The two photographs (below) show the Barrage in the course of construction across the Vaal River. This scheme will impound 13,633 million gallons of water at an ultimate cost of £5,150,000.
The site at which this work is being carried out is 25 miles down stream from the Vereeniging Railway Bridge, and it will conserve a permanent water supply for a distance of 40 miles along the course of the river, with a considerable length of the reservoir being upon the Vereeniging Estates Company's properties. The site was chosen as the most suitable after a survey of the bed of the river over a length of 130 miles.
The chief object of the scheme is to provide a permanent and reliable water supply to Johannesburg. It is estimated that there will be available for pumping to Johannesburg twenty million gallons per day for one year even if no new water should enter the reservoir. 1,800 million gallons are impounded and reserved for riparian owners of whom the Vereeniging Estates Company is amongst the largest. An Intake, Pumping Station and Mechanical Filtering Plant are
being constructed at a point about 1.5 miles below the Railway Bridge at Vereeniging. The Pumping Station is being constructed at Vereeniging so that it may be adjacent to the Railway and the coalfields.
The Barrage consists of a series of steel gates installed between concrete piers. There are 35 piers and two abutments, each 8 feet thick, 35 feet long and 34 feet 6 inches high. There are 36 steel gates each 25 feet high, the clear opening being 30 feet; the gates are 32 feet 6 inches wide and weigh 26 tons each. With the balance weight, operating gear and other appurtenances, the total weight of the gear for each opening is about 100 tons. The pressure on each gate is roughly 300 tons when the reservoir is full.
The gates will be fully raised during flood periods. The average velocity during high flood is about 9 ft/secs. When the gates are raised to their highest position, there will be a clearance of 7.4 feet above the highest known flood level which was 26 feet 6 inches deep at the site of the Barrage in November 1917; the calculated discharge at that time was 183,000 cubic feet per second.