By Nicolette Scrooby

A massive water tower expected to provide high-lying areas in Beacon Bay and adjoining areas with water for the next 50 years is to be completed within the next two months.

Civil engineers said yesterday the mammoth 640 ton water bowl still had to be raised by nine metres ? a job that should be completed by tomorrow, said consulting engineer Bill Godfrey.

The structure will eventually tower 36 metres into the air ? the equivalent of about 14 storeys ? above the Nompumelelo settlement near Beacon Bay.

Design engineer Tony du Preez said the idea behind the elevated tank was to use gravity to create the water pressure.

"Once the water is pumped into the bowl at the top, you are essentially saving costs by letting gravity work for you," Du Preez said. Godfrey said the final part of the hoisting was the trickiest as it had to be done in one operation.

Construction of the tower started in February last year. Engineers explained yesterday how it was all put together.

The reinforced concrete base ? called a pile cap ? is 1,5m thick and is founded on 36 reinforced concrete piles bored into bedrock.

Once the base was completed, construction was then concentrated on a shaft, four metres in diameter, that was cast into sections which took three months to construct to its full height.

While the shaft was being cast, work had also started on the water retaining bowl with its 600 000 litre capacity. The shaft is 19m in diameter and seven metres high.

On the ground, a massive scaffolding was used to support the bowl while it was cast, using reinforced concrete.

Site engineer Kolin Pillay said the decision to opt for this particular construction method was due mainly to safety considerations and availability of scaffolding material at that particular point in time.

"The higher up the shaft you go, the more windy it gets, and working conditions become risky on bad weather days," he said. Yesterday around midday, for example, wind speed near the top of the tower was about 18km/h, while on the ground it was only about 5km/h.

The 640 ton bowl is hoisted up the shaft at roughly one metre per hour using a post tensioning jacking system and steel wire cables.

Monitoring of the hoisting process is very comprehensive with regular checks carried out to ensure the bowl remains level and no component is overstressed.

"You cannot afford the smallest mistake when building a structure of this nature. You have to do numerous calculations, then get someone else to check your calculations over and over.

"You have to take care and reinforce the tower so that it will be able to withstand extreme wind conditions," said Godfrey.

Du Preez said the water tower was part of Buffalo City Municipality's forward planning procedure. Once completed in the next two months, it would kick in to operation immediately.