Mountain Scholar :: Browsing by Author "Arabi, Mazdak, committee member"

Browsing by Author "Arabi, Mazdak, committee member"

Now showing 1 - 20 of 44

Open Access
A collaborative planning framework for integrated urban water management with an application in dual water supply: a case study in Fort Collins, Colorado
(Colorado State University. Libraries, 2018) Cole, Jeanne Reilly, author; Sharvelle, Sybil, advisor; Grigg, Neil, advisor; Arabi, Mazdak, committee member; Goemans, Chris, committee member
Urban water management is essential to our quality of life. As much of our urban water supply infrastructure reaches the end of its useful life, water managers are using the opportunity to explore alternative strategies that may enable them to better meet modern urban water challenges. Water managers must navigate the labyrinth of balancing stakeholder needs, considering all costs and benefits, reducing decision risk, and, most importantly, ensuring public health and protecting the environment. Innovative water managers need guidance and tools to help manage this complex decision space. This dissertation proposes a collaborative, risk-informed, triple bottom line, multi-criteria decision analysis (CRTM) planning framework for integrated urban water management decisions. The CRTM framework emerged from the obstacles and stakeholder needs encountered during a study evaluating alternative dual water supply strategies in Fort Collins, Colorado. The study evaluated four strategies for the dual supply of raw and treated water including centralized and decentralized water treatment, varying distribution system scales, and integration of existing irrigation ditches with raw water landscape irrigation systems. The results suggest that while the alternative dual water supply strategies offer many social and environmental benefits, the optimal strategies are dependent on local conditions and stakeholder priorities. The sensitivity analysis revealed the key parameters driving uncertainty in alternative performance were regulatory and political reinforcing the importance of participation from a wide variety of stakeholders. Evaluation of the decision process suggests the CRTM framework increased knowledge sharing between study participants. Stakeholder contributions enabled a comprehensive evaluation of the option space while examining the financial, social and environmental benefits and trade-offs of the alternatives. Most importantly, evolving the framework successfully maintained stakeholder participation throughout the study.
Open Access
A cross sector evaluation comparing nutrient removal strategies in urban water systems
(Colorado State University. Libraries, 2019) Hodgson, Brock, author; Sharvelle, Sybil, advisor; Arabi, Mazdak, committee member; Carlson, Ken, committee member; Hoag, Dana, committee member
Water supply management and reduction of nutrient pollution from urban water systems are two of the most important issues facing utility managers today. To better protect water supplies, many states have or are establishing total nitrogen (TN) and/or total phosphorous (TP) loading restrictions from urban water systems. Traditionally, these targets are met by wastewater treatment facility (WWTF) improvements, but stringent regulations can make this challenging and costly. As regulations increase it may be necessary or more cost effective to consider additional options for nutrient removal from urban water systems including water management practices or stormwater control measures (SCMs). There are a wide range treatment approaches that can be considered at a WWTF for improving nutrient removal but evaluating these scenarios can be challenging and is traditionally accomplished via mechanistic models specific to individual WWTFs requiring process expertise and a rigorous sampling and analysis program. Water management practices are traditionally considered for water supply improvement, however there is little research to characterize the impact on water quality. There is a need for additional research and tools that facilitate estimating effectiveness of various nutrient removal technologies and consider cross sector strategies and tradeoffs between adoption of practices. To understand the impacts of water management practices, the impact of indoor conservation, source separation, and graywater and effluent reuse on WWTF influent and effluent and downstream water quality was characterized identifying which practices can potentially help meet nutrient reduction targets. For WWTF technologies, previously calibrated and validated mechanistic models were used to develop a simplified empirical model to more easily estimate and compare the effectiveness of various WWTF technologies as a function of influent wastewater quality. The findings from the water management practice evaluation and WWTF treatment comparison provided the framework for conducting an urban water systems evaluation by using the developed empirical models combined with the benefit of stormwater control measures (SCMs) characterized via the Simple Method to evaluate a multitude of strategies for meeting nutrient removal targets in the urban water system. Lastly, this research considered the impacts on biosolids management with the increase of liquid stream removal at the WWTF. The research identified source separation and effluent reuse as frequent part of effective nutrient removal strategies and part of an optimal nutrient removal strategy, and even necessary under stringent nutrient requirements. In terms of wastewater treatment, the benefit of adopting more advanced wastewater treatment processes will be most beneficial in carbon limited WWTFs, and negligible when there is adequate carbon for biological nitrogen and phosphorous removal. This includes sophisticated processes like nitrite shunt and 5-Stage Bardenpho and sidestream processes like struvite precipitation and ammonia stripping. While improvements to WWTF are likely with adoption of stringent nutrient regulations a multi objective optimization identified water management practices and SCMs to be part of all non-dominated nutrient removal strategies. As nutrient requirements become more stringent, the options for WWTFs in terms of processes are limited and frequently a combination of water management practices and SCMs is necessary. This was demonstrated via a systems analysis of cost-effective nutrient removal solutions in urban water systems that can be easily applied to other urban systems because of the empirical models developed with this research. These tools are necessary to help utility managers identify optimal nutrient removal strategies. As utilities invest in improvements to WWTF operations, there may also be notable impacts on biosolids management, primarily in terms of phosphorous, which may limit land application rates resulting in additional cost or disposal of biosolids that historically have been beneficially used in agriculture. These impacts must also be considered by utility managers when considering optimal nutrient removal strategies from urban water systems.
