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A plan is in the works to try to bring the delta back to life.
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Frans Lanting / Corbis
Back on Course
The Colorado River’s delta is dying. Can a historic experiment bring back its waters?

By Cody Crane | for Science World

The Colorado River is the lifeblood of the American Southwest. It supplies water to more than 36 million people, has transformed the desert into farmland, and allows cities like Los Angeles, Phoenix, and Las Vegas to thrive. But quenching the region’s thirst for water has come at a price.

The mighty river once traveled all the way from Colorado’s Rocky Mountains to the Gulf of California. Now, dams harness the river’s water for human use. As a result, the river no longer reaches the ocean. Without water, the once-fertile delta at the river’s mouth has become dry and barren. But a plan is in the works to try to bring the delta back to life.

On March 23, engineers opened the Morelos Dam near the U.S.-Mexico border to release a temporary burst of water. This pulse flow allowed the Colorado River to reach the sea for the first time in 16 years. The surge mimicked natural spring floods that could help revive the river’s delta.

TAMING A RIVER

Nearly a century ago, seven states divvied up the Colorado River’s water. Each agreed to siphon off a specific amount each year for uses from drinking and bathing to irrigating crops. Later on, Mexico also got a share.

To manage the river’s resources, the U.S. government built a series of dams. The dams harness the river’s hydropower, generating electricity for the Southwest’s major cities. They also form a system of reservoirs, including the largest in the country, Lake Mead. These artificial lakes can store four times the river’s yearly flow.

“The reservoirs are like the river basin’s bank accounts,” says Taylor Hawes. She’s the director of the Colorado River Program at The Nature Conservancy, an environmental organization that works in more than 30 countries. Reservoirs provide a place to save up water for not-so-rainy days—like right now.

TAPPED OUT

When the Colorado’s water was originally parceled out, it was one of the wettest times on record for the river. But for the past 14 years, the Southwest has suffered an intense drought. And the area’s population continues to grow. Today, the river can’t provide enough water for everyone’s needs.

To stave off water shortages, states have been forced to tap into their “savings” and to rely more on groundwater trapped in soil and rock. It’s being rapidly sucked dry.

These approaches can help in the short term, but a new agreement between Mexico and the U.S. could improve how people share water resources. Under the agreement, Mexico will store some of its share of the Colorado’s water in Lake Mead and will receive less water when reserves are low. Those measures would boost water supplies upstream during dry times. In return, Mexico gets help restoring the delta—which would help bring back the birds, marine life, and other animals that once lived there. Tourism, fisheries, and the local culture would all benefit.

RESCUE PLAN

In wetter times, on and off since the 1960s, the Colorado managed to complete its journey to the sea. During those rare times, floods temporarily brought life back to the delta. Seeing the difference a little water could make gave scientists the idea for this year’s pulse flow.

“Just add water and you get an amazing recovery,” says Eloise Kendy, a hydrologist at the Nature Conservancy who worked on the pulse flow.

To make the pulse flow possible, Mexico gave up some of its share of the Colorado’s water, about 123 billion liters (33 billion gallons). That may sound like a lot, but it’s less than 1 percent of what would naturally flow into the river’s delta if there were no dams.

Kendy and other scientists had to figure out how to use that scant amount of water to the greatest effect. They considered the pulse’s timing, duration, and rate of flow. These factors affected the size of their engineered flood, how long it would last, and how quickly it would recede. If floodwaters were too high, they could swamp surrounding towns and farms. Too low, and they might not reach where needed.

Cottonwood and willow trees native to the delta rely on floods to reproduce. Scientists wanted the pulse flow to occur when the plants released their seeds to help new seedlings take root and grow. Over the next few years, researchers will monitor how native plants, wildlife, and groundwater supplies respond. If the pulse flow is successful, they plan to repeat it every five years.

The project serves as a model of how to manage rivers sustainably for both people and nature, says Kendy. “A lot of rivers in the West have problems. We used them to make the deserts bloom and build cities. We didn’t think about the environment,” she says. “But it’s possible to restore them. If we can do it in the Colorado River Delta, we can do it anywhere.”

This article originally appeared in the September 15, 2014 issue of Science World magazine. To find out more about Science World's great resources, click here.