Facts and Figures
- Dam Type: Concrete gravity-arch
- Length: 1244 ft (379 m)
- Height: 726.4 ft (221 m)
- Base width: 660 feet (201m)
- Crest width: 45 ft (14 m)
- Volume: 3,250,000 cu yd (2,480,000 m3)
- Discharge capacity of spillway: 400,000 cu ft/s (11,000 m3/s)
- Construction began: 1931
- Construction cost: $49 million
- Reservoir created: Lake Mead
- Reservoir capacity: 35.2 km3 (28,500,000 acre·ft)
- Catchment area: 167,800 sq mi (435,000 km2)
- Reservoir surface area: 247 sq mi (640 km2)
- Maximum water depth: 590ft
- Number of workers at peak: 5,251
- First use of hard hats? High scalers took cloth hats and dipped them in tar, allowing them to harden. Initially called “hard boiled hats”.
I found this diagram fascinating. I hope you enjoy it too. Courtesy of WikiMedia. The upper cofferdam was wider then the dam itself! It was 750-ft wide, 96-ft tall and constructed of 650,000 cubic yards of material.
Foundations and Scaling
The foundations of the dam needed to be cleaned of all eroded soil and sediment. 1.5 million cubic yards of material was removed, and the weathered rock was scaled off to fresh rock. Holes up to 150-ft deep were drilled to grout the foundation of the dam to prevent the creation of uplift pressures. And here is something I didn’t know (from Wikipedia):
The workers were under severe time constraints due to the beginning of the concrete pour, and when they encountered hot springs or cavities too large to readily fill, they moved on without resolving the problem. A total of 58 of the 393 holes were incompletely filled. After the dam was completed and the lake began to fill, large numbers of significant leaks into the dam caused the Bureau of Reclamation to look into the situation. It found that the work had been incompletely done, and was based on less than a full understanding of the canyon’s geology. New holes were drilled from inspection galleries inside the dam into the surrounding bedrock. It took nine years (1938–47) under relative secrecy, to complete the supplemental grout curtain.
Hoover Dam Bypass Project
A joint project between the Arizona and Nevada DOT’s, the rerouting of US 93 away from the crowded Hoover Dam is nearing completion. The showpiece of this so-called “Hoover Dam Bypass” project is of course the Pat Tillman Memorial Bridge spanning the Colorado River, just downstream of the canyon. I know a few of the folks that worked on engineering geology and geotechnical aspects of the bridge, I’ll try to get some more info to share at some point. Let’s just say the photos I’ve seen of the investigations are pretty spectacular (see links below for a couple).
Declining water levels could spell major problems
Even as the Country is celebrating the 75th Anniversary of the dedication of the Hoover Dam, it’s ability to generate electricity for a power-hungry southwest may be in jeopardy because of declining water levels. According to an article at Circle of Blue, the reservoir is only about 41% full, having declined 130-ft since 1999. If the USBR projections are correct, next month the water levels will reach levels not seen since it was filled in the 1930s. The article goes into details about what the low levels could mean to the turbines and the power generating infrastructure of the dam, a very interesting article.
Hoover Dam Stories and Links
- Hoover Dam, 3.25-million-yd. marvel, turns 75 – Source: ConcreteProducts.com
- Bureau of Reclamation: Lower Colorado Region – Hoover Dam
- Hoover Dam Bypass Project – Source: Slope Indicator
- Hoover Dam Bypass – Design Activities – Source: HooverDamBypass.org
- Directional Drilling for rerouting power cables for new Hoover Dam Visitor’s Center – Source: Layne Christensen Company
- Hoover Dam FAQs – Source: USBR
- Hoover Dam – Source: Wikipedia