Browsing by Author "Bailey, Ryan, advisor"
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Item Open Access Assessing impacts of rainfall patterns, population growth, and sea level rise on groundwater supply in the Republic of Maldives(Colorado State University. Libraries, 2016) Deng, Chenda, author; Bailey, Ryan, advisor; Grigg, Neil, committee member; Sanford, William E., committee memberGroundwater resources of the Republic of the Maldives are threatened by a variety of factors including variable future rainfall patterns, continued population growth and associated pumping demands, rising sea level, and contamination from the land surface. The Maldives is composed of approximately 2,000 coral islands residing in 26 atolls in the Indian Ocean, with each coral island less than a few square kilometers in surface area and less than a few meters in elevation. This thesis uses numerical modeling techniques to assess the influence of variable rainfall patterns, increased pumping due to population growth, and sea level rise on fresh groundwater supply of the coral islands that comprise the Maldives. The density-dependent groundwater flow and solute transport model SUTRA (Saturated Unsaturated Transport) is used for all simulations, with the model simulating the spatial extent of the freshwater lens in the aquifer of the coral islands. The thesis first assesses changes in groundwater supply due to variable rainfall patterns in the coming decades, a key component of water resources management for the country. Using a suite of two-dimensional vertical cross-section models, time-dependent thickness of the freshwater lens is simulated for a range of island sizes (200 m to 1100 m) during the time period of 2011 to 2050, with recharge to the freshwater lens calculated using rainfall patterns provided by General Circulation Models (GCM) for the three distinct geographic regions (north, central, south) of the Maldives. Results show that average lens thickness of islands in all three geographic regions during the 2031-2050 time period is slightly greater than during the 2011-2030 time period, indicating a mild increase in future available groundwater supply under predicted conditions. Average lens thickness during 2011-2030 for islands of 200 m, 400 m, 600 m, and 1100 m width is 0.5 m, 3.0 m, 7.0 m, and 12.2 m, respectively, with these values increasing by 1-5% during 2031-2050 time period. However, these results do not include the effect of sea level rise. To quantify the total available groundwater on a representative island and to provide accurate simulation of the effect of radial pumping on the freshwater lens, a three dimensional model is created for the island of Gan (Area: 598 ha, Population: 4,280) to evaluate the impact of increasing pumping and sea-level rise on future groundwater resources. Simulations covering the 2012-2050 period are used to compare scenarios of future rainfall, pumping vs. non-pumping, varying rates of population growth and hence of groundwater pumping, and sea level rise (0.5 m by 2100) vs. no sea level rise. Results indicate that the total freshwater volume increases about 19% under the effects of future rainfall patterns. If moderate pumping is included, with rates increasing at 1.76% to correspond with increasing population, the volume increases only by 12%. If just considering sea level rise, then the volume decreases by 14%. With aggressive pumping, corresponding to an annual population growth rate of 9%, but no sea level rise, the volume decreases by 24%. With aggressive pumping and sea level rise, the freshwater lens is rapidly depleted. This study quantifies the major future impacts on groundwater of the atoll islands in Maldives. Similar methodologies using output from GCMs can be used for other atoll island nations, such as the Republic of Marshall Islands, Federated States of Micronesia, and Gilbert Islands. For the Maldives, results from this study can be used in conjunction with population growth estimates to determine the feasibility of including groundwater in water resources planning and management for the country.Item Open Access Assessing the on-farm effects of removing salts from irrigation water(Colorado State University. Libraries, 2023) Shrestha, Sanskriti, author; Bailey, Ryan, advisor; Sharvelle, Sybil, committee member; Butters, Gregory, committee memberIn dry and semi-arid places where precipitation is insufficient to sustain a regular percolation of water through the soil, salt-induced land degradation is frequent. Desalination of irrigation water is an emerging alternative that can be utilized to repurpose our salt-affected agricultural lands, thus providing an avenue for sustaining the growing production demands with limited water and land resources. Therefore, a combination of fieldwork, modeling and soil sensor records was implemented to evaluate the feasibility of an on-farm Reverse Osmosis (RO) system, in terms of crop yield and soil salinity, for the desalination of irrigation water over three growing periods. Four types of treatment systems were applied to 16 experimental field plots at the Arkansas