What is a flood?

Des Moines River out of its banks
In June 2008, the Des Moines River water levels rose and flooded surrounding land.

A flood is an overflow of water that submerges land which is normally dry. Floods occur when there is more water in a river, lake, or stream than the body of water can hold. The excess water spills over onto the land. Floods occur frequently when there is excess rain and when the ground is saturated and cannot hold more water. Flooding can also happen when the waterways and ground are still frozen or iced over and there is a sudden warming that causes snow to melt quickly, and it cannot soak into the frozen ground.

Flooding is the most common natural disaster worldwide, and it happens in rural and urban areas.

 

swans in flooded field
Trumpeter swans enjoy a flooded and picked corn field.

Real Life Events

Show students news clips or documentaries about floods that have occurred, or flooding in general. You could also ask students to research recent flooding events in your area. Ask your students about their experiences with flooding and/or have them interview people who have been affected by flooding. Review statistics about damages, losses, and environmental impact of flooding.

What Contributes to Flooding and Water Quality Issues

  • Wetlands act as natural filters to clean and slow the flow of water, increasing absorption of water into the land. When wetlands are drained or tiled, the water they would otherwise hold and would slowly be absorbed by the land flows directly to rivers, streams, and lakes.
  • Vegetation holds soil in place and soaks up excess water. When large areas of vegetation are removed water washes over the land (instead of being absorbed) and into rivers and streams. This excess water contributes to the flooding of these bodies of water, carrying soil and other materials with it.
  • Soil carried into lakes, rivers, and streams muddies the water. As soil particles settle out of the water, the sediment fills in the water body and decreases its capacity (amount of water it can hold).
  • Improper damming of rivers and streams causes flooding upstream. During periods of excess rain the extra water has no other place to go except out of the river banks and over the land. Improper damming can also cause flooding downstream when excess amounts of water are released to compensate for excess water upstream.

Flood plains (the flat areas along rivers and streams) are part of the river system and it is normal for flooding to occur in these areas during wet seasons. When flood plains are developed (buildings, roads, etc.), they are susceptible to flooding.

When dikes (or berms or levies) are built to contain water in the channel, it moves downstream more quickly, which means water flows can be more erratic. Water moves downstream more quickly and can cause worse floods when water levels go over the levies.

These Aquatic WILD activities can help you and your students learn about watersheds, how water moves on the land, and more!

  • Wetland Metaphors (grades 3-5) – describe the characteristics of wetlands and evaluate the importance of wetlands to wildlife and humans
  • Watershed (grades 3-5) – describe the characteristics of watersheds, discuss the role of watersheds in providing wildlife habitat as well as human habitat, and give examples of watershed conservation
  • To Dam or Not to Dam (grades 6-8) – portray individuals representing differing perspectives and concerns related to a complex issue
  • What’s in the Water? (grades 6-8) – identify major sources of aquatic pollution and make inferences about the potential effects of a variety of aquatic pollutants on wildlife and wildlife habitat
  • Where Does the Water Run? (grades 6-8, 9-12) – design and implement a field investigation involving relationships between levels of precipitation, runoff, and percentage of impervious ground cover

Utilize Project-Based Learning around a water issue or topic!

Links for Learning

Cross-reference to these Aquatic WILD units: