NZ’s Wet Season has begun

Is your basement, garage, underground flat and / or storage area ready for the upcoming wet season by being protected against flooding?

Spring has started with a wet bang in New Zealand, especially in Auckland. In 2017 an additional 5% (L/sqm) in rain fall is expected when compared with 2016 stats. Storms are more frequent, heavy and short resulting in “flash floods”.

How does the ground respond to flash floods and what solutions are available?

The earth’s condition prior to rainfall is very important to determine the outcome when a flash storm hits. Has it been raining slowly for a few days prior or was the ground dry?

For example in Auckland many suburbs have been developed on clay (predominantly West Auckland and Northern areas) and still don’t have access to the public storm water system. Such properties rely on the stormwater management system within the boundary which is often in form of a soakhole or if lucky a curb discharge.

Unlike areas such as Mt Wellington or Onehunga that have access to underground volcanic cavities, or the public system, homes that manage their own stormwater rely on soil percolation. In simple terms “how quick can my ground soak the water?” The higher the rate, the higher the soakage reducing risk of flooding.

Lower percolation values are common and when they apply, alternative methods need to be used to manage stormwater. If nothing is done, a high level of surface water will result in flooding and over a longer period of time the ground will be charged with so much water it will expanding to a point where underground streams may result finding the least path of resistance into your basement area if no protection is available.

Site conditions such as the following play a critical role:

  • Level of elevation
  • Ground type
  •  Percolation values (soakage tests can be done)
  • Depth of areas affected
  • Current stormwater management system

In the following pictures (Birkenhead Auckland) you can see some of the processes we use to tackle ground water (not in order of works). Are you affected? Call us for a ground water solution.