Rivers and Groundwater Systems: Floods

Rivers and Groundwater Systems: Floods

Types of Floods

While all of the types of floods left areas of land submerged under water, they were different in terms of the environments in which they occurred. Some occurred along river banks, one was near the sea, and another was off the Gulf of Mexico. Floods are most often categorized based on the environment in which they occur. The five main types of floods are:

riverine: associated with rivers
coastal and estuarine: associated with oceans and estuaries
ice-jam: with ice
urban: associated with urban runoff
arroyos: occur in dry areas that have ephemeral rivers

Look at each picture to see if you can tell the flood environment it represents. You can roll over each picture with your mouse to learn more about it.

Next: Section C, page 9

These homes are partially submerged by a riverine flood, which is a type of flood that occurs when a stream of any kind—usually a river—overflows its banks. The flat area around a river that is affected by floods is called the floodplain. Riverine floods may happen as a result of any of the flood causes you have learned about, such as excessive rain, landslides, snowmelt, etc. A flash flood is a special kind of riverine flood that happens very quickly, when there is a sudden release of water from a stream because of unusually high rainfall or snowmelt or when water is suddenly released by the breaking of a dam, etc.

Coastal floods take place along ocean coasts. An estuary is a part of a coast where river water meets ocean water. Estuarine floods also take place near oceans. Both of these kinds of floods happen when storm surge pushes the water over the land during intense storms. Tsunami-triggered floods from earthquakes also fall under this category.

Ice can cause a flood when it jams up a river and disrupts the normal flow, causing water to spill over its banks. This kind of flood is called an ice-jam flood, and it is especially common in the spring when large pieces of ice begin to break off of melting icebergs. Similar types of floods are caused by obstructions from landslides.

Urban floods happen when urban runoff accumulates quickly with nowhere to go. Urban floods most often take place in large cities, where there are lots of impervious surfaces. When unusually high rainfall hits the area, all the water cannot infiltrate the ground, so it quickly becomes urban runoff. Without anywhere to go, the resulting water floods the city.

An arroyos flood takes place in an area that is usually dry or where ephemeral rivers flow. Since the area is usually dry, heavy seasonal rains can quickly flood the area, as water begins to quickly flow down normally dry channels, like the one you see here. Arroyos is a Spanish word that means an intermittently dry creek.