About

Auckland Council has designed this Stormwater Device Sizing Tool ("the Tool") so users can estimate the amount of stormwater that needs to be mitigated under the Auckland Unitary Plan rules. It also provides an estimate of the correct minimum sizing for devices designed to mitigate those stormwater volumes.

The Tool is intended to be used for initial estimation and validation purposes. It is not a substitute for professional expert advice and design.

The Tool is based on the 2016 interpretation of the Unitary Plan rules for Auckland.

What is included

Five calculators are provided:

  1. Retention and detention volume calculator, which provides an estimate of the volume of stormwater that needs to be mitigated (either as a retained or detained volume) at a specific site. Using the volumes estimated in this calculator, users can then estimate the sizing for individual devices (with the calculators below).
  2. Rainwater tanks
  3. Swale without check dams
  4. Swales with check dams
  5. Bioretention devices

What is excluded

The Tool does not include

  • A calculator for estimating Water Quality Volumes.
  • Wetland sizing. Designers have to contact Council directly prior to any wetland designs.
  • Pond sizing. Designers have to contact Council directly prior to any pond designs.
  • Pervious paving.

How to use the tool

Step 1:

Use the retention and detention calculator, and the site-specific constraints of your development, to estimate the minimum retention and detention volumes you need to mitigate in order to comply with the Auckland Unitary Plan. Fill in all Green cells with your site-specific constraints. The resultant calculations are in Blue cells. If an error has occurred this will appear as a Red cell and you will need to input a valid datum.

Step 2:

Decide which stormwater device/s you will be using at your site. Manually transfer the calculated volumes from Step 1 to the device/s of your choice. You can split the retention and detention volume between a number of devices or choose to mitigate the entire volume using only one device. Fill each Green cell with the specific constraints of your site and use the output Blue cells as the basis for your design.

Step 3:

You can choose to print or save your calculations as a PDF using the "Download" button

Step 4:

Please provide us with any feedback, so we can continuously improve this Tool.

 

For any feedback, please email wsd@aucklandcouncil.govt.nz.