Debris-flow impact, vulnerability, and response

Abstract

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.

Minimizing economic impacts from post-fire debris flows in the western United States

“…However, the occurrence of the fire sets up a condition where debris flows may be expected under a predictable set of rainfall intensity and duration conditions (Staley et al 2013). Public notifications and evacuation orders can be issued when storms are expected that could exceed threshold values for debris-flow generation (Santi et al 2011). This activity significantly decreases the likelihood that people will be present when a debris flow occurs, relative to a completely random event.…”

“…This activity significantly decreases the likelihood that people will be present when a debris flow occurs, relative to a completely random event. Quantifying residual human-life risk after issuance of public notifications and evacuation orders is complicated by the effects of personal risk acceptance, risk awareness, and ''warning fatigue'' (e.g., Mackie 2014); as Santi et al (2011) discuss, people do not always evacuate the area even when warned of an event. However, with additional study, it may be possible to account for the human-life-risk aspect of post-fire debris flows in this framework; this would essentially result in an increase to damages associated with certain structures.…”

Qualitative study of disaster preparedness in an Indonesian village: Interviews with survivors of flash flooding near Bandung

“…Conversely, inadequate public awareness, lack of disaster preparedness, weak governance, lack of coordination among the concerned government agencies, insufficient financial resources, and deficient technical knowledge contribute to the loss of life and property through natural disasters (Tuladhar et al 2015). Poor people tend to be the most vulnerable (Santi et al 2011).…”

Improvement in quantifying debris flow risk for post-wildfire emergency response

“…Debris flows that occurred near San Bernardino, California after the 2003 Olds and Grand Prix fire illustrate the threat to public safety. A major storm event happened only months after the fire was contained and triggered sixtyeight debris flows including two which were responsible for sixteen fatalities within the burned canyons (Restrepo et al 2008;Santi et al 2011). These deaths occurred despite evacuation of campgrounds and widespread warning efforts prior to the storm.…”