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

State of Saldanha Bay & Langebaan Lagoon 2011
Sediments
5 SEDIMENTS
5.1 Shoreline erosion in Saldanha Bay and Langebaan lagoon
5.1.1 Background
The majority of sandy beaches worldwide are affected by erosion - a problem which has been greatly
exacerbated by development of human settlements in the coastal zone (Bird 1985). Globally, 70% of
beaches are classed as receding; 20–30% are stable, while 10% are accreting (Schlacher et al. 2008).
Under natural conditions, sea level rise would cause the entire coastal system, including beach and
dune systems, to retreat inland. In instances where coastal systems are bound by barriers, walls, or
heavily vegetated dunes, these features are likely to restrict inland migration and would result in
beach loss rather than migration (Feagin et al. 2005). Salt marshes are under immediate threat if the
rate of sea level rise exceeds that of vertical accretion.
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).
Windblown sand is likely to have been, a major part of the Langebaan/Saldanha system.
Many of the beaches, particularly Spreeuwalle, have dune fields associated with them. The largest
dune field in the area is the Geelbek dunefield. This dune field lies directly to the southeast of the
Langebaan Lagoon. The south-easterly wind that predominates in summer would tend to transport
sand from 17 mile beach (Yzerfontein) to the Geelbek dunes and in turn from the Geelbek Dunes
into Langebaan (Gericke 2008).
Inside Saldanha Bay, where wave action is of greater significance than inside the protected
Langebaan Lagoon, littoral drift is a major factor in sediment transport. While waves on the west
coast typically originate in the South or South West, they tend to refract around the headlands at the
mouth of the Bay and approach the shore from the West or North West, particularly along the
section of coast between Spreeuwalle and the North Langebaan beach. The predominant littoral
drift is therefore in a southerly direction, rather than a northerly direction as observed on the rest of
the West Coast (Compton, 2004).
It is not clear whether storms in the Saldanha/Langebaan region will increase in frequency or
intensity but it is a possible scenario of global climate change, which coupled with long term changes
in sea level and average wave height, could result in greater shifts in shoreline over less time. This
may necessitate greater setback lines for development that those currently in place (Gericke 2008).
5.1.2 Human impacts on the system
Over the years, several major changes have taken place in Saldanha Bay which are likely to have
affected the sedimentary system. These include construction of the Marcus Island causeway and the
Transnet Ore Terminal in the early 1970s, the ongoing construction of residential and commercial
properties on the beachfront, dredging in the bay, the slow, steady encroachment of vegetation on
the Geelbek dune system, and ongoing dredging that takes place around the Ore Terminal.
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