Floodline, Riparian Zone, 32 m or 100 m? The Lines That Control Building Near a River

Four different lines decide what you can do next to a river in South Africa, and they come from four different laws. The 1:100-year floodline is a hydraulic line drawn from a flood model. The regulated area of a watercourse decides whether you need a water use authorisation. The 32 m distance in the environmental impact assessment (EIA) regulations decides whether you need environmental authorisation. And municipal buffers in land use schemes and policies control what you may build.

None of them is, on its own, a national “no-build” line. Mixing them up is the most common reason a project near a river is designed around the wrong boundary.

Not sure which line governs your site? We determine the 1:100-year floodline and map it against the regulated area and your municipality's buffers, so the buildable area is clear before the layout is drawn.

Floodline determination

The four lines at a glance

Line	Set by	How it is drawn	What it triggers
1:100-year floodline	National Water Act section 144; municipal schemes	Flood model of the flood with a 1% chance of being equalled or exceeded in any year	Must be shown on township layout plans; many municipal schemes restrict building inside it
Regulated area of a watercourse	GN 4167 of 2023 (Department of Water and Sanitation)	The 1:100-year floodline or riparian edge, whichever is further; otherwise 100 m from the watercourse; 500 m around a wetland	A section 21(c) and (i) water use authorisation for work inside it
32 m from a watercourse	NEMA EIA Regulations, Listing Notice 1	Measured from the edge of the watercourse, unless a development setback has been adopted	Environmental authorisation for structures of 100 m² or more
Municipal buffers	Land use schemes, by-laws and policies	Fixed distances that vary by municipality	Development control: what you may build and where

Two more lines apply to particular land uses: the CARA flood area for farming, and the GN 704 floodlines for mines. Both are covered at the end.

The 1:100-year floodline

The floodline comes from section 144 of the National Water Act:

“no person may establish a township unless the layout plan shows, in a form acceptable to the local authority concerned, lines indicating the maximum level likely to be reached by floodwaters on average once in every 100 years.”

It is drawn by modelling the design flood: hydrology to estimate the flow, then hydraulics to turn the flow into water levels on the terrain. “Once in every 100 years” is an average. The 1:100-year flood has a 1% chance of being equalled or exceeded in any year, and two can occur in consecutive years; our post on 1:50 vs 1:100-year floodlines explains the difference.

What section 144 does not do: it does not say who determines the line, and it does not ban building below it. It requires the line to be shown on township layout plans. The restrictions come from municipalities, for example:

• Johannesburg’s Land Use Scheme (clause 50(3)(a)) permits no development within the area flooded by a 1:100-year flood, or within the riparian zone plus a buffer of 30, 32 or 50 m, whichever is greater.
• Cape Town’s floodplain policy requires floors above the 1:100-year flood level and allows some development between the 50- and 100-year lines only on conditions the City sets.
• Ekurhuleni’s 2014 town planning scheme treats land below the 1:100-year line as a building restriction area: no building without the City’s approval of special precautions.

The regulated area of a watercourse

The Department of Water and Sanitation controls work that impedes or diverts flow (section 21(c)) or alters the bed, banks, course or characteristics of a watercourse (section 21(i)). The current General Authorisation for these uses is GN 4167 of 8 December 2023, which superseded GN 509 of 2016. It defines the regulated area of a watercourse as:

“(a) The outer edge of the 1 in 100-year flood line or delineated riparian habitat, whichever is the greatest distance, measured from the middle of the watercourse of a river, spring, natural channel, dams and lakes;”

Where no 1:100-year floodline or riparian area has been determined, it is the area within 100 m of the edge of the watercourse. Around a wetland or pan, it is a 500 m radius from the delineated boundary.

Work inside the regulated area needs authorisation. The DWS risk matrix, completed by a SACNASP-registered professional, decides the route: a Low risk rating can be registered under the General Authorisation, while Medium or High needs a full water use licence. Our post on crossing a watercourse covers the process.

Common myth: “DWS uses a 32 m buffer.” It does not. The 32 m distance comes from the environmental regulations below.

The 32 m distance in the EIA regulations

The 32 m figure comes from Listing Notice 1 of the EIA Regulations under the National Environmental Management Act (NEMA). Activity 12 lists the development of dams, weirs or structures with a footprint of 100 m² or more:

“(a) within a watercourse; (b) in front of a development setback; or (c) if no development setback exists, within 32 metres of a watercourse, measured from the edge of a watercourse”

Activity 12 excludes development within an urban area and within existing road and railway reserves. Activity 19 separately lists moving more than 10 m³ of material into or out of a watercourse, with no urban exclusion. In listed sensitive areas, Listing Notice 3 lowers the footprint threshold to 10 m².

Common myth: “32 m is a no-build buffer.” It is a trigger for environmental authorisation, normally from the provincial environment department. It is measured from the edge of the watercourse, not the centre line, and an adopted development setback replaces it.

Municipal buffers

Municipalities set their own distances, and they differ:

Municipality	Buffer or rule	Document
Johannesburg	1:100-year flood area, or riparian zone plus 30, 32 or 50 m, whichever is greater	Land Use Scheme 2018, clause 50(3)(a)
Cape Town	10 to 40 m from top of bank for watercourses; up to 75 m for wetlands; at least 10 m for concrete canals	Floodplain and River Corridor Management Policy 2009
George	1:100-year floodline, or 32 m from the watercourse edge where no floodline has been determined	Integrated Zoning Scheme By-law, section 21(3)
Mbombela	1:100-year floodline or a 32 m riparian buffer inside the urban edge (100 m outside it)	Land Use Scheme 2019, clause 6.8.1

Check your own municipality’s scheme and policies before relying on any of these. Our post on checking whether a property is in a floodline lists where each municipality publishes its flood information.

Two more lines: farms and mines

Farming (CARA). The regulations under the Conservation of Agricultural Resources Act define the “flood area” by the 1:10-year flood. Without written permission, no land user may cultivate land within the flood area of a watercourse or within 10 m of it, or drain or cultivate a vlei, marsh or water sponge. Land already cultivated before the regulations started is exempt.

Mines (GN 704). Regulation 4 keeps residue deposits, dams and reservoirs outside the 1:100-year floodline and at least 100 m from a watercourse, and mining itself outside the 1:50-year floodline or 100 m, whichever is greater. Mine floodline studies therefore usually map both lines.

How the lines work together on a site

On a site next to a river, all four lines can apply at once, and each one leads to a different approval:

1. Determine the 1:100-year floodline, and have the riparian habitat delineated where a wetland or riparian zone may extend beyond it.
2. Map the regulated area from those lines. Anything you build, cross or alter inside it goes through the DWS risk matrix.
3. Check the 32 m distance and the footprints of anything near the watercourse, and whether the site is inside an urban area, to see whether environmental authorisation is triggered.
4. Apply the municipal buffer and rules from the land use scheme and any floodplain policy.

The most restrictive line sets the building envelope, but each approval is separate: a municipal approval does not cover the water use authorisation, and neither covers environmental authorisation. Our guide to every law that applies to a site near a river sets out each one.

See our floodline determination and water use licence services, or send us the site details if you are not sure which lines apply.

This post explains the documents listed below. Requirements change and are applied case by case, so confirm them with the relevant authority before relying on them.