Browsing by Author "Williams, Megan Elizabeth"

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    Antidune simulations using continuum-based models
    (2024) Escauriaza Mesa, Cristián Rodrigo; Williams, Megan Elizabeth
    The interactions of supercritical flows with sand or gravel beds in river channels or tidal inlets lead to the formation of antidunes. These bedforms are generally identified as nearly periodic sedimentary patterns of symmetrical shape that are in phase with the surface waves in the flow and have important effects on flow resistance and bedload transport. In addition, they play a fundamental role on morphodynamical processes in estuarine systems, on the scour around hydraulic infrastructure, and their bed signature can help to interpret paleofloods from sedimentary records. Despite the importance and ubiquity of antidunes in environmental flows, very few numerical simulations have captured their dynamics. In this work, we develop a model that couples the shallow-water and Exner equations in two-dimensions (2D) and demonstrate that a higher-level theory can reproduce the experimental antidune results of Pascal et al. (2021), independent of interactions at the particle scale. The flows are characterised by Froude numbers between 1.31 and 1.45, sediment diameters of d50=2.9$$ {d}_{50}=2.9 $$ mm and with 3 degrees mean bed slopes. Using this information, we aim to identify the minimum requirements for a numerical model to capture in detail the migration of these bedforms. We use spectral analysis and compute statistics of bed elevation to determine the relevant temporal and spatial scales associated to the antidune propagation. The results of the model yield new insights on the mechanisms of bedform migration, providing tools to improve their description and assess the morphodynamic feedbacks.
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    Tidal energy resource assessment in the Strait of Magellan in Chilean Patagonia
    (2025) Suárez, Leandro; Guerra, Maricarmen; Williams, Megan Elizabeth; Escauriaza Mesa, Cristián Rodrigo
    This paper has been subjected to single-blind peer review.Tidal energy industry is reaching maturity, with various pilot sites demonstrating the ability of hydrokinetic devices to generate electricity. As tidal turbines become more reliable, it is important to obtain detailed characterizations of tidal resources at potential sites. The Strait of Magellan, in the Patagonia region of Southern Chile, is an inland connection between the Pacific and the Atlantic Oceans with strong tidal currents. To assess the magnitude of the tidal energy resources in this area, field surveys including Acoustic Doppler Current Profilers (ADCP), and tidal gauge measurements were carried out in the vicinity of a narrows in the strait. The data helped to validate a detailed numerical model to assess the hydrodynamic characterization of the area.
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    Using a robust decision making (RDM) approach to explore current and future vulnerabilities of a semi-arid coastal basin: a case study of the Quilimarí basin in Chile
    (2025) Poblete López, David Nicolás; Vicuña Díaz, Sebastián; Aedo, Sebastián; Molina-Pérez, Edmundo; Cortés, Hermilo; Melo Contreras, Óscar; Ocampo-Melgar, Anahí; Tesen Arambulo, Kiara Aimee; Suárez Poch, Francisco Ignacio; Herane Espinosa, Juan Pablo; Meza, Francisco Javier; Duarte Becerra, Katherine Mariela; González Santander, Diego Nicolás; Leray, Sarah; Williams, Megan Elizabeth; Gaxiola, Aurora; Alfaro, Gabriela; Morales Moraga, David Alejandro
    Climate change, land use alterations, human activities, and regulatory frameworks all contribute to deep uncertainties that define water security in hydrological basins. This is particularly significant in drylands where water scarcity limits agricultural productivity. Robust Decision Making (RDM) is an effective approach for identifying strategies that perform well under uncertainty across a wide range of possible futures. One of RDM’s key strengths is its ability to guide decisions without relying on precise future predictions, emphasizing robustness rather than optimality. This study focuses on the Quilimarí River basin, located in the semi-arid coastal region of Chile, where groundwater is the primary water source. Small coastal communities rely on shallow boreholes, which have become brackish due to saline intrusion. We present the initial stages of implementing an RDM process with key local decisionmakers to explore the expected impacts of socio-hydrological stressors and uncertainties on the main water-dependent objectives. Different levels and approaches of participation during the 2 years of RDM process enabled the identification of critical concerns raised by local stakeholders and government agencies, the uncertainties likely to affect these issues, and potential actions for improving outcomes. To explore current and future vulnerabilities we used a WEAP-MODFLOW water resources model that integrates data on extraction wells, irrigation schemes, agricultural production, potable water supply, and associated costs, including saline intrusion processes. The model simulates trade-offs between different objectives, such as groundwater extraction for agriculture and job creation versus potable water for rural communities. The vulnerability exploration scenarios suggest a complex future, with up to a 40% reduction in precipitation and increased water demand from household and tourism use. To cope with the impacts associated with these global change scenarios a series of adaptation options were tested. Overall, desalination emerged as a favorable option for local human consumption demands, although tested only under basin-level metrics. This study illustrates valuable insights on how the water management strategies under uncertainty can benefit from local engagement towards testing robust decisions in arid and semi-arid coastal basis around the world.