Stream Bank Erosion

This video shows Mr. Mesick next to Stafford Creek and images of a house that is in danger of collapsing into the creek due to erosion. Streambanks have changed drastically over time due to human activity. The majority of urban streams today have cut-banks due to the increased volume of water reaching the stream during precipitation events. The amount of water reaching our streams in urban communities has increased due to the increase in impermeable surfaces, such as concrete, asphalt and building roofs. Streams with a higher volume of water also have a higher stream velocity, which accelerates the erosion of the bottom and sides of the stream, which is why we see the steep drop-off leading to the stream in the majority of our urban streams. This phenomena presents a serious issue in urban environments where existing buildings were often built too close to the waterways. Now those buildings are eroding and may even collapse into the waterway. Streams also meander and streamflow tends to change over time. Many buildings have been built in the path of a future streamflow change. If the city attempts to solve the problem by stopping the flow of water from one direction, they could cause the water to start eroding a different person’s property, and then that property owner could sue the city for destroying their property. This exact problem occurred in Bettendorf, Iowa, along Stafford Creek with homes built in the 1970s very close to what was at that time a small drainage ditch with intermittent flow. Over the years, the drainage ditch has become a creek with constant flow throughout the year due to the increase of impermeable surfaces throughout the city.

• How can we stop a house in Bettendorf from falling into the creek?

• What should the banks of our local streams look like? 

Students could:

• Watch the phenomenon video and then be lead through creating a teacher-guided model showing the relationship between the amount of water that runs into a stream and how much erosion occurs within that stream. Teachers need to make sure that all students understand the science behind impermeable surfaces and how that increases water runoff, as well as why an increase in water increases stream velocity and erosion.  
• Use a computation representation that demonstrates why their proposed solution would work the best to stop a house in Bettendorf (or one in the local community or on the Youtube video in the related resources section) from falling into the creek due to streambank erosion.  
• Use the Iowa Geographic Map Server website to challenge students to find buildings/homes in their local community that could be at risk from being eroded away due to a stream meandering and changing direction. This website allows students to look at aerial photos of Iowa dating back to 1930 to figure out how streams have meandered in the past and thus predict how they might meander in the future.  If no buildings/homes are at risk, teachers could ask students to propose where houses should be built in a new development to avoid being eroded away by future drainage ditches, streams, creeks or rivers. 
• build models of their solution on a stream table, test their models and evaluate how well their models worked to figure out what material or design worked the best to solve the problem (connects to Engineering Design standards HS-ETS1-2 & HS-ETS1-3).

• KING 5 News - NBC Seattle | House Falling Into River: Video showcasing a house at risk of falling into a river in northwest America. Similar videos can be found of houses along the coast.
• Minnesota Department of Natural Resources (DNR): Streambank Erosion & Restoration: Incredible resource from the Minnesota DNR on streambank erosion and restoration.
• Iowa Geographic Map Server: Teachers and students can use this website to track how streams have meandered over time by clicking on the aerial images of the stream during different time periods. Aerial photos can date all the way back to 1930.
• University of Delaware | Permeable Vs. Impermeable Surfaces: The University of Delaware put together a website to help students understand the difference between impermeable and permeable surfaces.