Vaal Dam compartments

The account of my involvement with the LHWP covers the period in my career when I was Assistant Chief Engineer (Planning) – 1971-1975, Chief Engineer (Planning – 1975-1980), Managing Engineer (Water Resources) 1980-1987 and Deputy Director General (Water Resource Development) 1987-1991. A few further points during my time in the first mentioned post are worth mentioning. 

At the time, the second raising of the Vaal Dam was under consideration. While still in the Design Office, I had been asked to investigate the stability of the existing dam for its suitability to be raised. I found that the dam, as it was, was not even stable measured against existing criteria. For that reason, it was decided to construct a drainage tunnel in the foundations underneath the dam, install cables and raise the gates to increase the flood handling capacity. During these studies, I noticed that the reservoir behind the dam was very shallow, especially the upper portions along the Vaal stem as well as the Wilge stem. In order to reduce these losses and at the same time increase the flood capacity, I thought up a scheme to construct two low dams inside the reservoir – the one cutting off the shallow portion of the Vaal itself, the other one the shallow portion of the Wilge.

 Water would by preference be withdrawn from these upstream compartments by pumping to the main downstream one, from where it would be released in the normal way. More than half the storage capacity was in the latter, with very little surface area, hence less evaporation. I calculated the gain in yield and found it to be substantial. The two low dams in the reservoir could be made somewhat higher, with the extra capacity acting as flood absorbers. On 11 November 1974, I submitted my idea and calculations by letter to the Secretary, Dr JP Kriel. He unfortunately did not take it seriously, saying that it would be too difficult to construct these small dams under the reservoir water. I did not agree with him, because in my overseas travel, I had seen major works being constructed in even deeper and fast flowing water. (Think of the damming of the Easter Scheldt in the Netherlands and the diversion works in the Rhine in France!) However, that is where the matter ended and the original plans were executed.