What are the 3 most common floods?

Flooding is a significant natural hazard that affects millions of people worldwide each year. Floods can cause catastrophic damage to communities, infrastructure, and agriculture. Understanding the most common causes of flooding can help governments and communities better prepare for and mitigate flood risks. This article will examine the 3 most common types of floods: flash floods, urban floods, and river floods. For each flood type, we will explore what causes them, where they occur, and how to reduce their impacts. Having this knowledge can help save lives and property when the next floods come.

Table of Contents

Flash Floods

Flash floods are one of the most dangerous and destructive types of flooding. They occur when excessive rainfall accumulates faster than the ground can absorb it. Here are some key facts about flash floods:

Causes: Flash floods are usually triggered by slow-moving thunderstorms, tropical storms, hurricanes, or rapid snow melt.

Speed: Flash floods develop within minutes or hours after a period of intense rainfall over a given area.
Locations: They often occur in mountainous areas and valleys, but can happen anywhere heavy rainfall exceeds infiltration.
Impacts: Flash floods can roll boulders, tear out trees, destroy buildings and bridges, and scour new channels. Rapidly moving water only 2 feet deep can sweep cars off roads.

Deaths: They cause the most flood-related deaths of any flood type in the United States. Nearly half of all flash flood fatalities are people drowned in vehicles when drivers try to cross flooded roads.

Some of the most devastating flash floods in United States history include:

The 1972 Black Hills flood, which caused 238 deaths and $160 million in damages in western South Dakota.

The 1976 Big Thompson Canyon flood, which killed 143 people along the Big Thompson River in Colorado.
Flash floods in Kansas and Missouri in July 2017 that killed 20 people and caused over $3 billion in damage.

To reduce vulnerability to flash floods, communities can:

Improve flood warning systems to give people more time to evacuate.
Avoid building in high risk flash flood areas, such as canyon bottoms, slopes, and natural drainage channels.
Construct flood control structures, such as levees, culverts, and detention basins, to protect populated areas.

Educate the public about flash flood risks and safety precautions.

Public awareness and early warnings are the best defense against flash flood emergencies. Do not attempt to cross flash flooded roads or walk through flash flooded areas. Turn around, don’t drown.

Urban Floods

Urban flooding occurs when drainage systems are overwhelmed by heavy rainfall. With cities largely covered by impervious surfaces like roads, parking lots, and buildings, water cannot soak into the ground and instead runs rapidly into streams, storm drains, and infrastructure. Key facts about urban flooding include:

Causes: In addition to heavy rain, infrastructure issues like blocked drains, increased pavement, and outdated sewer systems can worsen urban flooding.
Locations: Urban flooding happens in towns and cities with poor drainage and high proportions of impervious surfaces.
Impacts: Floodwaters can submerge streets and buildings, trapping people and disrupting businesses and traffic. Flood damage to basements, vehicles, and public infrastructure can be costly.

Increased risk: As urban areas expand, more infrastructure is required to drain additional paved areas. Climate change also increases heavy rainfall events in some regions.

Some notorious urban floods include:

The July 2021 flood in Zhengzhou, China that inundated a subway system, killing over 300 people.

Flooding in Houston, Texas during Hurricane Harvey in 2017, which caused $125 billion in damage as rainfall overwhelmed infrastructure.
The summer 2022 floods in Dallas, Texas that flooded highways and stranded residents in their homes.

Strategies to reduce urban flooding include:

Using green infrastructure like rain gardens, green roofs, parks, and wetlands to absorb more stormwater.
Increasing drainage capacity by upgrading storm sewers, culverts, and retention basins.
Implementing stricter development regulations in floodplains and requiring flood-resilient designs for new construction.

Improving flood warning systems, emergency response, and community preparedness.

Ongoing investment in flood-adapted urban infrastructure is needed to reduce the human, economic, and environmental consequences of urban flooding worsened by cities’ built landscapes.

River Floods

River flooding, also called fluvial flooding, occurs when excessive rainfall causes a river to exceed its capacity and overflow its banks into surrounding floodplains. Here are the key characteristics of river floods:

Causes: Heavy or persistent rainfall, rapid snowmelt, ice jams, and dam failures can all trigger river floods.
Geography: Rivers with large drainage basins or in low-lying flat areas are most prone to widespread flooding.
Speed: River floods are generally slower to develop, taking days or weeks rather than hours like flash floods.

Impacts: Overflowing rivers can inundate homes and infrastructure for long periods. Floodwaters carry debris and pollutants picked up on their journey downstream.

Some of the most destructive river floods worldwide include:

The 1931 Yellow River flood in China, which killed 1-4 million people and was the deadliest natural disaster in modern history.

The 1993 Mississippi River flood across parts of the central United States, the costliest river flood with $15 billion in damage.
The 1998 Yangtze River flood, which killed over 3,000 people and left 13.8 million homeless in China.

River flood control methods involve:

Levees and floodwalls along rivers to contain high flows.
Improved channel depth and width to increase river capacity.
Watershed management, like restoring wetlands and forests, to slow and store floodwaters.

Floodplain regulation restricting high-risk development.
Flood insurance providing financial protection for residents.

River floods are common, naturally recurring events, so preparation and adaptation are essential for resilient communities along waterways.

Conclusion

In summary, the three most common flood types are flash floods, urban floods, and river floods. Flash floods strike quickly after downpours and cause deadly high-velocity flooding. Urbanization exacerbates flooding in cities when heavy rainfall overwhelms infrastructure. River floods occur when excessive volumes slowly overwhelm channels and spill into floodplains. Each flood type has different causes, behavior, locations, impacts, and solutions. Reducing flood risk requires a combination of hydrological forecasting, infrastructure improvements, proactive land use planning, and public education on flood safety. With climate change projected to increase heavy rainfall events and flooding in many regions, it is crucial that communities across the globe make themselves more flood resilient. Understanding common flood types and causes is the first step towards effective flood management and saving lives.