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Browsing by Author "Gates, Timothy K., advisor"

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    ItemOpen Access
    A spatial decision support system for basin scale assessment of improved management of water quantity and quality in stream-aquifer systems
    (Colorado State University. Libraries, 2008) Triana, Enrique, author; Labadie, John W., advisor; Gates, Timothy K., advisor
    Challenges in river basin management have intensified over the years, with expanding competition among water demands and emerging environmental concerns, increasing the complexity of the decision making framework. A State-of-the-art spatial-decision support system (River GeoDSS) is developed herein to provide assistance in evaluating management alternatives towards optimal utilization of water resources, providing a comprehensive treatment of water quantity and quality objectives based on conjunctive surface and groundwater modeling within the complex administrative and legal framework of river basin management. The River GeoDSS provides sophisticated tools that allow accurate system simulations and evaluation of strategies while minimizing the technological burden on the user. A unique characteristic of the River GeoDSS is the integration of models, tools, user interfaces and modules, all seamlessly incorporated in a geographic information system (GIS) environment that encourages the user to focus on interpreting and understanding system behavior to better design remediation strategies and solutions. The River GeoDSS incorporates Geo-MODSIM, a fully functional implementation of MODSIM within the ArcMap interface (ESRI, Inc.), and Geo-MODFLOW, a new MODFLOW-MT3DMS results analysis tool in the ArcMap interface. The modeling system is complemented with a new artificial neural networks (ANN) module for natural and irrigation return flow quantity and quality evaluation and salt transport through reservoirs, as well as with a new water quality module (WQM) for conservative salt transport modeling of conjunctive use of surface water and groundwater resources in the river basin network. In this research, innovative methodologies are developed for applying ANNs in efficiently coupling surface and groundwater models for basin-scale modeling of stream-aquifer interactions. The core River GeoDSS is customized to provide comprehensive analysis of alternative solutions to achieving agricultural, environmental, and water savings goals in the Lower Arkansas River Basin in Colorado while assuring physical, legal and administrative compliance. The River GeoDSS applied to the Arkansas River Valley allowed comparing benefits and improvements of management strategies, illustrated their potential to reduce waterlogging and soil salinity, salt load to the river, and non-beneficial evapotranspiration in a strategic planning environment.
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    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.
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    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.
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    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.
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    Calibration and uncertainty of a head-discharge relationship for overshot gates under field conditions
    (Colorado State University. Libraries, 2019) Kutlu, Caner, author; Gates, Timothy K., advisor; Venayagamoorthy, Karan, committee member; Butters, Gregory, committee member
    Adjustable overshot gates (pivot weirs) are commonly used to control discharge and water levels in irrigation water delivery networks. The degree to which this control can be achieved depends upon reliable relationships between flow rate and the hydraulic head upstream and downstream of the gate. Moreover, such relationships also can be used for flow measurements. This study aims to develop a head-discharge equation for free flow over a overshot gate, to describe its uncertainty, and to examine the impact of gate submergence on the equation. Previous research on the flow characteristics of overshot gates has been performed primarily in laboratories, with very little investigation of performance in the field. This thesis provides a report of a field study conducted on four Obermeyer-type pneumatically automated overshot gates, which were operated for irrigation water delivery in northern Colorado. Utilizing both classical and amended forms of the sharp-crested weir equation, Buckingham-Pi dimensional analysis, and incomplete self-similarity theory, head-discharge equations for free flow have been developed which are alternately dependent on and independent of the gate inclination angle. To estimate the flow rate, three fully-suppressed Obermeyer-type overshot gates with crest widths of 22 ft, 20 ft, and 15 ft, and respective lengths of 5 ft., 6.3 ft., 6.08 ft , were inspected for eight different inclination angles (α = 22.8°, 23.6°, 29.7°, 32.6°, 34.6°, 35.3°, 38.9°, 40.4°), under free flow conditions. The best-performing equation is of classical form and contains a discharge coefficient dependent on gate inclination angle. It can be used to relate the discharge to upstream hydraulic head with about ± 10 % (standard deviation range of residual error) for free flow conditions. This equation is applicable for inclination angles between 20° and 40° and for flow rates ranging from 20 to 330 ft3/s. To reduce uncertainty of the discharge coefficient and to prevent the misleading consequences of neglecting the velocity head in the approaching flow, the total upstream energy head was employed in the equation. The effect of velocity head was significant for flow estimation. Dependency of the equation on the gate and field characteristics was examined by testing the equation with field data for a different type of overshot gate. Alternate equations were developed which altered the classical form for a sharp-crested weir to include both a coefficient and an exponent that are dependent upon gate inclination angle, and which preserved the classical form and treated the discharge coefficient as a constant independent of gate inclination. Although, satisfactory results were obtained for these alternative forms, inclusion of the angle in the discharge coefficient alone was recommended for higher accuracy of flow rate estimation, particularly for larger overshot gates with inclination angles ranging from about 20° to about 40°. Furthermore, the modular limit of the overshot gates was investigated for a fourth Obermeyer gate with a crest width of 17 ft and a length of 5.8 ft. Up to a submergence ratio of 0.51, the submergence effect was not observed to decrease the flow rate over for the gate. More data for a higher submergence conditions are required to develop a modular limit and a head-discharge equation for submerged flow.
