A contour survey is a way to easily visually understand the vertical and horizontal shape (the “topography”) of your land. By understanding the land contours, you can easily visualise or map how water will flow across and through the property when it rains, where it will collect, where it might erode the soil and many other important water flow characteristics. From this simple base, you can even develop water flow models, stream maps and determine the best places to create dams and silt traps.
Contour surveys need to be conducted by a registered surveyor, right? Well, not all the time. A registered surveyor is required if the contour survey data is being used for construction or engineering purposes, or if the boundary data is being registered on a government cadastral (land title) system. Otherwise, surveyor certification is generally not required. We partner with a registered surveyor (yours or ours) where certification is required.
Contour surveys by a registered surveyor are more accurate than drone surveys, right? Well, not really. In theory, a surveyor’s PPK measurement system can achieve accuracy 5mm, but in reality the average accuracy used by surveyors on ground surveys is around 10-15mm, which is very similar to the accuracy achieved by a well-designed drone survey (15-25mm). Ground surveys typically measure around 5-6 points per square metre or less. Aerial surveys can measure 100s of points per square metre. You do the math!
A registered surveyor is faster and cheaper than a drone survey, right? Not at all! The area that a ground survey team can cover in a day can be covered by an aerial survey in 1-2 hours. The area a ground surveyor would take a week to complete can be done with a drone survey in a day or two. Both methods have similar processing times, although drone survey results are usually ready in a few days, while ground survey data can take weeks to process and deliver.
Precise aerial land mapping can only be achieved using LIDAR, right? Well, not really. We have used both and generally speaking any terrain with less than 50% tree cover can be mapped using a standard drone mapping camera with a reasonable degree of accuracy. Standard drone mapping relies on making connections (extrapolation) between visible ground points, just as a traditional ground survey does. Where there are doubts about accuracy due to long grass or thick vegetation, we can often underpin a drone mapping survey with government LIDAR data to confirm results (takes longer, but can be done). In reality, LIDAR mapping is generally more expensive, more time-consuming and can be less accurate than professional orthometric drone mapping. Please feel free to chat with us about this if you have concerns.
Why contour surveys are so important
Elevation data is essential for planning your home or any building construction projects, and following the contours of the land is the cheapest way to build roads and tracks through your property. For many types of agriculture, especially tree crops (like mangoes, macadamias, avocados, etc), planting along the contours of the land is the best strategy for maximum yield.
In construction projects, contour mapping is an essential tool to first understand the structure of the site, then calculate how much soil and other material needs to be added or removed to make the structure of the site fit the construction plan, and then to understand and verify how the terraforming of the land fits with the engineering design.
How to read a contour survey
In the most basic terms, a contour survey illustrates the elevation differences across your land, in regular intervals, from the lowest point to the highest point. Contour lines join points at the same elevation. The closer together the contour lines are, the steeper the section. The further apart the lines are, the shallower the rise or fall of the terrain.
Contour surveying is best illustrated using the image above, which shows the structure of an excavation surrounded by a bund wall. From the left side we can see the rising elevation of the bund wall with each 25cm increase in elevation indicated by a new contour line. Across the blue section we can see the highest part of a land, a bund wall which can be driven around for inspection and equipment movement. Then the elevations decrease again into the middle where the orange area indicates the lowest part of the pit, an area which is actually filled with water. Diagonal sections from the bund wall to the bottom of the pit show the locations of vehicle access tracks.
How to get a contour survey
Traditionally, topographical land surveys mean engaging a surveyor who would send a team of people to the site with survey poles and tripods and spend days, or even weeks, walking around every part of the site to measure points of different elevation. You would then wait weeks to see a large map of the site with all the survey results on it.
In the world of aerial contour mapping using drones, this kind of topographical mapping can be done in a matter of hours, or perhaps a day or two, using precision PPK-equipped mapping drones which can cover up to 400 acres of land per hour and still achieve real world precision of 2-3 cm in most cases, equivalent to that delivered by a traditional surveyor but with many more survey points and high-resolution mapping imagery to make the contours easier to comprehend.
An aerial contour mapping survey can identify many features traditional surveying might overlook, like hidden gullies and streams, natural watercourses, old abandoned tracks and areas that could be inaccessible entirely to a surveyor on foot.
To find out more about getting an aerial contour survey for your property or project, complete our simple aerial mapping enquiry form or phone Tony on 0439 383202.