Valley Research Center (Rocky Ford, CO), representing soil conditions of the Lower Arkansas River Valley (LARV), a region of which approximately 70% is affected by salt-induced crop yield loss. Statistical t-tests done on the data of the three seasons did not show any significant differences in the VMC, EC and biomass of the plots irrigated with the different treatments. Results of the tests for season 3, which showed an increase in t-values and a decrease in p-values demonstrated the need for a longer study period to gauge any significant effects. Similarly, the results of sensor data did not show a significant decrease in soil salinity for the study period. The average soil electrical conductivity (EC) showed a 20% to 26% reduction in soil salt mass in the fields irrigated with desalinated water over the three seasons, however, the EC results did not show a consistent decreasing trend across the 16 plots. A 6-year numerical modeling forecast done by the hydro-chemical model HYDRUS 1D simulating dry, average, and wet weather showed a 6% to 20% reduction in EC when desalination was applied to the fields. These preliminary results of the field and modeling approaches provide encouragement for the continuation of desalination treatments to see any substantial long-term effects.Item Open Access Assessing the salinity effects and economic feasibility of on-farm desalination technology in irrigated semi-arid regions(Colorado State University. Libraries, 2021) Barnes, Kaitlyn, author; Bailey, Ryan, advisor; Sharvelle, Sybil, committee member; Melzer, Suellen, committee memberHigh salinity levels in areas with intensive agricultural practices can inhibit agricultural productivity. Semi-arid regions where irrigation is used to support crop growth are particularly impacted by the quality of surface and groundwater sources. In this study, we use a combined numerical modeling and economic analysis approach to estimate the regional impact of an on-farm desalination technology on multi-decadal salinity fate and transport and explore whether the technology is viable to improve soil health, crop yield, and long-term profitability. A subsurface salt transport model (MODFLOW-RT3D) is applied to a 50,600-ha (125,000 acres) region in southeastern Colorado located within the Arkansas River Valley. The model simulates the reactive transport in soils and groundwater of 8 major salt ions (Ca+, Mg2+, Na+, K, SO42-, CO32-, HCO3-, and Cl-). Simulated values of average soil water concentration (TDS) are used to estimate crop relative yield with and without salt removal at various removal rates (Baseline – no salt removed; Unit removal – average of 60% salt removed; 100% salt removal) and time periods (5, 10, 15, 20, 25 years after desalination begins). The Unit removal rate is calibrated to align with a solar powered, reverse-osmosis desalination system that is currently being tested in semi-arid study area. For the Unit rate of 60% salt removal, the average TDS of the study area was found to decrease by an average of 20% over a period of 20 years, resulting in an increase in crop yield of 1.6 – 2.3%. Using data on regional production costs, crop prices, and the costs of building and operating the desalination system, we calculate the Net Present Value of production with the desalination unit. The results indicate that desalination does increase economic returns, particularly for high-valued specialty crops, such as melons and onions; however, these benefits are considerably less than the costs of operating the desalination technology.Item 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 memberAtolls 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.Item 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 memberIn 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.Item Embargo Long-term analysis of groundwater depletion in the High Plains Aquifer: historical, predictive, and solutions(Colorado State University. Libraries, 2024) Nozari, Soheil, author; Bailey, Ryan, advisor; Niemann, Jeffrey, committee member; Ronayne, Michael, committee member; Suter, Jordan, committee memberSemi-arid agricultural regions worldwide are heavily dependent on groundwater storage in a handful of large and over-exploited aquifers, such as the High Plains Aquifer (HPA) in the U.S. High Plains Region. The HPA, one of the world's largest freshwater aquifers, serves as the primary source of irrigation water in the High Plains Region. The socioeconomic development in the High Plains Region has come at the expense of significant groundwater depletion in the HPA. The ongoing depletion of the HPA poses risks to livelihoods of rural communities, local ecosystems, and national food security. Addressing this issue necessitates the formulation of groundwater management policies that aim to reduce groundwater extraction, while minimizing associated economic costs over a multi-generational timeframe, all in the context of climate change. To inform the formulation of effective policies, it is crucial to develop a suite of decision support tools that empower local managers and planners to assess