Dam the drought
CAPE Town is served by a number of dams which have a fixed capacity for storing water, irrespective of the amount of rain falling in their catchment areas.
Options for building additional dams in this fairly densely populated area are severely limited and once the dams are full, water, which could have been used by the residents of the city, will pour over the spillways into rivers and streams and eventually into False Bay or the South Atlantic.
I have been looking at aerial views of the Theewaterskloof Dam and have formed the opinion, rightly or wrongly, that it is a very inefficient water storage facility. There seem to be large areas of shallow water which dry out at times due to a combination of utilisation and evaporation.
It occurs to me this might be a good time to dredge and extend the deeper areas and to use the resultant spoil to reclaim land, either around the edge of the dam or in the form of islands or peninsulas.
This would have the combined effect of creating more deep water capacity for storage in the rainy season and reducing the surface area, and consequent loss of water due to evaporation in summer.
Taking it a step further, into the realms of fantasy perhaps, reclaimed land could be used to create a waterside community (eco-friendly of course) similar to that on the edge of the Hartbeespoort Dam, to offset the cost of dredging.
A small Cutter Suction Dredge could recover 4 000 cubic metres per hour, making space for an additional 32 000 cubic metres (kilolitres) of water per working day come the rainy season.
The storage capacity of the dam could, in theory, be increased by almost a quarter of a million cubic metres/ kilolitres in just a seven-day week and the spoil recovered could be used to create an island over 20 000 square metres in area and 10 metres high.
A larger dredge or a number of dredges could significantly increase the storage capacity of the dam and reduce the loss due to evaporation within a relatively short time.
Once the storage capacity had been increased the population of greater Cape Town would reap the benefit for years to come.
As it happens, dredgers of the type required to carry out this task are built at the Damen Shipyard in Table Bay docks, obviating the need for the expenditure of foreign exchange.
The process suggested, although undeniably costly, could provide work for local residents who could be employed to man and maintain the dredger or dredgers, and to spread out the dredged spoil and plant grass, reeds or fynbos in order to prevent erosion.
It’s just a thought. Bill Rice. Simon’s Town