Types of Flood Hazards

Flooding is one of the deadliest weather hazards in the U.S. and comes in second place after heat for causing the most deaths per year. While flooding may seem like a simple concept where water rises, there are different types to be aware of. 

Flash Flooding
Flash flooding is pretty self-explanatory, flooding happens in a flash which typically develops within 6 hours. Flash flooding can be caused by various factors, but the most common cause is from heavy thunderstorms. Sudden downpours can quickly raise the water levels along creeks and streams as well as in urban areas where it's harder for water to soak into the ground. Mountainous terrain is well known to have flash floods since the steep terrain will quickly concentrate water into one area. 

River Flooding
River flooding occurs when water rises above its banks due to dam failures, rapid snowmelt, ice jams, or heavy rain. If river flooding is bad enough, major roadways could be cutoff, with homes and businesses possibly needing an evacuation.

Storm Surge
With tropical cyclones, storm surge takes most lives which is why it’s so important to heed evacuation orders if given. High winds will push water inland, undermining building foundations and cutting off areas from high ground. Storm surge will literally change coastal areas due to the amount of erosion from battering waves. Tropical cyclones are not the only culprit though, storm surge is also caused by other weather phenomena such as nor’easters and severe storms. 

Burn Scars/Debris Flows
After a wildfire, the soil properties change keeping the ground from absorbing water. Once rain falls, water will easily collect towards a low point in the terrain where floods arise. Lack of vegetation can also end in a debris flow, where once dry soil turns into a liquid state after heavy rainfall. Debris flows are known to take out roadways, structures, and trees. 

Ice Jams/Debris Jams
When ice breaks up, it may collect into one area along a stream and cause flooding upstream. The same can be said about debris jams where a collection of fallen branches/trees and soil create a natural dam. Once a jam breaks, flash flooding may be a concern downstream. Migratory patterns from wildlife could be disrupted by jams as well. 

Snowmelt
Melting snow is especially hazardous when there is heavy snowpack and a period of warming temperatures. A frozen ground and additional heavy rain during snowmelt adds to flooding concerns in area creeks and streams. The changeover to spring is a common period where flooding from snowmelt occurs.

Dry Wash
In dry areas in the Desert Southwest of the U.S., monsoonal moisture in the summer can quickly change conditions with thunderstorms popping up daily. Heavy rain from these storms will easily collect into canyons and river beds. Dry, hard soil takes longer to absorb heavy rainfall than more saturated soil leading to flash flooding. 

Dam Breaks/Levee Failure
Heavy rain, landslides, and earthquakes are some of the factors that will lead to a dam failure with little warning at times. Overtopping, excessive seepage and structural failure are the three main types of failures that cause an obvious threat to communities downstream. 

No matter the type of flooding it’s important to keep up with any weather updates and listen to local authorities in case the threat arises to your life and property. Don’t forget to “Turn Around, Don’t Drown” since flooded areas will easily carry a person or vehicle downstream.