the outcomes of various groundwater management policies amidst climate change. The primary goal of this dissertation is to enhance the capacity to project the future of groundwater systems in semi-arid agricultural areas, particularly within the High Plains Region, as a coupled human-natural system, under various groundwater management schemes in the face of climate change. To achieve this goal, a number of tools were developed that incorporate a spectrum of modeling approaches, from the increasingly popular data-driven models to the state-of-the-art hydro-economic models. First, a data-driven modeling framework was developed and tested that is fast to employ and yet provides reliable long-term groundwater level (GWL) forecasts as a function of climatic and anthropogenic factors. The modeling framework utilizes the random forests (RF) technique in combination with ordinary kriging and was tested for the HPA in Finney County, southwest Kansas. The introduction of groundwater withdrawal potential as a new surrogate for pumping intensity empowers the RF model to capture decline in groundwater depletion rate as the system progresses towards aquifer depletion and/or as a result of well retirement policies. The RF model was applied over the period from 2017 to 2099 using 20 downscaled global climate models (GCMs) for two representative concentration pathways (RCPs), RCP4.5 and RCP8.5. The findings indicate that, under status quo management and average climate conditions, the aquifer will no longer be able to sustain irrigated agriculture in most of the county by 2060. Additionally, the difference in climate scenarios will likely shift the aquifer's depletion time frame by up to 15 years in most of the study area. The long-term combined impact of well retirement plans and climate conditions on groundwater depletion trends imply well retirement policies do not lead to sustained groundwater savings. In the next step, an agent-based hydro-economic model (ABM-MODFLOW) was developed for a portion of the HPA in eastern Colorado and northwest Kansas, with the aim of addressing the current limitations of hydro-economic models. Through interdisciplinary collaboration, each component of the ABM-MODFLOW was particularly designed to meet specific research objectives. Planting and irrigation decisions were simulated in the ABM-MODFLOW using a detailed representation of real-world farmers. Additionally, well capacity was incorporated as a constraint on irrigation duration. A subsequent thorough validation of the ABM-MODFLOW was conducted to establish its credibility. The validation results indicate satisfactory performance in reproducing historical data and trends. They also reveal the ABM-MODFLOW's superiority over the standalone groundwater model in simulating the groundwater system. The historical simulation outcomes also underscore the impact of soil type on agents' profitability, especially for those with limited irrigation capacities. Overall, the highest profits are earned by agents with high irrigation capacities and fine soils, while the lowest are achieved by those with low irrigation capacities and coarse soils. Lastly, the ABM-MODFLOW was employed to project the coevolution of human activities, crops, and the groundwater system amidst climate change, both with and without policy interventions. The ABM-MODFLOW simulations involved 32 climate scenarios from 16 downscaled GCMs for two RCPs, RCP4.5 and RCP8.5. Additionally, three groundwater management policy instruments were explored: irrigated land retirement, irrigation well retirement, and authorized pump rate reduction. The simulation outcomes reveal that the groundwater depletion rate decreases over time, primarily due to rising summer temperatures from climate change that limit corn production, a water-intensive crop, in the region. Moreover, these rising temperatures hamper the economic benefits of policies, since the early conserved groundwater is predominantly used for winter wheat irrigation in the later years, a crop with substantially lower irrigation value than corn.Item Open Access Monitoring groundwater-surface water interaction and nutrient mass exchange in the riparian corridor of the Lower Arkansas River Valley, Colorado(Colorado State University. Libraries, 2015) Huizenga, Alexander Paul, author; Bailey, Ryan, advisor; Gates, Timothy, advisor; Covino, Timothy, committee memberThe Lower Arkansas River Valley in southeastern Colorado is an irrigated, agricultural valley suffering from high concentrations of nutrients (Nitrogen N; phosphorus P) and salts in the coupled groundwater-surface water system. The majority of data collection efforts and associated spatial analysis of concentrations and mass loadings from the aquifer to the stream network have been performed at the regional scale (> 500 km²). These regional scale assessments have indicated that river riparian areas play a major role in controlling nutrient mass flux to the Arkansas River and its tributaries. However, the water and nutrient mass exchange within the riparian-stream system have not yet been investigated in detail. The objective