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How does urbanisation impact the water cycle?

The natural water cycle cannot function properly in urban areas because buildings, concrete and other sealed surfaces prevent water from soaking into the ground.

As a result, natural water flows are altered and stormwater is created.

Stormwater is rain that has collected on roofs, roads, footpaths and other sealed surfaces. It flows directly into our waterways via the stormwater drainage network.

In urban areas, water cycle problems include:

Pollution

When water comes in contact with urban surfaces such as roofs, roads and footpaths, it becomes contaminated with oil, metals, litter and other pollutants. This is what we call stormwater.

Stormwater drains do not usually have any treatment systems, so pollutants are carried directly into our waterways, bays and oceans.

Waterway flushing

When it rains, the volume of stormwater entering the waterways in urban areas increases. Water that would usually soak into the ground floods into the stormwater drainage network, where it is transported directly to our waterways.

High volumes of stormwater impact our waterways by:

  • damaging the habitat for aquatic animals, such as fish and invertebrates
  • disturbing the breeding cycles of aquatic animals
  • eroding stream banks
  • increasing turbidity and pollution levels
  • altering natural flood cycles.

Flooding

During heavy rainfall events, large volumes of stormwater collect on sealed surfaces and flow into the stormwater drainage network. Flooding can occur when the volume of stormwater exceeds the capacity of the stormwater drains. This can cause flooding in areas not necessarily close to waterways.

Decreased soil moisture

Most urban surfaces are sealed, or impermeable. They prevent rainwater from soaking into the soil as it does in the natural water cycle.

Low soil moisture in urban areas can impede healthy growth of plants, so irrigation is required to keep trees, plants and grass healthy.  In Melbourne, many of the trees have developed shallow root systems as a result of years of surface irrigation, making them unstable.

The impact of Urbanisation on the water cycle

Flooding
Waterway pollution
Stormwater runoff
Low soil moisture

Move your mouse over the picture to learn more about how urban development impacts the natural water cycle.

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This website was delivered in partnership with the State Government of Victoria