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Hazard mapping in the Arequipa region of Peru: remote methods for hazard inventories and characterization, and participatory design to improve map usability
Grady, Cassidy L.
Grady, Cassidy L.
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2023
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Abstract
Small communities in the Arequipa region of Peru are susceptible to geological hazards such as landslides, flooding, debris flows, and rockfall that impact their lives and livelihoods. In order to design a plan to mitigate these hazards, it is necessary to be aware of their locations, extents, and processes. A hazard inventory provides this information, but the only inventory available for Arequipa has limited data that is not sufficient for identifying hazards on a community-scale. Rockfall hazards, specifically, are widespread in the region and can destroy property and cause injury or death. People in these communities may be fully aware of the hazards that surround them, but they do not have the tools to adequately address the impacts. One tool that can be created from a hazard inventory is a hazard rating map useful for mitigation and development planning. When creating maps of communities, incorporation of local community knowledge and preferences is essential to design an accessible and usable map. However, it can be difficult to access rural communities, which encourages further development of a remote method to characterize the preliminary hazard ratings of a site prior to a field visit.
Three objectives are addressed in this thesis: 1) to remotely inventory common geological hazards in 13 communities, 2) to develop a remote method for rockfall hazard characterization for application at a community-scale, and 3) to collaborate with community members to design useful hazard maps. Thirteen communities located in geographically diverse areas of Arequipa were chosen for geological hazard inventory development. The communities situated in river valleys experience the highest proportion of flooding hazards. Also, rockfall is present to varying degrees at all sites, which provided an opportunity to further advance methods for remote rockfall hazard characterization. An array of hazard mapping techniques were used to develop rockfall inventories from aerial imagery, followed by field confirmation and prediction of runout distance using empirical models. A semi-automated method was developed as a GIS-based model that characterizes the generation and transport of rockfall. The generation component criteria consisted of source zone height, slope angle, and rockmass structural condition. Transport was characterized by rockfall runout distance, rockfall trajectory paths, and hazard ratings of corresponding source zones. This methodology delivers preliminary hazard maps from remotely-available data that improve upon current approaches in the literature. Application to other regions in the world with similar climatic and geomorphic settings as Arequipa is possible. Building on the rockfall hazard study, hazard map usability was investigated with the community members of Achoma. Direct input on map design was sought from the community in two workshops with older and younger participants. It was clear that they valued representation and accuracy the most in map design. Inclusion of the Majes Canal was essential for orientation and cultural significance. This information is crucial to communicate hazards more effectively and create a useful resource for communities in the form of maps.
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