The project that would become the Orange-Fish River Tunnel was conceived as one half of an inseparable pair. A dam had to be built across the Orange River to capture the water, and a tunnel had to be driven south to deliver it. Neither piece of infrastructure served any purpose without the other. The Gariep Dam, completed in 1971, provided the reservoir. The tunnel, running due south from the dam's shore at Oviston to the Teebus Spruit outlet, provided the conduit. Together, they formed the Orange-Fish Water Scheme, diverting water from the Orange River into the Great Fish River and onward to irrigate thousands of hectares of Karoo farmland that had suffered chronic shortages for decades. The arid landscape, where existing dams had been losing capacity to heavy silt deposits, finally had a reliable supply.

Before a single drill bit touched rock, the builders constructed three towns. Oviston went up at the tunnel's northern end. Mid-shaft occupied the Suurberg plateau, roughly 180 meters higher than either end. Teebus anchored the south. Each included a clubhouse, tennis courts, a community hall, primary school, and clinic -- the infrastructure of daily life for the workers and their families who would spend nearly a decade underground and above it. Oviston also housed a power station and an 80-kilometer transmission line to electrify the tunnel works. These were not camps. They were communities, purpose-built for a project with a definite end date. When the tunnel was finished, the towns lost their reason to exist.

The tunnel's finished diameter is 5.35 meters, lined with 9 inches of mass concrete. Every meter was excavated by the drill-and-blast technique -- no tunnel boring machines, just explosives and human judgment. The lining process ran on a punishing weekly rhythm: concrete arrived Monday morning and poured without stopping until Saturday afternoon. A specially formulated mix containing 50% pulverised fuel ash allowed the concrete to remain workable for up to six hours after mixing, while accelerators let crews move the travelling shutter after just eighteen hours of curing. The shutter advanced roughly 300 meters per week. At various points between 80 and 380 meters below the surface, workers encountered hazards that no schedule could anticipate. South of Shaft 2, a drill punctured a water-bearing fissure that flooded a mile of tunnel within 24 hours. On the plateau section, a drive intersected a pocket of methane gas that ignited and burned for three months.

The contract documents anticipated one construction fatality for every mile of tunnel. That grim arithmetic proved roughly accurate. The Inlet section, built by a French-Italian-South African consortium called Batignolles-Cogefar-African Batignolles, recorded 17 deaths, nearly all in railway operations rather than tunnelling itself. At each tunnel entry, workers placed a small statue of Saint Barbara, patron saint of those who use explosives -- tunnellers, miners, and artillerymen -- in a carved alcove. The Plateau section, contracted to Orange River Contractors, suffered 34 fatalities across its three deep vertical shafts. The Outlet section, built by a South African-Italian joint venture, completed the path to the Great Fish River. In total, 51 workers died building the tunnel. The project's chief design engineer, Sir Alan Muir-Wood -- known as 'the father of modern tunnelling' -- oversaw the work alongside Barry Kidd, the senior site engineer, who died young before construction was finished.

The tunnel's intake tower at Oviston, on the south bank of the Gariep Reservoir, is an unusual structure. Seen from above, it is shaped like a four-leaf clover, with each lobe containing an inlet gate at a different depth. This design allows operators to draw water from whichever reservoir level offers the best quality at any given time, adjusting for seasonal changes in temperature, sediment, and algal growth. Each of the four inlets can be sealed independently, permitting the entire tunnel to be dewatered for maintenance without draining the reservoir. The tunnel itself descends on a self-cleansing gradient of 1 in 2,000 from north to south, steep enough for the flow to prevent sediment buildup, gentle enough to control the water's speed. Its maximum throughput is 54 cubic meters per second -- enough to transform the Eastern Cape's agricultural prospects and supply water as far as Port Elizabeth.