Debris-flow impact, vulnerability, and response

This paper calls attention to vulnerable groups that are disproportionately affected by smaller, less-publicized debris flow events and do not always receive the advantages of recent technical advances. The most vulnerable groups tend to be economically restricted to live in relatively inexpensive and more dangerous locations, are often forced to live in topographically cramped areas due to expansion and development, and have limited influence and power needed to bring about mitigative efforts. Technical issues have long been the focus for debris-flow hazard reduction, but the collective judgment of many of those working toward natural hazards reduction, especially in developing countries, is that socio-cultural issues are at least as important as technical choices on the effectiveness of hazard and risk-reduction efforts. This awareness may result in (1) selecting simple designs that use local materials, local construction techniques and skills, and that recognize limited financial means; (2) selecting mitigative methods that require minimal maintenance, can withstand exposure to vandalism and scavenging, and will minimize misappropriation of resources; and (3) capitalizing on local techniques of dealing with other hazards, such as flooding, earthquakes, and landslides. Because of the difficulty in predicting and controlling debris flows, it is useful if mitigative systems can employ multiple elements to enhance the chance of success. These can include: education of the local populace, avoidance and warning to the degree possible, and some combination of channelization and interception of debris. For watersheds disturbed by fire, logging, mining, or construction, hillside treatment can be added to the mitigative methods to reduce water flow and sediment transport. Examples provided in this paper show that these mitigative systems can be tailored to fit widely varying socio-cultural settings, with different geological characteristics and different debris flow-triggering events.