What Is A Topographical Survey? 2023 Guide
Unveiling the Role of Topographical Land Surveys in Construction and Engineering: A Comprehensive Overview of What, Why, and How They’re Used.
Article By: Tom Ayre
Last Update: January 2023
In this article, we explain what a topographical survey is and why they are crucial when undertaking building projects.
Before a construction projects begins, a design for the site needs to be formed. This is usually undertaken by an Architect. The plans drawn up need to be accurate and buildable. A topographical survey and the drawings provided form a basis to design from to ensure that the design and build goes smoothly.Find out more below:
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What Is a Topographical Land Survey?
A topographical land survey is a detailed measurement and recording of the position and height of man-made and natural features within a specific area. The resulting data is used to create various types of information such as CAD drawings, contour maps, and terrain models.
Topographical surveys are utilised by a range of professions including architects, engineers, building contractors to effectively visualise, plan and develop their projects. The drawings and information produced by the survey work are used as a base to design from.
A topographical survey is a crucial component of a successful construction or engineering project. Position and height data recorded by the survey can help prevent costly problems such as building in unsuitable areas.
An example of an unsuitable area which could be revealed by the topographic survey include:
- Close to a watercourse / drain and prone to flooding.
- Next to large trees, which may cause issues with ground swell / roots.
- Too close to a boundary, which may cause issues with council permissions.
Another benefit of a commissioning a topographical survey from the start of a project is that it will make the setting out engineer’s job much easier. A topographical survey will leave a number of fixed reference markers on site, such as nails in concrete. These positions can then be utilised when setting out the new design so that elements such as foundations, brickwork, new trees etc are in place in the correct position.
What Information Do Topographical Surveys Gather?
Topographical surveys (sometimes referred to as “topos”) record a range of information on site and are usually referenced back to a national grid co-ordinate system. This allows the surveyed information to be tied in with other mapping products which are also aligned to a national grid system. In the United Kingdom this is dealt with by the Ordnance Survey.
The features of a topographical site survey depend on the client requirements / the complexity of the project. Examples of what information is typically surveyed includes:
- Land heights.
- Tree locations.
- Existing buildings.
- Change in surfaces.
- Boundary locations.
- Overhead power lines
The process in obtaining a topographical survey is simple. The key component when commissioning a topographic land surveying company is to ensure you have a suitable specification for your chosen surveyors to work from. A specification from RICS (Royal Institute of Chartered Surveyors) would be a good place to start. Once you have a specification then carefully choose a surveying company. It is always worth checking reviews, previous work, and insurances to see if they are the right company for your scheme.
How Are Topographical Surveys Undertaken?
A Topographical survey is typically undertaken by a land surveying company who utilise a range of high-tech equipment such as GPS devices, total stations and 3D scanners to accurately and quickly survey areas of land such as fields, woods, marsh, urban areas and more.
The devices used for the survey are very precise and usually require ongoing calibration to ensure their reliability. Modern equipment such as robotic total stations allows surveys to be undertaken by a surveyor without the need for an assistant!
A topographical land survey starts with a desktop study of the land to ascertain the key elements that need surveying and to get a plan of action together.
Once on site, the first thing to arrange is the survey control network. These fixed positions in and around the site that are used to reference the various setup locations back to. The idea of the survey control is that it is a permanent, fixed, co-ordinated location. The survey control is usually in the form of survey nails placed into something solid like a road, pavement, concrete slab etc. The survey control network is usually set out using a total station.
The survey control network can then be orientated and located to a GPS controlled network. In the UK we generally use OSGB36 for position and OSTN15 for height. The idea of the GPS control is the site can be positioned and referenced back to a location in the real world.
A GPS network is set up using a GPS system that allows a precision position to be obtained. This is usually undertaken using a GPS RTK system such as a Leica GS08 . The piece of equipment allows the user to obtain an accurate position (usually 10 to 20 mm). When surveying in the survey control, it is typical to survey in a number of points and then apply the best fit model to get the most accurate real world position.
Once you have your survey control in place, the topographical surveying can begin. Typically, a topographical survey is undertaken using a total station. A total station is a piece of equipment that can accurately survey the individual points in a very accurate manner. These points can then be set with lines between them to start forming an illustration of something. For instance, to indicate a wall, you might have 2 points joined with a line.
The total station is orientated and positioned relative to the survey control network. This involves surveying a number of control points, which the instrument can then use to calculate a position and orientation. Once the surveying of the various elements can begin.
Surveying the various elements around the site involves turning the total station, aiming and measuring. The instrument sends out a beam of light, which then reflects back to the total station. The instrument knows how far around a circle it is looking, along with the angle and distance to the point. Using this information, it can precisely position the point using trigonometry.
Once the surveyor has picked up all the information from a setup location, it is time to move and then re position the total station back to the control network.
Eventually, the surveyor will have a lot of point information of the various elements they have surveyed such as walls, spot heights, trees etc. This information is then processed in the office and translated into a CAD drawing for the client.
The Importance Of Topographical Surveys
Whether you are building a new house or designing a new railway line, a topographical survey is essential when land is being developed.
Without accurate drawings and design data, it’s difficult to plan a project accurately and safely. The surveyed information allows designers to see exactly how the current site is arranged and includes accurate, co-ordinated positions and associated heights of items.
Without a survey, you may not know about important issues regarding your site that may be costly to fix further along the line. Examples include:
- Building too close to something such as a boundary. Planning might be rejected!
- Building too high from the ground, again, planning may be rejected.
- Developing an area with lots of trees and vegetation. May be too expensive to clear?
- Does the ground level change a lot? Moving earth is expensive, so optimising this early on can help with costs.
What Projects Require A Topographical Survey?
Here are a few examples of construction and engineering projects that may require a topographical survey:
Land development projects: Topographical surveys are often used in land development projects to provide a detailed map of the site and its features, which can be used to plan the layout and design of the development.
Road and highway construction: Topographical surveys are used in road and highway construction projects to provide detailed information about the terrain and features of the site, which can be used to plan the route and design of the road.
Building construction: Topographical surveys can be used in building construction projects to provide detailed information about the site and its features, which can be used to plan the layout and design of the building and its foundations.
Utility construction: Topographical surveys are often used in utility construction projects, such as water and sewage systems, to provide detailed information about the site and its features, which can be used to plan the route and design of the utilities.
- Environmental projects: Topographical surveys can be used in a variety of environmental projects, including site assessments, habitat restoration, and natural resource management. In these projects, topographical surveys can be used to map the features of a site and to assess the impact of development or other activities on the environment.
- New build developments.
- Large extensions.
- Large landscaping schemes.
- New / updated drainage.
- Drainage schemes.
- Earth moving projects.
- Dredging / river works.
What Are The Benefits Of a Topographical Survey?
A topographical survey is a key component when designing anything on an existing piece of land. It is important to know the precise position and layout of various items to ensure the design is buildable and efficient. It would be problematic designing a building to be placed over an existing large tree, for instance. The builder would arrive, ready to build, and then have to worry about removing the tree or changing the design, all of which are very costly.
A topographical survey will help you design more effectively and assist in avoiding future problems and making your land as efficient as possible.
- Optimising the positions for what you are designing, such as new buildings and structures.
- Avoiding potential planning application refusals.
- Reduce potential costs by identifying objects that may cause delays in construction.
In principle, a topographical survey will get your designs off to the best start, as you will have all the existing positional information of a site. You can then be confident that the design being built will fit and be properly built, with the likelihood of less on-site issues.
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