Ponencia
Hydrogeomorphic Investigation of the 2015 Atacama Floods, Northern Chile
Registration in:
1130940
Author
Wilcox, Andrew C
Escauriaza-Mesa, Cristián Rodrigo
Mignot, Emmanuel
Gironas, Jorge A
Cienfuegos, Rodrigo
Mao, Luca
Institutions
Abstract
In March 2015 unusual atmospheric conditions over the Atacama Desert of northern Chile, the driest
area on Earth outside of Antarctica, produced many years worth of rainfall in a 24hour
period. The
resulting sedimentrich
floods caused dozens of deaths and/or disappearances, over $1 billion in
estimated damage, and widespread geomorphic change. Here we describe the hydrologic and
geomorphic drivers and responses to the 2015 Atacama floods, including characterization of the
hydrologic forcing, water and sediment routing from source areas in the upper watershed to the
outlet at the Pacific Ocean, and urban flooding impacts of this event. In a region where few direct
measurements of precipitation and discharge during these events are available, we combined
hydrologic and hydraulic modeling with field and aerial photograph interpretation of sediment
sources and geomorphic change. A remarkable element of the flood, particularly with respect to its
effects on urban areas, was its high sediment load. Despite widespread hillslope erosion in the form
of rilling and gullying initiated by overland flow, sediment from these sources typically did not reach
valley bottoms, and only limited, smallscale
mass wasting was observed. Field observations
indicated that the sediment load was primarily derived from dramatic erosion of channel bed, bank,
and floodplain material (i.e., valley fill). In the coastal city of Chañaral, flooding of the Salado River
produced maximum water depths over 6 m, metersthick
mud deposition in buildings and along city
streets, flow velocities larger than 8 m/s, and coastal erosion. Broader implications of studying the
Atacama flooding include hazard reduction, the history of copper mining and more than five decades
of contamination in many of the affected watersheds, and the Atacama’s status as a terrestrial
analog for Mars.