The importance of determining the natural or altered ground level before any construction commences can never be neglected in pre- and post-construction activities at a municipal level. First and foremost, this legal verification requires the sign-off of a professionally registered land surveyor, and the implications of not adhering to this stipulation have major legal implications.
By Hans Kaderli* and Altus Strydom**
There are a range of complexities that must be considered. These include the imposition of natural ground height restrictions, stormwater management and issues with lateral support of buildings or structures. Land surveyors are often requested to conduct surveys where natural ground height is crucial. Examples include setting out building positions and floor heights from approved building plans. At times, it is then discovered that the contour detail on the plan and the actual ground contours totally disagree. Other key criteria include:
- confirmation of the vertical building line of the roof height or floor level, as defined by the relevant local authority
- confirming the horizontal building line of the building, as defined by the relevant local authority
- resolving disputes with natural flow of water over or across property
- resolving disputes with cut and fill during construction
- addressing disputes where garden walls are used as retaining walls
- responding to disputes where there are discrepancies between contours on plans that don’t conform with the status of the terrain.
In the case of sectional title surveys, land surveyors must issue a certificate prior to lodgement with the surveyor general noting that no building encroaches building lines or height restrictions. This needs to be determined by actual survey and research. Equally important for all buildings is the confirmation of flood lines to counter disputes that might arise during severe storms, the 2022 Kwazulu-Natal floods being a case in point.
But what is the true definition of natural ground level?
In general terms and definitions, most of the municipal zoning schemes refer to natural ground level as:
- The level of the land in its unmodified state, or
- when altered with the municipality’s approval, for the purpose of development, the altered ground level, subject to certain conditions.
Once the basic infrastructure is installed in any land development, where the natural ground level is altered – and therefore not in the original state – it cannot be referred to as ‘natural ground level’ unless approved by a local authority or similar institution.
Determination of natural or altered ground level
In this respect, it must be stressed that the determination of natural or altered ground level is the function of a spatial and mapping specialist (i.e. a professional registered with SAGC) and not a planning function.
This is a specialised field of survey where the density of ground survey points determines the accuracy of the contours. There are technical formulas that need to be applied to derive a certain accuracy of contours for design purposes.
The following are practical examples:
- If ground survey points are spaced at 20 m intervals, it is not possible to accurately determine 0.5 m contours on sloping terrain. The bigger the slope, the more closely the survey points need to be spaced.
If a dispute arises on a building site where 0.1 m to 0.3 m height differences are in dispute, then the spacing of ground survey points during the initial survey should have been 1.5 m to 2.5 m apart.
When confronted in court, only a person that is registered as a professional land surveyor or professional surveyor and registered in terms of the Geomatics Profession Act (No. 19 of 2013) will be able to survey and determine natural ground level.
Survey specification for a contour of natural height survey
Engineers, planners, architects or anybody that needs accurate heights or contours must be aware that a technical specification must be included in their request for proposal.
The person specifying accuracy must take the following into consideration:
- the purpose of the survey and design accuracy required
- accuracy of the surveyed point – to achieve the desired plan accuracy, the slope of the terrain plays an enormous role in the density of points surveyed
- design tolerance of equipment used. Internationally accepted standards are between 5 cm and 10 cm for contour surveys of building sites. Most conventional ground survey instruments (total stations) can achieve this accuracy but when GPS, drone and aerial survey equipment are used, the design tolerance must be specified as well.
The next question then is what should the accuracy of contour lines be on a plan? Internationally accepted standards vary, but in general indicate that the vertical accuracy standard requires that the elevation of 90% of all points tested must be correct within half of the contour interval.
Here’s an example to illustrate the point. With a contour interval of 1 m, the map must correctly show 90% of all points tested to be within 0.5 m of the actual elevation. The effect of this is that if an engineer wants to design to 10 cm accuracy, 90% of points surveyed must be within an accuracy of 5 cm to accurately depict the situation on the ground.
Ways to determine natural or altered ground
There are various ways of determining natural or altered ground, which include the following:
- actual ground survey methods and creating digital terrain models
- aerial survey methods
- sourcing old contour plans and referencing them to the current state of the land
- data filed with the Office of the Chief Directorate: National Geo-spatial Information.
The methodology used is dependent on the accuracy required. For example, you cannot determine 1 m contours by aerial survey if the terrain is not clear of tall grass, trees and shrubs.
Relevant court cases
The importance of the correct determination of natural or altered ground level is addressed in various court case outcomes. For reference, readers can access a range of court cases online referring to natural ground level disputes.
