Introduction

Flash floods are one of the most lethal natural events in wilderness settings. They have little warning and can turn serene streams into raging rivers in a few minutes. This report outlines the nature of flash floods, danger signs, warning signs, and most importantly, how to avoid flash floods among wilderness travelers.

Understanding Flash Floods

Flash floods are rapid increases in water level, usually within six hours of the event. Flash floods are characterized by rapid rise, high speed, and ability to carry debris. Flash floods are most commonly found in wilderness conditions following intense rainfall, dam failure, or snowmelt.

Risk Factors

Various factors increase flash flood risk in wilderness settings:

• Impervious surfaces and poor vegetation
• Slot and narrow canyon morphology
• Recent burn areas
• Drainage basins in areas of steep terrain
• Past flood-regime areas
• Monsoon areas

Warning Signs

Identify potential flash flood situations:

• Abrupt water turbidity or debris changes
• Distant rumbling noises
• Abrupt rise in water level, even slight
• Unpredictable precipitation, particularly heavy rain
• Dark gathering clouds upstream
• Weather notices from surrounding areas

Prevention Strategies

Pre-Trip Planning

• Study past flood regimes at your destination to learn about conditions to expect.
• Monitor weather reports just in time to depart
• Understand local topography and have multiple high-ground evacuation routes
• Let others know your route and approximate return time
• Bring emergency communication equipment with you

Campsite Location

• Never camp in creek bottoms, washes, or low spots
• Mark camps on high ground at least 100 feet higher than water sources
• Mark various routes of evacuation from your camp to high ground
• Look at the whole watershed drainage basin above you

In Rain Events

• Stay in contact with local officials frequently
• Evacuate immediately upon the first indication of water rise
• Take higher ground immediately in case of worsening conditions
• Avoid wading through flowing water more than ankle deep

Emergency Response

• Operate moving to higher ground as more important than salvaging equipment
• Move in a direction opposite to water flow to higher ground
• Avoid bridges or structures that are collapsing
• If stranded in water that is rising, release heavy equipment and swim diagonally away from the current to shore

Case Studies

There are multiple wilderness fatalities annually due to flash flooding. The 1997 Antelope Canyon tragedy, the 2015 Zion National Park canyoneering accident, and many other instances which are being repeated in desert southwestern areas where monsoon storms are creating unusually hazardous conditions are some examples.

Conclusion

Prevention of flash flood in backcountry settings to a great extent depends on awareness, education, and pre-incident decision-making. Knowledge of the warning signs, recognition of the warning signs, and existing mechanisms for prevention can reduce exposure of backcountry travelers to such dangerous natural phenomena.