Gatun Dam - Construction

Construction

As described in History of the Panama Canal, the canal effort was begun by a French company (La Societe International du Canal Interoceanique) in 1883 to 1889. With poor exploration of the options and with poor information of the costs the French company planned to construct a sea-level canal linking the two coasts. They initially thought they could do this for about $120 million. After spending about one billion Francs (about $300,000,000) losing about 22,000 workers and going bankrupt the French effort essentially ceased. A sea level canal would not have required the dam to be built but would have still required extensive provisions made to accommodate the ever changing Chagres River flow. When the United States took over the 10 miles (16 km) wide Canal Zone and resumed building the canal on 4 May 1904 almost two years were spent in infra-structure preparation, mosquito abatement (the newly discovered vector spreading Yellow fever and Malaria), Panama Railroad improvements and planning before the work got up to full speed. After reviewing the options and costs, in 1906 a lock-based canal was decided upon and agreed to by President Theodore Roosevelt.

Even before the lock canal decision was made, Major George Washington Goethals (United States Army Corps of Engineers), the chief engineer from 1907 to 1914 of the construction effort, had already carried out an investigation under John Frank Stevens (chief engineer, 1905–1907) into determining the suitability of the land at Gatun for the building of a large dam there. Extensive test borings were made to determine the suitability of the land, and pressure tests were carried out on the material to be used in construction to determine its durability.

The Gatun Dam serves two important purposes: it controls the ever varying Chagres River and creates Gatun Lake. The lake at about 85 feet (26 m) elevation provides an elevated path for ships across most of the Isthmus of Panama including through the treacherous V shaped Gaillard Cut (Culebra ship Channel). This saved excavating literally millions of cubic yards of material that would have been necessary for a sea level canal. The lake height is regulated by spillways that control the water flow out of the dam to obtain an almost constant height in wet or dry seasons. The lake also acts a massive reservoir to work the locks on both the Pacific Ocean and Atlantic Ocean ends of the canal and provides via hydro-electric generators about 6 MW of electrical power needed to run the locks and dam. After finishing the dam and filling Gatun Lake it was dredged where necessary to obtain a clear ship channel across the lake.

The Gatun location was in most ways ideal for a dam; upstream of the dam site the hills enclosing the Chagres River opened very wide around the area that is now Gatun Lake. Over a narrow gap the hills close to a relatively narrow gap with a natural rock-based channel in the centre. This allows a moderately sized dam to enclose a huge body of water, which both provides passage for ships across much of the isthmus, and provides a reservoir of water with which to operate the locks. The central hill was the ideal solid base for the construction of the concrete spillway and its dam, the main part of the dam being earth. The only problem was the huge scale of the dam required massive rock and dirt fill that was provided by about 100 trainloads of waste rock deposited into two parallel walls of waste rock about 2,700 feet (820 m) apart every day for several years from the Culebra Cut (now called the Gaillard Cut) and the Gatun Locks excavation. Between these waste rock walls an impervious core was created by using a hydraulic fill technique which pumped millions of cubic yards of clay material and water into the area between the rock walls. This fill was made by digging up the soft clay present in the valley below where dredges excavated the clay and water and loaded it into pumps that delivered it up into a pond created between the inner and outer walls of the dam. The pumped mixture was allowed to sit until the clay settled out with the excess water being drawn off and pumped back downstream. This dried and hardened material created a solid core of "natural" cement at the core of the dam.

After the dam was built to its desired height, the entire up-stream side was armoured to prevent wave action damaging the dam by placing large boulders on the face, particularly where there is strong wave action.

The dam contains some 17,000,000 cubic metres (22,000,000 cu yd) of material and is about 2,700 feet (820 m) wide at its base, about 105 feet (32 m) high and 7,500 feet (2,300 m) long. The dam weighs some 27,000,000 long tons (30,000,000 short tons). It covers 1.17 square kilometres (290 acres) of ground, and contains enough earth and rock to build a wall 1½ metres high and 29 cm thick (or four foot eight inches high and a foot thick) around the earth at the equator.