5. Study area parameters

5.1 Estuary

Estuary - where the river meets the sea. SANBI declared the Salt River catchment up to the 5m contour line an estuary, see Figure 69. “An estuary is 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 fresh water derived from land drainage”(cited in EWISA, no date). “A partially or fully enclosed body of water which is open to the sea permanently or periodically. The upstream boundary of an estuary is the extent of tidal influence”. (cited in EWISA, no date)

“In South Africa an estuary is considered to be that portion of a river system which has, or can from time to time have contact with the sea. Hence, during floods an estuary can become a river mouth with no seawater entering the formerly estuarine area. Conversely, when there is little or no fluvial input an estuary can be isolated from the sandbar and become a lagoon which may become fresh, or hypersaline, or even completely dry” (CSIR 1992)(cited in Ethekwini Municipality, no date).

With the draining of the Paarden Eiland area and the canalisation of the Salt River most of the estuarine benefits are suppressed. There is no space for estuarine flora and fauna, sedimentation becomes a problem during heavy rain fall. The loss of the salt marsh to urbanisation is countered by flooding and the inability of the dry land to clean air or polluted water. Cape Town has in the Table Bay area only 2 estuaries, the Diep River estuary north of the Salt

River canal and the Salt River estuary. The Salt River canal drains a substantial urban area (250km²) into the Table Bay. With the stormwater comes the pollution from roads, waste water treatment works, informal settlements and industrial areas. This polluted stormwater is drained fast directly towards the sea.

“Many of the estuaries in the City of Cape Town have been heavily impacted by activities in their catchments. These coastal systems receive polluted water from upstream, with discharge regimes that are not natural. As a result, the City’s estuaries are in poor condition, and tend to be dominated by stands of the common reed, Phragmites australis, which thrives in these altered conditions. Estuaries are all considered to be of very high functional importance and ecological sensitivity, and are subject to a very high level of threat, due to their position in the catchment”(Snaddon and Day, 2009).

The Salt River is only recently recognised as a canal in an estuary. The National Biodiversity Assessment mapped it in its 2018 report as an estuary, using the 5m contour line as its boundary, see diagram 56. "Key drivers and pressures in the estuarine realm are freshwater flow reduction, water quality issues, fishing pressure, habitat modification, estuary mouth manipulation, biological invasion and climate change" (SANBI, 2018). There was no estuary definition found for a canal in an estuary in the literature reviewed.