A contour survey provides a detailed map of the land's surface, indicating the natural and man-made features. For new homeowners, understanding this survey is important, as it influences the design, planning, and construction of your new home.
In this blog post, we'll break down the key elements of a survey plan and a contour survey, ensuring you understand its significance and can confidently interpret the information provided to you.
The Role of RP (Real Property) and SP (Survey Plan) in Contour Surveys
Before a contour survey can be developed, it's important to understand the significance of Real Property (RP) and Survey Plan (SP) in the process.
What is an RP (Real Property)?
An RP, or Real Property description, refers to the legal description of a piece of land. It includes details such as lot number, plan number, and locality. The RP/SP is important as it provides a unique identifier for the property, ensuring there is no ambiguity about the land being surveyed.
What is an SP (Survey Plan)?
An SP, or Survey Plan, is a detailed plan that shows the boundaries of a property. It includes precise measurements and bearings, indicating the exact dimensions and location of the property. The Survey Plan is created by a licensed surveyor and is used to define the legal boundaries of the land.
Distinguishing Between RP and SP in Australian Real Property
In the context of Australian Real Property, the terms RP (Real Property) and SP (Survey Plan) are distinct but closely related.
An RP (Real Property) description refers to the legal documentation that provides a unique identifier for a property, detailing its lot and plan number, and is often used in legal and transactional contexts.
On the other hand, an SP (Survey Plan) is a detailed graphical representation created by a licensed surveyor, showing the precise boundaries, dimensions, and reference points of a property. The SP is typically used during the planning and development stages to ensure accurate construction and compliance with local regulations. While the RP provides the legal framework for identifying a property, the SP offers the technical details necessary for physical land development. You would commonly find an RP in legal documents such as titles and deeds, whereas an SP is used in engineering, architectural, and construction planning.
Why are RP and SP Needed Before a Contour Plan?
- Establishing Legal Boundaries: Before a contour survey can be conducted, the legal boundaries of the property must be clearly defined. The SP provides these boundaries, ensuring the contour survey accurately maps the area within the property's limits.
- Accurate Reference Points: The SP includes permanent survey marks (PSM) and other reference points that are essential for accurate contour mapping. These reference points provide a baseline for the elevation and contour measurements.
- Regulatory Compliance: Having an RP and SP ensures the survey complies with local regulations and standards. It guarantees that the contour survey is conducted within the legally defined property boundaries, avoiding potential disputes with neighbouring properties.
- Integration with Other Plans: The SP allows for the integration of the contour survey with other plans and documents related to the property. This integration is vital for comprehensive planning and development processes.
What is a Contour Survey?
A contour survey, also known as a topographic survey, maps out the elevation and contours of the land. This survey helps architects, engineers, and builders understand the lay of the land and make informed decisions about design and construction.
Key Elements of a Contour Survey
- Contours: These are lines on the map that connect points of equal elevation. The spacing between contour lines indicates the steepness of the slope; closely spaced lines show steep slopes, while widely spaced lines indicate gentle slopes.
- Reduced Levels (RL): These are heights above a standard reference point, often sea level, known as the Australian Height Datum (AHD). RLs are crucial for determining the elevation of various points on the land.
- Ground Level and Natural Ground Level (NGL): Ground level refers to the current surface level of the site. NGL is the undisturbed natural surface of the land before any construction or excavation.
- Cut and Fill Lines: These lines indicate where the land will be excavated (cut) and where the excavated material will be placed (fill) to create a level building platform.
- Batters: These are the sloped surfaces created by cutting or filling the land. Batters are essential for stabilising the soil and preventing erosion.
- North Arrow/Compass: This shows the orientation of the survey plan, helping you understand the directions and how the site is aligned.
- Overland Flow Potential: This indicates areas where water might flow across the land during heavy rain, which is crucial for planning drainage and preventing water logging.
- Services Locations: These are the positions of existing utilities such as water, sewer, electricity, and gas lines. Knowing these locations helps avoid damaging them during construction.
- Survey Pegs: These are markers placed on the ground to indicate key points measured during the survey. They help in accurately transferring the survey data to the construction site.
Site Photos
Your survey will take a photo of the unimproved site prior to carrying out the survey. Below is an example of what you will receive from them.
Interpreting the Legend
The legend on a contour survey provides explanations for the various symbols and abbreviations used. Here are some common items:
- O/H Light: Overhead light.
- S/Water Pit: Stormwater pit.
- Fire Hydrant: Indicates the location of a fire hydrant.
- Water Valve: Location of a water control valve.
- Mountable Kerb: A kerb that vehicles can drive over.
- Non-Mount Kerb: A kerb that vehicles cannot drive over.
- Ref R.L.: Reference reduced level.
- Datum: The reference point from which elevations are measured.
- PSM Marks: Permanent Survey Marks used for consistent reference points.
Scale of the Contour Plan
Contour plans are typically drawn to a scale of 1:200, meaning 1 unit on the plan equals 200 units on the ground. This scale allows for detailed representation of the site while maintaining an overall view and to make it easier to print the contours on regular sized paper, like A3.
Easements and Flood Levels
- Easements: Legal rights to use a portion of the land for specific purposes, such as utility lines or drainage. Building on easements is usually restricted.
- Flood Levels: Indications of potential flood zones based on historical data and predictions. This information is vital for designing flood-resistant structures.
How to Read the Plan
To effectively read a contour plan, follow these steps:
- Orient Yourself: Use the north arrow to align the plan with the actual site.
- Identify Key Features: Look for contour lines, RLs, easements, and other critical elements.
- Understand Elevations: Pay attention to the contour intervals and reduced levels to grasp the land's elevation changes.
- Check for Services: Locate all utility lines and services to avoid issues during construction.
- Look at the Cut and Fill Lines: Once the outline of the house is located from the boundaries (boundary setbacks) calculate the difference between the Platform Level and the Natural Ground level at both the base of the Cut and the Toe of the batter. From these two calculations you can see if retaining walls or what type of landscaping may be required to hold the platform in its place.
- Review the Legend: Familiarise yourself with the symbols and abbreviations used on the plan.
Importance of a Contour Survey
A contour survey is indispensable for:
- Accurate Design: Ensuring the design fits the land's topography.
- Proper Drainage: Planning for adequate drainage to prevent water issues.
- Cost Estimation: Determining the amount of cut and fill required, impacting construction costs.
- Regulatory Compliance: Meeting council requirements and obtaining necessary approvals.
- Locating and Siting the House: Ensuring the house is sited in accordance with estate and council setback requirements. The contour survey helps determine the best location for the house on the lot, ensuring it complies with local regulations regarding distances from property boundaries, easements, and other features.
Conclusion
Understanding a contour survey helps you to make informed decisions about your new build. By knowing the key elements and their significance, you can better communicate with your builder and ensure a smooth construction process.
Keep this guide handy as you review your contour survey, and don't hesitate to ask your surveyor or builder for further clarification on any points.
For a practical reference, we added a typical contour plan in this blog post so you can read and reference it as you familiarise yourself with these elements.
Additional Information:
Below is a typical soil test and a compaction certificate that you may receive from your developer.
Compaction Certificate
Soil test
Soil test bore setout. We nominate to our engineer where we would like our bores to be done. This is setout in relation to the shape of the house/floor plan setback from the boundaries. Ideally you want your bores to be at the front and back of the house, spread out.
Note this is for a different site not Lot 695
