Lake Mead: How Low Can You Flow?

It was a sweltering 108-degree June day when I landed in Las Vegas, Nevada. I was there to give a talk about water and sustainability at the University Council on Water Resources 2015 conference. While I was there, my colleagues and I took a quick tour of Hoover Dam and Lake Mead. The dam holds the Colorado River to form the lake, the largest reservoir in the US.

Lake Mead supplies 90 percent of Las Vegas' drinking water. I had just listened to a discussion about the future of drinking water in the city, given by Zane Marshall, the Director of the Resources & Facilities Department of the Southern Nevada Water Authority/Las Vegas Valley Water District. Let's just say that ensuring the future of drinking water in the city will be a definite challenge.

The level in the lake is low, as evidenced by the brightly colored "bathtub ring" left on the walls of the canyon as the water level has receded. I was surprised to see how wide the ring has gotten. (Check out the photos of Lake Mead, Hoover Dam and Las Vegas in the slide show.) In 2006, I went to Las Vegas with family and we took a drive to the dam. The ring seemed wide then, but it's definitely grown.

It wasn't always so low. Lake Mead hit a record high elevation of 1,220 feet above sea level in the summer 1941, just five years after completion of the dam, but the level has fluctuated and been in decline ever since. The entire Colorado River Basin has been in a drought for 15 years, causing water levels in the reservoir to plummet.

On June 23rd the water's elevation level dipped below 1,075 feet, a level that, if maintained, could have triggered a call for a water shortage by the US Bureau of Reclamation, the agency that manages the Colorado River system storage reservoirs. Fortunately, snow melt from heavy spring storms in the Rockies brought the water level back up, so a shortage won't be declared this year - and maybe not even next year.

A lake level of just 1,075 feet is also problematic because it is only 25 feet above the water intake tunnel for the city of Las Vegas, which relies so heavily on Lake Mead. To ensure sufficient future access to water from the lake, the city is nearing completion of a new tunnel that will draw water from an elevation level of 875 feet, giving the city access to cooler water from a deeper part of the lake (cooler, deeper water generally has a higher quality). The city will still get water even if lake levels fall below what's known as "dead pool" or the level below which water would no longer flow past Hoover Dam.

Constructed between 1931 and 1936, during the Great Depression, Hoover Dam was originally built for flood control and to provide hydroelectric power and irrigation water from the Colorado River. The scale was massive - such a large concrete structure had never been built before. It took 3,250,000 cubic yards of concrete to build, and employed thousands of workers.

The Colorado River runs for 1,450 miles and drains a watershed that encompasses seven US and two Mexican states. In addition to Nevada, downstream users that could eventually lose water include California, Arizona and northern Mexico. The Colorado River Compact controls use of the river, which is generally considered to be over-allocated, meaning there is more water on paper than there is in the river to distribute.

Early on, the city of Las Vegas realized that Lake Mead could provide a stable source of drinking water to the rapidly growing city. In total, the Colorado River provides water to nearly 40 million people for municipal and agricultural uses, seven National Wildlife Refuges, four National Recreation Areas and 11 National Parks. It also can provide more than 4,200 megawatts of electricity from hydroelectric facilities like the Hoover Dam. It is so overused that the river no longer reaches its delta in the Gulf of Mexico.

Standing in the hot sun and looking out over the lake, I felt a sense of urgency. Like Lake Mead, the Colorado River's survival has never been more threatened, and there has never been more of a need for conservation and efficiency from all of its users. People throughout the Southwest are just beginning to understand that all of their actions - from the water they drink, to the food they eat, to the energy they consume - have implications for the Colorado River. This is important because people who understand their own water use are better able to understand decisions made at the municipal, state and river basin level, and why sometimes-drastic measures have to be taken to limit water use.

GRACE's Water Footprint Calculator is an easy and fun way for anyone in the US to learn about his or her water use. It's also a great first step in understanding the water scarcity that everyone in the Southwest faces. There are plenty of tips at the end of the Calculator that will help you find out how to lower your water footprint, a critical action if we're going to learn to live with the "bathtub ring," and try to use the Colorado River - and all of our other rivers - sustainably, now and into the future.