Geology & Flash Floods

Goal

Students learn that water flows downhill on land and that the shape of the land and the ability of water to soak into the ground influences whether a rainstorm causes a flash flood.

Engage students with a video of flash flooding occurring in a natural environment.

  • Flash Flood: This 5-minute video shows how a creek can fill to flood level in seconds. After having students watch the video ask whether any of them have visited an area where this could happen. Have they seen it happen? Survey student knowledge about where the water could be coming from to fill this creek so quickly. Students should recognize that a storm upstream could have added water to this creek, or that a dam upstream was opened.

Explore by having students build models to learn how topography and the permeability of the land affect flash flooding.

  • Topography models
    • Crumple a Watershed: This activity gives students a quick and easy way to model a watershed and can be adapted for various grades. While a map that shows topographic relief is a part of this activity, you can substitute online relief maps or videos that show birds-eye views of topographic relief.
    • Build Your Own Watershed: In this activity, students develop a more elaborate model of a watershed. You may wish to monitor student use of spray bottles during this activity.
  • Porosity and permeability models
    • The GLOBE Program: Just Passing Through: Have students set up the demonstration if time allows, or set it up beforehand and focus on student observations of the model.
    • Soil Moisture - SMAP Block Pattern: Have students obtain in situ measurements of soil moisture that are consistent with soil measurements from NASA's Soil Moisture Active Passive (SMAP) satellite.
    • Porosity and Water Flow in Soils: An advanced activity for high school students.

Evaluate by having students apply what they have learned about the shape of the land and porosity to another context.

  • Tell students that flash flooding is also common in urban settings. Ask students why that might be.  Ask students to write a paragraph to describe, based on what they have learned about flash flooding in mountain environments, why flash floods might happen in urban settings. Student answers should include (1) the impermeability of urban surfaces such as concrete, asphalt, and buildings, which prevent water from soaking into the ground and (2) that a flash flood would depend on the topography of the city.