What are Floods?

Flooding is a weather-related natural disaster event in which water overflows onto land that is normally dry. Floods can be as low as a few inches of water, or enough to cover entire houses, and flooding periods also vary from minutes to many weeks. Floods are the most widespread of any other natural disaster and have different types depending on the weather and precipitation of the land area. Floods can be categorized into 3 major types, Fluvial, Pluvial and Coastal. Fluvial floods occur in and around lakes or rivers and are the most common type of flooding. Pluvial flooding is the event of increased rainfall independent of any surrounding body of water, so they can happen anywhere. Pluvial flash floods often take place near flatter terrain and after heavy rainfall. Lastly, Coastal flooding is simply a seawater flooding taking place along the coast and is caused by more than just rain but rather storm surges and high tides. Specific types of floods include flash flooding, river flooding, tropical storm flooding, debris flows, ice jams and snowmelt flooding. Levee and damn failures are considered another type in itself, but they are common causes for different kinds of floods. (CD)

Types of Floods

Flash Flooding

Flash Flooding is a flood that builds up within 6 hours of the existing cause. The causes include heavy rain, debris or ice jams, and failures from dams or levees. This type of flood has rapid amounts of water over low-lying areas but does not have to be in the same area where heavy rain occurs. Flash floods happen most commonly in the western part of the United States due to the low-lying areas. Harsh thunderstorms or multiple storms over the same area cause sudden downpours and urban areas are especially susceptible to because of the concrete or asphalt surfaces that make it hard for water to get into the soil underneath. For rural and mountainous areas, flash flooding is even more dangerous because of the increasing speed from travelling downhill. (CD)

Flash flooding is typically under the base severity but can be categorized as considerable or Considerable describes a flash flood that regards imminent or urgent action to protect lives and property. Catastrophic is rare and describes a flash flood that is a threat to life and the floodwaters have risen to unprecedented levels bringing catastrophic damage. (CD)

A notable flash flood happened on August 4th, 2009, in Louisville, Arkansas. The Louisville International Airport reported 4.53 inches of rainfall, with 3 inches of that rain falling in just one hour, breaking the previous record that occurred back in 1879. Major roads were closed, and a few water rescues were performed in the surrounding area, along with several buildings basements on Louisville’s campus flooded. (CD)

River Flooding

River Flooding occurs in which river levels are high enough to overflow their main channels. This event happens from heavy rain or snow melting, but also from failures of dams. River flooding is categorized between Minor, Moderate and Major, depending on the height of the water and the impact it has on the surrounding environment and these categories are coordinated between the National Weather Service and local officials, meaning there are different numeric values that categorize a river flood. (CD)

Minor river flooding rivers flowing into rural areas and farmland and are rarely documented as their height does not exceed evacuation procedures. (CD)

Moderate flooding has the water level to be high enough that businesses and homes are at risk and evacuations could be necessary. An example of this was the Mississippi River Flood during 2007. This occurred after a historic estimate of 11 to 15 inches of rain over 2 days for specific counties in Minnesota and Wisconsin. These counties were declared a Federal Disaster area and over 4,200 homes were damaged. (CD)

Major flooding has numerous evacuations across towns. Most major river floods become record floods of water levels. One memorable flood in this category was the Meramec River Flood of 2016, in which lasting 3 days killed 20 people along with 7,000 buildings damaged. Another example of this was the 1997 Red River Flood. The cause was when the last of 8 blizzards in April were so harsh that the snow melting made the river rise to 54.33 feet, and the aggregate damage cost was an estimated $5 billion. (CD)

