El Salvador - GFDRR

I. DESCRIPTION OF THE EVENT | 15
As consequence of all this, the mission noted that the towns and cities located near rivers adjacent to
the San Vicente volcano directly suffered the impact of the lahars that flowed along the main river channels,
with severe consequences on housing and urban infrastructure in Verapaz, San Vicente and Guadalupe.
Likewise, homes and towns, including a vacation center, located on the banks of Lake Ilopango were
covered by landslides and their foundations were eroded due to the action of water. The destruction of
bridges and damage to culverts and drains along many roads were significant. In others, cuts occurred due
to deposits of loose materials, rocks and mud. Extensive areas used for agriculture on alluvial fans were
covered with gravel and sand due to flooding. Sedimentation from mud deposits in numerous rivers and
especially in Lake Ilopango caused floods and the lake’s natural drainage was blocked. This drainage had
already been blocked during the 2001 earthquakes and the incomplete drainage work and construction
of a drainage system collapsed due to the erosion of gabions and walls, exposing its fragility due to the
narrowness of the outlet.
Schematically, the event is described as follows: in terms of climate, a combination of a low-pressure
system and a tropical storm occurred, causing high levels of concentrated rainfall (from a return level between
100 and 300 years), with differential consequences:
a) At the San Vicente (Chinchontepec) volcano, lahars occurred; in geology these are called
“torrential landslides on volcanic lands.”
b) A very large amount of solids, in a proportion of 0.60 to 1 with respect to water.
c) In the lower courses of rivers, the prior siltation of streams in their channnels caused more
widespread flooding.
When the current reached the coastal strip, which is elevated with respect to the plain and in which
highways parallel to the coast, resorts and beach houses have been constructed, the coast’s natural drainage
was obstructed and the mouths of rivers overflowed, causing new outlets to open that brought about
destruction on the coast.