Assessment of hydro-geomorphological hazard potentials in the Chilean semiarid coastal range and its impacts on La Serena city, Coquimbo Region

Two micro-catchments, tributaries of the Elqui River in the coastal range of the semiarid central-northern Chile were analyzed to establish the hazard potentials associated with extreme rainfall and their effects on the urban area of La Serena city. Geomorphological mapping was performed identifying the morphological features associated with inherited and present-day processes, through photointerpretation and field work. To assess the geohazard potentials related to extreme precipitation events, a detailed terrain analysis was performed deriving topographic indices that in turn characterize the related process potentials. Extreme rainfall events were calculated with a decadal recurrence (>60 mm/day) and are subsequently associated with El Niño (ENSO) and Pacific Decadal Oscillation (PDO warm phase) events. We applied a simple storm flow model using a 20-year return period reflecting a disastrous flood event that affected the La Serena urban area in June 2011. The results highlight the spatial distribution of the hazard potentials in the two Elqui tributaries and their effects on the La Serena urban area. We show that areas subject to intensive land use change and urban sprawl associated with the lower marine terrace and river mouth of the Elqui River are of very high flooding and tsunami risk.