A pragmatic approach to debris flow hazard mapping in areas affected by Hurricane Mitch: example from NW Nicaragua

Although developing countries are vulnerable to landslide hazard, they generally lack policies for hazard assessment and mitigation. This may be attributed to the scarcity of good quality data on which to base any sound hazard assessment in addition to insufficient funds and lack of political will. Thus, there is an urgent need for developing feasible methodologies of landslide hazard assessment and mitigation, which can be readily tested and implemented under the conditions found in these countries. To this end, we selected an area of about 20 km 2 badly affected by Hurricane Mitch in October 1998, in the Departamento de Chinandega (NW Nicaragua). Mass movements (mainly debris flows) produced during the Hurricane Mitch rainfall event were investigated using two sets of aerial photographs at 1:60,000 and 1:40,000 scales. Data concerning regolith composition and thickness, landslide dimensions, failure slope angle and land use were obtained for 150 mass movements, and over 450 landslides were mapped at 1:10,000 scale in the field. A pragmatic approach was used to produce a qualitative hazard (sensu lato) assessment, based on the concepts of number of events recorded, predictability and susceptibility. This case study shows that a hazard assessment that is useful for management may be possible even where data are limited. Despite its inherent limitations, similar pragmatic approaches could help the sustainable development of other rural and sparsely populated areas of Central America.