of this thesis is to enhance understanding of hydro-chemical stream-aquifer processes at the reach scale (< 5 km) along the main stem of the Arkansas River and along a major tributary. Using a suite of in-stream instruments and observation wells, a 4.7 km reach of the Arkansas River and a 2 km reach of Timpas Creek were monitored to quantify spatio-temporal groundwater-surface water interaction and mass inputs and outputs of nutrients. The total volume of water flowing into and out of each study reach was quantified using existing stream gages for upstream flow measurements and developing new stream gages for downstream flow measurements. Stage-discharge relationships were developed at the downstream locations using in-stream water level loggers and periodic flow measurements using Acoustic Doppler Velocimeters (ADVs). Monitoring included growing season length and 24-hour monitoring of flow and water quality. Using these monitoring data, mass balance calculations were used to quantify groundwater-surface water interactions and nutrient mass exchanges and loadings. For growing season length analysis, surface water samples were collected and in-situ measurements were made at the stream gaging sites every two weeks during the study period to provide a data set on fluxes into and out of each reach during the irrigation season. The two 24-hour sampling events were performed in June and October of 2014 to compare groundwater-surface water exchange and mass loadings at the beginning and end of the growing season. Composite water quality samples for total N, nitrate as nitrogen (NO₃‾; as N), nitrite as nitrogen (NO₂‾; as N), ammonium as nitrogen (NH₄⁺ as N), total P, and dissolved salts were collected at the gage locations every 2 hours using ISCO automatic samplers along with in-situ measurements of water level, temperature, and specific conductance. Water quality samples, along with in-situ measurements, were also collected from transects of shallow monitoring wells installed in the riparian corridor and on the banks of each reach during sampling events. These water quality data, as well as estimated gradients of groundwater hydraulic head between monitoring wells, were used to inform mass loading calculations. Growing season length monitoring results from the Arkansas River show decreases in NO₃‾ and total N concentrations ranging from 35% to 66% from upstream to downstream along the study reach. A growing season NO₃‾ mass balance performed on the Arkansas River indicated that 73% of the total NO₃‾ lost from the system can be attributed to in-channel and hyporheic processes. In addition, analysis of the water table elevations along the river suggest that there is an oscillation of the groundwater gradients during high flow periods. 24-hour monitoring suggests minimal upstream to downstream changes in total phosphorus loadings in the Arkansas River early in the growing season; however, there was a 29% increase in loadings in October. NO₃‾ loadings decreased 14% in June between the upstream and downstream monitoring stations, and an average of 41% in October. Groundwater and pore water sample results suggested extensive mixing of surface and groundwater in the Arkansas River, but indicated little exchange in Timpas Creek. These samples also suggest that denitrification occurs in both the riparian floodplain and hyporheic zones of the Arkansas River and Timpas Creek, while phosphorus immobilization and mobilization in groundwater is highly variable in these systems. These results provide a better understanding of hydro-chemical groundwater-surface interactions within the region and indicate the role of riparian and hyporheic zones in controlling and mitigating groundwater and surface water nutrient loadings to the stream network. The information derived from this study provides knowledge of hydro-chemical processes on small to medium spatial and temporal scales and provides a valuable contrast in controlling processes between main-stem and tributary riparian areas. This project also provides a database for future small to medium scale groundwater-surface water modeling efforts in the Lower Arkansas River Valley to further elucidate processes that govern nutrient mass transport in the riparian-stream system, with implications for regional-scale processes.Item Open Access Quantifying climate change impacts on future water resources and salinity transport in a high semi-arid watershed using the APEX-MODFLOW-Salt model(Colorado State University. Libraries, 2023) Balakrishnan, Jaya Vignesh, author; Bailey, Ryan, advisor; Arabi, Mazdak, advisor; Ronayne, Michael, committee memberHigh salinity mobilization and movement from salt laden deposits in semi-arid landscape poses threat to impairment of soil and water resources worldwide. Semi-arid regions in the world are expected to experience rising temperatures and lower precipitation, which will impact water supply and likely spatio-temporal patterns of salinity loads affecting downstream water quality. No studies have evaluated salt fate and transport from high desert landscapes under the influence of future climate