Open Access
A probabilistic and environmental impact assessment of a cyanobacteria-based biorefinery
(Colorado State University. Libraries, 2021) Beattie, Audrey, author; Quinn, Jason C., advisor; Arabi, Mazdak, committee member; Marchese, Anthony, committee member
Microbial based biofuels represent a potential promising solution as an environmentally favorable transportation fuel. Cyanobacteria have many of the same advantages as microalgae: ability for rapid growth in otherwise non-arable regions, suitability for genetic engineering, and simple nutritional needs. Additionally, cyanobacteria can be engineered to secrete valuable co-products that can be harvested independent from the produced biomass. However, little work has been done to identify the processes and the economic and environmental impacts associated with a large-scale cyanobacteria-to-fuels facility. The present study is a concurrent techno-economic and life cycle assessment of a facility that generates fuels and methyl laurate, an oleochemical, from the cyanobacterial species Synechocystis sp. PCC 6803. The biorefinery model includes all aspects of cultivation, separation of the secreted methyl laurate, biomass harvesting and fuel processing via hydrothermal liquefaction (HTL) of the dewatered biomass. The assessments leverage Monte Carlo analysis (MCA) to address uncertainty and variability inherent in the most significant input parameters, replacing them with probabilistic functions. For the facility configuration producing both fuels and the oleochemical co-product, the MCA average minimum fuel selling price (MFSP) is $2.47 per liter or $9.34 per gallon of gasoline equivalent (gge) with the corresponding average global warming potential determined to be 118 g CO2-eq/MJ-1. The case producing only fuels results in an MCA average MFSP of $2.01/L-1 ($7.60/gge) and an average environmental impact of 100 g CO2-eq/MJ-1. These results are compared to static optimistic and conservative scenario analysis estimates, illustrating the over- and under-estimation of outcomes associated with non-stochastic methods. Suggested facility improvements include increases in pond productivity of both the biomass and methyl laurate oil production, as well as improvements to carbon utilization and bio-crude yield from HTL processing.
Embargo
Addressing barriers to the wide-scale implementation of roof runoff and stormwater collection and use projects for non-potable end uses in the U.S.
(Colorado State University. Libraries, 2023) Alja'fari, Jumana Hamdi Mahmoud, author; Sharvelle, Sybil, advisor; Arabi, Mazdak, committee member; De Long, Susan, committee member; Nelson, Tracy, committee member
Roof runoff and stormwater have the potential to serve as important local water sources and diversify the water budget portfolio in regions with dwindling water supplies and increasing populations. Due to the lack of guidance regulating the use of roof runoff for non-potable end uses, characterizing its microbial quality is necessary to promote roof runoff use across the U.S. Similarly, the degree of stormwater microbial contamination is still not well understood, and uncertainty about the required treatment is a barrier for the implementation of stormwater capture and use (SCU) projects. Stormwater runoff could become contaminated with human fecal matter in areas with aging infrastructure where raw wastewater exfiltrate from sewer networks to stormwater collection networks, areas with homeless encampments, or areas with sanitary sewer overflows (SSOs). Stormwater practitioners wanting to benefit from stormwater to augment the available water resources struggle with the selection and design of efficient stormwater treatment trains that are protective of public health for the designated end use. Knowledge of the degree to which stormwater is contaminated with human fecal matter, termed here as the human fecal contamination analog (HFCA), is critical for the design process and estimating the required pathogen log reduction targets (LRTs).To address the barrier to wide-scale implementations of roof runoff collection and use projects, a 2-year research study was designed to examine roof runoff microbial quality in four U.S. cities: Fort Collins, CO; Tucson, AZ; Baltimore, MD; and Miami, FL. Sample collection was conducted as part of a citizen science approach. The occurrence and concentrations of indicator organisms (E. coli and enterococci) and potentially human-infectious pathogens (PHIPs) including Salmonella spp., Campylobacter spp., Giardia duodenalis, and Cryptosporidium parvum in roof runoff were determined using culture methods and digital droplet polymerase chain reaction (ddPCR), respectively. E. coli and enterococci were detected in 73.4% and 96.2% of the analyzed samples, respectively. Concentrations of both E. coli and enterococci ranged from <0 log10 to >3.38 log10 MPN/100 mL. Salmonella spp. invA, Campylobacter spp. ceuE, and G. duodenalis β – giardin gene targets were detected in 8.9%, 2.5%, and 5.1% of the analyzed samples, respectively. Campylobacter spp. mapA and C. parvum 18S rRNA gene targets were not detected in any of the analyzed samples. This dataset represents the largest-scale study to date of enteric pathogens in U.S. roof runoff collections and will inform treatment targets for different non-potable end uses for roof runoff. To address barriers to the wide-scale implementation of SCU projects for non-potable end uses, stormwater microbial contamination originating from human fecal matter was examined using the detection frequencies and concentrations of human microbial source tracking (MST) markers and PHIPs observed in stormwater. Measurements of human MST markers in wet weather flows, dry weather flows, and influent wastewater in addition to measurements of viral and protozoan pathogens in wet weather flows and influent wastewater were compiled through a systematic review. Human MST marker and PHIP datasets were statistically analyzed and used to estimate HFCAs based on relative concentrations of microbial contaminants in stormwater compared to municipal wastewater. Analytical statistical distributions of the original data, unpaired Monte Carlo simulation, and paired Monte Carlo simulation were applied for the estimates of HFCAs in wet and dry weather flows. Estimates of human MST-based HFCAs are more reliable than PHIP-based HFCAs because the current PHIP datasets are limited by detection limits and the range of data observed within the statistical distributions. Unpaired Monte Carlo simulations and analytical statistical distributions were found to be the best methods for the estimation of human MST-based HFCAs in wet and dry weather flows which ranged from <10-7.0 to 10-1.5 and 10-12 to 10-2.6, respectively. Pathogen LRTs were determined in this study using HFCAHuman MST Markers and previously published quantitative microbial risk assessments (QMRAs) to guide the selection of stormwater treatment process trains based on the intended end use (e.g., unrestricted irrigation or indoor use) of stormwater. Combinations of stormwater treatment trains at varying HFCA levels were evaluated based on complexity and reliability of the suggested trains. To use stormwater safely for unrestricted irrigation and indoor uses, treatment trains containing both filtration and disinfection unit processes are required. The HFCA threshold beyond which the complexity of stormwater trains becomes considerably higher is 10-4. Performance evaluation of the suggested stormwater treatment trains revealed that trains consisting of membrane filtration and at least two disinfection unit treatment processes, specifically ultraviolet (UV) and ozone (O3) or UV and chloramine are recommended at HFCA values of 10-3, 10-2, and 10-1. At HFCA value of 10-4, a treatment train consisting of membrane filtration and O3 or chloramine is recommended. The use of free chlorination at all HFCA levels is not recommended due to the high continuous monitoring requirements associated with the use of free Cl2.
