State of the Bay Report 2010-Final - Anchor Environmental

Anchor Environmental
Figure 4.9. A) Under natural circumstances, dune vegetation can “move” with the beach as it erodes and
accrete under the influence of natural processes. B) Protection of infrastructure erected too
close to the high water mark, on the other hand, necessitates construction of artificial barriers
and leads to the loss of the beach ecosystem and associated amenities.
The movement of beach sediment is a result of a process called “littoral drift” driven mainly
by wave action. As the waves hit the shore they do so at an angle thereby displacing sediment along
the shore. Beaches in areas prone to violent storms will have greater potential for sedimentary
change, which will occur in single events rather than by long term trends. It is not clear whether
storms in the Saldanha/Langebaan region will increase in frequency or intensity but it is a possible
scenario, which coupled with long term changes in sea level and average wave height, would result
in greater shifts in shoreline over less time. This may necessitate greater setback lines for
development that those currently in place (Gericke 2008).
4.3.3.1 Changes in beach and dune morphology in Saldanha Bay and Langebaan Lagoon
Beach erosion in Saldanha Bay, particularly at Langebaan Beach, has been the subject of
much controversy in recent years. Ongoing erosion for the past 30 years has been documented with
the loss of over 100 m of beach since 1960 with 40 m just in the last 5 years (McClarty et al. 2006;
Gericke 2008). In some places the width of the beach has been reduced by as much as 150 m,
leaving the house built on the first set of dunes unprotected against storm damage (Gericke 2008,
Figure 4.9).
Gericke (2008) studied aerial photographs from Saldanha Bay between 1960 and 2000, to
assess changes to beaches, coastal dunes and salt marshes, due to sedimentary forces, and the
possible influence of anthropogenic factors. He focussed on two sites, Langebaan Beach (opposite
the town of Langebaan) and Spreeuwalle (situated between Lynch point and the ore terminal).
These two beaches fluctuated considerably in size over this 40 year period (Figure 4.10). The
trajectory of change on the two beaches was initially similar, both beaches reached a low point in
1972 (the lowest recorded in the case of Spreeuwalle) following which time they both increased in
size until 1982 whereafter their paths diverged. Langebaan beach began declining precipitously in
size at this point, a trend which continued until the end of the monitoring period (2000) where it
reached the small size on record. By contrast, the beach at Spreeuwalle continued increasing slowly
in size from 1983 until the end of the monitoring period. Nett change over the 40 year period was
quite different for the two beaches, with Spreewalle having increased in area by 32,101 m 2 by the
end of the period, while Langebaan beach had decreased in area by 179,322 m 2 .
State of the Bay 2010: Saldanha Bay and Langebaan Lagoon 55