Natural hazards on alluvial fans: The Venezuela debris flow and flash flood disaster

Abstract

, rainstorms induced thousands of landslides along the Cordillera de la Costa, Vargas, northern Venezuela. Rainfall on December 2-3 totaled 200 millimeters (8 inches) and was followed by a major storm (911 millimeters, or 36 inches) on December 14 through 16. Debris flows and flash floods on alluvial fans inundated coastal communities, caused severe property destruction, and resulted in a death toll estimated at 19,000 people. Because most of the coastal zone in Vargas consists of steep mountain fronts that rise abruptly from the Caribbean Sea, the alluvial fans are the only areas where slopes are not too steep to build. Rebuilding and reoccupation of these areas requires careful determination of potential hazard zones to avoid future loss of life and property.

Surficial patterns of debris flow deposition on alluvial fans in Death Valley, CA using airborne laser swath mapping data

“…Recently, debris flows and society have become more intertwined as urban sprawl and a desire of individuals to move to cooler, secluded locations with a view has brought more people into areas prone to debris flow events. Debris flows and floods are two of the most destructive phenomena tied to human development on alluvial fans (Larsen et al, 2001). One of the important factors in understanding the potential hazards associated with active debris flow processes on fans and equally important in regards to fan evolution is determining the spatial patterns of debris flow deposition.…”

Regional prioritisation of flood risk in mountainous areas

“…as having sediment concentrations ranging from 20 to 47 % by volume and shear strengths lower than about 40 N m −2 ; and (iii) debris flows as being non-Newtonian visco-plastic or dilatant fluids with laminar flow and uniform concentration profiles, with sediment concentrations ranging from 47 to 77 % by volume and shear strengths greater than about 40 N m −2 . Debris-flow-dominated areas can be subject to hyperconcentrated flows as well as clear water floods (Larsen et al, 2001;Santo et al, 2015;Lavigne and Suwa, 2004), depending on the hydroclimatic conditions and the availability of sediments (Jakob, 2005); occurrence of all types in the same watersheds has been reported (Larsen et al, 2001;Santo et al, 2015). Therefore, the areas exposed to clear water floods and debris flows were combined.…”

Short-term evolution of an active basin–fan system, Aspromonte, south Italy

“…Their dynamics are often characterised by extremely intensive alternation of waxing and waning phases, depending on the balance between the debris budget provided by feeder basins through feeder channel(s) and the erosive and transport capacity of flowing water. More recently, the attention of researchers has been focused on fans because they are increasingly becoming an attraction point for human settlement, and the risk on fans is increasing (Larsen et al, 2001;Santangelo et al, 2011). Clearly, activity phases of fans also alternate with resting phases of morphodynamics.…”