Eli Lazarus , Evan B Goldstein , Luke Taylor , Hannah Williams 

Extreme geohazard events can change landscape morphology by redistributing huge volumes of sediment. Event-driven sediment deposition is typically studied in unbuilt settings – despite the ubiquity of occurrence and high economic cost of these geohazard impacts in built environments. Moreover, sedimentary consequences of extreme events in built settings tend to go unrecorded because they are rapidly cleared, at significant expense, from streets and roads to facilitate emergency response. Reducing disaster costs requires an ability to predict disaster impacts, which itself requires comprehensive measurement and study of the physical consequences of disaster events. Here, using a database of post-storm aerial imagery, we measure plan-view geometric characteristics of sandy washover deposits in built and unbuilt settings following five different hurricane strikes along the Atlantic and Gulf Coasts of the US since 2011. We identify systematic similarities and differences between washover morphology in built and unbuilt environments, which we further explore with a simplified numerical model. Our findings suggest that the fabric of the built environment – specifically, the built fraction of the depositional zone – exerts a fundamental control on the form of large deposits. Accounting for the influence of the built fabric on the morphodynamics of flow-driven geohazards is a tractable step toward improved forecasts of hazard impacts and disaster risk reduction.