| Main Page | General Information | Catchment Characteristics | Land and Estuary Uses | Ecology |
| Threats | References | Water Quality | Hydrodynamics and mouth dynamics | Climate |
|
GAMTOOS ESTUARY: Physical Features |
||||
|
|
Topography |
|
After the confluence of the Groot River and Kouga River, the Gamtoos River meander through a broad alluvial floodplain for a distance of 90 km. At the upper end of the estuary, i.e. where the Loeriespruit joins the Gamtoos, 8,5km from the mouth, it is approximately 80m wide and flows between steepsided almost parallel banks approximately 2,5 m high. From the new national highway bridge the river broadens gradually towards the mouth and the banks flatten out to form an extensive tidal marsh behind the coastal dunes. (Ref 1) |
|
The tidal salt marsh to the north of the former main channel consists of a broad flat area approximately 79 ha in extent covered with halophytic vegetation. On the seaward side of the former main channel, an island of saltmarsh exists, surrounded by numerous tidal pools which are encroached upon by shifting sand dunes. The substrate of these pools consists of silt brought down during floods and much of the now barren low lying areas between the dunes is being colonized by halophytic vegetation such as Sarcocornia spp. (Ref 1) |
|
|
Bathymetry |
|
According to GF van Wyk there were no particularly deep areas in the river below the old national road bridge (Van Wyk 1963). His field notes of a survey done in 1956 record a depth of approximately 1,8 m in mid-stream at low tide opposite the old boat launching site. The depth of water in the former main channel is very variable and numerous mud banks at a depth of approximately 0,5m at low tide occur in the stretch of water from the old boat launching site to its confluence with the present main channel. The isolated lagoon at the eastern extremity basin on the landward side. This was confirmed by C Gaigher in 1980 who estimated the deepest part of this lagoon to be at least 3m. (Ref 1) |
|
|
Obstructions |
|
Three major structures cross the lower part of the Gamtoos River. The old national road bridge which is a single lane, steel girder construction spanning the entire water course, crosses the river 6,8 km from the mouth. From this point the river runs alongside a sandstone cliff at the base of which the original gravel road to the mouth was constructed. (Ref 1) |
|
|
A water pipeline to Port Elizabeth from the Paul Sauer Dam crosses the river below the old national road bridge, 5,3 km from the mouth. A few hundred metres below this the bridge for the new national coastal freeway has been built. This bridge also spans the entire main water-course of the river but its approach from the west consists of a substantial embankment across the floodplain which, as has previously been mentioned, is subject to inundation when the river comes down in flood. (Ref 1) |