This layer maps the estuarine functional zone for South Africa’s estuaries. The estuarine functional zone is defined by the 5 m topographical contour (as indicative of 5 m above mean sea level). The estuarine functional zone includes:

• Open water area;
• Estuarine habitat (sand and mudflats, rock and plant communities); and
• Floodplain area.

The 5 m contour has the following biodiversity and planning advantages:

• The 5 m contour encapsulates most dynamic areas influenced by long-term estuarine sediment processes, i.e. sediment stored or eroded during floods, changes in channel configuration, aeolian transport processes and changes due to coastal storms. Allowing for natural variability is important as these are some of the key physical processes that drives biodiversity along the SA coastline;
• The 5 m contour encompasses the floodplain and estuarine vegetation that contribute detritus (food) and provides refuge to the systems. Note, salt-marsh vegetation can occur further than 500 m away at a number of the larger estuaries, such as the Olifants, Berg, Goukou and Klein Brak. Most estuarine-associated biota occur under the 5 m contour, as this is as far as the influence of the ocean can be detected on land.
• Temporarily open/closed estuaries (75% of South African estuaries) can close at levels of between 2.5 and 4.5 m. The 5 m contour allows for water-level increases due to back-flooding under closed mouth conditions or wave action from wind;
• In most cases, the 5 m contour allows for the inclusion of a buffer zone of terrestrial vegetation that represents the transition between terrestrial and coastal ecosystems.
• The 5 m contour should provide a buffer zone that can allow an estuary to retreat in the future in the event of sea-level rise due to climate change. It also allows for the inclusion of some terrestrial fringe vegetation that contribute detritus to the system and refuge areas during floods;
• An accurate delineation of the high-water mark is not available for the entire South African coastline;
• Flood lines (1:50/1:100) for estuaries are often inaccurately determined under open mouth conditions, which leads to underestimation of flood heights. In the absence of long term berm height data (which can vary substantially under different climatic conditions) the 5 m contour provides the best protection against natural hazards such as floods and storms.
• The 5 m contour minimizes the risk of pollution to estuaries. Septic tanks are sunk about 2 m into the ground. During closed mouth conditions (and very high tides) density differences between fresh and salt water causes drainage problems or infrastructure damages if tanks are not situated not above the 5 m contour.
• As water resources development and land-use change in the catchment can lead to the changes in mouth behaviour, i.e. change estuary type from permanently open to temporarily open, e.g. Uilkraals, this level is taken as the default for all systems in South Africa;
• The 5 m contour data is available from Chief Directorate: Surveys & Mapping, Mowbray, as a GIS layer or on black-and-white 1:10 000 orthographic maps. More detailed data are not available on a national scale.

For all the above mentioned reasons it should be clear that in some cases, the estuarine functional zone goes beyond the 5m contour, for one or more of the following reasons:

• In deeply incised floodplains, where the river/estuary bed may be metres below the mapped floodplain area, tidal action and/or back-flooding may be detected further upstream than indicated by the 5 m contour as indicated on the topographical map. This is an artefact of the mapping process and may need site-specific data to correct.
• For some narrow, deeply incised estuaries with very large catchments the 1: 10 year flood line maybe above the 5 m contour (little floodplain area versus significant flood volume), e.g. Mzimkulu. In such cases it is recommended that a detail topographical survey be conducted and a flood line estimate be done following engineering principals to demarcate more dynamic areas and indicate flood risk on a more local scale.
• The littoral active zones adjacent to an estuary can stretch beyond the 5 m contour, e.g. dune field next to Duiwenhoks and Sundays, and should be incorporate in the estuarine functional zone in site specific cases.

For more information see:

• Harrison, T.D. 2004. Physico-chemical characteristics of South African estuaries in relation to the zoogeography of the region. Estuarine, Coastal and Shelf Science 61: 73-87.
• Harrison, T.D., Cooper, J.A.G. & Ramm, A.E.L. 2000. State of South African estuaries: geomorphology, ichthyofauna, water quality and aesthetics. State of the Environment Series, Report No. 2. Department of Environmental Affairs and Tourism. 127pp.
• Taljaard S, Adams JB, Turpie JK, Van Niekerk L and Demetriades N (2008). Water Resource Protection and Assessment Policy Implementation Process. Resource Directed Measures for protection of water resources: Methodology for the Determination of the Ecological Water Requirements for Estuaries. Version 2. Pretoria: DWAF.
• Turpie JK 2005. Priority Estuaries for Conservation on the Wild Coast, South Africa. Wild Coast Conservation and Sustainable Development Project.
• Turpie, JK and Clark, BM 2007. Development of a Conservation Plan for temperate South African estuaries on the basis of biodiversity importance, ecosystem health and economic costs and benefits. Report for the C.A.P.E. Estuaries programme.
• Van Niekerk L and Taljaard S (2007). Proposed generic framework for Estuarine Management Plans. Version 1. Submitted to C.A.P.E. Estuaries Management Programme.
• Whitfield AK and Bate G (eds) (2008). A Review of information on temporarily open/closed estuaries in the Warm and Cool Temperate biogeographic regions of South Africa, with particular emphasis on the influence of river flow on these systems. WRC Report No 1581/1/07. ISBN 978-1-77005-518-6.
• Whitfield, A.K. 1992. A characterisation of southern African estuarine systems. Southern African Journal of Aquatic Sciences 12: 89-103.
• Whitfield, A.K. 2000. Available scientific information on individual estuarine systems. WRC Report no. 577/3/00.

Examples (Click to enlarge)

Cool temperate floodplain Bot/Kleinmond Estuary

Warm temperature floodplain Sout (East) and Groot (West) Estuaries

Subtropical floodplain Nhlabane, Richard's Bay and Mhlathuze Estuaries