Theses and Dissertations

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    Resilience of transportation network during post-earthquake emergency response and recovery stages
    (Colorado State University. Libraries, 2023) Wu, Yangyang, author; Chen, Suren, advisor; Bradley, Thomas, committee member; Mahmoud, Hussam, committee member; Jia, Gaofeng, committee member
    Earthquakes can cause casualty, injuries, and extensive infrastructure damages and significantly disrupt transportation networks. Disrupted transportation networks resulting from damaged bridges or debris may cause delays on emergency response activities and impact traffic efficiency and safety during the post-earthquake recovery stage. A functioning post-hazard transportation network is the backbone to support the effective emergency response and maintain efficient post-hazard recovery plans of the whole community. The main purpose of this dissertation is to model and improve the resilience performance of transportation networks during both post-earthquake emergency response and recovery stages. It is expected that the proposed methodologies in this dissertation will help making risk-informed decisions in terms of pre-hazard mitigation planning, emergency medical service management, and post-earthquake restoration planning to enhance the resilience of transportation networks. A suite of novel methodologies is proposed to evaluate and enhance the resilience performance of transportation networks subjected to major earthquakes in this dissertation. Firstly, a resilience modeling framework of traffic networks is developed to simulate the transportation performance during post-earthquake emergency medical response considering interactions between infrastructures, people, and hazard. Secondly, a new approach is proposed to quantify the comprehensive redundancy of transportation networks during post-earthquake emergency medical response considering search-and-rescue efforts and life vitality decay. Thirdly, a methodology is proposed to evaluate the resilience performance of traffic networks in private-vehicle-based post-earthquake emergency medical response considering bridge failure, building debris, and emergency traffic flow. Fourthly, a novel methodology is proposed to assess the post-earthquake resilience of transportation networks considering link functionality, travel time and traffic safety. Finally, a model to simulate time-dependent resilience of degraded transportation networks during post-hazard recovery period is developed to incorporate the time-evolving travel demand of the community.
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    Open Access
    Optimization of sustainability and resilience for transportation projects
    (Colorado State University. Libraries, 2023) Kumar, Shantanu, author; Mehany, Mohammed Hashem, advisor; Grigg, Neil, committee member; Abdallah, Moatassem, committee member; Atadero, Rebecca, committee member; Fisher, Gwen, committee member
    The state of America's infrastructure is old and has been deteriorating and is in need for severe rehabilitation and maintenance. The population has been increasing which has increased the demand for new transportation projects over the last decade. Therefore, it is essential to not just construct new transportation projects but invest in the rehabilitation and maintenance of the existing infrastructure. The transportation sector has the highest greenhouse gas (GHG) emissions among all infrastructure projects. In the transportation sector, the roads and highways subsector have the highest associated emissions which calls for projects in this subsector to be more sustainable. Concurrently, it has been observed that the frequency of natural disasters has increased exponentially in the last few decades which has increased the need to be more resilient. Sustainability and resilience are intertwined but different concepts that need to be explored and analyzed together. Both sustainability and resilience have been quantified using a variety of different methods, and rating system have been one of the most common and widely used methods across the globe for infrastructure projects. In North America (especially the US), the ENVISION rating system created through join efforts of the Harvard graduate School of Design's Zofnass Program of Sustainable Infrastructure and the Institute of Sustainable Infrastructure, has been the most widely used rating system for various infrastructure projects, especially transportation projects. Often, achieving sustainability and resilience is associated with a higher cost. This research proposed optimizing sustainability and resilience while minimizing the life cycle cost (LCC) and GHG emissions using the NSGA-II algorithm. It takes input of all possible strategies within the different dimensions of sustainability and resilience and uses the abovementioned algorithm to determine a list of pareto optimal solutions. These solutions represent a space of acceptable solutions which have high sustainability and resilience while also having low GHG emissions and LCC. This model is intended to assist stakeholder in making decisions to improve the sustainability and resilience while promoting a life cycle thinking. It also provides a unique database creation idea for keeping all sustainable and resilient strategies for different infrastructure projects in one place which can promote an open access feature as more transportation agencies and stakeholders buy-in to the idea of using this model.
