Streambank Erosion: Washing Away Misconceptions

Mist along the Credit River.

In Caledon, the Credit River flows through natural landscapes and broad valleys. If you look closely at the river in this area you’ll notice that the streambank is eroding – and in this case, it isn’t a bad thing.

Erosion is a natural process that benefits streams. It moves sediment (silt, sand and pebbles that make up the stream bottom) and organic material (like broken down leaves and branches) releasing food for fish and aquatic insects downstream. It creates new habitats in undercut banks or around fallen trees.

Streamflow in a naturally stable stream is constantly eroding sediment from the outside bank and depositing sediment on the inside bank. This allows the stream to move through the landscape over time while keeping the same overall width and depth.

This graphic below shows real erosion over the last eight years in a section of the Credit River. The amount of lost sediment (erosion) is about equal to the amount of gained sediment (deposition). When a stream erodes and deposits material in this way, the stream is ‘dynamically stable’ and this is a sign of a healthy stream.

Eight years of a dynamically stable cross-section of the Credit River in Caledon.

Certainly not all erosion is healthy. Erosion is a problem when property and infrastructure, like roads and bridges, are at risk. It’s also a problem when a stream is rapidly becoming wider or deeper. This means material is being eroded away but very little is being deposited. This can happen to streams in urban areas where there is less natural space to absorb rainfall or snow melt. This results in more runoff into streams from hard surfaces like roads, parking lots and roadways.

People doing research beside river
CVC monitoring staff surveying erosion and deposition in the Credit River.

Through our Integrated Watershed Monitoring Program (IWMP), we measure erosion and deposition in streams throughout the Credit River Watershed. This information helps us better understand the habitat conditions for fish and other aquatic life and can identify areas where erosion may become a problem. Learn more at cvc.ca/iwmp.

By CVC’s Kyle Swanson, Technician, Watershed Monitoring

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