Risk assessment due to debris flows in Paz de Río-Colombia

摘要

Paz de Río is an important economic area of Colombia where iron mines produce most of the mineral for the steel production in the country. Along the La Chapa creek some debris flows have occurred since 1963 producing economic losses and human deaths at Santa Teresa village. Economical losses are related to disruption of the main access to La Chapa iron mine facilities, and flooding of Paz de Río due to damming of Chicamocha River, the main drainage system of the region, which is blocked by debris flows. The local authority for Natural Disaster Management (CREPAD) jointly with the Universidad Nacional de Colombia carries out the risk evaluation related to potential debris flows along the creek. The study models the debris flow using the FLO2D software considering the geological, geomorphologic, topographic and hydrological setting of the area. As main sediment source we considered the potential volume of material supplied by a large landslide at the upper part of the creek basin, known locally as the Mesa Alta landslide, whereas sediment production due to landslides within the basin was considered as point inflows along the creek. Physical vulnerability was evaluated by using the Leone (1999) approach, which considers the flow height and its relation with the structure height, whereas social vulnerability was evaluated by considering factors as population density, people age, literacy level and economical income. Risk assessment was based on the Liu and Lei (2003) approach in which risk is defined graphically considering critical threshold curves obtained from vulnerability and hazard values. Risk for different elements within the influence area of the creek was evaluated and mitigation measures including engineering works were proposed, the influence of these measures on hazard and risk was also evaluated.