uncertainties. This study quantifies the impact of future climate change on hydrology and salinity transport and their total watershed yield in the Gunnison River Watershed (GRW) (14,608 km2), Colorado, using the APEX-MODFLOW-Salt hydro-chemical watershed model and three different CMIP5 climate models output downscaled by Multivariate Adaptive Constructed Analogs (MACA), each for two climate scenarios, RCP4.5, and RCP8.5, for the period 2020–2099. The APEX-MODFLOW-Salt model accounts for transport of hydrology and major salt ions (SO42-, Cl-, CO32-, HCO3-, Ca2+, Na+, Mg2+, and K+) to in-stream loading via various hydrological pathways (surface runoff, rainfall erosional runoff, soil lateral flow, quick return flow and groundwater discharge to streams). Results indicate that varying trends in precipitation output from different climate models with different RCP yields varying trends in annual average water yield (mm/ year) with predicted maximum and minimum change of +7.3% and -13.4% but annual average salinity loads (kg/year) discharged via watershed outlet simulation increased consistently with maximum and minimum change of +9.6% and +4.1% from the baseline scenario of 2007-2017. From the results, this conjunction of APEX-MODFLOW-Salt model with downscaled future climate forcings can be a helpful modeling framework for investigating hydrology and salt mobilization, transport, and export in both historical and predictive settings for salt-affected watersheds in the world.Item Open Access Quantifying the impact of climate extremes on salt mobilization and loading in non-developed, high desert landscapes(Colorado State University. Libraries, 2022) Henson, Eleanor, author; Bailey, Ryan, advisor; Morrison, Ryan, committee member; Leisz, Stephen, committee memberExcess salt loading acts as a chemical stressor in water bodies and can have significant impacts on water quality. High salinity threatens sustainable crop production globally and is especially prevalent in semi-arid and arid regions. For this reason, salt transport in irrigated semi-arid and arid regions has been intensively studied. However, comparatively little research has been conducted to evaluate the salinity contributions of dominantly non-irrigated basins, and to my knowledge, no previous research has evaluated the changes in salt loads from upland semi-arid catchments in the face of climate change and extreme climate events. This research utilizes the Soil and Water Assessment Tool (SWAT) and a coupled salinity module (SWAT-Salt), applied to a natural watershed, to fill this knowledge gap. SWAT-Salt simulates the reactive transport of 8 major salt ions, SO42-, Cl-, CO32-, HCO3-, Ca2+, Na+, Mg2+, and K+, in the soil-aquifer-stream system of a watershed, with salt mass transported via major hydrologic pathways (surface runoff, percolation, recharge, soil lateral flow, upflux, and groundwater discharge). Specifically, this study has two major research objectives: 1) develop an accurate SWAT-Salt model that can estimate salinity loads from a largely undeveloped, upland desert catchment, the Purgatoire River Basin in Colorado, USA; and 2) quantify changes in predicted salt loads in the Purgatoire River Basin with increasing storm intensity. The SWAT-Salt model developed in this study was used to evaluate the contribution of salt to the Arkansas River from the Purgatoire River, a dominantly non-irrigated desert catchment in southeastern Colorado. The ~8,935 km2 Purgatoire River basin is susceptible to high salt transport due to very high topographic slopes, dry climatic conditions, and sparse vegetation. Much of the natural salt in this region has been deposited from 20,000 years of weathering the Mancos Shale formation. Calibration and validation of the salinity module was evaluated through comparisons of measured and simulated in-stream loads of individual salt ions during the period 1990-2010. Model results indicate that 76% of the salt in the Purgatoire River comes from groundwater sources, and ~24% of the salt comes from landscape soil lateral flow. Sulfate, calcium, and bicarbonate account for ~56%, ~20%, and 14% of the total salt load, respectively. The impact of climate change on salt transport and mobilization was evaluated through model scenarios of increasing storm intensity (5% and 35% increases in daily precipitation for the most extreme storms) congruent with global climate models. Results suggest that if the largest storm events increase in intensity by the maximum predicted value of 35%, the total salt mass exported from the Purgatoire River watershed would increase by 73%. If the largest storm events increase in intensity by the median predicted value of 5%, the total salt mass exported would increase by 12%. Similar results are expected but should be evaluated for other upland desert catchments. From this thesis, I conclude that: 1) natural, largely undeveloped basins can export significant salt loads to downstream agricultural regions; 2) Future increasing storm intensity with changing climatic conditions can have a large impact on salt exports from high-desert landscapes; and 