|Fig. 1: Lake Mead water levels. [1-6] (Source: N. Brackbill)|
The Colorado River Basin is entering its sixteenth year of drought.  Tree ring studies suggest that this is its fourth worst drought in the last 1000 years.  The western drought has caused severe wildfire conditions and affected food production, not to mention induced guilt in the minds of every Californian taking a longer than normal shower. However, the drought is having another serious and rarely discussed side effect: reduced hydropower from the Hoover Dam, which is operating at around 75 to 80 percent of its full capacity. [2,3] Overall, hydropower generates 52% of renewable energy and 6% of all the energy in the United States, and is the cheapest source of electricity for the Southwest, at 1.83 cents per kilowatt-hour. 
The Hoover Dam was constructed from 1931-1935, primarily to regulate the flow of the Colorado River, which marks the border between Nevada and Arizona, as well as create a reservoir, Lake Mead. The power plant was constructed in 1936 to harness the energy of the flowing water. The basic idea behind hydropower is the same as wind power: stick a turbine into a material (air or water) that is flowing. The flowing material causes the turbine to spin, transforming the mechanical energy of the flowing material into mechanical energy of the turbine spinning, which is then used to spin a magnet near a copper coil, creating electricity.
Hydropower plants get water to flow quickly by using the difference in gravitational potential energy between the upper part of the river, before the dam, and the lower part of the river, after the dam. In other words, the water is allowed to fall down a pipe, and picks up a lot of speed, which is eventually used to turn the turbines at the bottom of the dam, which for the Hoover Powerplant is currently 430 feet below lake level.  The amount of energy generated depends on the pressure of the water falling down this pipe.
However, as water flows out of Lake Mead, through the turbine, and downstream, the water in Lake Mead must be replenished, and that is not happening because of the drought. In fact, Lake Mead is running a water deficit of 400 billion gallons per year, causing the water level in the lake to drop by 130 feet since 1999. [3,5] It reached an all time low level of 1074 feet in May 2016, only 37% of full capacity. [1,6] The lake was last at capacity (1225 ft) in 1983. 
These low water levels cause the pressure of the water falling down the pipe to decrease, meaning not as much power can be generated from the plant. In fact, if the water levels get below 1050 feet, the plant will have to be shut down.  The low water pressure causes the turbines to rattle, and can cause serious damage if not shut down. These turbines are being replaced by newer ones that could keep the plant operational down to 950 feet.  The lowest intake pipe is at 900 feet, below which no water will be able to drain out of Lake Mead. Fig. 1 compares the current levels to these milestones.
The drought in the Western United States has many negative consequences. While the drought's effect on hydropower, one of the United States' most prominent sources of clean and renewable energy, is not emphasized, it is clear that action needs to be taken to make sure the people of the Southwest United States get both the water and power they need from the Colorado River Basin.
© Nora Brackbill. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 K. Ritter, "Study: Next US President Must Act Fast on Colorado River," U.S. News and World Report, 31 Oct 16.
 T. C. Frankel, "Western Drought Steals Clean Energy Along With Fresh Water at Power Plants," Washington Post, 26 Apr 15.
 C. Dineen, "Drought and California's Role in the Colorado River Compact," J. Legis. 42, 211 (2016).
 M. Weiser, "The Hydropower Paradox: Is This Energy as Clean as It Seems?," The Guardian, 6 Nov 16.
 C. Harvey, "'Climate Change Is Water Change' - Why the Colorado River System Is Headed For Major Trouble," Washington Post, 19 Aug 16.
 B. Finley, "Feds May Order First Cuts in Water From Colorado River," Denver Post, 5 Nov 16.