Page 36 - Bulletin 23- 2020
P. 36
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DEVELOPMENT OF SANDVLEI AS A RECREATIONAL AMENITY:
THE MARINA DA GAMA PROJECT
Gerald Rosenthal
Early history
In the early 1800s, Sandvlei was a natural lake with an open water area of about 2 sq km (200
hectares). It was surrounded by a much larger area of reeded swamp which also extended
some 2 km northwards towards the present-day suburbs of Kirstenhof and Retreat. The vlei
was fed by streams from the Steenberg – Constantiaberg mountains: the Keyser -
Spaanschemat, and Diep - Sand rivers provide the main natural drainage paths from the Tokai
- Constantia valley in the west and north.
Because this area has a considerable seasonal variation in rainfall, a sand bar naturally forms
at the coast at the end of the winter rains. A 50-year average indicates that, of an annual local
rainfall total of about 1000mm, 75% occurs between April and October, when flooding is
likely to occur if the sand bar is closed.
During the dryer summer months, the coastal sandbar effectively dams the estuary and the
water level drops as a result of evaporation and seepage.
In the natural situation, at the beginning of winter when flooding occurs, the overtopping
water erodes the coastal sandbar. At this time, with each high tide the seawater flows freely
into the vlei and there is a substantial increase in the salinity of the vlei water near the mouth.
This has the positive effect of killing freshwater aquatic weed at the southern end of the vlei.
The fish are tolerant to the change in salinity and each type migrates to an appropriate area.
Until 1882, when the suburban railway was built across the northern section of the vlei, the
north-western fringes provided an excellent place for watering cattle and the open water was
used for boating. Some well-watered vegetable farms were established to the north of the
vlei.
With time, the vlei has become shallower and the aquatic weed has spread. Despite several
attempts to dredge the vlei and to improve the conditions for sailing, by the 1960s the main
body of the water of Sandvlei had become a waterweed-choked lake about a quarter of its
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