Morelos Dam

On Thursday the U.S. Bureau of Reclamation began diverting salty irrigation drainage water from the Wellton-Mohawk Irrigation and Drainage District into the Colorado River bed below Morelos Dam on the U.S.-Mexico border, while the canal which normally carries it to the river's delta on the Gulf of California is repaired. This marks the first time since 2014 that a significant amount of water will be discharged into the river bed here.

Repairs began this week on the U.S. Bypass Drain, the canal which carries irrigation drainage water from eastern Yuma County to the Cienega de Golfo de Santa Clara on the Gulf of California. 

The concrete-lined channel has been taking the discharge water from the Wellton-Mohawk Irrigation and Drainage District, as well as some from the Gila Valley, to the Gulf of California since the 1970s, and the section which crosses the border needs maintenance, said Doug Hendrix, spokesman for the U.S. Bureau of Reclamation. 

 “What’s going to happen is they’re going to clean the existing sediment out of the channel, and they’re going to look for damaged sections, areas which are cracked or rotored away and replace those, and then work on the headwalls and sidewalls, those types of things,” he said. 

The repairs, expected to take three to four months, will affect the Colorado River both at the base of Morelos Dam and at the wetlands on the gulf, as one location gets the water the other is accustomed to having. 

“Because Reclamation is doing these repairs on the bypass canal, they have no place else to put the water, so they have a turnout from that bypass canal into the river, just below the dam, and they can leave it there because it doesn’t mix with the water Mexico is taking for its farmers,” said Jennifer Pitt, Colorado River program director for Audubon. 

The irrigation discharge water’s high salt content is the reason it’s transported separately instead of allowed to flow back into the river, and it is not suitable for humans to drink or swim in. Warning signs will be posted in the area south of Morelos Dam, where the water will be diverted.

The bypass drain has been transporting the irrigation return water to the gulf since the 1970s, because the water was increasing the salinity of the water being diverted by Mexico for agricultural use, under the terms of a treaty signed in 1944. 

The Cienega wetlands southeast of San Luis Rio Colorado, Son., were an unintended consequence of the bypass canal, which brought water back to a section of the mostly dried-out Colorado River delta. Today it covers about 25,000 acres and is part of the Mexican national park system.

It serves as important habitat for numerous species, including endangered ones like the Yuma Ridgway’s rail and desert pupfish, Pitt said. The potential effects of depriving the wetlands of one-quarter to one-third of its annual water flow are unknown. 

“There are a lot of eyes in particular on the Yuma Ridgway’s rail, because it is endangered and there are some studies which have estimated that 70 percent of that bird’s whole population is at the Cienega,” Pitt said.

“There’s also new work being done to see how much those birds move around, do they migrate,” she added, with Audubon working with the University of Idaho to fit the birds with radio collars, to monitor their reaction to the decreasing water level. 

“Will they move somewhere else in the Cienega? Will they fly somewhere else? We don’t know. We’re going to learn some things, about the birds,” she said. 

The Cienega is also popular with outdoor enthusiasts, and has a boat dock near the primary port of entry for visitors, Pitt said.

“I honestly don’t know whether the water level will drop to where that dock can’t be used anymore, or whether that will be fine,” Pitt said. “So I don’t know whether that major point of recreational access will be interrupted.” 

Flows in the bypass drain were interrupted for a period of eight or nine months back in the early 1990s, so the fact the wetlands survived that period is a good sign, she said. 

About 90 miles to the north at Morelos Dam, the irrigation drainage water which normally goes straight to the wetlands at the gulf will instead be diverted to the “Limitrophe” (a French word meaning “border”), the 30 miles of the river which form the border between Arizona and the Mexican state of Baja California to the west.

The Cocopah Indian Tribe and BOR have been working for about 10 years to reclaim this part of the river from salt cedars and other invasive species and plant native cottonwood, willow and mesquite trees. A standing body of water extends about 7 to 10 miles south in the river channel from the base of the dam.

“(More) water in the river channel, you’d think that would be a good thing,” Pitt said. “But the plants that grow on the river channel are different from the plants that grow out in the Cienega.

“And particularly the plants that are of the greatest interest as habitat, particularly the area which has been restored under the U.S.-Mexico agreement, those plants are not particularly salt-tolerant,” she said. “So there was a question about whether this water would help or harm, and we just don’t know.” 

The saline drainage water isn’t expected to reach the river banks where the trees are growing, but it will eventually get absorbed into the groundwater table, which does come into contact with them.  

“And the groundwater is going to come into more contact with the tree roots, and we don’t know, when you add a somewhat saltier water on top of a groundwater which is not as salty, does it mix? Does it not mix? We don’t know. 

“This water has gone into the river channel before, but I don’t think it’s ever been studied. So we’re going to learn a lot, and that’s a good thing,” she said.

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