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To spatially define and delineate the estuarine functional zone of South African estuaries, which includes the upstream and coastal boundaries (Van Niekerk et al. in prep). To be used in the National Biodiversity Assessment: Estuarine Component. This information was also used for the National Estuary Health Assessment and national estuaries conservation planning (Van Niekerk and Turpie 2010). The data can also be used in the development of Estuarine Management Plans (Van Niekerk and Taljaard 2007) required under the National Environmental Management Act: Integrated Coastal Management Act (No 24 of 2008) on a local municipal scale and for Ecological Flow Requirements (i.e. Reserves) studies required under the National Water Act (No 36 of 1998) for Department of Water Affairs (DWAF 2008). It is also referred to in the Environmental Impact Assessment Regulations published in June 2010 under the National Environmental Management Act (No 107 of 1998).

CSIR

In international literature, an estuary is defined as a semi-enclosed coastal body of water which has a free connection with the open sea and within which sea water is measurably diluted with freshwater derived from land (Elliott and McLusky, 2002; Cameron & Pritchard 1963; Pritchard 1967). South Africa’s estuaries are relatively small in comparison with those of the northern hemisphere and the mean annual runoff of South African rivers is more variable, fluctuating between floods, and extremely low to zero river inflow which has led to a number of different definitions for South African estuaries that recognises that these estuaries may not necessarily have a ‘free connection with the sea’ but are ‘either permanently or periodically open to the sea’. (Day, 1980; Day, 1981; Heydorn, 1989, CSIR 1992). While Fairbridge (1980) proposed setting the upstream extent of an estuary as the limit of tidal rise, in some instances in South Africa, e.g. the Bot and Klein estuarine lakes, salinity penetration can be detected further upstream than tidal variation. This phenomenon stems from the fact that South African estuaries are microtidal (< 2m tidal range) and in large systems the tidal rise can be barely discernible (< 5 cm) and easily masked by wind action, while more subtle hydrodynamic processes such as diffusion drive salinity penetration further upstream. In such cases the inland limit of salinity penetration represents the upstream boundary of an estuarine system.

In this assessment an estuary is defined as ‘‘a partially enclosed permanent water body, either continuously or periodically open to the sea on decadal time scales, extending as far as the upper limit of tidal action or salinity penetration. During floods an estuary can become a river mouth with no seawater entering the formerly estuarine area or when there is little or no fluvial input an estuary can be isolated from the sea by a sandbar and become a lagoon which may become fresh or hypersaline”.

There are over 371 river outlets along the SA coast, but not all of these are deemed functional estuarine systems, i.e. representative of significant biological activity (Harrison et al 2000). Since South Africa has a very variable climate and high energy coastal conditions, even systems that only open sporadically to the sea (e.g. every 4 – 10 years) are utilised by estuarine associated or dependent biota, e.g. by fish as nursery areas. The assessment therefore considered all permanent coastal water bodies (i.e. water bodies that do not dry out) that are sporadically linked to the sea as potentially estuarine systems, e.g. the Groen and Spoeg estuaries along the arid west coast were included, while ephemeral systems such as the Holgat, which dries out, were excluded from the assessment. In addition, using existing information and data sets (vegetation and fish) and anecdotal information, all systems were evaluated by a panel of national experts and listed as functional or not (Harrison et al 2000). Some very small (< 500 m in length) permanent coastal water bodies that links rivers to the sea – were excluded from this assessment until such time as field studies indicated that they should be considered as functional estuaries. Rivers entering the sea as waterfalls, e.g. those along the Tsitsikamma coast, were also excluded. In addition, a few small highly modified systems in urban areas were also excluded from the assessment on the basis that they were not - functional systems.

Mapping was undertaken for nearly 300 functional estuarine systems along the South African coastline. For each estuary the estuarine functional zone (estuarine ecosystem area) and open water areas were digitized using Spot 5 imagery (2008) and Google Earth. For the most part the images were relatively cloud free, but where cloudy conditions occurred on the SPOT 5 imagery Google images were used. The lateral boundaries included all the associated wetlands, intertidal mud and sand flats, beaches and foreshore environments that are affected by riverine or tidal flood events (Edgar, 1999).The 5 m topographical contour (obtained

from Chief Directorate Surveys and Mapping) was used as the boundary to delineate the floodplains. Where the 5 m contour was not available in digital format, orthophoto’s (1:10 000) were scanned, georeferenced and the 5 m contour was digitized. Where no orthophoto’s were available (13 systems) floodplains were mapped from Spot 5 imagery using changes in topography and vegetation types as indicators. From this delineation spatial data such as area, length and perimeter (estuary coastline) and distance to next system could be inferred.

The estuary mouth was taken as the downstream boundary of an estuary, or where the mouth was closed the middle of the sand berm between the open water and the sea. The upstream boundary was determined as far as tidal variation or salinity penetration occurred, whichever penetrates furthest upstream. This is in line with recent scientific studies and the administrative definition of a South African estuary (Van Niekerk and Taljaard 2007, DWAF 2008). Where possible the upstream boundary was derived from the literature, expert judgment or field observations. In a number of systems no data were available and the upper boundary was taken as the 5 m topographical contour (bearing in mind that tidal range in South Africa is microtidal (< 2 m) and sand bars at closed estuary mouth can build up as high as + 4 m MSL). The upper boundaries were also screened against other existing spatial delineations, e.g. the KwaZulu Natal Estuaries database (Version 1.00.02) and the delineation developed for Durban estuaries (Forbes and Demetriades 2008) with preference given to the data from the larger scale studies. Spatially files were converted to GoogleEarth (KMZ formats) and mailed for review to members of the Consortium for Estuarine Research and Management (CERM) for comment.

SANS 1878

FGDC-STD-001-1998