Open Access
Aircraft survivability modeling, evaluation, and optimization for multi-UAV operational scenarios
(Colorado State University. Libraries, 2021) Lunsford, Ian, author; Bradley, Thomas, advisor; Borky, John, committee member; Shahroudi, Kamran, committee member; Arabi, Mazdak, committee member
The unmanned aerial vehicle (UAV) has become a prominent aircraft design throughout aerospace applications including commercial, civilian, and military. A UAV is preferred in some missions and applications due to its unique abilities compared to manned aircraft. This dissertation aims to define an improved understanding of the concepts and modeling of aircraft survivability, as applied to UAVs. Traditionally, survivability as a field has defined and considered survivability primarily in the context of manned aircraft, and single aircraft. With UAV's increasing importance in multi-UAV operational scenarios, it has become increasingly important to understand aircraft survivability for singles and groups of UAVs. This research effort has been structured into three research questions defining contributions in survivability modeling, validation, and UAV aircraft design. Research Question 1 seeks to demonstrate the feasibility of a parametric model of UAV survivability. The result is a UAV survivability model and simulation which illustrates key tradeoffs within UAV survivability. The effects on survivability on UAV design characteristics (speed, wing area, drag and lift coefficients) is quantified specific to the detailed lethal envelope simulation method. Research Question 2 aims to verify and validate the UAV survivability simulation, providing evidence of the predictive capability of the survivability simulation results. Evidence is presented for verification and validation through comparison to previous modeling efforts, through solicitation of expert opinion, and through parameter variability and sensitivity analysis. Lastly, Research Question 3 seeks to apply the simulation results to multi-UAV tactical evaluation and single aircraft design. The results illustrate the level of improvement that can be realized through UAV design including armoring (a 25% survivability improvement through 1000kg of armoring), speed increases (a 100 mph increase in cruise speed realizes a 14% decrease in killability), and other relevant design variables. Results also demonstrate that multi-UAV tactics can improve the survivability of UAVs in combat. Loyal wingman tactics are simulated to increase the survivability of a C-130J (equivalent UAV) from 19.8% to 40.0%. Other single UAV tactics such as fuel dumping, afterburners are evaluated under the same framework for their relative effectiveness. This dissertation answers the described research questions by presenting an aircraft survivability evaluation approach that relates survivability with modern UAV applications, emerging threats, multi-UAV tactics, and UAV design. Aircraft survivability encounters with modern UAV countermeasures are considered and simulated. UAV metrics of performance are modeled and simulated to describe aircraft design parameters sensitive to improving aircraft survivability. By evaluating aircraft survivability with a modern multi-UAV tactical perspective, this study seeks to provide the UAV designer with more complete vision of survivability-derived design criteria.
Open Access
An algorithm for accurate ionospheric total electron content and receiver bias estimation using GPS measurements
(Colorado State University. Libraries, 2016) Bourne, Harrison W., author; Morton, Yu, advisor; Arabi, Mazdak, committee member; Kreidenweis-Dandy, Sonia, committee member; Van Graas, Frank, committee member
The ionospheric total electron content (TEC) is the integrated electron density across a unit area. TEC is an important property of the ionosphere. Accurate estimation of TEC and TEC spatial distributions are needed for many space-based applications such as precise positioning, navigation, and timing. The Global Positioning System (GPS) provides one of the most versatile methods for measuring the ionosphere TEC, as it has global coverage, high temporal resolution, and relatively high spatial resolution. The objective of this thesis is to develop an algorithm for accurate estimation of the TEC using dual-frequency GPS receiver measurements and simultaneously estimate the receiver hardware bias in order to mitigate its effect on the TEC. This method assumes the TEC in the portion of sky visible to the receiver can be represented as a two dimensional sheet with an absolute value and spacial gradients with respect to latitude and longitude. A code-phase multipath noise estimation algorithm is integrated with the TEC estimation process to mitigate environmental multipath contamination of the measurements. The integrated algorithm produces an approximate map of local TEC using a single dual-frequency receiver while minimizing both multipath induced errors and the receiver hardware bias. The goal of this method is to provide an accurate map of the ionosphere TEC, in the region local to the receiver, without the need for a network of receivers and in the absence of knowledge of the receiver hardware induced bias. This thesis describes the algorithm, its implementation, and attempts to validate the method through comparison with incoherent scatter radar (ISR) data from low, mid, and high latitude locations.
Open Access
Analysis of nutrient removal at the Drake Water Reclamation Facility
(Colorado State University. Libraries, 2016) Mueller, Lincoln H., author; Sharvelle, Sybil, advisor; Arabi, Mazdak, committee member; Rice, Doug, committee member
Since the 1960’s, the Federal Government through the United States Environmental Protection Agency (USEPA) has been working to create and enforce regulations to protect and counteract the degradation experienced in the nation’s waterways due to increased nutrient loading (primarily phosphorus and nitrogen). The eutrophication caused by excess levels of these nutrients is not only an aesthetic issue, but is toxic to aquatic life and can also create issues detrimental to human health. In 2007, the Colorado Department of Public Health and Environment began working on new nutrient regulations for state dischargers, particularly larger Publicly Owned Treatment Works (POTWs) like the City of Fort Collins and its two wastewater treatment plants, Mulberry Water Reclamation Facility (MWRF) and Drake Water Reclamation Facility (DWRF). Since 2008, The City of Fort Collins has been upgrading its secondary treatment systems to Biological Nutrient Removal (BNR) in preparation for National Pollutant Discharge Elimination System (NPDES) permit compliance in 2020. Early in the design process, it was determined that DWRF suffered from a limitation in influent carbon for adequate nutrient removal and carbon addition would need to be considered. The City analyzed various local carbon sources and has been working to determine the viability of beer waste from local breweries as a viable carbon source. The overarching goal of this work is to evaluate the current nutrient removal efforts at DWRF to help determine if adjustments are required to the wastewater treatment Master Plan to consistently meet Colorado’s Regulation 85 nutrient discharge limits. This study included monitoring of nutrient water quality values at specific points in the treatment system while adding beer waste at varying flow rates and durations to determine its effect on the system. Different automated control strategies were tested using several dosage schemes including Oxidation Reduction Potential (ORP) values. Finally, water quality data was analyzed and compared alongside historical nitrogen and phosphorus values to evaluate the effects of the beer waste addition to effluent quality and plant removal performance. The initial values for effluent total inorganic nitrogen showed promise, averaging 9.79 mg/L in comparison to 12.05 mg/L when beer waste was not added. However, a mass balance comparison with influent nitrogen values showed no significant difference in BNR process performance for nitrogen with the beer addition. Effluent phosphorus values averaged 2.24 mg/L-P which was slightly lower than without beer waste addition (2.42 mg/L), but not considered a statistically significant decrease. During the study, an observation was made that adjusting time-of-day and flowrate of the dewatering centrate return significantly decreased effluent phosphorus concentrations down to 1.1 mg/L, significantly lower than P concentrations without beer addition (p < 0.05). An analysis of phosphorus removal at DWRF also highlighted the historical improvement of phosphorus removal as BNR improvements are brought on-line, even though the required effluent limits required by Regulation 85 have not been achieved yet. Overall, carbon addition via beer waste has shown to have positive impact on DWRF’s ability to remove nutrients. Lower effluent concentrations of nitrogen were achieved when beer waste was added to DWRF and lower effluent P concentrations were also achieved as long as centrate return flow was controlled. Additional study is required for long-term control of centrate return flows which may include the analysis of side-stream treatment solutions. Additional analysis to determine the role of beer waste addition independent of centrate flow returns is also recommended.
