Mountain Scholar :: Browsing by Author "Bailey, Ryan T., advisor"

Browsing by Author "Bailey, Ryan T., advisor"

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Open Access
A combined field analysis and modeling approach for assessing the impact of groundwater pumping on streamflow
(Colorado State University. Libraries, 2018) Flores, Luke, author; Bailey, Ryan T., advisor; Gates, Timothy K., committee member; Sanford, William E., committee member
The magnitude of volumetric water exchange between streams and alluvial aquifers impacts contaminant transport rates, channel erosion and sedimentation, nutrient loading, and aquatic and riparian habitat. Quantifying the interactions between stream water and groundwater is also critically important in regions where surface water and tributary groundwater are jointly administered under a prior appropriation doctrine, such as in the western United States. Of particular concern is the effect of a nearby pumping well on streamflow. When the cone of influence of a pumping well reaches a nearby stream, the resulting hydraulic gradient can induce enhanced seepage of streamflow into the aquifer or decrease the rate of groundwater discharge to the stream. The change in these rates is often modeled using analytical or numerical solutions, or some combination of both. Analytical solutions, although simple to apply, can produce discrepancies between field data and model output due to assumptions regarding stream and aquifer geometry and homogeneity of hydraulic parameters. Furthermore, the accuracy of such models has not been investigated in detail due to the difficulty in measuring streamflow loss in the field. In the first part of this thesis, a field experiment was conducted along a reach of the South Platte River in Denver, Colorado to estimate pumping-induced streamflow loss and groundwater head drawdown, and compare data against analytical modeling results. The analytical solutions proved accurate if streamflow was low and constant, but performed poorly if streamflow was high and variable. In particular, the models are not capable of accurately simulating the effects of increasing stream width and bank storage due to rapid increases in streamflow. To better account for these effects a new analytical modeling framework is introduced which accounts for all major factors contributing to streamflow loss for a given site for both periods of pumping and periods between pumping. For the reach analyzed herein, the method illustrates that pumping wells often only caused half of the given streamflow loss occurring along the reach. This method can be used in other stream-aquifer systems impacted by nearby pumping. The U.S. Geological Survey's three-dimensional finite-difference groundwater flow model, MODFLOW, was also used to assess the impacts of pumping on streamflow. While MODFLOW removes many of the restrictive assumptions that define analytical solutions, certain limitations persist when the program is applied on local, fine scales with dynamic interactions between a stream and alluvium. In particular, when the average stream width is greater than the computational grid cell size, the model will return systematically biased, grid-dependent results. Moreover, simulated streamflow loss will be limited in the range of values that can be modeled. To address these limitations, a new stream module is presented which (1) allows for streams to dynamically span multiple computational grid cells over a cross section to allow for a finer mesh; (2) computes streamflow and backwater stage along a stream reach using the quasi-steady dynamic wave approximation to the St. Venant equations, which allows for more accurate stream stages when normal flow cannot be assumed or a rating curve is not available; and (3) incorporates a process for computing streamflow loss when an unsaturated zone develops under the streambed. Streamflow loss is not assumed constant along a cross section. It is shown that most streamflow loss occurs along stream banks and over newly inundated areas after increases in upstream streamflow. The new module is tested against streamflow and groundwater data collected in a stream-aquifer system along the South Platte River in Denver, Colorado and to estimate the impact of nearby pumping wells on streamflow. When compared with existing stream modules more accurate results are obtained from the new module. The new module can be applied to other small-scale stream-aquifer systems.
Open Access
Analysis of selenium cycling and remediation in Colorado's Lower Arkansas River Valley using field methods and numerical modeling
(Colorado State University. Libraries, 2016) Romero, Erica C., author; Gates, Timothy K., advisor; Bailey, Ryan T., advisor; Hoag, Dana L. K., committee member
Groundwater and surface water concentrations of selenium (Se) threaten aquatic life and livestock as well as exceed regulatory standards in Colorado's Lower Arkansas River Valley (LARV). Se is naturally present in surface shale, weathered shale, and bedrock shale in the region. Excess nitrate (NO3) from irrigated agricultural practices oxidizes Se from seleno-pyrite present in shale and inhibits its chemical reduction to less toxic forms. Irrigation-induced return flows and evapotranspiration induce high concentrations of Se in the alluvial groundwater resulting in substantial nonpoint source loads to the stream system. This research uses three main components to address the need to better describe and find solutions to the problem of Se pollution in the LARV: (1) Se data collection in streams to characterize solute and sediment concentrations, (2) development of a conceptual model of in-stream Se reactions, and (3) application of existing calibrated groundwater models to explore alternative Se remediation strategies. Data in the form of Se solute samples, Se sediment samples, and related water properties were collected during four different sampling events in 2013 and 2014 at several locations in the stream network in an effort to understand the various species of Se and how they cycle through the surface water environment. A conceptual representation of the major chemical reactions of Se in the water column and sediments of streams was described and incorporated into the OTIS (One-Dimensional Transport with Inflow and Storage) computational model of stream reactive transport for future coupling to the MODFLOW-UZF and RT3D-UZF groundwater models. The new version of OTIS, now called OTIS-MULTI, allows for simulation of the cycling of multiple Se species in the river environment. Lastly, five best management practices (BMPs) were tested using MODFLOW-UZF and RT3D-UZF: improved irrigation efficiency (reduced irrigation), lining or sealing of canals to reduce seepage, lease fallowing of irrigated fields, improved fertilizer management (reduced fertilizer), and enhancement of riparian buffers. The impact of each of these BMPs on Se loading to the stream network was evaluated individually over three scenarios in which the adaption of each BMP is incrementally increased. In addition, various combinations of three and four BMPs were simulated and compared. Water samples gathered from the Arkansas River had total dissolved Se concentrations ranging from 6.1 to 32 μg/L (ICP method), compared to the Colorado chronic standard of 4.6 μg/L, while concentrations in samples gathered from tributaries ranged from 6.04 to 29 μg/L (ICP method). The groundwater and drinking water standard from the National Primary Drinking Water Regulations for selenium is 50 μg/L (USEPA, 2016). Concentrations of total Se (sorbed, reduced, and organic) in river bed sediments ranged from 0.16 to 0.36 μg/g with concentrations in river bank samples ranging from 0.26 to 1.78 μg/g. About 70 to 80% of Se in bed and bank sediments was found to be in a reduced or organic form. Analysis also reveals statistically significant high correlations of 0.70-1.00 between sorbed SeO3 (bed sediment (µg/g) and sorbed SeO4 (bed sediment) (µg/g); sorbed SeO3 (bed sediment (µg/g) and estimated precipitated and organic Se (bed sediment) (µg/g); sorbed SeO4 (bed sediment) (µg/g) and estimated precipitated and organic Se (bed sediment) (µg/g); ammonium (mg/L) and nitrite-nitrogen (NO2-N) (mg/L); NO3-N (mg/L) and total dissolved Se (µg/L); and sorbed SeO4 (bank sediment average (µg/g) and an estimate of precipitated and organic Se (bank sediment average) (µg/g). The conceptualization of key Se reactions was incorporated into OTIS-MULTI and must now be tested and calibrated for future application. The groundwater model results indicate that the individual BMP scenarios that most effectively decrease Se total mass loadings to the Arkansas River and its tributaries are: lease fallowing, resulting in a 15% decrease in predicted mass loading; reduced irrigation, with an 11% decrease; canal lining or sealing, with a 10% decrease; enhanced riparian buffer, with a 7% decrease; and reduced fertilizer, with a 3% decrease. In comparison, a BMP combination of lease fallowing, canal lining or sealing, enhanced riparian buffer, and reduced fertilizer was predicted to reduce loads by 46% and a combination of reduced irrigation, canal lining or sealing, enhanced riparian buffer, and reduced fertilizer by 44%. The hope, to be proven by future investigations, is that these reduced loads will contribute to lower concentrations in the river system.
