1980s to 2022 using the Mann‐Kendall significance test and Theil‐Sen's rate of change. Inter-daily temperature variability (ITV) changed over the 30+ year period of evaluation with mixed increases and decreases based on location and time period. Variability in the spring at 26 stations has increased upwards of 0.8°C per 30 years in the spring. Ninety percent of stations have increased in variability up to 1.0°C per 30 years in the fall. In the summer, Yampa area stations decreased in variability while the Rio Grande area stations increased, both significantly. Low elevation COOP stations demonstrated smaller increases in variability than high elevation SNOTEL stations in the Rio Grande watershed throughout all seasons. The Yampa watershed showed no similar elevational patterns, but rather decreased variability for SNOTEL stations with little change for variability for COOP stations. The scattered decreases in the Yampa area and at lower elevations emphasize the spatiotemporal variability of montane climatology and suggest increased ITV trends across the Rocky Mountain West are watershed and station specific.