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    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.
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    Exploring the contribution of crop water use to remotely sensed estimates of soil salinity in irrigated agriculture
    (Colorado State University. Libraries, 2023) Craig, Brian D., author; Chávez, José L., advisor; Gates, Timothy K., advisor; Butters, Gregory L., committee member
    Globally, 72% of the world's water withdrawals are used for agriculture. As the world's population continues to grow and increase its caloric intake, agricultural producers must provide more food and fiber with the same amount of water and soil, or less, due to expanding urbanization and climate change. In Colorado (CO, U.S.A.), agricultural producers in the South Platte and Arkansas River Basins, for instance, have been offered water transfer programs to temporarily or permanently transfer their water shares to municipalities and industry. Another challenge agricultural growers face is soil salinization, which needs to be monitored. In the Arkansas River basin, upflux from saline shallow groundwater tables consistently contributes to crop evapotranspiration (ET), leaving salts in the vadose zone. These salts accumulate over decades to the point where crop yields decline, threatening agricultural sustainability. Remote sensing is an economical tool to monitor salinity (e.g., soil electrical conductivity; EC, dS m-1) at large spatial scales. Existing remote sensing models that predict EC mostly utilize vegetation indices (VIs), which are arithmetic combinations of vegetation reflectances captured by discrete spectral bands. In this study, two additional explanatory variables were investigated: 1) the actual crop ET (ETa, mm d-1), and 2) the crop water stress index (CWSI). Calculations of ETa were performed using Landsat satellite multispectral imagery and a surface energy balance approach. This research was conducted over two growing seasons in commercial maize fields located within the Fairmont Drainage District near Swink, CO. Results indicate that models including ETa or CWSI with existing VIs improve the accuracy of soil EC mapping over models including VIs alone. The developed EC models are accurate within ±1 dS m-1 (Root Mean Squared Error), which is considered well within the precision required to make pragmatic field and ditch company-level management decisions.
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    Finding land and water management practices to reduce selenium and nitrate concentrations in an agricultural river valley applying a regional-scale stream-aquifer model
    (Colorado State University. Libraries, 2017) Shultz, Christopher David, author; Gates, Timothy K., advisor; Bailey, Ryan T., committee member; Hoag, Dana K., committee member
    The long-term practice of irrigated agriculture within the Lower Arkansas River Valley (LARV) in southeast Colorado has contributed to a number of land and water management concerns, including elevated concentrations of dissolved selenium (Se) and nitrate (NO3) in the stream-aquifer system. The goal of this study was to develop and calibrate a stream-aquifer flow and reactive transport model to simulate conditions within a representative region of the LARV, then to apply the model to evaluate the potential effectiveness of alternative land and water best management practices (BMPs) to improve conditions. Using a MODFLOW-SFR model to simulate groundwater and stream flow, linked to an RT3D-OTIS model to simulate reactive transport of solutes, enabled comprehensive regional-scale modeling of the coupled stream-aquifer system. Through an extensive calibration and testing process, including manual and automated calibration using PEST, parameter values were estimated and runs were conducted to describe spatiotemporal distributions of groundwater levels and concentrations, mass and return flow rates to streams, and stream concentrations for baseline conditions. Similar runs were conducted for individual and combined BMPs to analyze their effectiveness in reducing groundwater and stream water pollution from Se and NO3, assuming their broad implementation over the study regions. The considered BMPs include two land BMPs, namely reducing applied fertilizer application (RF), and enhancing riparian buffer zones (ERB); and three water BMPs, reducing applied irrigation (RI), lease-fallowing irrigated land (LF), and canal sealing to reduce seepage (CS). Results reveal substantial spatial and temporal variability in Se and NO3 concentrations over the region. Moreover, they show that by implementing such BMPs, Se and NO3 groundwater concentrations could be lowered by as much as 23% and 40%, respectively, and stream concentrations of Se and NO3 could be lowered by as much as 57% and 33%, respectively. The most effective stand-alone land BMP was ERB, and the most effective stand-alone water BMP was CS. By coupling groundwater and stream flow modeling, this study has provided a number of insights not perceived in precursor modeling studies in the study region which examined only groundwater concentrations and mass loading. Some of these findings include: (1) BMPs which alter water management alone are likely to result in an increase in NO3 concentration in the streams (this is because the chemical reduction of groundwater return flows through the riparian zone is so effective under baseline conditions that practices which lower rates of return flow, without also substantially lowering concentrations, diminish the dilution effect on stream flow), (2) lower mass loading of Se and NO3 to streams due to a BMP does not necessarily imply a lowering of stream concentration since there are interactive effects of concurrent reductions in return flow rates, and (3) though there are prospects for substantial lowering of total Se concentrations in streams in the LARV, it is unlikely that the current Colorado chronic standard of 4.6 µg L-1 for total Se could ever be achieved practically. Furthermore, the linked models presented in this thesis could be applied to other irrigated stream-aquifer systems to simulate reactive transport of Se and NO3.