Open Access
Assessing best management practices for the remediation of selenium in surface water in an irrigated agricultural river valley: sampling, modeling, and multi-criteria decision analysis
(Colorado State University. Libraries, 2016) Heesemann, Brent E., author; Gates, Timothy K., advisor; Bailey, Ryan T., advisor; Hoag, Dana L., committee member
The ecological impacts of selenium have been studied for decades and regulatory standards established in an effort to mitigate them. Agricultural activities in regions with high levels of alluvial selenium can lead to in-stream levels that far exceed regulatory limits. Agricultural best management practices (BMPs) are being considered to reduce in-stream selenium concentrations, but exploring the potential effectiveness of these BMPs can only be done after gaining an understanding of the in-stream processes that govern the speciation and transport of selenium in response to loading from irrigation return flows. This study uses extensive field data enhanced by numerical modeling to achieve this. In-stream water and sediment selenium samples, collected over a period of eight years in a region of Colorado’s Lower Arkansas River Valley, were analyzed. A sensitivity analysis (SA) was performed on a two part steady-state water quality / solute transport numerical model capable of simulating in-stream selenium processes. The combination of field data and SA was then used to calibrate an unsteady flow version of the model representative of the region to which it was applied. Dissolved and precipitated selenium species concentrations were accurately predicted by the calibrated model. Model simulations indicated that reduced fertilization is the BMP most effective at reducing in-stream SeO4 and NO3 concentrations out of the four BMPs examined. Reduced irrigation, land fallowing, and canal sealing indicated increases in in-stream SeO4 concentrations, likely caused by a concentration of SeO4 in the adjacent aquifer. Model results also indicated that the tributaries are impacted more by surface runoff as compared to lateral groundwater flows, while the opposite is true for the River. Although reasonable results were obtained from the model, further investigation into the computational processes and calibrated parameter values is required as part of future work. This study also examines the socio-economic feasibility of various BMPs, through the issuing survey to stakeholders in the study region and its evaluation using analytic hierarchy process multi-criteria decision analysis (MCDA). Reduced irrigation was determined to be the most feasible BMP based on the MCDA, with stakeholders showing a clear preference for economic concerns and placing a higher importance on salinity over SeO4 or NO3 concentrations. With model results indicating the effectiveness of various BMPs, and MCDA survey results providing insight into which of the BMPs are most likely to be accepted by stakeholders, it was possible to assess which BMPs are most appropriate for implementation in this study region. In considering both the results from the modeling study and the MCDA, it was determined that reduced fertilization is likely the single best BMP. To date there have been few if any studies utilizing both field data, numerical modeling, and MCDA to so comprehensively describe in-stream selenium processes and the future prospects for selenium remediation in an agricultural region in the western United States.
Open Access
Assessing groundwater storage and groundwater level fluctuations in the area of Fort Collins, Colorado
(Colorado State University. Libraries, 2018) Almahawis, Mohammed, author; Bailey, Ryan T., advisor; Scalia, Joseph, IV, committee member; Sanford, William E., committee member
Although groundwater is the main water supply for many municipalities worldwide, shallow groundwater can adversely affect urban areas via soil waterlogging and impacts on building foundations and general city infrastructure. A quantitative assessment of groundwater levels and temporal fluctuations is needed to determine the extent to which groundwater should be managed to prevent these adverse conditions. This thesis assesses past and current groundwater storage and groundwater levels in the city limits of Fort Collins, Colorado, a moderate-sized municipality situated in the Front Range of the Rocky Mountains in the western United States. Currently, Fort Collins uses only surface water for its water supply, with the underlying unconfined alluvial aquifer mostly unused and close to ground surface. The assessment includes developing quantitative groundwater maps (depth to water table, water table elevation, and saturated thickness), estimating groundwater recharge and change in storage during large rainfall events, and defining areas with risk of high groundwater level. Observed depth to water table data from various sources was collected for two-time frames (1959-1979 and 2000-2017). The Stanford Geostatistical Modeling Software (SGeMS) was used to interpolate soil and groundwater data, and a Geographic Information System (GIS) was used to develop maps, estimate the storage, and define areas with potential risk of high groundwater level. Also, the Natural Resources Conservation Service's (NRCS) curve number method was performed to quantify recharge from high-intensity rainfall events. NRCS curve number method is a widely used method to quantify the amount of runoff due to a rainfall event. Comparing results from the two-time frames, the depth to water table in the study area has increased slightly (0.32 m) with a 3.9 m current average depth to the water table. Storage has decreased from 126.8 million m3 to 122 million m3, largely due to pumping groundwater for irrigation in the northeast area of the city limits. Approximately 10% of parcels in the Fort Collins area are at risk of high groundwater level. Most parcels along the Cache La Poudre River have problems with high groundwater level. The amount of recharge to the shallow aquifer in the Fort Collins area due to 10 and 100-year return-period storms is approximately equal to 1.9 million m3 and 3.3 million m3, respectively. Also, the percentage of the parcels at risk of high groundwater table will increase to 11% and 12%, respectively. The resulting groundwater maps, and the response of water table to rainfall events, can assist city water managers with identifying areas of potential risk to shallow groundwater conditions. In addition, the methods applied in this thesis can be used for other urban areas containing a shallow alluvial aquifer.
Open Access
Assessing irrigation-influenced groundwater flow and transport pathways along a reach of the Arkansas River in Colorado
(Colorado State University. Libraries, 2016) Criswell, David Todd, author; Gates, Timothy K., advisor; Bailey, Ryan T., advisor; Covino, Timothy P., committee member
Recent studies have concluded that stream reaches are not simply gaining or losing to groundwater but are best described as a mosaic of exchanges that contrast between flowpaths of varying lengths and directions which inherently influence solute residence times. These residence times directly affect chemical speciation of solutes such as salts, nitrate, selenium, and uranium and have the opportunity to undergo microbial dissimilatory reduction in the shallow riparian zone and the deeper sub-surface. To improve water quality and the overall health of these natural systems requires engineering intervention supported by reliable data and calibrated models. A three-dimensional numerical flow model (MODFLOW-UZF2) is used to simulate unsaturated and saturated groundwater flow, with linkage to a streamflow routing model (SFR2), for a 5-km reach of the Arkansas River near Rocky Ford, Colorado. The reach-scale model provides increased discretization of previous regional-scale models developed for the Arkansas River Basin, using 50 x 50 m grid cells and dividing the Quaternary alluvium that represents the unconfined aquifer into 10 layers. This discretization facilitates an enhanced view of groundwater pathways near the river which is essential for future solute transport evaluation and for consideration of alternative best management practices. Model calibration is performed on hydraulic conductivity (K) in the upper three layers, K in the lower seven layers, and specific yield (Sy) of the entire aquifer by applying an Ensemble Kalman Filter (EnKF) using observed groundwater hydraulic head and stream stage data. The EnKF method accounts for uncertainty derived from field measurements and spatial heterogeneity in parameters calibrated using a Monte-Carlo based process to produce 200 realizations in comparison to error-prone measurements of hydraulic groundwater hydraulic head and stream stage as calibration targets. The calibrated transient model produced Nash-Sutcliffe Efficiency (NSE) values of 0.86 and 0.99, respectively, for the calibration and evaluation periods for calibration targets using the ensemble mean of realizations. Realizations of calibrated parameters produced by the EnKF exhibit the equally-likely spatial distributions of aquifer flow and storage characteristics possible in the area, while MODPATH simulations display the associated groundwater flowpaths possible under such conditions. The mean residence time of a stream-destined fluid particle within the riparian zone was estimated as 1.8 years. Simulated flowpaths to the stream were highly variable given different geologic conditions produced by EnKF, with flowpaths to some stream reaches differing in direction as much as approximately 90° and transit times differing sometimes by decades. The simulated average annual groundwater return flow to the stream was 70 m3 d-1. Simulated average annual return flow was highly variable along the study reach and ranged from -250 to a little over 250 m3 d-1 with a CV of 1.4. The mean percentage of shallow (within the top three model layers) groundwater return flow to flow in aquifer layers beneath the stream was 27% with a CV of 0.58. Simulated groundwater flowpaths were superimposed upon a map of shallow shale units residing in the study region, demonstrating how groundwater flowpaths may interact with regional seleniferous shale layers. Results hold major implications for biogeochemical processes occurring in the sub-surface of the riparian area and the hyporheic zone that have an important influence on solute concentrations. Results may be used to aid decision makers in the implementation of best management practices and to further understand contaminant sources and fate.
