Hoover Dam Hydropower Assignment

Background: Hoover Dam is one of the Bureau of Reclamation’s multipurpose projects on the Colorado River. These projects control floods; they store water for irrigation, municipal, and industrial use; and they provide hydroelectric power, recreation, and fish and wildlife habitat.

The Dam is a concrete arch-gravity type of dam, in which the water load is carried by 1) the sheer weight of the dam (gravity), and 2) the arch-shape pushing back on the water. The first concrete for the dam was placed on June 6, 1933, and the last concrete was placed on May 29, 1935.

The dam was built in “blocks” of concrete, varying in size from approximately 60-ft square at the upstream face to about 25-ft square at the downstream face. Adjacent blocks were locked together by concrete “keys” to keep them from sliding past one another. After the concrete was cooled, a cement and water mixture called grout was forced into the spaces to form a monolithic (one-piece) structure.

There are 17 main Francis turbines (basically big waterwheels) in the Powerhouse. The water is channeled to the turbines through four penstocks at a speed of about 85 mph. The “nameplate” rating of the powerhouse is 2,080 MW, which would only be reached if all turbines were running at full speed, which they never are. In practice, the power generated is only a small fraction of this.

Map: The Colorado River system drains 7 States, and contains 15 dams along the main river.

Below: “Black Canyon” was chosen for the dam site, the steep walls providing good anchorage for the dam.

Below: Placing the concrete in “blocks” allowed it to cool faster. Grout was placed between the blocks.

Below: Cutaway “side views” of the dam. Water elevation behind the dam is 715 feet.

Hoover Dam Hydropower Assignment (just turn-in this portion!)

Name and date submitted (3 pts):

Answer the questions below, showing all your work. Turn-in (this portion only) as an email attachment.

(6 questions, 100 points possible)

Problems:

1. Calculate the water pressure at the bottom of the dam when the water level is at 715-ft. a. In pounds per square inch (lbs/in2)

b. In Pascals (N/m2)

2. Calculate the force in pounds due to water pressure pushing along the base of the dam in a strip 1 ft. high x 290 ft. wide.

3. According the table below, Lake Mead contains 35,703 million cubic meters of stored water. a. Convert this to gallons.

b. Convert this to cubic feet (ft3).

4. According to the figure below, Hoover Dam handles about 13,000 ft3/s flowrate on average (you can verify here https://www.usbr.gov/lc/region/g4000/hourly/rivops.html)

a. Convert this flowrate to m3/s

b. Referring to the table above (Reservoir Volumes), how many years (report your answer to the 1/10ths place) would it take to empty Lake Mead at this rate, if no water flowed into the Lake during this period? In other words, how many years’ capacity are stored in Lake Mead?

5. Using the online Hydro-Power Calculator (https://www.engineeringtoolbox.com/hydropower-d_1359.html), estimate the theoretical power in MW available from Hoover Dam. Use the “head” from question #1 above (you may first need to convert it to meters!), and the “volume flow” in m3/s from question #4. Use a realistic Hydropower “efficiency” – you may want to research this.

6. How does your theoretical power calculation from question #5 compare with the “nameplate rating” of 2,080 MW for Hoover Dam? What does this suggest about the original design of the Powerhouse?