Knowing the dangers and safety considerations of flash flooding during stormy weather and runoff conditions can save lives
As winter turns to spring in the Rocky Mountains, snow runoff and spring storms can cause flash floods. As the name suggests, flash floods are flooding that occurs swiftly (according to USGS within 3-6 hours of heavy rainfall or other causes) potentially catching people unawares. Western Colorado is particularly prone to this natural catastrophe due to its precipitous mountains.
Mountains are predisposed to heavy rain fall due to what is called the orographic effect. As air sweeps up the mountainside, climbing in elevation and dropping in temperature, the clouds anchored around the summits are affected by the cold, high-elevation temperature. Subsequently, the clouds release moisture, resulting in heavy storms in the high country.
During a downpour, the rugged mountain terrain factors into the flood hazard. Much of the landscape is comprised of a rock layer with a thin layer of surface soil. The thin layer of soil easily washes away in these storms, creating channels of exposed rock through which water can easily flow. Of course, the water does not absorb into the rock layer and flows directly into runoff.
Another major contributing factor are wildfires. Where wildfires are common the resulting burn scars contribute to the risk of flash flooding. Any vegetation that would serve as a runoff-reducing layer of “forest litter” would have been consumed, leaving a loose, ashy, burnt top layer. The intense temperature changes can further create a “hydrophobic layer” underneath; simply, a layer of water-repelling earth. Any water from storms that would normally be absorbed runs over the hydrophobic layer, accumulating loose debris and ash from the top layer, possibly resulting in a “debris flow.” The high risk of flash floods in burn scar areas can last years.
Like wildfires, droughts are also common to Colorado. Parched, drought-dried earth is not particularly absorbent and offers poor support for vegetative growth. A sudden, heavy downpour — instead of soaking into the earth — will quickly turn to runoff, flooding the dry earth.
FAST AND POWERFUL
Flash floods are extremely dangerous: they happen so swiftly that they can catch peoples unawares. They are also immensely powerful, harnessing the power to overtake huge objects such as trees and boulders. While there are many factors that can contribute to the scale of and damage caused by a flood, all swiftly moving bodies of water are quite dangerous. Each ought to be approached with respect and a healthy amount of fear.
As a trip leader certified in swiftwater rescue, I would often make the point in safety speeches of the possibility of drowning in even just a foot of water. A swiftly moving current, even in shallow water, is strong enough to overtake a person. If a foot were to become entrapped between rocks while the person is pushed face-down by the current (commonly referred to as a “foot entrapment”), it would be very difficult for the person to escape, and would involve a difficult, multi-person rescue.
Adventuring in the spring, regardless of the outdoor activity or mode of travel, runs the risk of encountering a flash flood due to mountain snow runoff and high-country spring storms. Preparedness is key to maximizing enjoyment and staying safe in the outdoors.
It is best to pay attention to the weather conditions and avoid outdoor adventures in stormy weather. Weather is fickle in the high country, and a sunny day can turn cloudy and precipitous rapidly despite a favorable weather forecast. Furthermore, mountain snow runoff may be flooding creeks, inundating the rivers, washing over trails, or causing mud or landslides. Consulting sources like USGS can be immensely helpful in pre-trip planning. They help especially around creeks and rivers, where floods are more predictable.
When adventuring, be mindful of your surroundings and always have an escape route planned.
As stated, rapidly moving water currents are extremely strong. Never attempt to cross a swiftly flowing stream on foot, on a bike, or in a motor vehicle, even if the current is shallow. If a rapidly moving stream is rushing across trail, do not attempt to cross it.
WHILE RIVER FLOATING
Flood waters carry debris, especially if flooding happens around a burn scar. The debris, carried by the flowing water, can be difficult to for paddlers and floaters to see in mud-laden waters; thus quite dangerous to boat and swimmer alike. Whether in or by a river, creek, or low-lying area flooded with muddy, thick water (known as debris flow), it is best to get to higher ground as quickly as possible.
One last safety consideration: Flash floods and debris flows can obstruct and wash out trails and trail markers. Without them, it easy to become lost. Simply bringing a GPS, a map of the trail, or someone who knows the trial well can mean the difference between a great trip and getting lost.
LIS MCLAUGHLIN is a full-time manufacturer in the cannabis industry and freelance writer based in Durango, Colorado. In her free time, she is an outdoor recreationalist, fitness enthusiast and avid pursuer of knowledge.