Why Has Urban Flooding Become a More Prominent Problem?

Why Has Urban Flooding Become a More Prominent Problem?

Since we are seeing an increase in more urbanized areas lately, we've also been experienced more flooding than previous years. Apparently, this isn’t coincidental. According to The United States Geological Survey (USGS), the changes in land use associated with urban development affect flooding in numerous ways. In this article we examine not only how urbanization is causing floods but also actions that can help prevent them.


image © Robert Lawton

image © Robert Lawton

How is Urbanization Causing Floods?

A person is waiting for a taxi in the rain and suddenly a wall of water is splashed their way. It's a familiar urban scene and one that often gets imitated in movies. How can this happen when there are numerous storm drains installed within cities?

Finding the exact reason why an area of the city experiences flooding is surprisingly difficult since there are numerous contributing factors that can be the cause.  Some of the most common reasons include: 

  • The removal of vegetation and soil. 

  • Grading the land surface.

  • Inefficient drainage networks leading to increased runoff.

  • Alterations to stream channels.

  • Increase of impermeable surfaces such as roads, roofs, parking lots and sidewalks.


image © WIki Commons

image © WIki Commons

Why Has Urban Flooding Become a More Prominent Problem?

Whenever rain or snowfall happens, it soaks back into the earth by being absorbed by grasslands, parks, residential lawns, or anywhere that soil is exposed. Cities of course, are notorious for having minimal opportunities for water to soak back into the earth because of impermeable surfaces. When analyzing cities in the United States, according to the Multi-Resolution Land Characteristics Consortium (MRLC), up to 40 percent of the land in cities is impervious. It's a percentile that has been continuously rising over the years as cities undergo further development with urban sprawling.  

image © Wiki Commons

image © Wiki Commons

What Actions Help to Prevent Urban Floods?

In a suburban area, while flooding can occur due to flash floods, coastal floods, or river floods, they are less likely to experience flooding as a result of a heavy rainfall like an urban area can. This is because in addition to storm drains, they have more land masses that can naturally absorb rain - something that is removed for cities.

So how can cities prevent floods?

  • Infiltration Trenches

  • Permeable Pavements

  • Soil Amendments

  • Flood Walls

  • Increase green spaces 

Since urbanization is known to increase the frequency and volume of floods, it's important for urban planners to evaluate the solutions that help with reducing runoff from urban areas during the planning process. While certain aspects can be added after the city is designed like soil amendments and green spaces, it can become costly to implement other techniques after the city block has been constructed. 


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