Open Access
Assessing benefits and consequences of water conservation and fit for purpose water systems
(Colorado State University. Libraries, 2020) Patel, Saloni N., author; Sharvelle, Sybil, advisor; Arabi, Mazdak, committee member; Nelson, Tracy, committee member
Rising population accompanied with urbanization is increasingly challenging the resilience and capacity of traditional water management system. The migration of the human population to urban areas has given birth to sprawling new developments and re-developments which poses serious challenges to conserve and manage water. Water managers and policy makers are faced with an arduous task to enhance conventional water management systems by implementing Integrated Urban Water Management and hybrid centralized-decentralized systems. To enable informed decisions on water demand management strategies based on water demand reduction, cost, energy savings, etc., understanding benefits and consequences is of utmost importance. Benefits and consequences of water conservation and reuse are seldom considered while making quantitative decisions, mainly due to lack of supporting data or methodology. This research fills this knowledge gap by providing methodology on identifying, developing and quantifying a set of indicators that measure performance for water demand reduction strategies including conservation strategies and use of alternate water sources (i.e., fit for purpose water) in triple bottom line (TBL) categories. Literature review, triple bottom line (TBL) evaluation, and Multi-Criteria Decision Analyses (MCDA) were used to develop a set of indicators to assess water demand reduction strategies. To demonstrate the use of indicators to inform water management decisions, TBL indicator analysis was performed on Globeville-Elyria-Swansea (GES) community in Denver, Colorado using Integrated Urban Water Model (IUWM). The results from TBL indicator analysis suggests that use of stormwater performed well across all indicator categories, it achieved high water demand reduction, was energy efficient and also publicly accepted. Further cost comparison and MCDA scores revealed, Stormwater for Potable & Irrigation as the top performing end use. Use of stormwater as a supply has potential for large reduction in demand for traditional supplies and also offers notable social and environmental benefits. Water rights issues and costs remain barriers for adoption of this practice that need to be overcome to realize the benefits.
Open Access
Assessing the use of dual-drainage modeling to determine the effects of green stormwater infrastructure networks on events of roadway flooding
(Colorado State University. Libraries, 2020) Knight, Kathryn, author; Bhaskar, Aditi, advisor; Arabi, Mazdak, committee member; Kampf, Stephanie, committee member
Roadway flooding occurs when a stormwater network does not have the capacity to drain all runoff generated by precipitation. Roadway flooding causes damage to infrastructure and property, risks to human health and safety, and disruptions to transportation systems. Green stormwater infrastructure (GSI) has been increasingly used to reduce stormwater input to the subsurface stormwater network, stormwater draining to urban streams, and to improve water quality. It is unclear how GSI interacts with surface runoff and stormwater structures to affect the spatial extent and distribution of roadway flooding. This interaction was explored using a dual drainage model with individual stormwater structures represented, fine spatial resolution, and bidirectional flow between the subsurface stormwater network and surface runoff. The model was developed using the Stormwater Management Model for PC (PCSWMM) in the urban watershed Harvard Gulch in Denver, Colorado. We examined how dual drainage modeling could reveal the effect of converting between 1% and 5% of directly connected impervious area (DCIA) in the watershed to bioretention GSI on the extent, depth, and distribution of roadway flooding. Results of the surface flooding model were generally co-located with resident reports related to flooding within the study area. Results show that even for 1% of DCIA converted to GSI, the extent and mean depth of roadway flooding was reduced for the duration of the simulation, and increasing GSI conversion further reduced roadway flooding depth and extent. We found diminishing returns in the roadway flood extent reduction per additional percentage of DCIA converted to GSI beyond 2.5%, whereas diminishing returns occurred beyond 1% conversion to GSI for mean roadway flood depth reduction. This work also examined the limitations to the accurate representation of roadway flooding due to incomplete input data, a lack of observational data for urban floods, GSI placement methods, and high computational demands. With future work to reduce limitations, detailed dual drainage modeling has the potential to better predict what strategies will mitigate roadway flooding.
