To calculate design rainfall depths for a given township within the Selwyn district follow the following procedure:

  1. Using table 1 [PDF, 13 KB], select the appropriate 'Rainfall gauge' and 'Scale factor' for the township of interest.
  2. Using the appropriate 'design rainfall table' [tables 2-7 [PDF, 24 KB]] multiply the given values by the 'scale factor' to calculate township specific rainfall depths.
  3. The township specific rainfall depths should then be multiplied by a factor to allow for climate change.  In the Selwyn district, it is generally accepted as being a factor of 1.16.

The above procedure shall be used for all urban development within Selwyn district.

Council reserves its right to use discretion when applying this rainfall data during assessment of applications for engineering approval.

Reference Material

  1. SDC Letter [PDF, 46 KB] to Environment Canterbury
  2. Opus Memo [PDF, 1856 KB] - Design rainfall scale factors
  3. Opus Report [PDF, 5788 KB] - Development of Design Rainfalls for Selwyn district
  4. Opus Memo [PDF, 662 KB] - Extended duration tables