Features of the Dam

This photo shows one of the drilling jumbos ready for action.

The government set aside 2565 days (a little over seven years) for the actual construction of the dam. This may seem generous, but in actuality such an enormous undertaking might have taken up to ten years. To keep to the tight schedule, Six Companies would be fined $3,000 for every day a project wasn’t completed on time.

Diverting the River

Hoover Dam was to be built directly in the path of the Colorado River. In order to do this, the river had to first be diverted. Four tunnels, two on each side of the river were to be drilled and blasted into the solid rock of Black Canyon. To accommodate the volume of the river, the tunnels would have to be massive, each with a diameter of 50 feet once lined with concrete.

It would have been folly in the time-consuming project if the drilling had been done piecemeal. Foreman Frank T. Crowe invented a contraption that could provide for up to thirty drills. Trucks were fitted with metal frames and platforms on which workers could stand. Once arranged on this new invention, a jumbo, men would drill long holes and then insert blasts into these holes. After the men moved a safe distance away, the dynamite was detonated, carving away pieces of the rock.

One of the most dangerous aspects of the job took place during this phase of construction. The dam needed to be anchored solidly to rock clean of defects and debris. Men were employed to pick and drill away at the surface of the canyon walls to ready it for the dam. Called high scalers, these workers were suspended high above the canyon floor from wooden seats attached to ropes. Because it was so dangerous, the job of a high scaler was also the highest paid laborer position during the project.

By September of 1931 the excavation of all four of the diversion tunnels was well underway. By drilling, blasting, and clearing, the process moved ahead 15 feet at a time. Once cleared of all lose rock, the tunnels were lined with concrete. Large forms were moved down the tunnels, allowing for each section to be poured separately.

In November of 1932, the tunnels were completed and ready for the diversion of the river.

The Dam

From a bridge suspended over the path of the river, trucks deposited tons of earth and debris in the path of the river. For almost 24 hours straight, the dumping continued until finally the river was blocked and forced to make its way through the diversion tunnels. After the river was diverted, men worked day and night to excavate thousands of years of sediment to reach the riverbed’s bedrock.

When the bedrock was fully unearthed, it was time to begin construction of the dam itself. It would be impossible to pour the concrete in one continuous stream. Instead, the dam was poured in column-like sections with spaces pumped full of grout. Concrete was made on site and carried to the dam via railways. A system of high wire cables and pulleys picked up the concrete buckets and swung each one over to be positioned and released from its container by waiting workmen. After flipping the latches that held the bucket closed, workers jumped back to avoid the torrent of concrete. Puddlers stomped through the concrete making it even and smooth. At first, the process of pouring concrete was slow and awkward. But as workers became more familiar with the process and machinery, it became much smoother and progressed at an incredible rate.

Because concrete gives off heat as it dries, Hoover Dam engineers needed a way to cool the dam. A system using pipes and refrigerated river water was developed. Cooled water ran through pipes inside the concrete blocks. When the block was finished, grout was poured into the pipe and sealed off.

The Spillways, Intake Towers, and Powerhouses

Located near the top of the dam, the two spillways were designed to manage possible overflow from the river. In the event of a flood, if water gets too high instead of going over the dam the water is forced into the spillways.

Work on the spillways began in 1932. Like the riverbed, the spillway channels had to first be excavated and cleared of all earth. Smaller tunnels were also excavated in order to connect the spillways with the diversion tunnels.

In addition to the spillways, workers also had to construct four intake towers. The intake towers, via more tunnels drilled through the canyon, would supply water to the powerhouses. The twin powerhouses would rest at the base of the downstream side of the dam, machined by various turbines and power generators.