El Salvador - GFDRR

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14 | <strong>El</strong> <strong>Salvador</strong>: Damage, Loss, and Needs Assesment GRAPH 1. RECORDED PRECIPITATION Precipitation recorded during the period between 7:00 a.m. on November 7 th and 7:00 a.m. on November 8 th at the weather stations of San Vicente, Tepezontes, Boquerón and Ilopango. Source: D-SNET/MARN. The key factors that contributed to the magnitude of the lahars were: a) The prior saturation of soils when rain intensity increased; thus the rain fell directly on the runoff area, making response time very short. b) The intensity of precipitation was high (over 20 mm/hr) over a long period of 7 hours and at an excessive level for 3 hours, causing extreme runoff. c) The presence of abundant eroded material, accumulated in river streams, increasing the sediment conveyed during the flood. The presence of this silt is associated with the 2001 earthquakes that caused various landslides and the depositing of materials in river channels.
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.
Page 1: El Salvador Damage, Loss, and Needs
Page 5 and 6: | iii ACKNOWLEDGEMENTS We wish to e
Page 7 and 8: Acknowledgement | v The external su
Page 9 and 10: | 1 PRESENTATION At the request of
Page 11 and 12: | 3 SUMMARY AND CONCLUSIONS Through
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AUSTRALIA BELGIUM BRAZIL CANADA DEN
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El Salvador - GFDRR

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