Christchurch City Council benchmark level values are available via the Canterbury Maps site. These values supersede all previously published benchmark data.
Benchmarks are levelled survey points assigned heights expressed in terms of a common reference surface (datum). In the case of Christchurch City Council, the datum used is known as Christchurch Drainage Datum (CDD).
Christchurch City Council Benchmarks enable the ready establishment of CDD normal-orthometric heights within the greater Christchurch area. They are predominately used to establish site level control for civil construction works.
The level value for the original fundamental mark for the network (A82) is now of historic interest only. It had a recorded height of 20.333 feet (6.197m) above Lyttelton Vertical Datum 1937 (mean sea level 1937) prior to the 4 September 2010 Darfield (Canterbury) earthquake.
Land Information New Zealand’s Hagley Fundamental (AF30) has been adopted as the new fundamental mark for Christchurch Drainage Datum.
Christchurch Drainage Datum is offset from Lyttelton Vertical Datum 1937 by -9.043m.
The earthquakes experienced in the Canterbury region between 4 September 2010 and 23 December 2011 put the integrity of the Council’s benchmark network in doubt.
In response to each seismic event a new Global Navigation Satellite System derived emergency response benchmark network was established as an interim measure to assist in the recovery effort. Once seismic activity had subsided to a permissible level a higher accuracy recovery response benchmark network was established using optical levelling methods (the January 2014 Benchmark Network).
The origin of Christchurch Drainage Datum (CDD) dates back to February 1876, the early days of the Christchurch Drainage Board, where the need for a common level was evident very early in the quest to control Christchurch's drainage issues.
An arbitrary figure of 50 feet (15.240m) above datum was chosen for the networks fundamental benchmark (A82), which was situated in the floor of ChristChurch Cathedral’s foyer. A value of 50 feet ensured that levels specified on engineering works in Christchurch City would be expressed as positive values, even when working in New Brighton and Sumner where infrastructure is often situated below sea level.
Christchurch Drainage Datum was initially called Christchurch Drainage Board Datum but upon amalgamation of the Drainage Board and it's activities into the Christchurch City Council the name was changed to Christchurch Drainage Datum (CDD).
Queries regarding the benchmark network can be sent to firstname.lastname@example.org
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