3) process-based models such as SWAT-Salt can be valuable in evaluating salt loadings from high-desert watersheds and can be applied to other watersheds worldwide.Item Open Access Salt mobilization and transport in an upland desert catchment of the Lower Arkansas River Basin of Colorado(Colorado State University. Libraries, 2021) Zimmer, Carly Elizabeth, author; Bailey, Ryan, advisor; Niemann, Jeffrey, committee member; Kampf, Stephanie, committee memberSalt loading can significantly alter water quality in large river basins. Salt deposits occur naturally and anthropogenically and are transported to water bodies through overland flow and other environmental factors. The mobilization and transport of salt in high-desert regions can hinder the sustainability of crop production in downstream irrigated regions. Salinity transport and loading has been extensively investigated in regions of irrigation. However, little research has been conducted regarding salt mobilization in analogous regions with high-desert characteristics and little cultivation. The goal of this thesis is to understand the mobilization of salt in predominantly undeveloped, uncultivated upland catchments in a semi-arid climate with sparse vegetation cover and steep gradients. The thesis is composed of two primary objectives. 1) Quantify the salt load contribution from the Purgatoire River Watershed, a high-desert watershed, to the Arkansas River, and 2) Identify possible major environmental factors that control the mobilization of salts in natural upland catchments. A variety of field and computational methods were used to complete these two objectives. Electrical conductivity (EC) data loggers were placed at two locations along the Purgatoire River to quantify in-stream salt ion (SO4, Ca, Na, Mg, HCO3, K, Cl) loading. Daily in-stream loading (kg/day) of each salt ion was estimated using laboratory results of a set of water samples (n = 10) at these sites and stochastic linear regression techniques. Results indicate that the overall mass loading of salt exported by the Purgatoire River to the Arkansas River, and the ratio of salt in the Arkansas River to the Purgatoire River, is significantly affected by annual rainfall. In 1990 (490 mm), the Purgatoire River exported approximately 64,600,000 kg of salt to the Arkansas River, accounting for 21.7% of the salt in the Arkansas River after merging. In 2020 (262 mm), the volume of annual precipitation fell by 47% and the Purgatoire River exported approximately 18,000,000 kg of salt, 72% less than 1990, to the Arkansas River accounting for 11.2% of the salt in the Arkansas River after merging. Results indicate that upstream desert catchments can have a large effect on salinity loads in irrigated river valleys such as the Arkansas River Valley. For objective 2, environmental factors investigated for salt mobilization control include precipitation depths, land use type, topographic slope, percent calcium carbonate (CaCO3) in soil, and percent calcium sulfate (CaSO4) in soil. These factors were used to compute a spatial varying salt mobilization index throughout the Purgatoire River Watershed. The resulting index map shows hot spots of potential salt mobilization, which can be verified through additional research. Similar maps can be made for other high-desert regions to investigate potential sites of salt mobilization.Item Open Access The fresh groundwater lenses in the Arabian Peninsula: formative, stability and management assessments(Colorado State University. Libraries, 2019) Alrashidi, Mosaed, author; Bailey, Ryan, advisor; Grigg, Neil, committee member; Sale, Thomas, committee member; Sanford, William, committee memberThe formation of fresh groundwater lenses (FGLs) overlying denser, saline or brackish groundwater is a fascinating hydrologic phenomenon that creates groundwater supplies of great potential value for humans and ecosystems in several formation settings, such as coastal areas, atoll islands, riverine floodplains, and subterranean oases in arid regions. In particular, FGLs in subterranean oases are a critical source of freshwater supply in arid regions, due to a general lack of perennial rivers and lakes. These FGLs are in danger of salinization due to natural events and anthropogenic stresses. Although extensive research has been conducted on FGLs in general, the FGLs in subterranean oases in arid regions have received less attention. Key knowledge gaps include the quantity and frequency of natural recharge to these FGLs; reliable estimates of environmental aquifer dispersivity at the scale of subterranean FGLs; the timing of lens development; and the impact of anthropogenic activities on lens dynamics. This dissertation focuses on the FGLs of subterranean oases in the Arabian Peninsula (AP), using the Rawdatain FGL in Kuwait as a case study. Among the FGLs in the AP, the Rawdatain FGL in Kuwait is perhaps a unique candidate because of its size and the availability of extensive subsurface data for the pre-development period. The main objectives of this study are as follows: (1) estimate long-term average annual recharge for the