Abstract

Oil–particle aggregate (OPA) formation, fragmentation, and settling govern the fate of oil that strands on sediment-rich shorelines, yet no publicly accessible, size-resolved software tool currently couples these three processes within a single population balance framework. Existing models either resolve OPA formation without breakup or resolve breakup from a prescribed initial distribution, forcing practitioners to chain tools manually. We address this gap by developing OPA-Z, a software tool whose kernel unifies (i) A-DROP coagulation/attachment, (ii) binary fragmentation and shell shredding, and (iii) an analytical advection–diffusion settling solution within a single discretized population balance model. The integrated kernel is wrapped in a graphical user interface (GUI) that enables non-expert scenario testing on a web-hosted application. Model inputs include oil properties (interfacial tension, viscosity, density), particle properties (sand, clay, mixtures, sizes, density), turbulence intensity, and water depth. Outputs include time-resolved OPA size distributions, oil trapping efficiency (OTE), oil-to-sediment ratio (OSR), and cumulative oil settled to the bed. The model operates in a pulse mode of oil release that simulates a slick arriving at the shorelines, representative of nearshore spill response scenarios such as beached oil remobilization or slick stranding events. Model fidelity is demonstrated by reproducing benchmark coagulation data in laboratory systems. The software is designed to integrate with GIS-based particle fields, supporting fast, transparent assessments of nearshore OPA fate to respond to oil spills and for contingency planning.

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