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    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.
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    Machine learning methods to facilitate optimal water allocation and management in irrigated river basins to comply with water law
    (Colorado State University. Libraries, 2019) Rohmat, Faizal Immaddudin Wira, author; Labadie, John W., advisor; Gates, Timothy K., advisor; Bailey, Ryan T., committee member; Anderson, Charles W., committee member
    The sustainability issues facing irrigated river basins are intensified by legal and institutional regulations imposed on the hydrologic system. Although solutions that would boost water savings and quality might prove to be feasible, such imposed institutional constraints could veto their implementation, rendering them legally ineffectual. The problems of basin-scale irrigation water management in a legally-constrained system are exemplified in the central alluvial valley of the Lower Arkansas River Basin (LARB) in Colorado, USA, and in the Tripa River Basin in Indonesia. In the LARB, water and land best management practices (BMPs) have been proposed to enhance the environment, conserve water, and boost productivity; however, the legal feasibility of their implementation in the basin hinder BMP adoption. In the Tripa river basin, the rapid growth of water demand pushes the proposal of new reservoir construction. However, inadequate water availability and the lack of water law enforcement requires the basin to seek water from adjacent basins, thereby raising legal and economic feasibility issues. To address these issues, an updated version of a decision support system (DSS) named River GeoDSS has been employed to model basin-scale behavior of the LARB for both historical (baseline) and BMP implementation scenarios. River GeoDSS uses GeoMODSIM as its water allocation component, which also handles water rights and uses a deep neural network (DNN) functionality to emulate calibrated regional MODFLOW-SFR2 models in modeling complex stream-aquifer interactions. The use of DNNs for emulation if critical for extrapolating the results of MODFLOW-SFR2 simulations to un-modeled portions of the basin and for compute-efficient analysis. The BMP implementations are found to introduce significant alterations to streamflows in the LARB, including shortages in flow deliveries to water right demands and in flow deficits at the Colorado-Kansas Stateline. To address this, an advanced Fuzzy-Mutation Linear Particle Swarm Optimization (Fuzzy-MLPSO) metaheuristic algorithm is applied to determine optimal operational policies for a new storage account in John Martin Reservoir for use in mitigating the side-effects of BMP implementation on water rights and the interstate compact. Prior to the implementation of Fuzzy-MLPSO, a dedicated study is conducted to develop the integration between MLPSO and GeoMODSIM, where it is applied in addressing the water allocation issue in the Tripa River Basin. The coupling of simulation (GeoMODSIM) and optimization (MLPSO) models provides optimal sizing of reservoirs and transbasin diversions along with optimal operation policies. Aside from that, this study shows that MLPSO converges faster compared to the original PSO with sufficiently smaller swarm size. The implementations of Fuzzy-MLPSO in the LARB provided optimal operational rules for a new storage account in John Martin Reservoir dedicated to abating the undesirable impacts of BMP implementation on water rights and Stateline flows. The Fuzzy-MLPSO processes inflow, storage, seasonal, and hydrologic states into divert-to-storage/release-from-storage decisions for the new storage account. Results show that concerns over shortages in meeting water rights demands and deficits to required Stateline flow due to otherwise beneficial BMP implementations can be addressed with optimized reservoir operations.
