Tarbela Dam is one of the world’s largest earth and rock-filled dams and the greatest water resource development project which was completed in 1976 as a component of the Indus Basin Project. The Dam is located on the river Indus known as the “Abbasin” or the father of the river at a distance of 130 KM (50 Miles) to the North West of Islamabad, in Distt Sawabi KPK.
Emerging from the land of glaciers on the northern slopes of the Kailash ranges, some 17,000 feet (5182 meters) above sea level, the river Indus has its source near Lake Mansrowar in the Himalayan catchment area. It flows over 1800 miles (2900 k. meters) before it outfalls into the Arabian Sea draining an area of about 372,000 square miles (964,261 sq. km). The World Bank accepted the Tarbela Dam Project as a part of the Settlement (Replacement) plan under the Indus Water Treaty in 1965. WAPDA has been entrusted with its execution on behalf of the Government of Pakistan. The construction of the Tarbela Dam was carried out in three stages to meet the diversion requirements of the river. In stage, I, the river Indus was allowed to flow in its natural channel while work was continued on the right bank where a 1500 feet (457 meters) long and 694 feet (212 meters) wide diversion channel was excavated and a 105 feet (32 meters) high buttress dam was constructed with its top elevation at 1,187 feet (362 meters). Construction under stage I lasted 2.5 years.
In stage II, the main embankment dam and the upstream blanket were constructed across the main valley of the river Indus while water remained diverted through the diversion channel. By the end of stage II, tunnels had been built for diversion purposes. The Stage II construction took 3 years to complete. Under stage III, the work was carried out on the closure of the diversion channel and construction of the dam in that portion while the river was made to flow through diversion tunnels. The remaining portion of the upstream blanket and the main dam at higher levels was also completed as part of stage III works.