Typical legal challenges refer to stormwater issues. In general terms and definitions, most of the Municipal Zoning Schemes refer to stormwater as water resulting from natural processes. Within this context, a judgment regarding stormwater addressed in the South Gauteng High Court – Pappalardo vs Hau (Case No. 63/08) – is worth noting.
Effectively, it says that you can only pass on water to an adjoining property when you can prove it’s ‘natural water’. Hence the verification of the original natural ground level becomes important to that proof. In absence of proof, the water cannot be passed on. This judgment clearly expresses the importance of having the natural or altered ground level recorded before any construction commences.
There were several cases where natural ground height was decided and ruled on, and all of them confirm the definition of natural or altered ground level as discussed above. Legal cases to note are Du Toit vs Knysna Municipality and others (2954/2014), and Buchanan vs Hope and other (654/2010).
Imposition of height restrictions on municipal planning level
Without the presence of the natural or altered ground level, and permanent reference marks for the datum of such ground level, the imposition of any height restriction (by any method) becomes a difficult, if somewhat impossible, task in any developed area.
Methods of defining a height restriction are vast. Possibilities include:
A 3D surface parallel to and above the existing natural or altered ground level. After consultation with a sample group of architects/draftspersons, it is apparent that this method is an acceptable approach. However, not all professionals drafting building plans have software that can produce such a surface. It must be stressed that the correct input data is of utmost importance with this method.
- Determination by a plane that is parallel to and above a certain height to the plane that is defined by connecting the highest cadastral beacon to the lowest cadastral beacon. This method is simple and can be calculated by most software packages.
- Determination of the centroid of a property and imposing a height restriction in a plane above that point. This method becomes challenging when a very irregular figure is dealt with.
- A certain plane on a height from street level to a distance away from the street and then following the natural ground level of the property.
- Different height restrictions can also be given to properties in close proximity by simply classing them in the percentage of slope of the land.
The purpose of this article is not to question the method of calculating the height imposition, but to stress the importance of recording the correct data to impose same.
Which Acts regulate the production of plans for municipal construction purposes?
Each municipality has its own specifications and management structures and should be scrutinised by professionals prior to construction. Aspects that need to be noted are the following:
- Internal municipal documentation: The town planning scheme or land use management regulation in operation at the time of application specifies height and building line restrictions.
- Building plan submission: Building plans are controlled by the National Building Regulations and Building Standards Act (No. 103 of 1977), but each municipality has its own interpretation.
Here, relevant clauses to note include:
- Administration Part A6 – Site Plans (c): the direction of true north, and if required by the local authority, the natural ground contours at suitable vertical intervals or spot levels at each corner of such site.
- Administration Part A7 – Layout Drawing (j): where required by the local authority, the levels of the floors relative to one another and to:
- the existing ground level surface
- the proposed finished ground surface
Risk management proposal
From the above commentary, it should be clear that the involvement of a professional land surveyor in all phases of pre- and post-construction are essentially for legal compliance. This includes the necessity of a comprehensive risk management survey.
The following observations support this:
- When looking at the relevant court cases, it is clear that in many cases the municipality was involved in the case, and this is a risk that they should not take.
- All stakeholders must comply with the stipulations of the National Building Regulations mentioned above.
- Unrecorded accurate natural ground level or altered ground level scenarios create risks for the public, engineers, local and central government.
- For municipalities, it is good land administration practice to record natural ground level (or in some cases altered ground level) in building control.
- Municipalities can assess all development and building plans and approve these prior to construction. Otherwise, the risk for the municipality is that they could issue a clearance/occupation certificate after construction and the owners might then start holding the municipality liable. In a nutshell, the municipal occupation certificate says what you have built is according to plan.
Certain municipalities already request the submission of a registered professional land surveyor’s certificate (i.e. contour plan of existing ground level, being natural or altered) to determine the natural ground level before any construction activities may commence.
It is then the duty of the land surveyor to determine the various positions of the roof ridges and plot them on the predetermined natural or altered ground level to ensure that the building will – after construction – complies with the height restrictions.
The role of a professional surveyor registered in terms of the Geomatics Profession Act is crucial in the determination of natural ground level.
To avoid future legal action and/or claims, the following is proposed:
- Affected parties subject the submission of any new building plans to the compulsory addition of the natural or altered ground level before construction.
- The addition of final floor or roof levels must refer to permanent height reference data before an occupation certificate is issued.
- All submissions must be accompanied by a certificate signed by a registered professional land surveyor that the building to be erected and depicted on the building plan complies with all horizontal and vertical height restrictions
Professional land surveyor at TMK Land Surveyors and member of the South African Geomatics Institute
**Professional land surveyor and board member of the South African Geomatics Institute (SAGI).
42-44 IMIESA June 2023