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    Open Access
    Large-scale remote sensing of geomorphic change in mulched and unmulched watersheds burned in the 2020 East Troublesome Fire, Colorado
    (Colorado State University. Libraries, 2023) Murray, John Thomas, author; Nelson, Peter, advisor; Kampf, Stephanie, committee member; Morrison, Ryan, committee member
    Elevated levels of sediment transport in post-wildfire landscapes can degrade the hydrologic and geomorphic processes of a river system, damage aquatic habitat, and pose a threat to downstream infrastructure. Hillslope mulching applications have proven to be effective at mitigating runoff and erosion at plot and hillslope scales but the impacts of mulching at the watershed scale remain generally unknown. We conducted repeat aerial surveys of one unmulched and five partially mulched watershed outlets (0.61-1.44 km2) to quantify erosion and deposition in the East Troublesome Fire burn scar. The objectives of the study were (1) to quantify volumes of erosion and deposition for hillslopes and channels for a variety of sites at a range of elevations (2) to identify and quantify the drivers of erosion and deposition and their relative contributions within and across watersheds (3) to determine the impact of slope, width, and vegetation cover on sediment storage and transport within watersheds; and (4) to assess the impacts of a large-scale aerial mulching operation at scales from hillslopes to watersheds. Multiple drone flights were conducted for each study site between July and October 2022. The earliest and latest surveys were differenced to produce DEM of Difference (DoD), with spatial resolutions ranging from 3.8 to 4.4 cm. Vertical uncertainties calculated from measurement uncertainty and Structure from Motion (SfM) errors were filtered out of the DoD at a 95% confidence interval (CI), resulting in maximum and mean detection thresholds of 11 and 4 cm, respectively. A supervised classification algorithm was used to filter out changes due to vegetation growth and decay, which varied in effectiveness across the six study sites. Hillslope erosion and deposition volumes were at least three times higher than near-channel volumes, with most sites being an order of magnitude higher. However, near-channel erosion and deposition magnitudes normalized by area were higher than normalized hillslope magnitudes at all sites. A bootstrap forest regression model was used to determine relationships between various site-specific parameters and erosion and deposition for each watershed individually, and for all six sites combined. The model indicated mean slope, absence of vegetation, mean differenced normalized burn ration (dNBR), and hillslope length to be strong drivers of erosion and deposition for the individual models. Total precipitation accumulation and maximum 60-minute rainfall intensity were stronger contributors in the combined models. Near-channel storage and transport was influenced by local relationships between width, stream power, and absence of vegetation. Mulch coverage area was found to be weakly correlated with erosion and deposition at the watershed scale, with contributions possibly being dependent on coverage rate. These findings emphasize the importance of applying mulch in areas where it is both necessary and can have a measurable impact on reducing erosion rates.
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    Open Access
    Energetics and dynamics of flow through baffle drop shafts using physical and computational model studies
    (Colorado State University. Libraries, 2023) Aluthwalage, Kasun Prabodha Sahabandu, author; Venayagamoorthy, Subhas Karan, advisor; Loc, Ho Huu, advisor; Nelson, Peter, committee member; Windom, Bret, committee member
    A drop shaft is one of the main hydraulic structures that is used to convey water from higher to lower elevations while dissipating potential energy in storm water management systems, water treatment plants, and hydropower stations. Drop shafts need to be adjusted for higher discharges because of the increased urban flooding due to climate change and rapid urbanization. Traditional baffle drop shafts have limited flow capacity and are unstable due to their asymmetric nature. The novel baffle drop shaft is proposed here for larger range of flow discharges. To the author's knowledge, there are no previous studies that have thoroughly investigated the energy dissipation potential of the novel baffle drop shaft. Hence, there is a need to establish a design relationship between key parameters such as the shaft diameter, baffle spacing, and discharge to inform best design practices. A 1:10 physical model study was carried out to investigate the energy dissipation of a novel baffle drop shaft using different discharges. Pressure and velocity were measured at two locations on the baffles using low range pressure sensors (100 mbar) and an electromagnetic velocity meter. Timed averaged pressure and velocity on the baffles increased with discharge. These averaged quantities were considered to calculate global and local energy dissipation through the shaft. The global