Christchurch Vertical Datums

Recently Christchurch City Council have updated their official height datum, from Christchurch Drainage Datum to the national vertical datum – New Zealand Vertical Datum 2016.

Background:

A height datum is a reference surface (zero point) that levels are measured from.  A good example of this is “mean sea level”, where heights are measured above the imaginary extension of the sea level under the land.

Christchurch Drainage Datum (CDD) was established in 1874.  A benchmark was set in the foyer of the Christ Church Cathedral, which was assigned an elevation of 50 feet.  This resulted in a height datum with a zero level 9.043m below the Lyttelton 1937 mean sea level datum.

There were some advantages to this lower height datum.  For example, underground pipes and infrastructure in low-lying areas could all have elevations greater than zero even though they were installed below sea level.

In more recent years, Christchurch has expanded, global positioning technology (GPS/GNSS) has advanced and data management systems have become much more standardised.  The bespoke nature of CDD has made it less and less compatible for its key purposes of supporting infrastructure, future planning, managing water resources, hazard planning and many more.

Land Information New Zealand (LINZ) has also introduced a new national height datum, known as New Zealand Vertical Datum 2016 (NZVD2016).  This covers the whole of New Zealand and replaces all the 13 official local vertical datums that formerly covered the country.  LINZ has recommended that all Councils adopt this height datum and Christchurch have now accepted NZVD2016 as their official height datum.

What this means for Christchurch

The Christchurch City Council are now requiring that all data supplied to them be in terms of NZVD2016.

Often there will be no change required for your projects.  If a project started in terms of CDD, it will most likely continue to be completed in those terms.

For new projects, any information that Council receives that has an elevation component will need to be in terms of NZVD2016.  This includes:

• Levels shown on topographic plans
• Building and resource consent plans
• Building set-out and location certificates
• Design and construction of civil infrastructure
• Levels related to flood management, including specified floor levels in flood management areas
• As-built information

Where as-built information is being submitted to Council for their asset database, there will be a requirement to submit in terms of NZVD2016.  We will work with you to ensure that the information is correctly converted and in the right terms for submitting to Council.

We will make sure we provide the site information that you need to get your development on the right track and in the correct terms.

If you would like more information, Christchurch City Council have some information on their website to explain this further Vertical Datum 2016 : Christchurch City Council.  LINZ also has information available to explain vertical datums further Vertical datums | Geodetic Guidance

As positioning experts, we are very familiar with the processes to manage heights in different reference systems and convert data between vertical datums.  We would be happy to assist you with understanding the impacts of this change on your project.