The following information relates to permanent reference marks (PRMs) and referencing requirements under rules 7.4, 16.4 and 17.1.
PRMs are required to have such physical attributes, and be placed in such locations, to provide a reasonable assurance that they should remain undisturbed and useable for at least 50 years [r 7.4.3(b)].
The rule only holds the surveyor to account where the mark's loss could have been reasonably foreseen at the time it was placed or used in the survey.
Although existing marks (eg old iron spikes and tubes) may have been in the ground for a long time or appear to be substantive, they must be assessed as to whether they can be expected to survive another 50 years.
Marks that are close to the surface of roads or footpaths or are in the likely building platform of an undeveloped urban lot or a ROW, are unlikely to satisfy these criteria. Marks buried at a safe depth, particularly in a rural environment, are more likely to meet these criteria.
Historically, some survey marks have been shown with a double circle where they were iron tubes or where, at that time of the survey, the mark was considered more durable than other marks. A new survey will need to re-assess any existing marks to determine whether they meet the criteria specified in rule 7.4.3. This includes an existing order 5 or higher control mark or where a mark was considered a PRM on an underlying survey.
Every cadastral survey required to have a witness mark must include a minimum of two PRMs [r 7.4.1(a)].
The requirement for two PRMs applies to a survey of new class C covenant boundaries in terms of rule 16 (Alternative requirements for covenant parcels) [r 16.4(c)] and rule 17 (Alternative requirements for non-primary parcels)[r 17.1(d)(iv)] .
A boundary reinstatement survey is not required to include a PRM [r 7.4.1(b)].
Each of the two PRMs required by rule 7.4.1(a) must be within 300 m for class A and 500 m for class B of any boundary point that is required to be witnessed [r 7.4.2] (as illustrated by the blue circles).
In addition to those two PRMs, other substantive marks such as trigs and control marks that meet the longevity criteria of rule 7.4.3(b), but do not fall within the prerequisite distances (as illustrated by Trig A), may be treated as additional PRMs for the purpose of the survey.
Line of sight between a PRM and any other non-boundary mark or boundary mark is not a requirement of the Rules.
A PRM may be used as a witness mark where it is within the distance specified for witness marks [rule 7.4.3(c)].