Xai-Xai IDP – DEMONSTRATION ACTIVITIES
7.1.8 Demarcation and Pegging of the Praia Velha Detailed Plan
This chapter refers to the pegging of the Praia Velha Detailed Plan, including 139 lots in the area known as the Praia Velha beachfront, between January 26 and February 11, 1999. The private company SUIMO Lda. was appointed provisional tendering agent (provisional Development Agency) for this crucial first step of implementation. Following the evaluation of four different bids the work was contracted to a joint venture of the national survey service of DINAGECA and the MHP GEOMATICS, prominent South-African surveying company.
The principal consideration for the co-operation was private company efficiency (MHP) backed by the legal and administrative framework, as well as on site support by the national surveying service (DINAGECA). It was proven that the national service is technically capable of providing the contracted service, however, the experience of the MHP was a valid speed and efficiency factor. The collaboration was a success in terms of personal and professional exchange and has led to the required results.
Standard practice demands that Y, X co-ordinates for a development project be referenced to the national co-ordinate system. Aerial mapping had previously been done and referenced to this system. While connecting our survey onto the national grid system of reference points, inconsistencies appeared between actual physical measurements and the mathematical distance based on the co-ordinates supplied.
This initial referencing is vital, not only to the survey at hand, but also to the success of the whole project. Our survey co-ordinates where derived from the mapping previously done and as such the physical position of the monument which we place, must conform to the design position as designed from the mapping.
The survey was undertaken in its totality with LEICA Real Time GPS. Two of the Primary National Reference points were visited in the area. As well as a secondary National reference point based in Xai-Xai itself. Comparison between GPS co-ordinates and the two Primary National Clark 1866 co-ordinates were shown to be contradictory.
To solve this discrepancy in the reference points, it was able to source the survey control points co-ordinates utilised by the previous surveyor and from this we were able to use the same reference points the previous surveyor used and maintain the consistency of our survey and the mapping. Finally, a system was devised whereby the relative co-ordinates of the map corresponded to measurements on the ground. The map was then positioned to match the existing structures, as well as possible.
The process then started by placing the property beacons. The methodology we used for this was that MHP surveyor would place steel pegs as the beacon and then the DINAGECA surveyors were referencing point and substituting the concrete blocks.
The area of survey was very bushy, in most places 2 meters high, what radically affected initial planning of the project and the survey methodology had to be revised, and required as follows:
Employment of substantially more labour was required to “cut lines through the dense vegetation”;
The time planned for the project would not be met;
Further additional labour had to be procured due to the heavy nature of each survey monument (concrete blocks weighing approximately 50kg) and the added logistical problems caused by the vegetation; and
Vehicular access to the site was also equally constrained by the dense vegetation.
The job became extremely labour intensive because of this and at one stage we where using 15 labourers to do the cutting and carrying of the heavy concrete beacons.