Tropical Storms/Storm Surges

Tropical storm flooding or storm surges occur when the rise in water in coastal areas is caused by severe storms and its winds, waves and atmospheric pressure. These can be extremely dangerous in states near large bodies of water, such as Charleston, South Carolina and Savannah, Georgia. Some cases have tides reaching over 20 feet if the storm surge coincides with an already high tide. Once storms reach shallower waters, the circulation caused by a storm’s strong winds is interfered with and the water begins to move upward and inland. Tropical storms such as hurricanes are sorted into 5 categories based on their wind speed, with 74 to 95 miles per hour winds for category 1 hurricanes and over 157 mile per hour winds for category 5 hurricanes. The waves from these storms and hurricanes have the most destructive power than any other type of flooding. Water weighs approximately 1,700 pounds per cubic yard, meaning that beaches and costal highways can be easily eroded away and the buildings that survive from the water can still be damaged from the erosion that weakens their foundations. Additionally, estuaries in which freshwater meets ocean saltwater can be intruded so the concentration of dissolved salts goes up in the mixed water and can kill vegetation or send animals living in specific water conditions away from their habitats. (CD)

Debris Flows

Debris flows are a specific type of flood that are commonly referred to as mudslides. Debris flows can include rocks, mud and even vehicles. They happen after heavy rainfall or intense rainfall, meaning at least a half inch of rain within an hour. Debris flows are very dangerous because of the inconsistent nature of what is being carried across channels. Sandbags and retaining walls can redirect floodwater and mud but the debris will keep moving until it hits an even bigger target, which could include homes. Debris flows can either be categorized into phase one or phase 2. Phase 1 debris flows have more liquid and sediment mixed and occur with faster movement. Phase 2 debris flow typically has stone and gravel and moves slower if the flow collides with larger objects, such as trees, boulders and vehicles. Areas with downhill slopes and burned areas from wildfires are the most susceptible because of the loss of soil strength over time, causing runoff and erosion. (CD)

A notable event of debris flow was at the 2014 landslide in Oso, Washington. While debris flows are a specific type of landslide because of the water mixed in along with its faster movement, the Oso landslide occurred due to heavy rainfall and had a history of erosion from the nearby Stillaguamish River. This landslide reached up to 70 feet in height and stretched over half a square mile long. This disaster killed 43 and injured 20 while also trapping people in their homes if it was not destroyed. Highway 530 was blocked and Darrington, the town east of Oso, became landlocked and required food banks for their relief goods. (CD)

Ice Jams & Snowmelt Floods

Ice jams and snowmelt flooding happen during different seasons, the former occurring in late winter and the latter during springtime. Ice jams are the event of pieces of ice pile up and becoming large enough to be an obstacle in a river and eventually cause a flashflood when the ice breaks. Snowmelt floods similarly have ice and snow piled on top of rivers and the sudden temperature change can saturate the soil, so the excess water flows into streams. The snow melting can make any ice jams worse and further damage soil around rivers and streams. Ice shoves transpire when wind and waves push chunks of ice. Ice shoves are very dangerous and are known to be able to shatter windows of large enough pieces strike houses. Alaska and the Great Lakes region are at risk of ice jams and snowmelt floods because of the known rapid temperature changes and the many rivers connecting to the large lakes. (CD)

An example of ice jams causing long term harm was during the 1984 St. Clair River ice jam. This lasted 24 days and the ice clogged almost 20 miles of river, which made cargo ships stranded at both ends of the river. The ice was formed in Lake Huron and said cargo ships broke up the pieces and the northern winds pushed it downstream into St. Clair River. The combination of the Great Lakes region’s winds and fluctuating temperatures caused thick pieces of ice to form and forced ice breakers to spend a significant amount of time clearing the river for ships. (CD)

Levee & Dam Failures

Finally, levees and dams are both designed to control water flow and if there is a breach in either one a flood can occur. Levees are made with the specific intent to prevent flooding for areas around rivers. Most levees are earthen embankments, which are constructed with compacted soil to create a rise in elevation to compensate for fluctuating river and costal water levels. If heavy rainfall were to occur next to an earthen embankment, the excess water could cause it to soften and lower the height overall. Most levee breaches occur from slope instability or rapid seepage (the rapid movement of water through soil). This kind of breaching leaves little opportunity for evacuation, but overtopping the embankment is likely to progress slower and allow anyone to evacuate the area. Depending on the materials made, some water can seep under parts of it, further weakening the embankment and creating a higher risk of the next set of heavy rain to become a flash flood. Next, Floodwalls are another type of levee and are anchored walls placed next to a body of water. Floodwalls are often created for higher water levels than traditional ones but can also be constructed where there is not enough space to create an earthen embankment. (CD)

