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This is the most recent version of the Estuarine Functional Zone Map. The map was developed
as a collaborative effort and delineates the Estuarine Functional Zone for South Africa (Van
Niekerk et al. 2019).
In South Africa, the EFZ is defined as the area that not only encapsulates the estuary
waterbody, but also the supporting physical and biological processes necessary for estuarine
function and health. It includes all dynamic areas influenced by long-term estuarine
sedimentary processes, i.e. sediment stored or eroded during floods, changes in channel
configuration, aeolian transport processes, and/or changes due to coastal storms. It also
encompasses the multiple ecotones of floodplain and estuarine vegetation that contribute
detritus (food source) to the estuary and/or provide refuge during high flow events. The EFZ
captures the natural, historical estuarine extent and should not be confused with
setback/management lines that often exclude developed areas. The EFZ purpose is to identify
the ‘space’ in which estuarine physical and biological functions take place over long time scales
(>decades). Development in the EFZ is captured as an aspect of habitat degradation or decline
in overall estuary condition.
The upstream boundary of the estuaries was determined as the limits of tidal variation or
salinity penetration, whichever penetrates furthest. The estuary mouth was taken as the
downstream boundary of an estuary. The highly dynamic nature of this area presents a
significant challenge to accessing change in biodiversity and even managing estuaries. To
account for this, and to allow for a seamless integration with the Marine and Coastal Realm, the
concept of ‘Estuarine Shore’ was introduced to reflect the dynamic nature of the interface
between estuaries and the coast. Estuarine Shores refers to sand berms or bars that form in
front of estuaries. They vary substantially in size and shape over decadal scales and can be
completely absent during a flood or a near permanent feature during periods of low flow.
Estuarine Shore was defined as the area from the base of the foredune, or where this line
would be if dunes were present, to the back of the surf zone. The full extent of the Estuarine
Shore is encapsulated in the EFZs and not be considered separate from the functional unit. The
surfzone was included to reflect a continuum in estuarine-marine connectivity through estuarine
inputs to the surfzone, either as direct flow through an open mouth or in seepage through the
berm in a closed system. |