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    Modeling nonpoint-source uranium pollution in an irrigated stream-aquifer system: calibration and simulation
    (Colorado State University. Libraries, 2024) Qurban, Ibraheem A., author; Gates, Timothy K., advisor; Bailey, Ryan T., committee member; Grigg, Neil S., committee member; Ippolito, James A., committee member
    The Lower Arkansas River Valley (LARV) in southeastern Colorado has been a source of significant agricultural productivity for well over a century, primarily due to extensive irrigation practices. Mirroring trends seen in other semi-arid irrigated areas globally, however, irrigated agriculture in the LARV has resulted in several challenges for the region. In addition to the emergence of waterlogging and soil salinization, leading to decreased crop yields, elevated levels of nutrients and trace elements have appeared in the soil and water. Among these constituents, uranium (U), along with co-contaminants selenium (Se) and nitrate (NO3), has shown particularly high concentrations in groundwater, surface water, and soils. These heightened concentrations pose environmental concerns, impacting human health and the well-being of aquatic life such as fish and waterfowl. Careful monitoring and management practices are crucial to prevent potential harm to water resources. The main goal of this research is to develop a comprehensive numerical model for assessing U pollution in a stream-aquifer system within a large irrigated area. To achieve this, a computational model is built and tested that can predict with reasonable accuracy how U, along with Se and NO3, are mobilized and move within a coupled system of streams and groundwater. The approach combines two key modeling components: a MODFLOW package, which handles the simulation of groundwater and stream flow dynamics, and an RT3D package, which addresses the reactive transport of U, Se, and nitrogen (N) species in both groundwater and interconnected streams. RT3D relies on the simulated flows generated by MODFLOW to track the movement of U, Se, and N species between streams and the aquifer in the irrigated landscape, updating daily to adequately capture changes over time. This integrated model provides an understanding of how these contaminants behave and interact within the stream-aquifer system, aiding in effective pollution assessment and providing insights valuable to the planning of management strategies. The coupled MODFLOW-RT3D flow and reactive transport model is applied to a 550 km² area within the LARV, stretching from Lamar, Colorado, to the Colorado-Kansas border and spanning a period of 14 years. The flow package is compared with observations of groundwater hydraulic head and stream flow, along with estimates of return flow along the Arkansas River. The reactive transport package is assessed by comparing predicted U, Se, and NO3 concentrations against data collected from groundwater monitoring wells and stream sampling sites along with estimates of solute mass loads to the river. To calibrate and refine the model, the PESTPP-iES iterative ensemble smoother (iES) software is employed. This calibration process is dedicated to enhancing the model's accuracy in predicting both flow and transport dynamics. PESTPP-iES addresses calibration uncertainty by establishing prior frequency distributions for key model parameters based on data and expertise, then iteratively adjusts these parameters during calibration to align model predictions with observed data. Post-calibration, posterior distributions reflect updated parameter values and reduced uncertainties. Demonstrating a strong alignment with concentrations of CNO3, CSe, and CU values found in groundwater, streams, and the mass loading entering the Arkansas River, outcomes of the model-based simulations reveal a substantial violation of the Colorado chronic standard (85th percentile = 30 μg/L) for CU throughout the study region. On average, simulated CNO3, CSe, and CU values for groundwater in non-riparian areas in the region are 3.6 mg/L, 41 µg/L, and 126 µg/L, compared to respective averages of 4 mg/L, 53 µg/L, and 112 µg/L observed in monitoring wells. When considering the 85th percentile of simulated CNO3, CSe, and CU values, the figures for non-riparian groundwater are 6 mg/L, 50 µg/L, and 218 µg/L, respectively. Groundwater in riparian areas shows lower average simulated CNO3, CSe, and CU values of 3 mg/L, 26 µg/L, and 72 µg/L, respectively, and 85th percentile values of 5 mg/L, 41 µg/L, and 152 µg/L. Additionally, simulated average mass loading rates for NO3, Se, and U along the river are 8.8 kg/day per km, 0.05 kg/day per km, and 0.27 kg/day/km respectively, compared to stochastic mass balance estimates of 9.2 kg/day per km , 0.06 kg/day per km , and 0.23 kg/day per km. The simulated 85th percentile CNO3, CSe, and CU values in the Arkansas River are 1 mg/L, 11 μg/L, and 87 μg/L, respectively. Notably, the simulated U levels in groundwater exceed the chronic standard across 44% of the region. Along the Arkansas River, concentrations consistently surpass the chronic standard, averaging 2.9 times higher. Predicted Se concentrations also show significant exceedances of the chronic standard, while NO3 violations are slight to moderate. The varying pollutant levels across the region highlight specific areas of concern that require targeted attention, indicating potential contributing factors to these hotspots. Findings outline how serious and widespread the problem is in the LARV, providing a starting point for comparing potential pollution reduction from alternative water and land best management strategies (BMPs) to be explored in future applications of the calibrated model.
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    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.