Dams are also barriers against bodies of water prone to flooding but regulate the flow of the river so during flood seasons the magnitude can be significantly lowered. Most of the smaller dams are used in this way, but the fewer and larger dams have hydropower generation facilities. Dam failures are common with smaller dams and have multiple causes depending on the construction. It was reported that from January of 2005 to June 2013, there were 173 dam failures. The biggest cause of dam failures is overtopping, the event of heavy rainfall or inadequate spillway designs causing water to spill over the top of a dam. Foundation defects of the settlement or piping problems are also issues that dams deal with, which if not filtered properly sink holes can form from soil particles within the dam. (CD)

The famous example is Hoover Dam, one of the tallest concrete dams in the world as its 660 feet thick at the base and 726 feet tall. Its reservoir stores water that irrigates 2 million acres from California and Nevada to Arizona. Over 1.3 million people use its hydroelectric power, but it also holds back flood waters along with over 50 other dams from the Colorado River. One historical dam failure happened in 1976 with the Teton earthen dam in Idaho. It had a width of 3,200 feet that covered 17 miles. On June 5th, 1976, a leak appeared, and the hole quickly grew to 25 feet in diameter due to the pressure of holding almost 260,000 acre-feet of water. After 6 hours of the initial burst, the entire reservoir was drained, and the neighboring towns were hit with harsh floodwaters. 11 deaths and more than $2 billion to infrastructure were reported and the dam has not been rebuilt to this day. (CD)

Cause and Effect of Floods

Although the factors that contribute to floods are diverse and complex, scientists still believe that harsh precipitation events including hurricanes and severe storms can be attributed to climate change. The Southwest region of the US has had less and less annual precipitation while the Midwest, Great Plains and the Northeast regions have increased along with their intensity of precipitation. In the United States’ history of single-day extreme precipitation events, 9 of the top 10 years occurred since the 1990s. Scientists anticipate more flash and fluvial floods for the rest of the decade and well into the twenty-first century from this increase in extreme precipitation. (CD)

Scientists have also predicted the US seal levels to rise to almost 10 inches within the next 30 years, especially in the Northeast region and parts of the western Gulf of Mexico. Rising sea levels are strongly associated with high tides and therefore storm surges. Statistically, a rare flood has a 1% probability to occur in any given year (also known as the 100-year flood), but with the rising sea levels in the future that chance of occurrence will be up to 8 times more likely. Not only will there be more coastal floods and storms surges happening, but the worst of the worst floods have an even bigger likelihood. (CD)

Community Impact

As previously mentioned, floods have a large economic impact due to the damage to buildings and the blockade of roadways that disrupts economic activity. A small river flood can block a highway that small towns need for importing and exporting, or an ice jam can clog a lake that key cargo ships pass through daily. According to one study, they found that over the last 40 years the cost from floods and hurricanes has reached over $1 billion each year, accounting for inflation. Losses in infrastructure, agriculture, business interruption expenses and storm cleanup have all made flooding a rising concern if the future is expected to come with worse weather events. (CD)

Knowing key socioeconomic factors that relate to floods is important too from a public health stand. Social factors such as low education and English-language challenges can make a common flood very difficult to anticipate and recover from. Studies have shown that low-income households are more likely to live in flood-prone areas and therefore could lack the necessary resources for flood preparation and evacuation. There is an association with inadequate infrastructure in these same areas so a cycle of decline in wealth for households and communities is formed because any and all of their investments go back to recovering from floods. Addressing these factors, as well as susceptible demographics, such as children, older adults with chronic health conditions and non-native English speakers, are important to creating policies that educate and assist flood-prone communities. (CD)

