State of the Bay Report 2010-Final - Anchor Environmental

Relative Area (x 1 000 m 2 )
150
100
50
0
-50
-100
-150
-200
-250
Anchor Environmental
1955 1960 1965 1970 1975 1980 1985 1990 1995 2000
Figure 4.10. Change in relative beach area, in thousands of m 2 , since 1960 to 2000 in Paradise and
Spreeuwal beaches, based on aerial photographs (Figure courtesy of J. Gericke 2008).
His conclusion regarding these changes were as follows:
The reason for the marked dip in the sediment area in 1977 is unexplained and could relate to
the tide the day the picture was taken, which was not recorded, or transitory storm influence.
The significant increase in sediment accumulation since 1977 to 1988 in Spreeuwal beach is
attributed to the construction of the harbour wall between 1973 and 1976, and subsequent
filling in of the wall with close to 250,000 m 2 of beach sand. After the construction, however,
sediment has been trapped at Spreeuwal beach due to the harbour decreasing the longshore
drift south towards Langebaan beach and (McClarty 2008).
The sediment area at Langebaan beach also increased between 1977 and 1988, and is attributed
to the additional beach sand added to Spreeuwal beach and an increase in the littoral drift of the
sediment to Langebaan beach. After 1988, however, the significant drop in sediment area of
about 270,000 m 2 between 1988 and 2000 is, at least, partially related to sediment transport
being cut off by the harbour wall. It would be expected that should the sands at Lentjiesklip 1, 2
and 3 become depleted, Langebaan beach would lose sediment at a more rapid rate.
In summary, 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
northern corner of the beach, reducing the supply of sands to the beaches further south. He also
pointed out that changes on the two beaches are at times out-of-sync from one another, with major
accretion and erosion events on Langebaan beach lagging that at Spreeuwalle by as much as five
years. These reasons advocated for this is that there are a number of beaches in between these two
sites that act 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
State of the Bay 2010: Saldanha Bay and Langebaan Lagoon 56
Year
Langebaan Beach Spreeuwal Beach