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    New insights into flow over sharp-crested and pivot weirs using computational fluid dynamics
    (Colorado State University. Libraries, 2021) Sinclair, Joseph, author; Venayagamoorthy, Subhas Karan, advisor; Gates, Timothy K., advisor; Gao, Xinfeng, committee member
    Irrigation for agriculture is the highest use of fresh water in the world. Efficient and equitable access and distribution of this water is vital to survival of the Earth's population. Open channels are the most common means of conveying water for agricultural irrigation and hydraulic structures are often used in these open channels to regulate and measure flow to achieve desired conditions. Sharp-crested weirs are one of the most popular of these structures and pivot weirs are quickly becoming a more widely used hydraulic structure. The purpose of this study was to reexamine both types of weirs to better understand how they operate for flow regulation and measurement and to provide insights into the flow structure around the weir. Computational fluid dynamics, or CFD, was the primary tool used, with a commercial code called FLOW-3D being the specific software selected. Prior to investigating the weirs, preliminary studies were carried out to identify the best-practices in building an open-channel and hydraulic flow simulation in FLOW-3D. It was found that because FLOW-3D has no method of specifying developed flow prior to entering the model domain, additional care had to be taken to develop flow within the computational domain. The upstream length in the models was often extended to give the simulated flow more time and distance to develop. Additionally, the first-cell height had to be within a certain dimension to produce accurate velocity profiles due to the use of the logarithmic law of the wall boundary condition to solve for velocity in the first cell. Finally, a study analyzing the effects of the simulated downstream distance after a free-flowing sharp-crested weir revealed that the downstream distance has no effect on upstream flow. The sharp-crested weir parametric study analyzed velocity and pressure profiles over the crest, several calculated discharge coefficients, and turbulence flow structures upstream of the weir using high-resolution two-dimensional simulations. Three distinct operating regimes were identified based on the profiles over the crest as well as plots of the discharge coefficient against h/P where h is the upstream potentiometric head above the weir crest and P is the height of the crest above the channel bed. The first regime, the high-acceleration regime, occurs when h/P < 0.6. Flow accelerates greatly near the weir crest which results in negative pressure. The discharge coefficient has a negative linear trend with h/P in this regime. The next region occurs where 0.6 < h/P < 2.0 and is called the ideal-operating regime. In this regime, flow is not experiencing acceleration or inundation and better maintains the assumptions used in deriving the classical rating equation. The discharge coefficient is relatively constant in this case and a single value can be used with minimal error for all flow rates within this range. The final regime, the weir-inundated regime, is where h/P > 2.0. The weir is often submerged here and the effect of the weir on the flow is diminished due to the high depth of flow. Turbulence patterns upstream of the weir appear to have a relationship to the Reynolds number, Re, of the flow with eddies reaching a minimum size at a Re = 70,000. The region of smallest eddy size correlated to the ideal-operating regime, again lending to the hypothesis that flow is more efficiently controlled within this regime. Six flow rates at five different gate angles (27°, 47°, 57°, 72°, and 90°) were tested for the pivot weir study. After analysis of the h/P values and discharge coefficients, it was found that the flow rates bounding the ideal-operating regime shift lower in magnitude as the gate angle decreases. Each angle also has an associated relatively constant discharge coefficient in its ideal-operating regime, meaning a single coefficient value may be used with minimal error. Comparison of the average discharge coefficient for each angle revealed a minimum value at 72° and a maximum value at 27°. The fraction of the total upstream mechanical energy head comprised of the velocity head was found to increase as gate angle decreased. Visual contours of velocity and pressure depicted how the flow changes as it approaches weirs of varying angles, with the recirculation zone moving from upstream of the weir to solely downstream of the weir for angles below 47°. Plots of the non-dimensional pressure and velocity profiles over the weir crest revealed that velocity over the crest increases as the inclination angle decreases. At the 47° weir, the flow acceleration created a region of negative relative pressure close to the weir. These results highlight how flow over both the sharp-crested weir and pivot weir varies considerably. Thus, caution must be exercised in using empirical discharge coefficients for a broad range of h/P value.
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    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.
