OCEANOGRAPHY OF THE SOUTHERN AFRICAN REGION
The wave refraction discussed here "organises" the
waves as they propagate towards the coastline, so that they
arrive with their crest more or less parallel to the coastline.
There is sometimes a small angle between the wave crests
and the coastline, as off the Natal coast, which leads to a
residual alongshore drift current capable of carrying sediment, so that coastal engineers have to be careful that their
sea structures in the shore zone do not interfere with the
prevailing longshore currents. If there is an interference, it
may mean that sediment will pile up on one side ofthe structure and be scoured away from the other side. These
longshore currents can be dangerous to swimmers and
anglers.
TIDES
The tides can be characterised as a very long wavelength
wave which circulates around the oceans. Unlike the surface waves discussed in the previous section, which are generated by the wind and have a restoring force due to gravity,
the tide wave is generated by the gravitational forces of the
sun and moon and has restoring forces of gravity and the
Coriolis force (due to the rotating earth). In the open ocean,
the tide wave is seldom greater than one metre, but as this
wave (or tide) propagates into shallower water the local
resonance effects can amplify the height of the tide up to
about 16 metres in some places. This resonance is lacking
off the southern African coast except at Beira, where the
maximum tidal range is 6.4 m. As one proceeds up the coast
to Beira, higher ranges of the tide are apparent.
Off the South African coast the maximum tidal range is
about two metres between successive high and low spring
tides. Moreover, the times of a particular phase of the tide
(for example a high tide) are almost simultaneous on the
west coast between Walvis Bay and Cape Town. On the east
coast, the tide propagates up the coast and arrives on average about 35 minutes later at Durban than at Cape Town.
Since the tide can be considered as a wave, as it advances
and recedes the individual water particles oscillate backwards and forwards. These oscillations lead to tidal currents: onshore as the tide flows in and offshore as the tide
ebbs out. Because of the generally small tidal heights
around South Africa, the tidal currents are also weak, except in regions where there may be a narrowing constriction
such as between the Knysna heads or through river mouths
like those of the Kowie, Swartkops, etc.
In conclusion, from this brief survey, it can be appreciated that southern Africa occupies an extremely interesting and unique position as regards current and wave
systems. In addition, it should be emphasised, especially to
those who only visit the coast infrequently, that even
though the sea can look benign and inviting, changes occur
rapidly. Anyone venturing into the unforgiving marine environment should always obtain as much information about
local conditions as is possible.
Further reading:
BRANCH. G. M. and M. L. BRANCH. 1981. The Living Shores of Southern
Africa. C. Struik, Cape Town, 272 pp.
HARRIS, T. F. W. 1978. "Review of coastal currents in southern African
waters". SANCOR REPORT 30, CSIR, Pretoria, 103 pp.
References:
BANG, N. D. 1970. "Major eddies and frontal structures in the Agulhas
Current retroflexion area in March 1969". Symposium on Oceanography in
S.A., CSIR.
BANG, N. D. 1973. "Oceanography: Oceanographic environment of Southern
Africa". The Standard Encyclopaedia of Southern Africa, 8, 282-286, Nasau
Ltd., Cape Town.
HARRIS, T. F. W. and D. VAN FOREEST. 1977. The Agulhas Currcilt
system. Department of Oceanography, Univ. Cape Town. 37 pp.
NELSON, G. and L. HUTCHINGS. 1983. "The Benguela upwelling area".
Progress in Oceanography, 12, 333-356.
Ichthyology in South Africa
A few early travellers to the Cape described and in some
cases illustrated the fishes they encountered, and several
species were taken to Europe to be described by the great
zoologists of thee 18th and 19th centuries. Linnaeus, Bloch,
Schneider, Cuvier and Valenciennes all named fishes from
South Africa, Andrew Smith, a physician who became the
first director of the South African Museum in Cape Town,
published his Illustrations of the Zoology of South Africa in
serial fashion from 1838 to 1849. This important work con28
tained descriptions and illustrations of 41 fishes as well as
many other animals. Additional descriptions and illustrations of sharks by Smith were used by Muller and Henle
(1841) in their monumental work on elasmobranchs.
In the latter half of the 19th century, Gunther, Bleeker,
Kaup, Steindachner and Castelnau were describing new
South African fishes. At the turn of the century, Boulenger
(Gunther's successor at the British Museum) described several new species from South Africa, J, D, F, Gilchrist can be
The wave refraction discussed here "organises" the
waves as they propagate towards the coastline, so that they
arrive with their crest more or less parallel to the coastline.
