Stormwater and foundations

About stormwater


Stormwater Diagram, source


Stormwater can pose significant risks to the stability and integrity of building foundations. With the increase in extreme weather events due to climate change, understanding the effects of stormwater on foundations has become more crucial than ever for property owners, engineers, and urban planners.


Stormwater management and drainage systems

In Perth, where sandy soils are prevalent, proper drainage systems are crucial for residential properties. Sandy soils are particularly susceptible to erosion caused by stormwater runoff. When drainage systems are inadequate or poorly designed, stormwater can wash away the sand beneath foundations, creating voids and leading to subsidence issues.


Subsidence occurs when the ground beneath a structure sinks or settles unevenly. This can cause serious damage to buildings, including cracks in walls, uneven floors, and structural instability. As stormwater carries away sand, it creates cavities beneath the foundation, compromising its stability and leading to subsidence over time.


Groundwater related subsidence, source


To mitigate subsidence issues, it’s essential to implement effective drainage systems that properly manage stormwater runoff. This includes installing gutters, downspouts, and drainage pipes to direct water away from the foundation. Additionally, proper grading and landscaping can help prevent water from pooling around the property, further reducing the risk of erosion and subsidence.

Regular inspection and maintenance of drainage systems are also vital to ensure they remain effective over time. This includes clearing debris from gutters and ensuring that downspouts are directing water away from the foundation.


Overall, investing in the correct drainage systems for Perth’s sandy soil is crucial for preserving the integrity of residential properties and preventing costly damage caused by subsidence.


Calculate storm water runoff

Understanding the measurements of stormwater roof runoff and the size of soakwells is crucial for managing subsidence and protecting foundations.

Here’s an easy explanation:

1. Stormwater Roof Runoff

  • Stormwater roof runoff refers to the rainwater that flows off the roof of a house during a rainfall event.
  • To measure stormwater roof runoff, you can estimate the amount of rainfall that falls on the roof and calculate the volume of water that will flow off the roof surface.
  • This measurement helps determine the quantity of water that needs to be managed and directed away from the foundation to prevent issues like subsidence.

2. Size of Soakwells

  • Soakwells are underground structures designed to capture and temporarily hold stormwater runoff, allowing it to slowly infiltrate into the soil.
  • The size of soakwells needed for a property depends on factors such as the size of the roof, the amount of rainfall, and the soil’s permeability.
  • To determine the appropriate size of soakwells, you’ll need to calculate the volume of stormwater runoff generated by the roof and ensure that the soakwells have sufficient capacity to accommodate this volume.
  • Larger roofs or areas with heavy rainfall may require larger soakwells to handle the increased runoff.

Why It’s Important

  • Proper management of stormwater runoff is essential for protecting the foundation of your home.
  • Excessive water pooling around the foundation can lead to soil erosion, subsidence, and structural damage over time.
  • By directing stormwater away from the foundation and into soakwells, you can help prevent these issues and maintain the stability and integrity of your home’s foundation.

How to Implement

  • Consult with a drainage specialist or engineer to assess your property’s needs and determine the appropriate size and placement of soakwells.
  • Install gutters and downspouts on your roof to collect and channel rainwater into the soakwells.
  • Ensure that the soakwells are properly maintained and periodically inspected to prevent blockages and ensure efficient drainage.


By understanding the measurements of stormwater roof runoff and the size of soakwells needed to manage it effectively, homeowners can take proactive steps to protect their homes from subsidence and foundation damage caused by excess water runoff.

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