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    Regional selenium cycling in an irrigated agricultural groundwater system: conceptualization, modeling, and mitigation
    (Colorado State University. Libraries, 2012) Bailey, Ryan T., author; Gates, Timothy K., advisor; Baù, Domenico A., advisor; Arabi, Mazdak, committee member; Ronayne, Michael J., committee member; Ma, Liwang, committee member
    Selenium (Se) is an element that occurs naturally as a trace constituent in geologic formations and associated soils and, although an essential nutrient for animals and humans, can prove detrimental to health at high concentrations. Over the previous decades, the presence of either deficient or elevated concentrations of Se in groundwater, surface water, and associated plants and cultivated crops has emerged as a serious issue in many regions of the world, including the United States, northern and western Europe, the Middle East, and East Asia. Regardless of the nature of concern regarding Se, whether concentrations are deficient or elevated in water supplies and cultivated crops, there is a basic need for a thorough description of the movement and chemical processes of Se within a dynamic soil-aquifer system influenced by agricultural practices, and for the development of numerical simulation tools that allow these processes to be simulated in assessing baseline conditions and exploring remediation best-management practices (BMPs). While the individual processes controlling Se speciation, transformation, and movement within soil systems have been well documented, their synthesis into a comprehensive numerical model of Se fate and transport within an alluvial aquifer system influenced by agricultural practices has not yet been realized. This dissertation presents the development of a numerical model that can simulate the fate and transport of Se species in irrigation-influenced agricultural soil and groundwater systems at a regional scale. The model was developed by first, linking RT3D, modified to handle multi-species reactive transport in variably-saturated porous media, to MODFLOW, which uses the UZF1 (Unsaturated Zone Flow) package to simulate groundwater flow in the unsaturated zone; and second, developing an Se reaction module for RT3D that accounts for the cycling, chemical activity, and transport of Se species in regional-scale agricultural soil and groundwater systems. The module also accounts for the influence of other chemical species such as dissolved oxygen and nitrate (NO3). The resulting model, referred to as UZF-RT3DAG, is applied to a 50,600 ha regional site in the Lower Arkansas River Valley (LARV) in southeastern Colorado for the years 2006 through 2009. Using the calibrated model, multiple BMPs for remediation of Se contamination in the LARV are investigated. These strategies include decreasing annual loading of nitrogen fertilizer, decreasing species concentration in canal water, decreasing applied volume of irrigation water, and increasing chemical activity within riparian areas. Research results are presented through a series of published and submitted articles and modeling results that outline the progression of model development and model application. Results of the BMP scenario testing indicate that alternative land-management practices can have a significant impact in decreasing the concentration of dissolved Se in groundwater by up to 5-8% as well as mass loadings of Se to the Arkansas River by as much as 20-30%. Practices also have a significant impact on decreasing NO3 concentrations and loadings by up to 50% and 45%, respectively. As the alluvial aquifer in the LARV is similar to other Se-contaminated aquifer systems, the results of this research are pertinent to the assessment and remediation of Se contamination world-wide.
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    Regional-scale groundwater flow and salt transport models for exploring agro-environmental remediation strategies in an irrigated river valley
    (Colorado State University. Libraries, 2014) Morway, Eric D., author; Gates, Timothy K., advisor; Labadie, John W., committee member; Baù, Domenico A., committee member; Ronayne, Michael J., committee member
    To view the abstract, please see the full text of the document.
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    Simulating the fate and transport of salinity species in a semi-arid agricultural groundwater system: model development and application
    (Colorado State University. Libraries, 2018) Tavakoli Kivi, Saman, author; Bailey, Ryan T., advisor; Gates, Timothy K., advisor; Ronayne, Michael J., committee member; Bhaskar, Aditi, committee member
    Many irrigated agricultural areas worldwide suffer from salinization of soil, groundwater, and nearby river systems. Increased salinity concentrations, which can lead to decreased crop yield, are due principally to the presence of salt minerals and high rates of evapotranspiration. High groundwater salt loading to nearby river systems also affects downstream areas when saline river water is diverted for additional uses. Irrigation-induced salinity is the principal water quality problem in the semi-arid region of the western United States due to the extensive background quantities of salt in rocks and soils. Due to the importance of the problem and the complex hydro-chemical processes involved in salinity fate and transport, a physically-based spatially-distributed numerical model is needed to assess soil and groundwater salinity at the regional scale. Although several salinity transport models have been developed in recent decades, these models focus on salt species at the small scale (i.e. soil profile or field), and no attempts thus far have been made at simulating the fate, storage, and transport of individual interacting salt ions at the regional scale within a river basin. The required model must be able to handle variably-saturated groundwater systems; sources and sinks of groundwater within an agricultural system such as canal seepage, infiltrated water from flood and sprinkler irrigation, groundwater pumping, and evapotranspiration from both the unsaturated and shallow saturated zones; root zone processes such as salt ions cycling, crop uptake, and leaching to the water table; addition of salt mass via fertilizer and irrigation water; chemical kinetics affecting salt ions such as the influence of dissolved oxygen and nitrate on the chemical processes of anions such as sulfate (SO4); and equilibrium chemistry processes such as precipitation-dissolution, complexation, and cation exchange. This dissertation develops a physically-based, spatially-distributed groundwater reactive transport model that simulates the fate and transport of major salt ions in an agricultural groundwater system and can be applied to regional scale areas to address salinity problems. The model is developed by 1) constructing an equilibrium chemistry model that includes all the fate and transport processes that affect salt ions in an agricultural soil-groundwater system, including precipitation-dissolution of salt minerals, ions complexation, and cation exchange; and 2) coupling the module with UZF-RT3D (Bailey et al., 2013) a MODFLOW-based numerical modeling code that simulates the transport of multiple interacting reactive solutes in a variably-saturated soil-groundwater system. The model accounts for dissolved oxygen, nitrogen cycling in the soil-plant system (crop uptake, organic matter decomposition, mineralization/immobilization), oxidation-reduction reactions, including chemical reduction of dissolved oxygen and nitrate in the presence of marine shale, and sorption. UZF-RT3D has been amended to also include processes that directly affect SO4, one of the major salt ions, such as sulfur cycling in the plant-soil system and the release of SO4 from pyrite (FeS2)-laden marine shale in the presence of dissolved oxygen and nitrate. The developed model is applied to a salinity-affected irrigated alluvial stream-aquifer region to demonstrate its applicability and to assess remediation strategies on soil and groundwater salinity, salt mass loading to streams, and crop yield. The study area is a 500 km2 region of the Lower Arkansas River Valley (LARV) in southeastern Colorado, with the model tested against an extensive set of field data (soil salinity, groundwater salinity, salt loading from the aquifer to the Arkansas River) for the years 2006-2009. Parameter estimation is accomplished via a mixed manual-automated method, with estimation of both equilibrium and kinetic chemical parameters. Research results are presented through published and submitted articles. Results of preliminary best management practice (BMP) scenario testing indicates that reducing the volume of applied irrigation water and sealing earthen irrigation canals can have a significant effect on the root zone salinity, groundwater salinity, groundwater salt loading from the aquifer to the river network, and crop yield.
