By KEVAN WILLIAMS

A 2013 aerial view of the Morelos Dam on the Colorado River. Mexico is in the background. Photo: Bureau of Reclamation.

The once expansive and vibrant Colorado River Delta has been dry for a long time. Most of the river’s water is currently captured and siphoned off at numerous upstream dams, leaving empty riverbeds and dry land where once there was a vast estuary. But as part of an agreement between the United States and Mexico known as “Minute 319,” a spring pulse flow has returned the dry Lower Colorado River to life, at least temporarily. The pulse flow is an artificial release of water from upstream dams, designed to mimic the sustained high flows of a snow melt or significant rainfall. More than 100,000 acre-feet of water is now moving down the old river channel, making steady progress toward the sea.

Although occasional high flows have washed down the river, for many decades it’s been largely dry, with devastating ecological consequences. Invasive plants such as tamarisk (also known as salt cedar) have been creeping into the region, taking advantage of changing conditions, and native species have struggled to hold on.

Morelos Dam in 2014, peak flow. Photo: U.S. Border Patrol.

But efforts are under way to change that, and those will be supported by the pulse flow. “You have five sites in Mexico and one in Arizona that are part of an active restoration project,” says Jack Simes, the area planning officer for the Bureau of Reclamation’s Southern California Area Office. “They’ve got all these seedlings that they’ve put in place, and the intent is to stimulate these seedlings with a freshening flow,” he says. Those seedlings include native cottonwood and willow trees.

Research accompanies this effort. “They’ve got a number of monitoring stations set up,” Simes says. Those stations will track groundwater depth and soil moisture. “They measured it before the water got there, they’re measuring as it gets there, and they’ll measure it after [the pulse flow ends],” he says.

“It is a one-time event at this point,” Simes says, but Minute 319 also calls for ongoing negotiations between the United States and Mexico. The goal is to develop a long-term plan to revive the delta. “Following this pulse flow, the intent is to get a base flow going,” Simes says.