Strategy for Flood Mitigation in Mocoties Basin, Merida, Venezuela, after the Torrential Event on February 11th, 2005

摘要

The Mocoties basin is located in the Venezuelan Andes, southwest of Merida State. It has an area of 524.4 Km~2, in a high mountain region with 70 % of its area having a slope of more than 60%. On February 11th, 2005, it had one the most catastrophic floods in Venezuelan history. There was an estimated discharge of 900 m~3/s after a rainfall of 110 mm fell upon saturated soils. This happened between 4 pm and 1 am. 99 people were killed and 5,000 were disenfranchised. In addition 622 houses were totally destroyed, 588 were partially destroyed and 30 Km of road was severely damaged. Bridges, rural schools, crops and cars were also damaged. The public services, water supply, electricity, sewers, and telephone lines were affected. The storm increased its destructive power by moving downstream through the main river channel. This river channel is 53 Km long and descends from 3,600 meters to 320 meters above sea level. The storm took place almost simultaneously over the small lateral watersheds, which generated a lot of debris flows. The annual rainfall varies between 1,200 mm per year in the lower regions and 685 in the upper regions. The most frequent rocks are gneisses, schist, and granites in a region with a system of geologic faults and seismic activity. The Mocoties basin belongs to three municipalities. The actual population is 87,554 people, distributed mostly in three main towns and in small rural villages located in the alluvial fan and terraces. The people located in the upper regions cultivate potatoes, carrots and flowers. In the middle regions people cultivate coffee without tree shade. The forest covers 30 % of the basin. The main road which connects the towns with the rest of the country is located closely parallel to the river making it highly vulnerable. In this paper we present a summary of the damages of this event and also identify areas that are still at risk. We will propose a set of indicators that may be used to monitor the risk evolution. Also, we will propose programs as an integrated approach to a) mitigate the hydro-geomorphogic hazards by means of the reduction, retention, delay and/or diversion of the liquid and solid discharge and b) control the development of the socioeconomic activities in high risk areas.