State of the Bay Report 2011-Final.pdf - Anchor Environmental

Beach Width (m)
State of Saldanha Bay & Langebaan Lagoon 2011
Sediments
30
25
20
15
10
5
0
1998 2000 2002 2004 2006 2008 2010 2012 2014
Figure 5.4
Variation in beach width across a transect of the central section of Spreeuwalle beach (Source:
Gericke 2012).
Gericke (2008) also analysed the Geelbek dune system and the loss of bare sands in this area
over the period 1960 to 2000. He recorded a massive 70% reduction of bare sands from close to 13
million m 2 present in 1960 to less than 4 million m 2 in 2000.
Gericke (2008) concluded that the construction of the ore terminal had led to a reduction in
sediment transport from Spreeuwalle beach which is currently being trapped in the northern corner
of the beach, reducing the supply of sands to the beaches further south. Changes on the two
beaches are often out-of-sync with one another, with major accretion and erosion events on
Langebaan beach lagging behind Spreeuwalle by a period of up to five years. The reasons advocated
for this include the possibility that beaches in between these two sites are acting as intermediate
reservoirs for sediment. If this is indeed correct, then changes on these beaches, notably the recent
erosion observed on the southern end of Spreeuwalle beach (possibly linked to a severe storm event
in 2008) does not bode well for what will happen to Langebaan beach in the future.
Alien vegetation encroachment by Port Jackson (Acacia saligna) and Rooikraans (Acacia
cyclops) is thought to be a contributing factor in the loss of sand from the Geelbek dune system. The
consequences of this encroachment at Langebaan have not yet been studied. However, it is known
that heavily vegetated dunes restrict the natural movement of dune systems and possible inland
migration of the coastal system (Feagin 2005). The salt marshes on Langebaan Lagoon have not
suffered any significant changes in area over the same time period (Gericke 2008).
5.1.3.1 Northern Langebaan beach erosion management measures
In 1997, after severe storms resulted in the loss of residential properties, the need to protect and
restore northern Langebaan beach became apparent. A temporary solution was sought through the
construction of three sections of rock revetment along the beach (Figure 5.5), mostly in an effort to
prevent any further loss of property. Erosion continued along the sections of coastline adjacent to
the revetment, however. This prompted the then Department of Environmental Affairs and Tourism
(now the Branch: Oceans and Coasts, of the Department of Environmental Affairs) to contract
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