There is sometimes a small angle between the wave crests
and the coastline, as off the Natal coast, which leads to a
residual alongshore drift current capable of carrying sediment, so that coastal engineers have to be careful that their
sea structures in the shore zone do not interfere with the
prevailing longshore currents. If there is an interference, it
may mean that sediment will pile up on one side ofthe structure and be scoured away from the other side. These
longshore currents can be dangerous to swimmers and
anglers.
TIDES
The tides can be characterised as a very long wavelength
wave which circulates around the oceans. Unlike the surface waves discussed in the previous section, which are generated by the wind and have a restoring force due to gravity,
the tide wave is generated by the gravitational forces of the
sun and moon and has restoring forces of gravity and the
Coriolis force (due to the rotating earth). In the open ocean,
the tide wave is seldom greater than one metre, but as this
wave (or tide) propagates into shallower water the local
resonance effects can amplify the height of the tide up to
about 16 metres in some places. This resonance is lacking
off the southern African coast except at Beira, where the
maximum tidal range is 6.4 m. As one proceeds up the coast
to Beira, higher ranges of the tide are apparent.
Off the South African coast the maximum tidal range is
about two metres between successive high and low spring
tides. Moreover, the times of a particular phase of the tide
(for example a high tide) are almost simultaneous on the
west coast between Walvis Bay and Cape Town. On the east
coast, the tide propagates up the coast and arrives on average about 35 minutes later at Durban than at Cape Town.
Since the tide can be considered as a wave, as it advances
and recedes the individual water particles oscillate backwards and forwards. These oscillations lead to tidal currents: onshore as the tide flows in and offshore as the tide
ebbs out. Because of the generally small tidal heights
around South Africa, the tidal currents are also weak, except in regions where there may be a narrowing constriction
such as between the Knysna heads or through river mouths
like those of the Kowie, Swartkops, etc.
In conclusion, from this brief survey, it can be appreciated that southern Africa occupies an extremely interesting and unique position as regards current and wave
systems. In addition, it should be emphasised, especially to
those who only visit the coast infrequently, that even
though the sea can look benign and inviting, changes occur
rapidly. Anyone venturing into the unforgiving marine environment should always obtain as much information about
local conditions as is possible.
Further reading:
BRANCH. G. M. and M. L. BRANCH. 1981. The Living Shores of Southern
Africa. C. Struik, Cape Town, 272 pp.
HARRIS, T. F. W. 1978. "Review of coastal currents in southern African
waters". SANCOR REPORT 30, CSIR, Pretoria, 103 pp.
References:
BANG, N. D. 1970. "Major eddies and frontal structures in the Agulhas
Current retroflexion area in March 1969". Symposium on Oceanography in
S.A., CSIR.
BANG, N. D. 1973. "Oceanography: Oceanographic environment of Southern
Africa". The Standard Encyclopaedia of Southern Africa, 8, 282-286, Nasau
Ltd., Cape Town.
HARRIS, T. F. W. and D. VAN FOREEST. 1977. The Agulhas Currcilt
system. Department of Oceanography, Univ. Cape Town. 37 pp.
NELSON, G. and L. HUTCHINGS. 1983. "The Benguela upwelling area".
Progress in Oceanography, 12, 333-356.
Ichthyology in South Africa
A few early travellers to the Cape described and in some
cases illustrated the fishes they encountered, and several
species were taken to Europe to be described by the great
zoologists of thee 18th and 19th centuries. Linnaeus, Bloch,
Schneider, Cuvier and Valenciennes all named fishes from
South Africa, Andrew Smith, a physician who became the
first director of the South African Museum in Cape Town,
published his Illustrations of the Zoology of South Africa in
serial fashion from 1838 to 1849. This important work con28
tained descriptions and illustrations of 41 fishes as well as
many other animals. Additional descriptions and illustrations of sharks by Smith were used by Muller and Henle
(1841) in their monumental work on elasmobranchs.
In the latter half of the 19th century, Gunther, Bleeker,
Kaup, Steindachner and Castelnau were describing new
South African fishes. At the turn of the century, Boulenger
(Gunther's successor at the British Museum) described several new species from South Africa, J, D, F, Gilchrist can be