energy dissipation efficiency was calculated based on the inlet and outlet channel flow data, and was found to range from 89.6% to 91.9%. The flow regime profiles were quite similar on each baffle section of the shaft; hence, we can consider the energy dissipation in each baffle to be equivalent. Under free-flow conditions, the energy dissipation efficiency decreases as the discharge increases. Physical models are costly and time-consuming for performing parametric studies of flowthrough such structures because each and every geometric configuration needs to be constructed in the lab. Computational Fluid Dynamics (CFD) is a more feasible option to conduct an in-depth investigation of the energetics and dynamics of flow in a baffle drop shaft since it is faster and more cost-effective than a physical model study. The CFD models have been built to simulate the hydraulic behavior of baffle drop shafts using OpenFOAM. This software is adaptable for modeling diverse flow issues due to the variety of models and numerical techniques that it incorporates. A suitable turbulence model that is commonly used in CFD for modeling turbulent flows such as in drop shafts is the RANS-based realizable k- ϵ model. Mesh sensitivity analysis was also performed to establish grid independences of the solution. Benchmark geometry CFD models were calibrated using four locations in the physical model, and velocity and pressure measurements at the edge of the baffle were used for validation with remarkable agreement. A parametric study was conducted using shaft diameters (D) of 0.8 m, 0.9 m, and 1 m, six baffle spacings (h) ranging from 0.23m to 0.48 m, and baffle rotating angles (θ) of 180◦, 250◦, and 270◦. Global energy dissipation efficiency (η) ranged from 92% to 97%. The η value decreased with discharge but was higher under free flow conditions in the baffle drop shaft. The geometric parameters D, h, and θ have little influence on energy dissipation. Considering structural integrity, available space, construction costs, and maintenance costs, the baffle drop shaft needs to be optimized to achieve the desired hydraulic performance. Maximum pressure was observed at the water jet impact location close to the outer shaft wall. Air entrainment is also a significant consideration in designing baffle drop shafts because its impact is critical in applications like hydro power generation. The bulking of the flow due to air entrainment needs to be considered to evaluate the maximum flow carrying capacity of baffle drop shafts. In summary, designing baffle drop shafts requires a multi-criteria approach that is mainly dependent on the design requirements on energy dissipation, structural integrity, construction costs, air entrainment, application, and location.
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    Open Access
    Evaluating post-fire geomorphic change on paired mulched and unmulched catchments using repeat drone surveys
    (Colorado State University. Libraries, 2023) Hayter, Lindsey, author; Nelson, Peter, advisor; Kampf, Stephanie, committee member; Morrison, Ryan, committee member
    Sediment redistribution after wildfire can dramatically alter a catchment and pose risks to local infrastructure and water quality. Mulch application is increasingly being used to mitigate post-fire hillslope runoff and erosion, although relatively little is known about its effects at the catchment scale. In this study we used repeat drone surveys to measure erosion and deposition across 6 small (0.5-1.5 km2) catchments, 3 mulched and 3 unmulched, in the 2020 Colorado Cameron Peak Fire burn scar. The objectives were to (1) quantify sediment volumes and spatial patterns of erosion and deposition on a catchment and channel scale, (2) compare geomorphic change to mulch coverage, vegetation cover, precipitation intensity, burn severity, and morphologic metrics, and (3) identify conditions in which mulch may be most appropriate based on findings. Initial drone surveys were gathered in the spring of 2022 shortly after mulching and were differenced to surveys collected in fall of 2022, capturing the erosional effects of a Colorado monsoon season within a 6.4 cm horizontal resolution DEM of Difference (DoD). Structure from motion (SfM) errors were thresholded out of the DoD to yield maximum and mean levels of detection at 14 cm and 5 cm respectively. Vegetation was filtered from the DoD by supervised classification of vegetation in the drone imagery. We found hillslope erosion dominated the sediment budget, with the mulched catchments eroding 141% more per area than the unmulched. A regression model suggested erosion to be most influenced by vegetation, hillslope length, and maximum 60-minute rainfall intensity. Channels were overall net depositional, and patterns of erosion and deposition in channels were controlled by changes in slope and stream power as well as local morphologic metrics. Our analysis does not find a significant impact of mulch at the catchment scale especially when coverage is low (~22%) and highlights the importance of understanding catchment attributes and processes when making post-fire treatment decisions.