Open Access
Assessing long-term conservation of groundwater resources in the Ogallala Aquifer Region using hydro-agronomic modeling
(Colorado State University. Libraries, 2022) Xiang, Zaichen, author; Bailey, Ryan T., advisor; Niemann, Jeffrey, committee member; Bhaskar, Aditi, committee member; Suter, Jordan, committee member
Groundwater is vital for domestic use, municipalities, agricultural irrigation, industrial processes, etc. Over the past century, excessive groundwater depletion has occurred globally and regionally, notably in arid and semi-arid regions, often due to providing irrigation water for crop cultivation. The High Plains Aquifer (HPA) is the largest freshwater aquifer in the United States and has experienced severe depletion in the past few decades due to excessive pumping for agricultural irrigation. There is a need to determine management strategies that conserve groundwater, thereby allowing irrigation for coming decades, while maintaining current levels of crop yield within the context of a changing climate. Numerical models can be useful tools in this effort. Hydrologic models can be used to assess current and future storage of groundwater and how this storage depends on system inputs and outputs, whereas agronomic models can be used to assess the impact of water availability on crop production. Linking these models to jointly assess groundwater storage and crop production can be helpful in exploring management practices that conserve groundwater and maintain crop yield under future possible climate conditions. The objectives of this dissertation are: i) to develop a linked modeling system between DSSAT, an agronomic model, and MODFLOW, a groundwater flow model to be used for evaluating long-term impacts of climate and management strategies on water use efficiency and farm profitability of agricultural systems while managing groundwater sustainably; ii) to use the DSSAT-MODFLOW modeling system in a global sensitivity analysis framework to determine the system factors (climate, soil, management, aquifer) that control crop yield and groundwater storage in a groundwater-stressed irrigated region, thereby pointing to possibilities of efficient management; and iii) to quantify the effect of groundwater conservation strategies and climate on crop yield and groundwater storage to identify irrigation and planting practices that will maintain adequate crop yield while minimizing groundwater depletion. These three objectives are applied to the hydro-agronomic system of Finney County, Kansas, which lies within the HPA. Major findings include: 1) climate-related parameters significantly affect crop yields, especially for maize and sorghum, and soybean and winter wheat yields are sensitive to a combination of cultivar genetic parameters, soil-related parameters, and climate-related parameters; 2) Climatic parameters account for 44%, 29%, 40%, and 36% variation in yield of maize, soybean, winter wheat, and sorghum; 3) Hydrogeologic parameters (aquifer hydraulic conductivity, aquifer specific yield, and riverbed conductance) have a relatively low influence on crop yields; 4) water table elevation, recharge, and irrigation pumping are considerably sensitive to soil- and climate-related parameters, while ET, river leakage, and groundwater/aquifer discharge are highly influenced by hydrogeological parameters (e.g., riverbed conductance, and specific yield); 5) the best management practice is the combination of implementing drip irrigation and planting quarter plots under both dry and wet future climate conditions. Other irrigation systems (sprinkler) and planting decisions (half-plots) can also be implemented without severe groundwater depletion. If crop yield is to be maintained in this region of the HPA, groundwater depletion can be minimized but not completely prevented. Results highlight the need for implementing new irrigation technologies, and likely changing crop type decisions (e.g., limiting corn cultivation) in coming decades in this region of the HPA. Results from this dissertation can be used in other groundwater-irrigated regions facing depletion of groundwater.
Open Access
Comparison of the Glover-Balmer solution with a calibrated groundwater model to estimate aquifer-stream interactions in an irrigated alluvial valley
(Colorado State University. Libraries, 2014) Mages, Cale A., author; Gates, Timothy K., advisor; Bailey, Ryan T., advisor; Sanford, William E., committee member
In many alluvial valleys wherein streams are hydraulically connected to the aquifer system, understanding and quantifying the impact of aquifer stresses (e.g. pumping, injection, recharge) on streamflow is of primary importance. Due to their relative simplicity and straightforward application, analytical models such as the Glover-Balmer solution often are employed to quantify these impacts. However, the predictive capacity of such models in intensively-irrigated systems, wherein canals, spatially-varying irrigation application patterns, and spatially-variable aquifer characteristics are often present, is not well known. In this study, the Glover-Balmer solution is compared to a calibrated MODFLOW-UZF numerical model for a study area within the Lower Arkansas River Valley in southeastern Colorado, USA. Comparison is made by simulating field-scale water extraction, addition, and fallowing scenarios, and comparing the predictions by both models of stream depletion or accretion. To create an ideal comparison, inputs to the Glover-Balmer model (stress, aquifer parameters) are obtained from the calibrated numerical model. Results for a few fallowing scenarios and from 52 extraction and addition scenarios from a variety of distances from the Arkansas River show that, under certain circumstances, the two models have good agreement in results, particularly in regions close (< about 0.5 to 1 km) to the river. However, due to aquifer heterogeneity and the overall hydrologic complexity in the natural system, results of the two models often diverge, with the Glover-Balmer model typically estimating greater impacts on the stream than the MODFLOW-UZF model. Suggested considerations are given for applying the Glover-Balmer solution, including the consideration of hydrologic components that may intercept or contribute to groundwater flow (such as irrigation canals, upflux to ET, groundwater storage, and tributaries), the potential influence of unsaturated zone processes, and changes in depletion/accretion locations and timing due to aquifer heterogeneity.
Open Access
Enhancement of coupled surface / subsurface flow models in watersheds: analysis, model development, optimization, and user accessibility
(Colorado State University. Libraries, 2018) Park, Seonggyu, author; Bailey, Ryan T., advisor; Grigg, Neil S., committee member; Ronayne, Michael J., committee member; Sale, Thomas, committee member
To view the abstract, please see the full text of the document.