Government Involvement

Federal Emergency Management Agency

Government involvement has changed in recent years to combat properties with higher susceptibility of floods. The Federal Emergency Management Agency has different programs and processes for declaring a flooding emergency, responding to emergencies, and recovering from emergencies. Their Public Assistance Program, for example, gives out grants to state, local, territorial and tribal governments, but also to non-profits so they know how to respond and recover from a flooding disaster. These grants help cover the costs of infrastructure loss and debris removal, as well as protective procedures for life-saving emergencies. ‘Pop-up” shelters and kitchens from these non-profits give survivors comfort and supplies to meet the immediate needs that larger authorities have to congregate before giving out. Once a disaster is declared within an area, the Disaster Survivor Assistant Team rallies community members for assistance and provide door-to-door referrals to community resources and relief for immediate needs. There are also Disaster Recover Centers across the US for personal concerns and status checks for survivors. Recovery is also managed using the National Disaster Recovery Framework, which allows agencies to coordinate with communities with federal assistance on flood protection and resource management. (CD)

Currently, there are over 50 private insurance companies that participate with FEMA to provide flood insurance, which covers what homeowners’ insurance can’t. Due to more frequent and worsening floods, the National Flood Insurance Program has implemented a new pricing approach that can create more transparency for a susceptible property’s flood risk. Historically, a household’s rate was measured on their elevation with county zones but never accounted for the unique cost of rebuilding. More variables have been incorporated to combat the pricing disparities, such as flood frequency, flood types and distance to water sources. Communities that exceed the minimum requirements of the National Flood Insurance Program can volunteer for the Community Rating System that helps floodplain management for flat areas adjacent to rivers and streams. These communities can receive rate discounts of between 5 to 45% depending on the rating system’s classification but will apply to the whole community rather than the individual house. Independent organizations, like First Street Foundation, have also created more available flood risk factors for properties and partnered with listing services such as Realtor.com for better understanding of flood risk while considering properties. (CD)

Failure of Hurricane Katrina

Next is an example of how poor disaster infrastructure and recovery has forever damaged Louisiana, and the cause of this event was Hurricane Katrina in 2005. The peak intensity winds made it category 5, but by the time it hit the gulf coast it weakened to category 3. The maximum surge exceeded 25 feet, and the preliminary estimate of damage costs were over $100 billion. Over 1500 people were killed either directly or indirectly from the storm surge that took the city of New Orleans, Louisiana years to return to somewhat normalcy. Some of these damages and deaths could have been prevented, and the Bush administration at the time knew that their current system of policies and agencies had to be reshaped in order to improve the functionality of disaster response. As far as response, the coordination between the federal and local governments at the time had no system for addressing a large-scale disaster with potential to destroy infrastructure. When the hurricane made landfall, the regional authorities could not communicate with each other or up to the state for a proper response, and the federal government were late to take over any responsibilities that these regional authorities conduct. The administration admits that “The federal officials struggled to perform responsibilities generally conducted by State and local authorities, such as the rescue of citizens stranded by the rising floodwaters, provision of law enforcement, and evacuation of the remaining population of New Orleans, all without the benefit of prior planning or a functioning State/local incident command structure to guide their efforts”. [1] They continue on stating that the local governments should be the first to respond to a disaster while the federal government uses its resources to aid a catastrophic-level disaster. (CD)

Another mistake the Bush administration admits with regards to Hurricane Katrina was the coordination within the federal agencies themselves. Their National Response Plan’s Mission Assignment process of paperwork and approvals delayed their response while agencies were acting independently causing more confusion and unnecessary documentation. Mayor of Baton Rouge, Louisiana noted that the hierarchy of power increased the confusion, as the Principal Federal Official lacked supervisory power over the Federal Coordinating Officers despite being apart from the Federal Emergency Management Agency, therefore execution of response was hindered. These structural weaknesses proved that federal agencies were not ready for a disaster of this nature. This created a domino effect for Louisiana as the majority of large hospitals and healthcare facilities were shut down or inoperable. All of the survivors facing chronic medical conditions isolated from the floods, which brought back the federal level to take responsibility for identifying and treating patients while reestablishing infrastructure. Going along with the federal structure taking a long time, the process of authorizing reimbursement for these medical services further delayed the ability to deliver treatment. Again, the Bush administration says they have learned their lesson and goes on with, “The Department of Health and Human Services should strengthen the Federal government’s capability to provide public health and medical support during a crisis.  This will require the improvement of command and control of public health resources, the development of deliberate plans, and additional investment in deployable operational resources”. [1] They are firmly aware of what was wrong, but that does not mean citizens can go back to their norm. (CD)