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    Stochastic analysis of flow and salt transport modeling in irrigation-drainage systems
    (Colorado State University. Libraries, 2012) Alzraiee, Ayman H., author; Garcia, Luis A., advisor; Gates, Timothy K., advisor; Bau, Domenico, committee member; Butters, Greg, committee member
    Sustainability of crop production in the Lower Arkansas River Basin in Colorado is seriously threatened by the continuous degradation of irrigated lands by the dual impact of soil salinization and waterlogging problems. Integration of improved irrigation practices, upgrades to the irrigation systems, and subsurface drainage are essential components of any plan to stop the deterioration of irrigated lands. Numerical simulations of irrigation and drainage systems are necessary to justify the consequent management actions. Despite the uncertainty of their predictions, numerical models are still indispensable decision support tools to investigate the feasibility of irrigation and drainage systems management plans. However, the uncertainties in input parameters to these models create a risk of misleading numerical results. That is beside the fact that the numerical models themselves are conceptual simplifications of the complex reality. The overarching objective of this dissertation is to investigate the impact of parameters uncertainty on the response of simulated irrigation-drainage systems. In the first part of the research, a Global Sensitivity Analysis (GSA) is conducted using a one-dimensional variably saturated problem to prioritize parameters according to their importance with respect to predefined performance indices. A number of GSA methods are employed for this purpose, and their comparative performances are investigated. Results show that only five parameters out of 18 parameters are responsible for around 73% of crop yield uncertainty. The second part introduces a method to reduce the computational requirements of Monte Carlo Simulations. Numerical simulation of variably saturated three-dimensional fields is typically a computationally intensive process, let alone Monte Carlo Simulations of such problems. In order to reduce the number of model evaluations while producing acceptable estimates of the output statistical properties, Cluster Analysis (CA) is used to group the input parameter realizations, e.g. hydraulic conductivity. The potentials of this approach are investigated using different: 1) clustering schemes; 2) clustering configurations, and 3) subsampling schemes. . Results show that response of 400 realizations ensemble can be efficiently approximated using selected 50 realizations. The third part of the research investigates the impact of input parameter uncertainty on the response of irrigation-drainage systems, particularly on crop yield and root zone hydrosalinity. The three-dimensional soil parameters, i.e. hydraulic conductivity, porosity, the pore size distribution (van Genuchten β) parameter, the inverse of the air entry pressure (van Genuchten α) parameter, the residual moisture content parameter, and dispersivity; are treated as spatial random processes. A sequential multivariate Monte Carlo simulation approach is implemented to produce correlated input parameter realizations. Other uncertain parameters that are considered in the study are irrigation application variability, irrigation water salinity, irrigation uniformity, preferential flow fraction, drain conductance coefficient, and crop yield model parameters. Results show that as the crop sensitivity to salinity increases, the crop yield standard deviation increases. The fourth part of the research investigates an approach for optimal sampling of multivariate spatial parameters in order to reduce their uncertainty. The Ensemble Kalman Filter is used as instrumentation to integrate the sampling of the hydraulic conductivity and the water level for a two-dimensional steady state problem. The possibility of combining designs for efficient prediction and for efficient geostatistical parameter estimation is also investigated. Moreover, the effect of relative prices of sampled parameters is also investigated. A multi-objective genetic algorithm is employed to solve the formulated integer optimization problem. Results reveal that the multi-objective genetic algorithm constitutes a convenient framework to integrate designs that are efficient for prediction and for geostatistical parameter estimation.