Open Access
Evaluating surface water–groundwater interactions in floodplains using SWAT+ and gwflow
(Colorado State University. Libraries, 2023) Schulz, Evan, author; Morrison, Ryan R., advisor; Bailey, Ryan T., advisor; Wohl, Ellen, committee member
Floodplains are essential ecosystems that provide a variety of economic, hydrologic, and ecologic services. Within floodplains, surface water-groundwater exchange plays an important role in facilitating biogeochemical processing and can have a strong influence on hydrology through infiltration or discharge of water. These functions can be difficult to assess due to the heterogeneity of floodplains and monitoring constraints, so numerical models are useful tools to estimate fluxes, especially at a large scale. In this study, the gwflow module of the SWAT+ (Soil and Water Assessment Tool) ecohydrological model quantified magnitudes and spatiotemporal patterns of floodplain surface water-groundwater exchange in a mountainous watershed using an updated version of the module that directly calculated floodplain-aquifer interactions during periods of floodplain inundation. The gwflow module is a spatially distributed groundwater modeling subroutine within the SWAT+ code that uses a gridded network and physically based equations to calculate groundwater storage, groundwater head, and groundwater fluxes. I used SWAT+ to model an area of 7,516 km2 in the Colorado Headwaters HUC8 watershed (14010001) and used streamflow data from USGS gages in the watershed for calibration and testing. I evaluated model performance for scenarios with and without simulated floodplain-groundwater exchange and for three gwflow grid cell sizes. Models that included floodplain-groundwater interactions outperformed those without such interactions and provided valuable information about floodplain inundation and exchange rates. Furthermore, I found that smaller gwflow cell sizes showed similar or better performance than larger cell sizes and simulated additional information about local variations in groundwater fluxes, especially within floodplains. Finally, my analyses on the location of floodplain fluxes in the watershed showed that wider areas of floodplains, "beads," exchanged a higher net and per area volume of water, as well as higher rates of exchange, than narrower areas, "strings." These outputs remained consistent across all studied cell sizes, with smaller cells simulating greater differences between bead and string floodplain regions. Study results show that floodplain surface water-groundwater exchange is a valuable process to include in hydrologic models, and model outputs could inform land conservation practices by indicating priority locations where substantial hydrologic exchange occurs.
Open Access
Finding water management practices to reduce selenium and nitrate concentrations in the irrigated stream-aquifer system along the lower reach of Colorado's Arkansas River Valley
(Colorado State University. Libraries, 2018) Qurban, Ibraheem A., author; Bailey, Ryan T., advisor; Gates, Timothy K., advisor; Suter, Jordan F., committee member
Agricultural productivity in the Lower Arkansas River Valley (LARV) in southeastern Colorado has been high over the last 100 years due to extensive irrigation practices. In the face of this high productivity, however, the LARV currently face many issues as a result of the long period of irrigation, including waterlogging and soil salinization, leading to a decline in crops yields and high concentrations of nutrients and trace elements. In particular, irrigation practices have led to high concentrations of selenium (Se) and nitrate (NO3) in groundwater, surface water, and soils, similar to other semi-arid irrigated watersheds worldwide. Environmental concerns due to these high concentrations include human health, health of fish and waterfowl, and eutrophication of surface water bodies. The objective of this thesis is to identify water management strategies that can lead to a decrease in the concentrations of Se and NO3 in groundwater and surface water in the LARV by evaluating the three-water management BMPs which is reduced irrigation (RI), lease fallowing of irrigated land (LF), and canal sealing (CS). This is accomplished by constructing and testing a computational model that simulates the fate and transport of Se and NO3 in a coupled irrigated stream-aquifer system, and then applying the model to evaluate selected best management practices (BMPs) to decrease the concentration of Se and NO3 to comply with Colorado water quality regulations. The modeling system consists of MODFLOW, which simulates groundwater and stream flow, and RT3D-OTIS, which simulates the reactive transport of the principal Se and nitrogen (N) species in groundwater and a connected stream network. RT3D-OTIS uses simulated flows from MODFLOW to exchange Se and N species' mass between streams and the aquifer on a daily time step. The coupled flow and reactive transport model is applied to an approximately 552 km² study region in the LARV between Lamar, Colorado and the Colorado-Kansas border. The model is tested against Se and NO3 concentrations measured in a network of groundwater monitoring wells and stream sampling site, and against return flows and mass loads to the river estimated from the mass balance. Model calibration was performed manually and by using PEST software tool, and the effects BMPs on Se and NO3 concentrations in groundwater, streams, and groundwater mass loadings to the Arkansas River within the stream-aquifer system are quantified. Three BMPs are considered RI, LF, and CS, which are simulated for a 40-year period and then compared to a baseline ("do nothing") scenario. The results indicate that implementation of the CS scenario might lead to lower groundwater concentrations of Se and NO3 by 40% and 38%, respectively, a reduction in groundwater mass loading to the Arkansas River by 100% and 60% for Se and NO3, and a reduction in stream concentrations of Se and NO3 by 30% and 40%, respectively. In contrast, the RI and LF scenario, while lowering the water table and in consequence the rate of groundwater return flow to the Arkansas River, leads to elevated groundwater concentrations of both Se and NO3 in the riparian areas, resulting in an overall increase in groundwater mass loading to the river. This may be due to changes in the rate of groundwater flow due to lower hydraulic gradients leading to longer residence times of NO3 in the aquifer, increasing the potential for the release of Se from the bedrock shale through oxidation processes. Also, lowering the water table due to reduced recharge from irrigation reduces the size of the saturated zone, perhaps contributing to a higher concentration of Se and NO3. Moreover, changes in water and mass flux between the saturated and unsaturated zone occur under RI and LF scenarios. As a consequence of these altered processes, the RI and LF scenarios do not decrease the in-stream concentrations of Se and NO3 in the Arkansas River, with values for Se and NO3 increasing by 15% and 8%, respectively under the RI scenario, and by 10% and 10.5% for the LF scenario. Further, the results are compared with results obtained from a modeling study in the Upstream Study Region of the Lower Arkansas River Valley, to determine the similarity and differences of BMP implementation in the two regions. Further assessment of localized BMPs should be performed to determine key regions where they should be implemented for the largest impact on Se and NO3. Combined water management BMPs and land management BMPs, like reduced fertilizer application and enhanced riparian buffers, should also be evaluated.
