A pipeline route and ground feature survey can be completed by several methods; conventional ground field survey, photogrammetry, airborne laser scanning or a combination of methods depending on project scope or site constraints.

When undertaking a route survey, the surveyor’s role is to determine the pipeline location on the ground whilst taking into consideration the various issues identified during desktop selection and specific client requirements. These issues include construction, environmental, topographical, existing infrastructure, landowner, cadastral and statutory constraints.

DCDB accuracies and adjustments

When undertaking a route survey all aspects of pipeline design need to be considered. These aspects include environmental, cultural heritage and landowner issues; local, state and federal planning requirements; the location of existing infrastructure and services; existing easement and cadastral boundaries; and, most importantly, construction constraints identified during desktop studies. Initial desktop route selection identifies the intended pipeline route utilising DCDB boundaries and the best photography and/or satellite imagery available.

Dependant on the geographical location of the project, it is important to understand the quoted positional accuracy of the DCDB. Ranging from 0.1 m to 200 m plus1 accuracies quoted for the DCDB depend on the quality of the survey information available at the time of its creation and the methods used to create the data set. In some rural areas the DCDB has simply been digitised or digitally traced from the best available maps or survey information, which in some cases would have been original parish maps and old cadastral plan series1.

The general experience of LandPartners Limited (LPL) has been that the accuracy of the DCDB is similar across the east coast of Australia and this should be considered during the FEED stage of the project, especially where it is proposed to parallel existing cadastral and easement boundaries. Further information relating to the quoted accuracies of the DCDB can be found on the government website for your state.

In Queensland, the Department of Natural Resources and Water (DNRW) provides information on the positional accuracy as well as information relating to existing or proposed data upgrade agreements the DNRW have with local government authorities.

LandPartners involvement with the DCDB creation and upgrade has existed over several decades. Initially involved in early 1986, LandPartners participated in the first pilot program; compiling, controlling and adjusting the DCDB for the western suburbs of Brisbane. More recently LandPartners was contracted to undertake the upgrade of the Cooloola Shire DCDB, which involved the ground controlling and compilation of approximately 21,500 parcels, completing this task in mid-2007 (see figure 1).

By using registered survey plans, an accurate location of the cadastral boundaries can be determined by a surveyor who will measure the position of registered survey marks on the ground during the route survey. This has proven to be a necessity for the majority of projects LandPartners has been involved with, and most recently, throughout our continuing work on the Western Corridor Recycled Water Project (WCRWP) for both the Western Pipeline Alliance (WPA) and Eastern Pipeline Alliance (EPA) where the pipeline route encounters varying DCDB accuracies from developed urban areas through to rural areas including very old rail and road corridors.

For the WPA, 80 km of complex cadastral boundaries have been surveyed, to ensure detailed pipeline design could be undertaken with confidence in relation to accurate property boundary locations. This process of surveying and compiling the cadastral boundaries for the entire WPA route from existing survey information resulted in the DCDB boundary information being adjusted to match the surveyed boundaries within the project’s GIS.

The process of adjusting the DCDB involved measuring sufficient cadastral survey marks to compile the cadastral boundaries from original survey plans. This process was undertaken for the relevant properties along the pipeline corridor and then integrated with the project GIS to ensure all parties working on the project were using the same accurate information. In older areas of the pipeline route, errors of up to 12 m were encountered between the DCDB and surveyed boundaries and up to 40 m between the surveyed boundaries and existing fence locations.

The cadastral survey for a pipeline route and subsequent update of DCDB boundaries is an important part of the design and FEED process for a project. By undertaking this prior to detailed engineering design, costly design changes can be minimised due to a more secure route location based on survey accurate cadastral boundaries. Using surveyed boundaries also provides confidence that the pipeline will be constructed within the correct property.

Aerial Photography and Photogrammetry for pipeline design

Photogrammetry is a common method used to perform a pipeline route and detail survey. Mapping from photography is a simple, proven technique used to provide large quantities of data and has shown to be an effective survey method in hilly terrain and open and urban areas, as well as providing easy capture of data for areas of constant route change.

Photogrammetry has the ability to provide digital survey data with equivalent accuracies to conventional field surveys by capturing the photography at lower altitudes. It is suitable for use in route selection for the engineering design stages of a pipeline. Aerial surveys also provide an alternative way of capturing data for areas with limited access such as highways, properties with landowner access issues, rough terrain or areas affected by heavy rainfall; which in some circumstances can hold up conventional ground survey for months.

Using photogrammetric techniques, it is possible to digitally map all ground features such as fence lines, creeks, rivers, roads, above ground services and topographical features, the same as would be done by conventional ground surveys. This process enables a Digital Terrain Model (DTM) to be created over the desired route and the easy extraction of route profiles anywhere within the mapped corridor.

In the undertaking of photogrammetry for a pipeline route, the capture of data over a specific corridor would be mapped allowing for the further extraction and processing of additional information at a later date in the occurrence of route changes. If required, additional information captured from the photography wouldn’t require further field survey if the revision is already covered by the existing photography. Side slope analysis from the DTM can also be completed and assessed against the project design criteria to highlight suitable and unsuitable side slopes (see figure 2). As with all forms of aerial survey, some ground completion is required in areas of dense tree cover, to locate underground services and connect to cadastral boundaries.

Aerial photography also provides a digital geo-referenced image that can be utilised for all route and environmental planning, pipeline design, risk assessment, overlays for alignment sheets and ongoing management of the project.

When combined with a software package such as Leica Virtual Explorer, geo-referenced images can be draped over the DTM created during the photogrammetry process. As the Leica package is freely distributed, the 3D image can be provided to consultants and clients via a DVD. This allows the end user to explore and analyse the entire data set as they wish, controlling location, speed, altitude and viewing angle removing the restrictions associated with 3D fly-throughs2.

Conclusion

Involved in numerous infrastructure projects over many years, LandPartners’ experience has shown that undertaking cadastral surveys of the registered easement and property boundaries constraining a pipeline is critical to the design and FEED stage of a project to ensure costly design changes are minimised.

Due to the various methods used to create the DCDB in some rural areas, the positional accuracy of the information available can be more than 200 m. It’s important to eliminate uncertainties in the cadastre when progressing a project to the FEED stage and to give confidence that the constructed location will be correct.

Captured digitally, aerial photography is an effective surveying tool and greatly benefits environmental, cultural and engineering studies. Data from aerial photography can be included in approval reports and will also form an integral component of a sophisticated project GIS. Teamed with intelligent software packages aerial photography can provide an end-user the ability to explore and analyse the data both remotely and as they wish.

To date, LandPartners has achieved great success by integrating its knowledge of cadastral surveying and aerial photography with the many other services they provide on projects which includes route mapping, GIS, environmental assessments and approvals, surveying and town planning.

References:

1. The Department of Natural Resources & Water Queensland http://www.nrw.qld.gov.au/property/mapping/dcdata/index.html 2. Leica Geosystems http://gi.leica-geosystems.com/LGISub1x253x0.aspx