Open Access
Autonomous management of cost, performance, and resource uncertainty for migration of applications to infrastructure-as-a-service (IaaS) clouds
(Colorado State University. Libraries, 2014) Lloyd, Wes J., author; Pallickara, Shrideep, advisor; Arabi, Mazdak, committee member; Bieman, James, committee member; David, Olaf, committee member; Massey, Daniel, committee member
Infrastructure-as-a-Service (IaaS) clouds abstract physical hardware to provide computing resources on demand as a software service. This abstraction leads to the simplistic view that computing resources are homogeneous and infinite scaling potential exists to easily resolve all performance challenges. Adoption of cloud computing, in practice however, presents many resource management challenges forcing practitioners to balance cost and performance tradeoffs to successfully migrate applications. These challenges can be broken down into three primary concerns that involve determining what, where, and when infrastructure should be provisioned. In this dissertation we address these challenges including: (1) performance variance from resource heterogeneity, virtualization overhead, and the plethora of vaguely defined resource types; (2) virtual machine (VM) placement, component composition, service isolation, provisioning variation, and resource contention for multitenancy; and (3) dynamic scaling and resource elasticity to alleviate performance bottlenecks. These resource management challenges are addressed through the development and evaluation of autonomous algorithms and methodologies that result in demonstrably better performance and lower monetary costs for application deployments to both public and private IaaS clouds. This dissertation makes three primary contributions to advance cloud infrastructure management for application hosting. First, it includes design of resource utilization models based on step-wise multiple linear regression and artificial neural networks that support prediction of better performing component compositions. The total number of possible compositions is governed by Bell's Number that results in a combinatorially explosive search space. Second, it includes algorithms to improve VM placements to mitigate resource heterogeneity and contention using a load-aware VM placement scheduler, and autonomous detection of under-performing VMs to spur replacement. Third, it describes a workload cost prediction methodology that harnesses regression models and heuristics to support determination of infrastructure alternatives that reduce hosting costs. Our methodology achieves infrastructure predictions with an average mean absolute error of only 0.3125 VMs for multiple workloads.
Open Access
Development of a GIS based tool to analyze produced water from oil and gas wells and prediction of equilibrium concentrations using CalcAQ
(Colorado State University. Libraries, 2013) Dhanasekar, Ashwin, author; Carlson, Kenneth H., advisor; Arabi, Mazdak, committee member; Sutton, Sally, committee member
New extraction techniques based on hydraulic fracturing and horizontal drilling have significantly increased the available oil and gas in the United States. Producing oil and gas from shale formations is the main source of these unconventional resources. When shale formations are hydraulically fractured to increase the permeability, up to 5 million gallons of water can be used for each well. The significant use of water has caused concerns by several stakeholders, particularly in regions that are constantly facing water shortages such as Texas or Colorado. After the well is fractured, large amounts of water return as frac flowback and then after the well is put into production, water that is coproduced with oil and gas must be collected for the life of the well. The produced water has hazardous characteristics since it has been in contact with oil and gas for millions of years and disposal or reuse is an important part of an oil and gas operation. Current water management for produced water includes underground injection and surface disposal or reuse. Owing to a large amount of total dissolved solids (TDS), metals and hydrocarbons (e.g. BTEX) in the produced water, the brine needs to be treated to achieve acceptable water quality for subsequent disposal or reuse. Reusing and recycling of produced water for drilling and fracturing after appropriate treatment has multiple advantages including less truck traffic and lower fresh water demands. The objective of the research in this thesis was to integrate the OLI chemical equilibrium model into the OWM (Optimized Water Management) tool framework to allow chemical equilibrium calculations to be made for each well and in the aggregate throughout the Wattenberg oil and gas field of northern Colorado. The calculations from this model can then be used as design criteria for treatment train definition based on the desired water disposal outcome. OLI Systems software was developed for the chemical and oil and gas industry and is well suited as a module for calculating chemical equilibrium values for produced water and frac flowback water. The research described in this thesis includes predictions of equilibrium chemistry, solids precipitation and scale forming index, based on water quality data collected in the field. The model can also predict requirements for combining and treating produced water streams to achieve process objectives. At the same time, water quality will be analyzed after detailed sampling from various parts of the field. Finally, water quality after precipitation, settling and filtration has been used to estimate the osmotic pressure and design reverse osmosis processes for different levels of TDS rejection. This will be integrated with a customized ArcGIS tool that will help in predicting treatment specifics on a spatial scale.
Open Access
Development of a watershed modeling selection program and simple equations as an alternative to complex watershed modeling
(Colorado State University. Libraries, 2013) Cho, Yongdeok, author; Roesner, Larry A., advisor; Grigg, Neil S., committee member; Arabi, Mazdak, committee member; Stednick, John, committee member
Population pressures, land-use conversion and its resulting pollution consequences appear to be the major diffuse pollution problems of today. Research also indicates that the increase in imperviousness of land due to urbanization increases the volume, rate of stormwater runoff causing increased channel erosion and flooding downstream, water quality contamination, aquatic biota, and drinking water supplies. In the past, negative impacts were never seriously considered as urbanization increased, but the attitude of citizens and governments are changing and people now want to retain, restore or rehabilitate existing waterways, and manage future urban and rural development in order to improve environmental conditions. Water quality management in the contributing watersheds is vital to the management of water quality in the main stem rivers. Hence, policy makers should decide which places should be considered for restoration projects based on priority analyses. To carry out these evaluations in Korea, mathematical models are needed to forecast the environmental results after applying watershed restoration measures. However, the scope of sophisticated watershed modeling is very complicated, expensive and time consuming, and not really required for planning level decision making. Therefore, simpler evaluation methods should be applied, that can adequately discern for planning purposes the changes in aquatic environmental quality that can be expected in different watersheds after adapting restoration or protective measures. Thus, this research proposed to create a simple equation specifically for watershed planning. To create such a simple equation, three main tasks were undertaken. The tasks are as follows: (1) the creation of a selection program for available watershed models, (2) establish simple equations to be used instead of watershed models, and (3) verify the simple equations by comparing them with a physically based model (HSPF). In regards to the first task mentioned above, this dissertation presents a review of thirty three watershed models available for watershed planning and shows that these watershed models can not easily be applied to large-scale planning projects that are being undertaken by South Korea like the Four River Restoration Project. One of the main reasons for their inapplicability is that they require vast amounts of data and significant application effort to be used in a prioritization project involving many watersheds (Roesner, personal commucation). In addition, it is vital to select an appropriate watershed model that are realistically models a watershed's conditions and more specifically, to match users' needs. However a selection program has not yet developed, as well. Therefore, eight factors were selected for task 1 to examine the specific characteristics of each of the 33 watershed models in great detail. Based on the results of the 8 factors proposed, the selection program was developed to screen which will be most useful to a project. Based on these literature reviews of the 33 available watershed models but unrealistically complex models, it was determined that a simpler model utilizing accessible base data, such as land use type, is needed to evaluate and prioritize watersheds in the feasibility stage of a spatially large projectstudies for national based projects (i.e. National level). A correlation study between land use types and water quality parameters has been published (Tu, 2011, Mehaffey et al., 2005, Schoonover et al., 2005, etc.), however, the research examined the correlation between land usage and water quality in great detail, but did not address any correlations to implement real-based watersheds. Therefore, Task 2 is the development of simple equstions, for this task, two important sub-tasks were undertaken 1) Hydrology (rainfall), geology (slope), and land usage data were analyzed to verify their relationships with the water quality (BOD, COD, T-N, T-P) in the watershed, and 2) Simple Equations were constructed based on Statistical Methods (Excel Solver, Statistical Analysis Systems) and Data Mining (Model Tree, Artificial Neural Network, and Radial Based Function) in order to prove their accuracy. Thus, if the equations are accurate, they can be used to prioritize basins within a watershed with respect to their impact on water quality in the mainstem river. For the final task, task 3, Simple Equations were verified by comparing them with a physically based model, HSPF, based upon the real-based watersheds which are located in South Korea in order to prove the Simple Equations are capable of being a reliable alternative to physically based models. These simple equations could be used to allow management to identify and prioritize restoration and rehabilitation areas in a watershed even though sufficient data had yet been collected to satisfy the requirements of a physically based model.