Open Access
High groundwater in irrigated regions: model development for assessing causes, identifying solutions, and exploring system dynamics
(Colorado State University. Libraries, 2021) Deng, Chenda, author; Bailey, Ryan T., advisor; Grigg, Neil, committee member; Niemann, Jeffrey, committee member; Paustian, Keith, committee member
Waterlogging occurs in irrigated areas around the world due to over-irrigation and lack of adequate natural or artificial drainage. This phenomenon can lead to adverse social, physical, economic, and environmental issues, such as: damage to crops and overall land productivity; soil salinization; and damage to homes and building foundations. Solutions to waterlogging include implementation of high-efficient irrigation practices, installation of artificial drainage systems, and increased groundwater pumping to lower the water table. However, in regions governed by strict water law, wherein groundwater pumping is constrained by impact on nearby surface water bodies, these practices can be challenging to implement. In addition, current engineering and modeling approaches used to quantify soil-groundwater and groundwater-surface water interactions are crude, perhaps leading to erroneous results. An accurate representation of groundwater state variables, groundwater sources and sinks, and plant-soil-water interaction is needed at the regional scale to assist with groundwater management issues. This dissertation enhances understanding of major hydrological processes and trade-offs in waterlogged agricultural areas, through the use of numerical modeling strategies. This is accomplished by developing numerical modeling tools to: (1) analyze and quantify the cause of high groundwater levels in highly managed, irrigated stream-aquifer systems; (2) assess the impact of artificial recharge ponds on groundwater levels, groundwater-surface water interactions, and stream depletions in irrigated stream-aquifer systems; (3) and gain a better understanding of plant-soil-water dynamics in irrigated areas with high water tables. These objectives use a combination of agroecosystem (DayCent) and groundwater flow (MODFLOW) models, sensitivity analysis, and management scenario analysis. Each of these sub-objectives is applied to the Gilcrest/LaSalle agricultural region within the South Platte River Basin in northeast Colorado, a region subject to high groundwater levels and associated waterlogging and infrastructure damage in the last 7 years. This region is also subject to strict water law, which constrains groundwater pumping due to the effect on the water rights of the nearby South Platte River. Results indicate that recharge from surface water irrigation, canal seepage, and groundwater pumping have the strongest influence on water table elevation, whereas precipitation recharge and recharge from groundwater irrigation have small influences from 1950 to 2012. Mitigation strategy implementation scenarios show that limiting canal seepage and transitioning > 50% of cultivated fields from surface water irrigation to groundwater irrigation can decrease the water table elevation by 1.5 m to 3 m over a 5-year period. Decreasing seepage from recharge ponds has a similar effect, decreasing water table elevation in local areas by up to 2.3 m. However, these decreases in water table elevation, while solving the problem of high groundwater levels for residential areas and cultivated fields, results in a decrease in groundwater discharge to the South Platte River. As the intent of the recharge ponds is to increase groundwater discharge and thereby offset stream depletions caused by groundwater pumping, mitigating high water table issues in the region can be achieved only by (1) modifying fluxes of sources and sinks of groundwater besides recharge pond seepage, or (2) modifying or relaxing the adjudication of water law, which dictates the need for offsetting pumping-induced stream depletion, in this region. The modeling tools developed in this dissertation, specifically the loose and tight coupling between DayCent and MODFLOW, can be used in the study region to quantify pumping-induced stream depletion, recharge pond induced stream accretion, and the interplay between them in space and time. In addition, these models can be used in other irrigated stream-aquifer systems to assess baseline conditions and explore possible effects of water management strategies.
Open Access
Improved assessment of nitrogen and phosphorus fate and transport for intensively managed irrigated stream-aquifer systems
(Colorado State University. Libraries, 2019) Wei, Xiaolu, author; Bailey, Ryan T., advisor; Arabi, Mazdak, committee member; Gates, Timothy K., committee member; Covino, Timothy, committee member
Nitrogen (N) and Phosphorus (P) are essential elements for animal nutrition and plant growth. However, over the previous decades, excessive loading of fertilizers in agricultural activities has led to elevated concentrations of N and P contaminations in surface waters and groundwater worldwide and associated eutrophication. Therefore, precisely understanding and representation of water movement and fate and transport of N and P within a complex dynamic groundwater-surface water system affected by agricultural practices is of essential importance for sustaining ecological health of the stream-aquifer environment while maintaining high agricultural productivity. Modeling tools often are used to assess N and P contamination and evaluate the impact of management practices. Such models include land surface-based watershed models such SWAT, and aquifer-based models that simulate spatially-distributed groundwater flow. However, SWAT simulates groundwater flow in a simplistic fashion and therefore is not suited for watersheds with complex groundwater flow patterns and groundwater-surface interactions, whereas groundwater models do not simulate land surface processes. This dissertation establishes the modeling capacity for assessing the movement, transformation, and storage of nitrate (NO₃) and soluble P in intensively managed irrigated stream-aquifer systems. This is accomplished by (1) developing a method to apply the SWAT model to such a system, and includes: designating each cultivated field as an individual hydrologic response unit (HRU), crop rotations to simulate the impact of changing crop types for each cultivated field, including N and P mass in irrigation water, and seepage from earthen irrigation canals into the aquifer; (2) simulating land surface hydrology, groundwater flow, and groundwater-surface water interactions in the system using the coupled flow model SWAT-MODFLOW, with the enhanced capability of linkage between SWAT groundwater irrigation HRUs and MODFLOW pumping cells, and the use of MODFLOW's EVT package to simulate groundwater evapotranspiration; and (3) linking RT3D, a widely used groundwater reactive solute transport model, to SWAT-MODFLOW to credibly represent of NO₃-N and soluble P fate and transport processes in irrigated agroecosystems to evaluate best management practices for nutrient contamination. This last phase will also address the uncertainty in system output (in-stream nutrient loads and concentrations, groundwater nutrient concentrations model predictions). Each modeling phase is applied to a 734 km² study region in the Lower Arkansas River Valley (LARV), an alluvial valley in Colorado, USA, which has been intensively irrigated for over 130 years and is threatened by shallow water tables and nutrient contamination. Multiple best management practices (BMPs) are investigated to analyze the effectiveness in reducing NO₃-N and soluble P contamination in the LARV. These strategies are related to irrigation management, nutrient management, water conveyance efficiency, and tillage operations. The most effective individual BMP in most areas is to decrease fertilizer by 30%, resulting in average NO₃-N and soluble P concentrations within the region could be reduced by 14% and 9%, respectively. This individual BMP could lower the average NO₃-N concentrations by 19% and soluble P concentrations by 2%. Combinations of using 30% irrigation reduction, 30% fertilization reduction, 60% canal seepage, and conservation tillage are predicted to have the greatest overall impact that can not only provide a decrease of groundwater concentration in NO₃-N up to 41% and soluble P concentration up to 8%, but also reduce the median of the in-stream NO₃-N and soluble P to meet the Colorado interim standard. As nutrient conditions within the Lower Arkansas River Valley are typical of those in many other intensively irrigated regions, the results of this dissertation and the developed modeling tools can be applied to other watersheds worldwide.
