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CAPACITY BUILDING FOR NATURAL DISASTER REDUCTION (CBNDR) REGIONAL ACTION PROGRAM FOR CENTRAL AMERICA (RAPCA)

“ANÁLISIS DE RIESGO POR INUNDACIONES Y DESLIZAMIENTOS DE TIERRA EN LA MICROCUENCA DEL ARENAL DE MONTSERRAT”

SAN SALVADOR, NOVIEMBRE DE 2003

Summary
The organization for the United Nations for the Education, Science and Culture (UNESCO) and the coordinating committee for thePrevention of Natural Disasters in Central America (CEPREDENAC) since 1,999 have been developing the Regional Action Program for Central America (RAPCA) with the technical collaboration of the International Institute for Geo-information Science and Earth Observation (ITC) and the financial support of the government of the Netherlands. This project has as its purpose the integration of existingknowledge about the occurrence of phenomenon and the use of geo-information techniques for the zonification of threats due to natural events and the transfer of these to institutes involved in the decision making of land management and land development process as well as the making of adequate legislation and regulation. In El Salvador the pilot project takes as a base the “Analysis of risks due toflooding and landslides in the Arenal de Monserrat Micro Basin.” For the development of this project we counted with the adequate computer equipment for the processing and reproduction of information, aerial photographs and satellite images, topographic and thematic maps; as well as existing literature on studies already realized complementing the information gathered from the field. A processing ofgeographic information center was established at the central offices of CNR-IGN for the corresponding analysis of the area of study. The conic conformal Lambert projection was used due to the fact that it is the projection currently used in El Salvador and the software utilized for the processing of the information were ILWIS, ArcView, ArcGis, PCRaster, and Excell for the hydrological calculations.The Basin has and area of 54.98 squared kilometers and its geographical coordinates are: in latitude 13°41’25.42” North and in longitude 89°15’07” West. Administratively the basin covers the municipalities of San Salvador, San Marcos, Antiguo Cuscatlán, Nuevo Cuscatlán, and Nueva San Salvador. The most ground is covered in San Salvador and Nueva San Salvador. The zone has frequent seismicactivity. Besides the volcanic activity considered active that predominantly includes pyroclastic material (formation in San Salvador in the late quaternary period), such as white soil and pumice. The relief is predominantly valley and mountainous with slopes form 5 to 25% that correspond to a wavy to slopy relief in the valley and in the mountainous region from 25 to 100% and in some cases even greaterslopes. The texture of the superficial layers for the most part are sandy and limey and in the interior layers alternating between sandy, limey, clay grounds above volcanic pomicíticas lava or slimy grounds with depths generally above 5 meters. The micro basin has a drainage network in which two are the most predominant: the Arenal de Monserrat River and the Mascota gorge. For the hydrologicalanalysis we have taken as a base the rain intensities for each of 5, 10, 15, 20, 30, 45, 60, 90, 150, 180, 240 and 360 minutes for a period of registry of 31 years. According to the records there have been normal averages of 20 to 40 mm per hour but there have been records of as much as 90 mm per hour (April of 2002). Because part of the capital city is inside the basin the population density is high.There are densities higher than 5,000 inhabitants per square kilometer and likewise some parcel densities oscillating between 50 to 100 square meters and these with densities of 15,000 to 7,500 per square kilometer. In 2002 61.5% of the total area of the basin is occupied by urban area therefore existing a high density of streets that include the Pan American Highway. Equally there exists many...
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