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    Uncertainty in measuring seepage from earthen irrigation canals using the inflow-outflow method and in evaluating the effectiveness of polyacrylamide applications for seepage reduction
    (Colorado State University. Libraries, 2015) Martin, Chad Allen, author; Gates, Timothy K., advisor; Cooley, Daniel S., committee member; Bailey, Ryan T., committee member
    Seepage losses from unlined irrigation canals account for a large fraction of the total volume of water diverted for agricultural use, and reduction of these losses can provide significant water quantity and water quality benefits. Quantifying seepage losses in canals and identifying areas where seepage is most prominent are crucial for determining the potential benefits of using seepage reduction technologies and materials. In recent years, polymers have been studied for their potential to reduce canal seepage, and the use of linear-anionic polyacrylamide (PAM) was studied as part of this analysis. To quantify seepage reduction, seepage rates must be estimated before and after application of linear-anionic polyacrylamide (LA-PAM). In this study, seepage rates from four earthen irrigation canals in the Lower Arkansas River Valley (LARV) of southeastern Colorado were estimated with repeated measurements using the inflow-outflow volume balance procedure. It is acknowledged that a significant degree of measurement error and variability is associated with using the inflow-outflow method; however, as is often the case, it was selected so that canal operations were not impacted and so that seepage studies could be conducted under normal flow conditions. To account for uncertainty related to using the inflow-outflow procedure, detailed uncertainty analysis was conducted by assigning estimated probability distribution functions to volume balance components then performing Monte Carlo simulation to calculate possible seepage values with associated probabilities. Based upon previous studies, it was assumed that flow rates could be measured with +/- 5% accuracy, evaporation at +/- 20% accuracy, and water stage within 0.04 to 0.06 feet (all over the 90% interpercentile range). Spatial and temporal variability in canal hydraulic geometry was assessed using field survey data and was incorporated into the uncertainty model, as were temporal variability in flow measurements. Monte Carlo simulation provided a range of seepage rates that could be expected for each inflow-outflow test based upon the pre-defined probable error ranges and probability distribution functions. Using the inflow-outflow method and field measurements directly for assessing variables, deterministic seepage rates were estimated for 77 seepage tests on four canals in the LARV. Canal flow rates varied between 25.8 and 374.2 ft³/s and averaged 127.9 ft³/s, while deterministic estimates of seepage varied between -0.72 and 1.53 (ft³/s) per acre of wetted perimeter with an average of 0.36 (ft³/s)/acre for all 77 tests. Deterministic seepage results from LA-PAM application studies on the earthen Lamar, Catlin, and Rocky Ford Highline canals in southeastern Colorado indicated that seepage could be reduced by 34-35%, 84-100%, and 66-74% for each canal, respectively. Uncertainty analysis was completed for 60 seepage tests on the Catlin and Rocky Ford Highline canals. To describe hydraulic geometry within the seepage test reaches of these canals, canal cross-sections were surveyed at 25 and 16 locations, respectively. Probability distribution functions were assigned to parameters used to estimate wetted perimeter and top width for each cross-section to account for measurement error and spatial uncertainty in hydraulic geometry. Probability distributions of errors in measuring canal flow rates and stage, and in calculating water surface evaporation also were accounted for. From stochastic analysis of these 60 seepage tests, mean values of estimated seepage were between -0.73 (ft³/s)/acre (gain) and 1.53 (ft³/s)/acre, averaging 0.32 (ft³/s)/acre. The average of the coefficient of variation values computed for each of the tests was 240% and the average 90th interpercentile range was 2.04 (ft³/s)/acre. For the Rocky Ford Highline Canal reaches untreated with LA-PAM sealant, mean values of canal seepage rates ranged from -0.26 to 1.09 (ft³/s)/acre, respectively, and averaged 0.44 (ft³/s)/acre. For reaches on the Catlin Canal untreated with LA-PAM, mean values of seepage ranged from 0.02 to 1.53 (ft³/s)/acre, respectively, and averaged 0.63 (ft³/s)/acre. For reaches on the Rocky Ford Highline Canal and Catlin Canal treated with LA-PAM, mean canal seepage rates values ranged from 0.25 to 0.57 (ft³/s)/acre, averaging 0.33 (ft³/s)/acre, and from -0.73 to 0.55 (ft³/s)/acre, averaging -0.01 (ft³/s)/acre, respectively. Comparisons of probability distributions for several pre- and post-PAM inflow-outflow tests suggest likely success in achieving seepage reduction with LA-PAM. Sensitivity analysis indicates that while the major effect on seepage uncertainty is error in measured flow rate at the upstream and downstream ends of the canal test reach, but that the magnitude and uncertainty of storage change due to unsteady flow also is a significant influence. Based upon the findings, recommendations for future seepage studies were provided, which have the ability to account for and reduce uncertainty of inflow-outflow measurements.