Open Access
Erosion mapping and sediment yield of the Kabul River Basin, Afghanistan
(Colorado State University. Libraries, 2013) Sahaar, Ahmad Shukran, author; Julien, Pierre Y., advisor; Arabi, Mazdak, committee member; Kampf, Stephanie K., committee member
Soil erosion by water is a serious issue in Afghanistan. Due to the geographic landscape, soil and climatic conditions, and the latest deforestation activities, there has been intensive soil erosion which has resulted in prolonged and great impact on social and economic development of the region. In fact, recent environmental assessment shows that decades of war and continuous drought have resulted in widespread environmental degradation throughout the country; therefore, mapping of soil erosion at the basin scale is urgently needed. The Kabul River Basin was selected for the purpose of erosion and sedimentation modeling due to its great socio-economic impact. The main objectives of this study include: (1) calculations of the annual average soil loss rates at the basin level; (2) spatial distribution of soil erosion rates at the basin level; (3) predictions of deforestation effects on sediment losses under different land cover scenarios at the watershed level; and (4) calculation of sediment delivery ratios based on soil erosion rates, and sediment yields at the sub-watershed levels in the basin. This study uses the Revised Universal Soil Loss Equation (RUSLE) model combined with Geographic Information System (GIS) techniques to analyze the gross soil loss rates and the spatial distribution of soil loss rates under different land uses. Digital elevation model (DEM), average annual precipitation data, land cover map and soil type map were used to define the parameters of the RUSLE model. The annual average soil loss rate of the Kabul River Basin was estimated to be 19 tons/acre/year (4748 tons/km2/year), and the gross mean annual soil loss rate found to be 47 million tons/year. By producing 57 % of the total annual average soil loss, rangelands were the primary contributor to the basin. In case of the spatial distribution of erosion rates at the Kabul River Basin, the relationship between probability and annual average soil loss rates were analyzed. The analysis indicated that up to sixty percent of the mean annual soil loss rates are in the range of tolerable soil loss rate (0 - 5 tons/acre/year). Moreover, northern part of the basin is prone to more extensive erosion than the southern part. The study predicted that if the forest region of the Kunar watershed is completely reduced to barren lands, the watershed will produce five times more sediment than the estimated soil loss rate from 1993's UN-FAO land cover map. The annual average soil loss rate in this watershed was about 29 tons/acre/year but it will increase to 149 tons/acre/year as deforestation continues to take place in the watershed. The range of sediment delivery ratios for the basin's rivers is 2.5 -10.8 %. Based on this evaluation, the sediment delivery ratio for the sediment gauging stations in the basin are in the similar range of predicted values by the methods of Boyce, Renfro, Williams and Maner.
Open Access
Evaluation and improvement of CERES-Maize evapotranspiration simulations under full and limited irrigation treatments in northern Colorado
(Colorado State University. Libraries, 2011) DeJonge, Kendall, author; Garcia, Luis, advisor; Andales, Allan, advisor; Arabi, Mazdak, committee member; Hansen, Neil C., committee member; Ascough, Jim, II, committee member
Population growth in urbanizing areas such as the Front Range of Colorado has led to increased pressure to transfer water from agriculture to municipalities. In some cases, farmers may remain agriculturally productive while practicing "limited or deficit irrigation," where substantial yields may be obtained with reduced water applications during the non-water sensitive growth stages. Savings in crop evapotranspiration (ET) could then be leased to municipalities or other entities as desired. This dissertation examined the benefit of limited irrigation in comparison with full irrigation in the northern Front Range of Colorado, in both an on-field context and in a crop modeling context. Because of Colorado water law the quantification of ET is especially important, as ET is considered a consumptive use of the crop and therefore can be transferred between entities. The overall goal was to improve understanding of both field and model maize yield response to limited water supplies, accurately simulate this management scenario with a crop growth model, and evaluate and improve model simulation of ET. This goal was achieved in the context of three studies that are included in this dissertation. First, the CERES-Maize corn growth model was calibrated and evaluated for full and limited irrigation of corn; the model generally simulated many aspects of crop growth, including yield, leaf area index, leaf growth, and phenology. The model performed better overall for the full irrigation treatment than the limited irrigation treatment. The model underestimated treatment differences in cumulative ET between treatments, simulating too little ET under full irrigation (-7.2% relative error over three years) and too much ET under limited irrigation (12.7% relative error over the same three years). Second, a global sensitivity analysis was performed on genotype and soil hydraulic parameters in addition to radiation use efficiency, using full and limited irrigation treatments and two global sensitivity analysis methods (Morris and Sobol'). Outputs evaluated included phenological stages, leaf growth, leaf area index, yield, and ET. The model showed similar sensitivities between treatments in regard to phenology and leaf expansion. However, leaf area index, yield, and ET were primarily sensitive to genotype parameters under full irrigation, but under limited irrigation showed increased sensitivity to soil hydraulic parameters. Results from both sensitivity analysis methods were highly correlated. Finally, the model processes that govern major aspects of the water balance, particularly the calculation of potential ET and the partitioning of this value into potential soil evaporation and potential plant transpiration, were evaluated and improved. A new equation for the crop coefficient as a function of LAI was added to better represent the ET demand based on plant canopy. This new formula, as well as a new coefficient determining ET partitioning, were evaluated using five years of management and weather data, and both irrigation treatments. Under full irrigation simulated yield was unchanged compared to previous simulations, while ET and water use efficiency (WUE) were simulated closer to observations. Under limited irrigation, ET and WUE simulations were improved, with RMSD reduced from 80.9 mm to 49.9 mm for ET and from 5.97 kg/ha-mm to 2.86 kg/ha-mm for WUE. While this model change is a significant improvement in regard to the estimation of ET under water stress, it is further recommended that future model changes attempt to incorporate physiological response to stress, such as stomatal conductance or canopy temperature, to better represent plant response to water stress.
