|NOTE: This circular has subsequently been edited to reflect an amendment to the Living Marine Resources Management Act 1995, effective from September 2007, that changed the coordination requirement for marine farm leases from AMG to MGA coordinates.|
Survey of Marine Farm Boundaries
Since the issue of the circular memorandum 1/1994 a number of surveys for marine leases have been submitted to this office for registration. Examination of such surveys has revealed that a large proportion of these surveys have contained gross errors in the derivation of the
MGA co-ordinates. The causes of these errors have commonly been such oversights as the acceptance of azimuths as grid bearings and failure to apply the correct scale correction to distances.
To assist surveyors in ensuring correctness of surveys through utilising checking procedures and also to facilitate effective office checking, adoption of the following guidelines is recommended when using conventional theodolite/EDM instrumentation to survey marine farms:
- Any traverse used to determine co-ordinates of a boundary point should be closed onto a. known point and open traverses avoided.
- Where only one control station has been used, there should be some check on its correct identification. This might be achieved by comparing the observed and calculated bearings to suitably located control points.
- In order to provide a check on the computation of co-ordinates for Lease corners, redundant field operations should be taken. Typically, this is achieved by radiating a corner from different stations on a closed traverse.
- Where grid distances are recorded on the survey notes they should be clearly labelled as, such to distinguish them from measured distances.
Robert S. Gane