The media hype about an imminent Kariba Dam failure

Thu, 23 Mar 2017 13:04:08 +0000

By Ronald Lwamba

 I joined the Department of Water Affairs in 1974 as a Water Engineer, after completing my civil engi-neering degree from the University of Zambia in 1974.

The Chairman of the Public Service Commis-sion summoned me to his office, Mr Ariel Phiri if I remember his name correctly. I was filled with trep-idation but I need not have worried.

He congratulated me for being the first Zambian Water Engineer in the department and that he had even informed his Excellency the President about my appointment.

I felt flattered. However my stay in the civil service was to be short lived and I resigned even though I had been promoted to Provincial Water Engineer, Copperbelt Province, after only nine months. This decision has haunted me to this day but it should be viewed in the context that salaries in the civil service in those days were very low but especially in view of the advice I got from a Mr Elfol, an Egyptian and Provincial Water Engineer, North Western Province, who was my boss. He said: “You are joining the Council as an Assistant Town Engineer and if you become Town Engineer you are only going to be in charge of a town but if you choose to remain you have a very chance of becom-ing Director of Water Affairs and you will be in charge of the entire country.” These were words of wisdom indeed with the benefit of hind sight! I joined Chingola Municipal Council as an Assistant Town Engineer in 1975 but was transferred to Livingstone Municipal Council by the Local Government Service Commission, headed by Mr Lavu Mulimba, on promotion as Deputy Town Engineer in 1976. After attaining my Masters degree in Wa-ter Resources Development from Roorkee University in India in 1979, I was promoted to the post of Town Engineer in the same year.

The sudden increase in the price of oil in 1974 and the fall in the price of copper had a devastating impact on the Zambian economy especially on Councils.

Most of the roads in Livingstone were gravel roads and were reasonably well maintained with the two graders the council had but they eventually broke down and could not be repaired because of lack of money and foreign exchange to buy spare parts. Even when money was available, foreign exchange was often not available. So the roads could not be graded. Pot holes could not be filled because there was no forex, as it became to be known, to import bitumen. Street lights could not be replaced. The late Geoff Zulu (MHSRIP) of the Zambia Daily Mail asked me about street lights in his area and I said I was not aware of them being off. The fol-lowing day on the front page of the Zambia Daily Mail was a screaming headline: TOWN ENGI-NEER IN THE DARK ABOUT STREET LIGHTS.   There was a chronic water shortage in Liv-ingstone although the water intake was on the Zambezi River, the fourth largest river in Africa and the water treatment works could not be expanded to cater for the increase in population because of lack of funds.

I would be incessantly asked this question at the Plans, Works and Development Committee meetings, popularly known as PWD in council circles, and I would give the analogy between a bumper harvest of maize and excess water – that you could have a bumper harvest and still have a mealie meal shortage if your milling capacity is limited and so it was with water.

The mechanical sew-age treatment plant could not be repaired for years and instead spewed raw sewage effluent into the Zambezi River but fortunately the sewer outfall was downstream of the water intake unlike in the City of Ndola where the mechanical sewage plant was sited upstream of the water treatment plant and so when the sewage mechanical plant broke down and could not be repaired because of lack of funds it became difficult to treat this water.

And so when the Council managed to secure some funds from the African Development Fund I recommended the use of oxidation ponds which only require oxygen from the air to treat the sewage and admittedly on a large area of land compared to a mechanical sew-age plant, but land is not at a premium in Zambia as it is in Europe. They also do not require spare parts to work as is the case with mechanical sewage plants.

So when there was talk of giving Councils powers to fire chief officers instead of the Local Govern-ment Service Commission I figured it would not be hard for the Council to find excuses to fire me and so I opted to resign for the second time in my life to join ZESCO after successfully applying for a job of Resident Engineer at Itezhitezhi Dam which had been advertised in 1987.

I do not think tears were shed at my resignation but a year later I happened to be in Livingstone when I met the learned counsel, Mr Noah Dindi, who was a very prominent lawyer in Livingstone, who told me that the Tongas had a saying that the services of a slave were only appreciated when he was no longer there. I doubt if he remembers it but I do. Equally, there is another saying in another local language which says that the one who is told a thing never forgets.

It was at Itezhitezhi in the late 1980s that I came to know about the problems at Kariba Dam. The first one was that of the one million cubic metres of mass concrete in the dam wall. It was suffering from an alkali-silica reaction (ASR), sometimes referred to as swelling of concrete in less technical terms, which was threatening the operation of the floodgates and other hydromechanical facilities. Simply put, the concrete was expanding.

In the 1950s aggregates for large dams were not tested for alkali-silica reactivity and more than 100 dams worldwide have suffered from the same phenomenon. Kariba’s coarse aggregate was crushed local gneiss, with a maximum nominal size of 200mm. Washed Zambezi river sand was used as the fine aggregate, and the Ordinary Portland Cement (OPC) used came from the Chilanga Cement Works, now Lafarge, in Chilanga. The alkali levels in the cement was not measured, which was common in the 1950s. The amount of cement used in the construction of the Kariba Dam, not to mention the cement used on the construction of a township on the Zimbabwean side, initially for housing construction workers, is mind boggling but when one looks at Chilanga town today, there is no evidence that the town ever benefitted from any of this money generated by the Chilanga Cement Works.

The amount of cement in the concrete (cement content) was relatively low, as was normal for large mass concrete dams. Most of the more than one million cubic metres of concrete in the dam wall had a cement content of 195kg/m3 and a water/cement (w/c) ratio of 0.6. A 3m thick layer on the upstream face had its cement content increased to 255kg/m3, with w/c ratio reduced to 0.5 for enhanced durabil-ity. For an average cement content of 200kg/m3, the one million cubic metres of concrete contained in the dam wall translates into 200 million kg of concrete or 40 million x 50 kg bags of cement! Even with these low cement contents, the risks of cracking due to the build up of heat resulting from the heat produced from a chemical reaction in the mixing of cement, aggregate and water (cement hy-dration) in the size of the planned amount of concrete poured at a time for Kariba required special at-tention by the Italian main contractor, Impresit.

Concrete was poured in blocks limited to 15m wide, 2.3m deep and up to 20m long. Cooling pipes were cast into the blocks and chilled water from a chiller plant on site circulated until the concrete had hardened and cooled. Finally the joints between the individual blocks were pressure grouted with ce-ment mortar to form a monolithic dam wall.

ASR was first detected in 1989 during a routine inspection and it is, therefore, not a new phenomenon as recent media reports seem to suggest.  Quartz embedded in the gneiss coarse aggregate was blamed, and extensive monitoring equipment was gradually installed over subsequent years. This swelling of concrete affected the operation of the floodgates, which was worked upon. A recent survey indicates that the dam was 80mm taller than when it first opened, a degree of expansion that seriously threatens the operation of the vital floodgate mechanisms once again.