What makes floods happen

They include:. River Flood. Coastal Flood. Storm Surge. Inland Flooding. Flash Flood. As you can infer from the list above, flooding can happen anywhere, including both coastal and inland locations. The first type of flooding we will explore is river flooding.

A river flood occurs when water levels rise over the top of river banks. This flooding can happen in all river and stream channels. Causes of River Flooding. River flooding typically happens for four reasons.

They are:. Excessive rain from tropical storm systems making landfall. Persistent thunderstorms over the same area for extended periods. Combined rainfall and snowmelt. Ice jam. More on Riverine Floods. River floods can happen suddenly or slowly. Sudden river flooding events occur more often on smaller rivers, rivers with steep valleys, rivers that flow for much of their length over impermeable terrain, and normally dry channels.

On the other hand, low-rising river floods typically occur in large rivers with large catchment areas. The next type of flood you should know about is a coastal flood. What is Coastal Flooding? A coastal flood is the inundation of normally dry land areas along the coast with seawater. Causes of Coastal Flooding.

Coastal flooding is typically a result of a combination of sea tidal surges, high winds, and barometric pressure. These conditions typically come from storms at sea like:. Tropical cyclones. Higher-than-average tides. Another type of flooding that is often associated with coastal flooding is storm surge. What is Storm Surge? Storm surge is an abnormal rise in water level in coastal areas over and above the regular astronomical tide.

Causes of Storm Surge. Storm surge is always a result meteorological storms that cause higher than normal tides on the coast. There are three parts of a storm that create this surge. Low atmospheric pressure. Learn about storm surge from one of our expert meteorologists, Andrew Rosenthal in the below snippet from our weather safety warmup webinar on hurricanes :. Storm surge is an extremely dangerous form of flooding. It can flood large coastal areas at the same time. It can also cause flooding very quickly.

Extreme flooding occurs when storm surge happens at the same time as high tide. This can cause storm tides to reach over 2o feet! Our meteorologists always stress that storm surge is the most dangerous aspect of any tropical system. It poses the most threat to both life and property.

For example, storm surge took the lives directly and indirectly of over 1, people during Hurricane Katrina. The next type of flood on our list is an inland flood. Some organizations refer to inland flooding as urban flooding. A flash flood is also a type of inland flood. What is an Inland Flood? An inland flood is flooding that occurs inland or not in a coastal area. Therefore, coastal flooding and storm surge are not inland floods. Causes of Inland Flooding. Rainfall is almost always to blame for inland floods.

Rain causes inland flooding in two ways. It can happen with steady rainfall over several days or it can happen because of a short and intense period of rainfall. Snowmelt also causes inland floods, although rainfall is a more common cause. Another way inland flooding happens is when water ways get blocked by debris, ice, or dams.

More on Inland Floods. Here are eight of the most common causes of flooding, both natural and human-induced. And the consequences of flooding can be savage. The simplest explanation for flooding is heavy rains. No matter where you live, you are surrounded by infrastructure and systems designed to move rainwater into appropriate basins and reservoirs. In most cases, the infrastructure does its job, and you never have to think about where the rain goes when it runs off.

In short, the drainage systems back up, and the water rises — sometimes into homes. This typically happens only in cases of sustained heavy rains over a long period. You do not necessarily need to have heavy rains to experience flooding in your area.

For example, if you live along a river and areas upstream from you experience heavy rains, it could lead to a serious overflow where you live. Most larger rivers include a series of dams to help manage large amounts of rainfall, and most river systems are managed by government authorities. Sometimes, however, those authorities have to make tough decisions about how to operate dams.

They often can manage the water and prevent flooding altogether — but not always. Several factors contribute to flash flooding. The two key elements are rainfall intensity and duration. Intensity is the rate of rainfall, and duration is how long the rain lasts. Topography, soil conditions, and ground cover also play an important role.

Flash floods occur within a few minutes or hours of excessive rainfall, a dam or levee failure, or a sudden release of water held by an ice jam. Flash floods can roll boulders, tear out trees, destroy buildings and bridges, and scour out new channels. Rapidly rising water can reach heights of 30 feet or more.

Furthermore, flash flood-producing rains can also trigger catastrophic mud slides. You will not always have a warning that these deadly, sudden floods are coming. Most flash flooding is caused by slow-moving thunderstorms, thunderstorms repeatedly moving over the same area, or heavy rains from hurricanes and tropical storms.

Occasionally, floating debris or ice can accumulate at a natural or man-made obstruction and restrict the flow of water. Water held back by the ice jam or debris dam can cause flooding upstream. Subsequent flash flooding can occur downstream if the obstruction should suddenly release. Identify where to go if told to evacuate. Choose several places Know your area's flood risk.

For information, call your local National Weather Service office, Red Cross chapter, or local emergency management agency. Check your homeowner's or renter's insurance. Homeowners' policies do not cover flooding. Contact your insurance agent to find out how to get flood insurance. Even 6 inches of fast-moving flood water can knock you off your feet, and a depth of 2 feet will float your car!

Failed dams and levees can cause catastrophic floods due to the intensive energy involved in the sudden burst of water. River floodplains and coastal areas are the most susceptible to flooding, however, it is possible for flooding to occur in areas with unusually long periods of heavy rainfall.

Bangladesh is the most flood prone area in the world. Bangladesh is vulnerable due to presence of a monsoon season which causes heavy rainfall.

Other factors which have contributed to flooding are deforestation in Nepal which has caused soil erosion. This had lead to the increased silt content in the rivers further downstream.

This decreases the carrying capacity of the rivers, causing the peak flow of the river to increase. Examples of the different types of floods can be found in the occurrence section.

Mississippi flood, USA In April parts of the Midwest received as much as 10 times the normal amount of rainfall which swelled the Mississippi and its 50 tributaries. The tributaries fill when the Mississippi rises causing local floods of small to medium magnitudes.

Due to the amount of water involved the tributaries were already inundated so the excess water in the Mississippi flooded counties in 9 states.

The water overwhelmed levees, erased towns and destroyed other infrastructures such as bridges and airports. The flood killed 45 people, displaced 50, people and inundated The Mississippi river had been altered and re-directed in the s. Dams and levees were built to deal with the changes in the river capacity.