Housing displacement and environmental hazards forced the state of Louisiana to take years to recover back to part of its original image before the hurricane struck. The largest housing crisis since the Dust Bowl, Louisiana once more was at the mercy of slow and bureaucratic processes of the federal government to allow its citizens to seek refuge outside the state. FEMA was criticized for prioritizing cruise ships and trailers for emergency shelters, which became too costly long term and took a long time to integrate other housing units from the departments of Housing and Urban Development (HUD), of Veterans Affairs (VA) and of Agriculture (USDA). Eventually HUD took over the housing plans using federal resources but by then the damage had been done. Next, the environmental impacts added more problems that the inefficient infrastructure had to deal with. Superfund waste sites and water treatment plants were destroyed accumulated over 2000 reported cases of pollution along with 7 million gallons of oil spilling onto the Gulf Coast. Not only did the federal agents have to perform rescue operations without proper coordination with local governments, but they had to do it in the 80 square miles of flooded waste and debris. Regarding debris, there were an estimated 118 million cubic yards of debris that took over 5 months just to remove 71 million. This along with private property complications further hampered recovery time. The Department of Homeland Security acknowledges that along with the Environmental Protection Agency they should oversee the data collection so responders can determine if the disaster environment is safe to act or to return after evacuation. These federal agencies have now updated their agendas and protocols so that another disaster does not create this many problems, but the state of Louisiana and its coastal cities will never forget this historic event. (CD)

Prevention

For preventing future floods, the Environmental Protection Agency recommends utilizing Green Infrastructure, which are management systems that help absorb rainfall. Examples include permeable pavements and rain gardens that help against runoff and erosion. One study in Ramsey County, Minnesota, found that implementation of eight underground infiltration trenches and eight rain gardens reduced rain runoff by 77% and 88% respectively. Smaller communities, site developers and even homeowners can access the public National Stormwater Calculator that estimates the amount of annual rainwater as well as the frequency of runoff. [2] For areas unsure about the high upfront costs of green infrastructure, the Geographic Information System identifies the cost-benefit effectiveness for its implementation and the quantities the amount of stormwater it could potentially manage. The Community-enabled Lifecycle Analysis of Stormwater Infrastructure Costs tool, or CLASIC tool lets uses analyze future precipitation rates and the costs of different stormwater management scenarios. An example of a community using these resources and finding success is the Milwaukee Metropolitan Sewerage District partnering with The Conservation Fund and creating the Greenseams program that in 2022 protected almost 5,000 acres of flood-prone land. This program also lowered the potential for future flows and contaminants into receiving rivers. (CD)

Conclusion

Floods have diverse types that encompass different dangers, making them one of the most complex types of natural disasters that the United States faces. Different regions have to deal with the same types of fluvial flood while also responding to special types depending on their climate, elevation and amount of annual rainfall. There are cost-effective solutions like green infrastructure, levees and dams, but poor construction and/or inspections can lead to leaks and cause a flood of their own. There were historic floods decades ago yet the current climate around the country has lead to heavier rainfall and more potentially worse floods than ever recorded. One of the biggest floods in the recent past came from Hurricane Katrina, in which there were critical gaps and systemic failures within coordination, preparedness, and recovery. This storm led to government agencies updating their frameworks and providing a better insurance model for flood-prone communities. Communities like these can rally together and implement green infrastructure to mitigate runoff for flood season but this is just a small step in the right direction. As long as the low-income households are disproportionately living in flood-prone areas, change will come at a slow pace. Escalating government awareness of these disparities as well as climate change will bring insight towards policy changes to fight against the uncertain force of natural disasters. (CD)