Open Access
Investigating best management practices to reduce selenium and nitrate contamination in a regional scale irrigated agricultural groundwater system: Lower Arkansas River Valley, southeastern Colorado
(Colorado State University. Libraries, 2015) Tummalapenta, Ravi Kumar, author; Bailey, Ryan T., advisor; Gates, Timothy K., committee member; Venayagamoorthy, Subhas K., committee member; Bauder, Troy A., committee member
The Lower Arkansas River Valley (LARV) is well known for its rich agricultural production, with 109,000 ha of irrigated area. Due to agricultural production extending for more than 100 years, the LARV now faces challenges of soil salinity, water logging from shallow groundwater tables, and a high concentration of selenium (Se, both within the alluvial aquifer system and within the Arkansas River and its tributaries). Se originates primarily from bedrock and outcropped marine shale, released due to chemical oxidation in the presence of dissolved oxygen and nitrate. Se is a dynamic element that is biologically essential for plants, animals and humans. However, it is known that Se can be harmful at elevated concentrations. Therefore, elevated concentration levels in the surface water and groundwater in the LARV are considered problematic, and methods must be found to decrease groundwater concentrations and Se loadings from the aquifer to the Arkansas River. This thesis assesses plausible methods that will decrease Selenium (Se) contamination in groundwater and surface water in the LARV. Best management practices (BMPs) to reduce selenium and nitrate mass loadings to the River Arkansas in a 55,200 ha area downstream of John Martin reservoir in the LARV were explored and analyzed using 18 scenarios. The UZF-MODFLOW and UZF-RT3D numerical models, calibrated against extensive sets of field data in the region, were used to simulate groundwater flow and the physical and chemical processes governing the fate and transport of Se and N species. Specific BMPs include reduction in the seasonal application of N fertilizer; decrease in concentration of selenate (CSeO4) and nitrate (CNO3) in canal water, representing treatment of water before application as irrigation water; reduction in irrigation application volumes; and combinations of these practices, along with fallowing of irrigated land. These practices are applied for a long term period (40 years) to observe the effects of each BMP on groundwater CSeO4 and CNO3 and on mass loadings from the aquifer to the Arkansas River. The BMPs are applied at varying levels: less aggressive (20%) to very aggressive (40%) of each practice. Results indicate that the highest aggressive combined scenario 40% reduction in N fertilizer reduction, 40% reduction in canal concentration, and 35% reduction in irrigation volume, with 25% irrigated land fallowing result in the highest decrease of mass loadings of SeO4 into the Arkansas River with 22.7%, followed by the less aggressive and highest aggressive combined scenarios of N fertilizer reduction, canal concentration reduction, and irrigation volume reduction with land fallowing showing decrease of mass loadings from 15% to 21%. For individual scenarios: the irrigation volume reduction scenario (13.1% to 13.4%) is followed by the canal concentration reduction scenario (3% to 6%); whereas the N fertilizer reduction scenario shows a minimum percent reduction (1.5% to 2.7%) as compared to the Baseline (“do-nothing” scenario). Similarly for NO3, results show that the highest aggressive combined scenario 40% reduction in N fertilizer reduction, 40% reduction in canal concentration, and 35% reduction in irrigation volume, with 25% irrigated land fallowing result in the highest decrease of mass loadings of NO3 to the Arkansas River with 34.7% followed by the less aggressive and very aggressive combined scenarios of N fertilizer reduction, canal concentration reduction, and irrigation volume reduction with land fallowing showing reduction of mass loadings from 15.5% to 30%. The results of individual BMPs is as follows: 35% irrigation volume reduction scenario (14.9%) is followed by 40% N fertilizer reduction scenario (14.5%); 20% irrigation volume reduction scenario (12%); 20% N fertilizer reduction scenario (8.3%); whereas 20% and 40% canal concentration reduction scenarios show minimum percent reduction (0.6% to 1.1%). The results are compared with results from a similar study recently performed in the Upstream Study Region of the LARV to observe the differences in BMP practices and their reduction of Se contamination in the study areas.
Open Access
Investigating the salinity impacts on current and future water use and crop production in a semi-arid agricultural watershed
(Colorado State University. Libraries, 2024) Hosseini Ghasemabadian, Pardis, author; Bailey, Ryan T., advisor; Arabi, Mazdak, committee member; Smith, Ryan, committee member; Andales, Allan, committee member
Soil salinity can have a significant impact on agricultural productivity and crop yield, particularly in arid and semi-arid irrigated watersheds wherein irrigation and inadequate drainage often combine to increase salt ion concentrations in soil water. In conjunction with intense irrigation in semi-arid agricultural regions, increasing population resulting in boosted water demand, adverse impacts of climate change on water availability, in other words, water scarcity, future land use and land cover changes, changes in applied irrigation practices, and introducing new point-sources and non-point sources of salinity in the region all can govern the salinity and crop yield consequently. Taking into account the aforementioned impactful components on crop reduction via salinity increase, the overall objective of this dissertation is to provide insights for policymakers to better address the current and future salinity issues to sustain crop production in semi-arid regions under progressive salinity. This will be accomplished by i) investigating the controlling factors on salinity in the soil, groundwater, and river water using the SWAT-Salt model which simulates the reactive transport of 8 major salt ions in major hydrological pathways applied to a 1118 km2 irrigated stream-aquifer system located within the Lower Arkansas River Valley (LARV) in southeastern Colorado, USA ii) Assessing the salinity impacts on crops production blue and green water footprint as a measurable indicator for water being used per unit of a given crop production using the SWAT-MODFLOW-Salt model applied to a 732 km2 irrigated stream-aquifer system located in the LARV, iii) quantify the impact of environmental factors alteration including changes in climatic and irrigation practices in the LARV on future salinity content and its impact on crop production in the region using the SWAT-MODFLOW-Salt model. To control salinity, more importantly in semi-arid irrigated areas, the principal step is to identify the key environmental and hydrologic factors that govern the fate and transport of salts in these irrigated regions. To accomplish this objective, global sensitivity analysis was applied to the newly developed SWAT-Salt model (Bailey et al., 2019), which simulates the reactive transport of 8 major salt ions (SO4, Ca, Mg, Na, K, Cl, CO3, and HCO3) in major hydrologic pathways in a watershed system. The model was applied to a saline 1118 km2 irrigated stream-aquifer system located within the Lower Arkansas River Valley in southeastern Colorado, USA. Multiple parameters including plant growth factors, stream channel factors, evaporation factors, surface runoff factors, and the initial mass concentrations of salt minerals MgSO4, MgCO3, CaSO4, CaCO3, and NaCl in the soils and in the aquifer were investigated for control on salinity in groundwater, soils, and streams. The Morris screening method was used to identify the most sensitive factors, followed by the Sobol' variance-based method to provide a final ranking and to identify interactions between factors. Results showed that salt ion concentration in soils and groundwater was controlled principally by hydrologic factors (evaporation, groundwater discharge and up flux, and surface runoff factors) as well as the initial amounts of salt minerals in soils. Salt concentration in the Arkansas River was governed by similar factors, likely due to salt ion mass in the streams controlled by surface runoff and groundwater discharge from the aquifer. Sustainable agriculture in intensively irrigated watersheds, especially those in arid and semi-arid regions, requires improved management practices to sustain crop production. This depends on factors such as climate, water resources, soil conditions, irrigation methods, and crop types. Of these factors, soil salinity and climate change are significant challenges to agricultural productivity. To investigate the long-term impact of salinity and climate change on crop production from 1999 to 2100 in irrigated semi-arid regions, we applied the water footprint (WF) concept using the hydro-chemical watershed model SWAT-MODFLOW-Salt, driven by five General Circulation Models (GCMs) and two climate scenarios (RCP4.5 and RCP8.5), to a 732 km2 irrigated stream-aquifer system within the Lower Arkansas River Valley (LARV), Colorado, USA. In this study we estimated the green (WFgreen), blue (WFblue), and total (WFtotal) crop production WFs for 29 crops in the region, both with and without considering the impact of salinity on crop yield. The results indicate that during the baseline period (1999-2009), the total annual average WFgreen, WFblue, and WFtotal increased by 7.6%, 4.4%, and 6.5%, respectively, under salinity stress, with crop yields decreasing by up to 4.6%, 1.6%, and 2.3% for green, blue, and total crop yield. The combined impact of salinity and the worst-case climate model (IPSL_CM5A_MR) under the higher emission scenario (RCP8.5) resulted in increases of 3.3%, 1.9%, and 3% in green, blue, and total crop production WFs. Additionally, the study found that the proportion of green, blue, and total crop production WFs in the LARV exceeded the world average. This discrepancy was attributed to various factors, including different spatial and temporal crop distribution, irrigation practices, soil types, and climate conditions. Notably, salinity stress had a more significant impact on green crop yield and green WF compared to blue crop yield and blue WF across all GCM models. This finding highlights the need to prioritize management practices that address salinity-associated challenges in the region. The adverse