Open Access
Excess nutrients and cultural eutrophication of the Cache la Poudre River: a study of the occurrence and transport of phosphorus
(Colorado State University. Libraries, 2011) Goodwin, Stephen A., author; Carlson, Kenneth, advisor; Arabi, Mazdak, committee member; Keske, Catherine, committee member
Excess nutrients resulting in eutrophication of surface waters has become one of the greatest water quality challenges of our time. The development of an effective nutrient management strategy is essential to protecting surface water quality, public health, aquatic ecosystems and economic interests. The complexity of cultural eutrophication and the influence of nutrients, especially in streams and rivers, has delayed the development of an effective regulation and a nationwide management strategy. Variations in hydrologic conditions, geology and both urban and agricultural land use can dramatically influence phosphorus loads to receiving waters. Furthermore, several complex mechanism exist within a river or stream (e.g. the phosphate buffer, light availability, hydraulic retention time, phosphorus spiraling, etc.) that change the concentration and impact of nutrient concentrations and resulting eutrophication. Temporal and spatial variations result in changing and often imprecise threshold between healthy and unhealthy ecosystems. For this reason, it is important for policy makers to understand how the assimilative nutrient capacity of waterways varies with environmental, seasonal and loading conditions, and that it is not the same for every watershed or even within the same waterway. A one-size-fits all technology solution or a state-wide numeric standard that does not account for these variations is misguided and will result in costly upgrades with minimal improvements to water quality. The most efficient nutrient management method is one that best matches the nutrient load delivered with the maximum assimilative capacity of the receiving water. This study provides an in-depth analysis of the Cache la Poudre River Watershed in Northern Colorado over the course of a year to examine the influence of different sources, transport pathways and hydrologic regimes on phosphorus concentrations along an urban-agricultural gradient. An extensive and comprehensive design of sampling locations was used to best capture the anthropogenic influence (e.g. wastewater treatment plants, concentrated feeding animal operations, land uses) and transport pathways (e.g. irrigation ditches, overland transport, streams and rivers) of phosphorus within the watershed. Exploratory models were used to better understand the influence of geospatial variables on the occurrence and transport of phosphorus within the watershed. The influence of phosphorus from wastewater treatment plants (WWTPS) to the Cache la Poudre River was examined in detail. A mass-balance of the phosphorus load in the river and the effluent from WWTPs was used to best estimate the influence of WWTPs. Projections of the influence proposed regulations that reduce WWTP effluent concentrations were made as well as the resulting impact to the river and water quality. The role of sediment was investigated to better characterize and explain the temporal variations of phosphorus concentrations within this complex system. A brief economic analysis and associated improvements to water quality are discussed as well as effective management strategies in the Cache la Poudre River Watershed. The objective of the study is to aid in the development of an efficient and effective nutrient management strategy for the Cache la Poudre River Basin and other similar mixed land use watersheds, as well as providing a foundation for creating a decision support system for water quality analysis, monitoring and management.
Open Access
Factors contributing to the adaptive capacity of South Platte River Basin water providers and implications for regional vulnerability
(Colorado State University. Libraries, 2019) Runyon, Amber N., author; Ojima, Dennis, advisor; Arabi, Mazdak, committee member; Betsill, Michele M., committee member; Boone, Randall B., committee member; McNeeley, Shannon, committee member
To view the abstract, please see the full text of the document.
Open Access
Human behavior in the context of water scarcity
(Colorado State University. Libraries, 2017) Maas, Alexander, author; Goemans, Christopher, advisor; Manning, Dale, advisor; Kroll, Stephan, committee member; Arabi, Mazdak, committee member
This dissertation in comprised of three chapters which use microeconomic principles and empirics to examine human behavior in the face of water scarcity. Chapter one uses an experiment to investigate the effect of threshold uncertainty on common pool resource (CPR) consumption decisions. Chapter two uses latent class analysis to endogenously identify unique household classes with respect to their water use decisions under various price and weather scenarios. Chapter three directly compares the residential water consumption decisions of households motivated primarily by social and environmental outcomes with households primarily motivated by cost and convenience. The overall goal of my work is to elucidate the behavior and motivation that leads to particular consumption decisions in the presence of water scarcity. Chapter one explicitly models a CPR in which uncertainty around a tipping point—stock level below which the resource is destroyed—can engender two distinct Nash Equilibria (NE), both of which lead to a Tragedy of the Commons. We theoretically and empirically test how differing levels of uncertainty around the location of this tipping point affects individual and group consumption choices. Our results suggest that the presence of uncertainty increases the likelihood that individuals choose the NE consistent with resource destruction (even though it is an inferior NE) and to ignore potential impacts on resource stocks. However, conditional on choosing the superior NE, increased uncertainty does not affect consumption rates in the experiment. In addition, we introduce tax and fine policies and find that they reduce overall consumption rates and the probability that individuals choose to destroy the resource. Chapter 2 and 3, do not explicitly model scarcity, but they examine household water consumption in the arid southwest where water scarcity is a pervasive concern. Both chapters two and three use data from Fort Collins Utilities to investigate household heterogeneity and water consumption decisions. Chapter 2 uses a finite mixture model to endogenously identify distinct water use patterns. Estimated price elasticities are consistent with previous literature and range from -0.1 in the spring for the unresponsive class to -0.8 in the summer for the responsive class. We find significant evidence that households classes exist and can generally be broken into high responsive and low responsive classes. Our results also suggest that changes in precipitation will have little effect on demand, but a 2 degree temperature increase will increase residential water demand throughout the city by approximately 5%. Lastly, chapter two investigates the burden of price increases and weather shocks across household class and income level. We find that the vast majority of water reductions due to price increases come from middle and high income homes. Chapter three is similar to chapter two in motivation, but distinct in methodology. Chapter 3 poses and attempts to answer a simple question: do households primarily motivated by environmental and social (E&S) consideration consume water differently than households motivated primarily by cost and convenience (C&C)? Results strongly indicate that E&S consumers use less water than (C&C) consumers. Results also suggest that E&S motivated households consume significantly more water as temperatures rise. However, there is no statistical difference between E&S and C&C consumers in their responses to changing price and precipitation.