Rawdatain FGL and investigate the timing of lens depletion due to climate change; (2) provide a realistic range of longitudinal (αL), horizontal transverse (αh), and vertical transverse (αv) dispersivity values for the aquifer; and (3) assess the impacts of historical and future anthropogenic activities and evaluate artificial recharge alternatives for lens recovery storage (LSR). In this study, a 3D density-dependent groundwater flow and solute transport model using the SEAWAT modeling code is developed using the following pre-development period calibration targets: (1) groundwater head, (2) spatially-variable total dissolved solids (TDS) groundwater concentration, (3-5) three groundwater volume targets, (6-8) three vertical thickness targets of stored groundwater of three different water quality TDS ranges (0−700, 700−1000, and 1000−2000 mg/L), and (9) geometrical shape features of the lens along cross-sections. In addition, groundwater age data of the Rawdatain FGL was used as an independent factor to constrain the dispersivity and recharge rate during the simulated period of lens development. Moreover, a sensitivity analysis was performed to explore the effects of the hydraulic conductivity, boundary conditions, and vertical transverse dispersivity on lens geometry. Based on a comparison of twelve annual recharge amount scenarios using a constant recharge mechanism (CRM) (R1 to R12: 0.2 to 5.0 million m³/year) with data targets, the R5 (0.5 million m³/year) recharge scenario is selected to represent the long-term average annual recharge. These results demonstrated that the annual natural replenishment of the Rawdatain FGL is minimal compared with its size. A macro-scale stability assessment shows that a 50% reduction in annual recharge within a 100-year time frame would reduce the lens volumes by 21%, 17% and 9% for the three water quality categories. A multi-criteria score-based method was performed to rank the best performance of 28 dispersivity sets (D1 to D28: 1 to 500 m) among all of the targets with an equal weight, on a scale of 0 to 300 x 106 m3. The results illustrated that the D16 dispersivity set (αL = 50 m: αh = 5 m: αv = 0.1 m) represents the best large-scale environmental dispersivity values for the Rawdatain FGL and can be used for analyzing the natural mixing between the ambient brackish water and fresh water. A new baseline model for the predevelopment period using a pulse recharge mechanism (PRM) was established to assess the recharge frequency along with the longitudinal dispersivity. The results revealed that the 50 m longitudinal dispersivity set and one pulse recharge every two years had the best performance, and they were selected to simulate the effects of the infrequent rainfall events and anthropogenic impacts simultaneously. During the groundwater abstraction from 1963 to 2018, the reduction in the stored volumes was 28%, 17% and 12% for the three quality categories. The future pumping scenarios (2019-2100) suggested that the 0.16×106 m3/year is a suitable alternative for long-term use, 0.5×106 m³/year)is an appropriate option for short-term use, and extraction scenarios greater than 1.0×106 m³/year will cause a remarkable degeneration of the Rawdatain FGL. Artificial recharge scenarios (2019-2028) imply that a successful LSR for the Rawdatain FGL depends on selecting appropriate well locations and amounts of injected water. For instance, the I2 alternative could achieve a 100% storage recovery within 7.5, 8 and 9 years for the three water quality categories. This study provides a first attempt to model the formation of a FGL, assess the historical anthropogenic stresses, and evaluate future management scenarios in subterranean oases in arid regions. Implementing multiple data targets and water age is a unique process of calibration that was helpful in eliminating several non-unique calibration parameters and in decreasing the uncertainty of the calibrated parameters. The methodology presented herein provides a general approach that can be extrapolated to other FGLs with similar climatic and environmental circumstances. The outputs of this dissertation enhance the understanding of the formation, stability, and management of these lenses and will be very valuable to water managers for establishing appropriate water supply plans for these valuable water reserves, leading to preferable future water security in the AP.Item Open Access The sustainability of atoll islands freshwater lenses under non-stationary climatic and anthropogenic stresses(Colorado State University. Libraries, 2017) Alsumaiei, Abdullah Ahmad, author; Bailey, Ryan, advisor; Grigg, Neil, committee member; Ronayne, Michael, committee member; Sale, Thomas, committee memberTo view the abstract, please see the full text of the document.Item Open Access Water resources on outer-lying islands in Micronesia(Colorado State University. Libraries, 2016) Beikmann, Alise Marie, author; Bailey, Ryan, advisor; Ettema, Robert, committee member; Grigg, Neil, committee member; Ronayne, Michael, committee memberTo view the abstract, please see the full text of the document.