effects of salinity on soil health, crop yield, and environmental ecosystem require comprehensive strategies for managing salinity in agricultural watersheds by adopting improved irrigation practices and effective salinity management strategies for mitigating these impacts and sustaining agricultural productivity in salinity-affected regions. The complex dynamics between various irrigation practices and soil salinity play a pivotal role in shaping agricultural productions and managing soil salinity. In semi-arid regions like the LARV, salinity poses a significant threat to agriculture, exacerbated by climate change and historic irrigation practices. To evaluate the interplay between salinity, climate change, and irrigation management in affecting crop yields within the Lower Arkansas River Valley (LARV), focusing on corn and alfalfa, we utilized the SWAT-MODFLOW-Salt model to examine how changes in irrigation management influence crop production under various scenarios projected through the year 2100. This study addresses the differential responses of corn and alfalfa to the impact of incremental increases and reductions in irrigation efficiency and irrigation water loss (5%, 10%, 15%, and 20%) on corn and alfalfa yields dynamics under salinity stress, utilizing projections from five global climate models under two distinct Representative Concentration Pathway (RCP) scenarios, RCP4.5 and RCP8.5 and two irrigation scenarios. The findings from irrigation practice scenario (1), maintaining a constant amount of irrigation water, revealed that corn yields improved by up to 13.8% under salinity stress and 16.5% under non-salinity conditions with a 20% increase in irrigation efficiency and a 20% reduction in water loss under RCP4.5. Alfalfa, demonstrating greater salinity tolerance, showed similar benefits, with yield increases of 9.1% under salinity stress and even higher improvements under non-salinity conditions. These results highlight the effectiveness of tailored irrigation practices in mitigating environmental stresses. In contrast, scenario (2), which involved reducing irrigation water by half, resulted in more pronounced negative outcomes. Corn yields exhibited greater sensitivity to salinity stress, with yield reductions ranging from -9.8% under salinity stress to -9.3% under non-salinity conditions, particularly under the RCP8.5 scenario. Alfalfa yields also declined, though less severely than corn, with reductions ranging from -8.9% under salinity stress to -8.3% under non-salinity conditions. Despite improvements in irrigation efficiency and reduced water loss, the adverse effects of salinity stress were not fully mitigated in scenario (2), emphasizing the need for adequate water availability to sustain crop yields under salinity and climate change pressures. The research highlights the importance of adopting advanced irrigation technologies and practices that not only counteract the adverse effects of salinity but also adapt to evolving climatic conditions. This study offers valuable insights for policymakers and agricultural managers on strategic water resource management to sustain crop yields in salinity-affected and water-limited agricultural systems. The results of this study can be used in decision-making regarding the most impactful land and water management strategies for controlling salinity transport and build-up in soils, both for this watershed and other similar semi-arid salinity-impacted watersheds for present and future purposes.
Open Access
Modeling artificial groundwater recharge and low-head hydroelectric production: a case study of southern Pakistan
(Colorado State University. Libraries, 2016) Siddiqui, Rafey Ahmed, author; Bailey, Ryan T., advisor; Grigg, Neil S., committee member; Sale, Thomas, committee member; Sanford, William, committee member
DHA City Karachi (DCK), a city designed for approximately one million people, is envisaged to become a satellite city to the second largest city in the world, Karachi, which has a population of 25 million. The upcoming city is located 21 miles north of main metropolitan Karachi in the arid southern part of Pakistan. The region receives little rainfall with an annual average of 217 mm and temperatures ranging from an average of 88°F in the summers to 68°F in the winters. The town has a projected water demand in the fully developed stage of 45 Million Gallons per Day (MGD) and 500 Mega Watts (MW) of electricity. Since water and electricity are prized and expensive commodities in the region, alternate and renewable sources of both need to be explored for DCK to meet its goal of sustainability and conservation. Two options for these sources, artificial recharge and hydroelectric product, are explored in this study. Artificial recharge to replenish groundwater resources is becoming more common in arid areas. In this thesis, the capacity of small lakes to produce significant seepage and recharge to the underlying aquifer within city limits is explored for DCK. The lakes are fed by treated effluent from Sewage Treatment Plants (STP), which then ponds and creates downward seepage to the water table. Artificial recharge and resulting groundwater flow within the aquifer is simulated using a three-dimensional groundwater flow model (MODFLOW). A variety of pumping scenarios are explored to determine the quantity of groundwater that can be pumped for water supply. An optimal placement of 50 pumps throughout the city also is determined, with drawdown used as the variable to be minimized so as to minimize pumping costs. In the fully developed stage of artificial recharge, the lakes feed almost 7.9 MGD of water to the aquifer, out of which 6.6 MGD can be pumped out and consumed sustainably on a daily basis through the 50 planned wells. Since DCK is to be developed and inhabited in 3 phases, analysis revealed that quantities of 1.4 and 3.5 MGD can be pumped out sustainably for the short and mid-term developmental plans. A sustainable hydroelectric system was also designed for using the hydraulic structures of the small lakes. System control was introduced by application of Artificial Neural Networks (ANN) and Model Predictive Control (MPC) to maintain the hydroelectric potential and constant head against variation in flow as delivered from the STPs. The results show an output of 13.92 MW of green and sustainable hydroelectricity which can be produced at a very low cost. A cost-benefit analysis projects a savings of $11,550 and $60,000 per day due to the artificial groundwater recharge and hydroelectric production respectively, with the cost of construction of these projects being paid off within 5 and 2 years at this rate, including the cost of operation and maintenance. Results, however, should be used with caution due to the preliminary nature of the models and calculations.
Open Access
Modeling the distribution of major salt ions in regional agricultural groundwater and surface water systems: model calibration and application
(Colorado State University. Libraries, 2020) Javed, Abdullah B., author; Gates, Timothy K., advisor; Bailey, Ryan T., advisor; Ronayne, Michael J., committee member
Irrigated lands in Colorado's Lower Arkansas River Valley (LARV), like many irrigated agricultural areas worldwide, suffer from salinization of soil, groundwater, and adjacent river systems. Waterlogging and salinization are prevalent throughout the LARV, which have diminished the crop yields and threatened the long-term sustainability of irrigated agriculture. Increased salinity concentrations are primarily due to the presence of salt minerals and high rates of evapotranspiration in the LARV, coupled with inefficient irrigation practices. Shallow groundwater in the LARV drives saline groundwater back to the stream network, thereby degrading the surface water quality, which affects the downstream areas where it evapo-concentrates when saline water is diverted for additional use. The goal of the current study is to develop, calibrate and test a physically-based, spatially distributed numerical model to assess soil, groundwater and surface water salinity at a regional scale to better understand the baseline nature of the problem. Several salinity models have been developed in recent decades; however, no attempts thus far have been made at simulating the fate, storage, and transport of salt ions at a regional scale in both groundwater and streams within an irrigated stream-aquifer system. The model used in this thesis links MODFLOW-SFR2, which simulates the groundwater heads and stream flows, with RT3D/SEC-OTIS which addresses reactive solute transport in variably- saturated soil and stream-aquifer systems. Sources and sinks within an agricultural system such as canal seepage, infiltrated water from flood and sprinkler irrigation, groundwater pumping, evapotranspiration from both the unsaturated and shallow saturated zones; root zone processes such as cycling of salt ions, crop uptake, and leaching to the water table; addition of salt mass via fertilizer and irrigation water; chemical kinetics affecting salt ions such as influence of dissolved oxygen and nitrate; equilibrium chemistry processes such as precipitation-dissolution, complexation and cation exchange; and 1D transport of salt ions in the streams due to advection, dispersion and sorption are addressed. The coupled flow and reactive transport model is applied to an approximately 552 km2 salinity-affected irrigated stream-aquifer system of the LARV between Lamar, Colorado and the Colorado-Kansas border. The model is tested against an extensive set of field data (soil salinity data from field salinity surveys, groundwater salinity collected from a network of groundwater monitoring wells, salt loading from the aquifer to the Arkansas River, and salt concentrations measured from in-stream sampling). Model calibration and parameter estimation include manual and automated calibration using PEST. Runs were conducted to describe the current levels of root zone salinity which markedly exceeds threshold levels for crop yield reduction. Spatiotemporal distribution of groundwater levels and concentrations, mass and return flow rates to streams, and stream concentrations are also simulated for current baseline conditions. The calibrated and tested regional scale salinity model is in need of further refinement but shows promise for future implementation to explore potential solution strategies for the irrigated valley of the LARV, and similar salt-afflicted areas of the world, by applying different best management practices.