Open Access
Impacts of conservation tillage on water quality and soil health characteristics under furrow irrigation
(Colorado State University. Libraries, 2017) Deleon, Emmanuel, author; Bauder, Troy, advisor; Fonte, Steven, committee member; Arabi, Mazdak, committee member
Furrow irrigation-induced sediment and nutrient loss continues to be a serious problem in the Western States of the US. Sediment and nutrients in runoff can eventually be discharged into streams and rivers impairing water quality, causing adverse effects on the environment and reducing soil productivity over time. Continuous intensive tillage along with excessive sediment and nutrient loss ultimately lead to the degradation of soil quality. We hypothesize that conservation tillage under furrow irrigation can reduce the sediment and nutrient losses in surface runoff as well as improve soil quality parameters. The objectives of this research are to compare two conservation tillage treatments, minimum tillage (MT) and strip tillage (ST), to a traditional conventional tillage (CT) system under furrow irrigation and understand the impacts of these practices on annual sediment and nutrient concentrations and loads from irrigation and storm events. We quantified total suspended solids (TSS), total Kejdahl nitrogen (TKN), nitrate (NO3), ammonium (NH4), total nitrogen in aqueous solution (TNa), total phosphorus (TP), dissolved reactive phosphorus (DRP), and total soluble phosphorus (TSP) loads from irrigation runoff over two growing seasons for the three treatments. Relative to CT, conservation tillage reduced TSS loads by 84% and 88% in 2015 and by 98% and 87% in 2016 for MT and ST, respectively. In 2015, TKN was reduced by 80% and 86% in MT and ST respectively when compared to CT. Total P was significantly higher in CT, with an 87% load reduction under MT and ST in 2015 and an 85% load reduction under MT in 2016. Total P concentration (mg L-1) correlated well with TSS concentrations (g L-1) (R2 = 0.72, P < 0.001). Total soluble P loads were significantly higher in the CT treatment when compared to the conservation treatments in the 2015 season. Reduced tillage and residue management in the conservation treatments improved irrigation flow parameters such as reduced runoff. The conservation treatments had a greater impact on sediment-bound than soluble nutrients largely due to surface residue reducing erosion in the furrows. Results show that reduced tillage and residue management are an effective best management practices (BMPs) in sediment and nutrient abatement in irrigation and storm runoff. Furrow irrigation is still practiced in 40% of all irrigated lands in Colorado and it is expected to continue across much of the State. Under furrow-irrigated systems, CT practices are common, but such practices can degrade soil quality. The project sought to examine the effects of conservation tillage on soil health at a production scale, understand relationships between soil parameters, and to evaluate the economic feasibility of conservation practices. Soil biological, physical, and chemical parameters were evaluated during the fifth and sixth years of a study (2015 and 2016) comparing two different management systems, MT and ST, verses CT (the control). Measurements included Active C (POXC), macrofauna diversity and abundance, aggregate stability, infiltration, and residue cover. POXC was significantly higher for MT when compared to CT and ST. Results from both years suggest that conservation treatments increased macrofauna abundance, especially earthworms, and diversity (richness) relative to the control. Aggregate stability was significantly higher in the conservation treatments for 2015, but not in 2016. Infiltration rates in the ST treatment was 18% higher when compared to CT. Residue cover was positively correlated with earthworm abundance while earthworm abundance was positively correlated with aggregated stability and infiltration. When comparing economic cost, and returns among systems, ST and MT treatments had a 39% and 32% greater net return when compared to CT plots. These preliminary results show potential for conservation tillage under furrow-irrigation to improve soil quality parameters as well as increasing net income.
Open Access
Implications of storage subsystem interactions on processing efficiency in data intensive computing
(Colorado State University. Libraries, 2015) Koneru, Hanisha, author; Pallickara, Shrideep, advisor; Pallickara, Sangmi, committee member; Arabi, Mazdak, committee member
Processing frameworks such as MapReduce allow development of programs that operate on voluminous on-disk data. These frameworks typically include support for multiple file/storage subsystems. This decoupling of processing frameworks from the underlying storage subsystem provides a great deal of flexibility in application development. However, as we demonstrate, this flexibility often exacts a price: performance. Given the data volumes, storage subsystems (such as HDFS, MongoDB, and HBase) disperse datasets over a collection of machines. Storage subsystems manage complexity relating to preservation of consistency, redundancy, failure recovery, throughput, and load balancing. Preserving these properties involve message exchanges between distributed subsystem components, updates to in-memory data structures, data movements, and coordination as datasets are staged and system conditions change. Storage subsystems prioritize these properties differently, leading to vastly different network, disk, memory, and CPU footprints for staging and accessing the same dataset. This thesis proposes a methodology for comparing and identifying the storage subsystem suited for the processing that is being performed on a dataset. We profile the network I/O, disk I/O, memory, and CPU costs introduced by a storage subsystem during data staging, data processing, and generation of results. We perform this analysis with different storage subsystems and applications with different disk-I/O to CPU processing ratios.
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.