Open Access
Occurrence and transport of salinity and selenium in a tile-drained irrigated agricultural system
(Colorado State University. Libraries, 2017) Daly, Miles Brian, author; Bailey, Ryan T., advisor; Gates, Timothy K., advisor; Butters, Gregory L., committee member
To view the abstract, please see the full text of the document.
Open Access
Quantifying future water resources availability and agricultural productivity in agro-urban river basins
(Colorado State University. Libraries, 2022) Aliyari, Fatemeh, author; Bailey, Ryan T., advisor; Arabi, Mazdak, committee member; Bhaskar, Aditi, committee member; Sanford, William E., committee member
Climate change can have an adverse effect on agricultural productivity and water availability in semi-arid regions, as decreases in surface water availability can lead to groundwater depletion and resultant losses in crop yield due to reduced water for irrigation. Competition between urban and agricultural areas intensifies groundwater exploitation as surface water rights are sold to growing municipalities. These inter-relationships necessitate an integrated management approach for surface water, groundwater, and crop yield as a holistic system. This dissertation provides a novel integrated hydrologic modeling approach to quantify future water resources and agricultural productivity in agro-urban river basins, particularly in arid and semi-arid regions where surface water and groundwater are managed conjunctively to sustain urban areas and food production capacity. This is accomplished by i) developing an integrated hydrologic modeling code that accounts for groundwater and surface water processes and exchanges in large regional-scale managed river basins, and demonstrating its use and performance in the economically diverse South Platte River Basin (SPRB), a 72,000 km2 river basin located primarily in the state of Colorado, USA; ii) using the model to understand possible future impacts imposed by climate variation on water resources (surface water and groundwater) and agricultural productivity; and iii) quantifying the combination impacts of agriculture-to-urban water trading and climate change on groundwater resources within the basin. This dissertation presents an updated version of SWAT-MODFLOW that allows application to large agro-urban river basins in semi-arid regions. SWAT provides land surface hydrologic and crop yield modeling, whereas MODFLOW provides subsurface hydrologic modeling. Specific code changes include linkage between MODFLOW pumping cells and SWAT HRUs for groundwater irrigation and joint groundwater and surface water irrigation routines. This conjunctive use, basin-scale long-term water resources, and crop yield modeling tool can be used to assess future water and agricultural management for large river basins across the world. The updated modeling code is applied to the South Platte River Basin, with model results tested against streamflow, groundwater head, and crop yield throughout the basin. To assess the climate change impacts on water resources and agricultural productivity, the coupled SWAT-MODFLOW modeling code is forced with five different CMIP5 climate models downscaled by Multivariate Adaptive Constructed Analogs (MACA), each for two climate scenarios, RCP4.5, and RCP8.5, for 1980-2100. In all climate models and emission scenarios, an increase of 3 to 5 °C in annual average temperature is projected by the end of the 21st century, whereas variation in projected precipitation depends on topography and distance from the mountains. Based on the results of this study, the worst-case climate model in the basin is IPSL-CM5A-MR-8.5. Under this climate scenario, for a 1 °C increase in temperature and the 1.3% reduction in annual precipitation, the basin will experience an 8.5% decrease in stream discharge, 2-5% decline in groundwater storage, and 11% reduction in crop yield. In recent decades, there has been a growing realization that developing additional water supplies to address new demands is not feasible. Instead, managing existing water supplies through reallocations is necessary to tackle water scarcity and climate change. However, third-party effects associated to water transfers has limited the growing water market. This study also quantifies the combination impacts of agriculture-to-urban water trading (widely known as 'buy and dry') and climate change on groundwater availability in semi-arid river basins through the end of 21st century, as groundwater pumping increases to satisfy irrigation water lost to the urban sector. For this analysis, we use the hydrological modeling tool SWAT-MODFLOW, forced by projected water trading amounts and two downscaled GCM climate models, each for two emission scenarios, RCP4.5 and 8.5. According to the results of this study, agriculture-to-urban water trading imposes an additional basin-wide 2% reduction in groundwater storage, as compared to changes due to climate. However, groundwater storage changes for local subbasins can be up to 8% and 10% through the mid-century and end of the century, respectively.
Open Access
Quantifying the impact of climate change and land use change on surface-subsurface nutrient dynamics in a Chesapeake Bay watershed
(Colorado State University. Libraries, 2023) Tuladhar, Avalokita, author; Bailey, Ryan T., advisor; Shanmugam, Mohana Sundaram, advisor; Smith, Ryan, committee member; Ross, Matthew, committee member
Nutrients such as nitrogen can be harmful to aquatic organisms when loaded to receive water in excessive amounts. Climate change, through possible increases in temperature and variable rainfall, may cause changes in nutrient loading patterns from watersheds. This study assesses the potential impact of climate and land use change on nitrate (NO3) loading in the Nanticoke River Watershed (NRW), Chesapeake Bay region, USA, using an updated version of SWAT+ watershed model that simulates groundwater nitrate fate and transport in a physically based spatially distributed manner. The nutrient loadings from the NRW eventually drain into the Chesapeake Bay, exacerbating eutrophication. The model was simulated for the 2000-2015 time, and tested against measured streamflow, in-stream nitrate loadings, and groundwater head at various stream gages and monitoring wells. Once tested, the model was used to simulate changes in hydrological and nitrate fluxes under two future climates, according to Representative Concentration Pathways (RCP) 4.5 and 8.5, and land use changes as projected by USGS's FORE-SCE model. The projected results show that in the future climate change is to be responsible for an 18-34% and 22-33% decrease in annual average streamflow and a 4-22% and 4-11% decrease in annual average nitrate loading as projected under RCP 4.5 and RCP 8.5 scenarios for future timelines (near 2024-2048, mid 2049-2073 and far future 2074-2099), respectively. The overall decrease in future streamflow is due to higher temperatures resulting in higher evapotranspiration during summer months, offsetting the additional precipitation. The decrease in nitrate loading in the channel is influenced by lower runoff, and elevated nitrate concentration in the soil, leading to increased leaching into groundwater. This surge in soil nitrate concentration results from reduced plant uptake of nitrate due to decreased plant growth/lower crop yields. The stunted plant growth is due to reduced mineralization of nitrogen in the soil which, in turn, is linked to decreasing soil water content and water stress from higher surface temperatures. As compared to the influence of climate, land use change resulted in a minor decrease in future nitrate loading. These results and insights can be used in future nutrient management for similar landscapes. In addition, we show that the updated SWAT+ model can be a useful tool in quantifying and investigating nitrate fate and transport dynamics in coupled surface-soil-aquifer-channel systems, particularly for systems with a strong hydraulic connection between the unconfined aquifer and channel network
Open Access
Salt transport and loading in tile-drained watersheds: observations, modeling, and management
(Colorado State University. Libraries, 2022) Addab, Haider, author; Bailey, Ryan T., advisor; Grigg, Neil, committee member; Arabi, Mazdak, committee member; Suter, Jordan, committee member
To view the abstract, please see the full text of the document.