The Colorado River met the sea Thursday for the first time in at least 16 years.
But it was just as much a case of the Gulf of California flowing upstream to meet the river as it was of the river reaching the gulf.
High tides from the gulf traveled 16 miles upstream of the river’s mouth to meet the river’s artificially induced “pulse flow” at around 3 to 3:15 p.m. Thursday, said Francisco Zamora, Colorado River Delta program director for the Sonoran Institute.
Zamora said he witnessed and photographed the event from a small aircraft, about 1,200 to 1,500 feet up. The jet was piloted by LightHawk Inc., an environmentally oriented flying service.
U.S. and Mexican authorities started releasing the pulse flow March 23 from Morelos Dam, at the international border, to try to restore the cottonwood and willow tree habitat along the river and to raise groundwater levels.
The river has flowed through the delta continuously since March 23. About 105,000 acre feet — enough for at least 200,000 households for a year — will have been released when the pulse flow ends on Sunday.
On Thursday, the river traveled in a channel a bit more than 30 feet wide, Zamora said. The tides had risen more than 15 feet above sea level.
The tides had to overcome a huge plug of sediment that had built up in the river channel for decades because river water that used to wash that sediment to the sea now flows rarely, after floods. Such floods haven’t occurred on the river since the late 1990s.
Here are some questions and answers on Thursday’s event. They were put to Zamora; Karl Flessa, a University of Arizona geosciences professor and co-director of the Delta environmental monitoring effort; and Jennifer Pitt, director of the Environmental Defense Fund’s Colorado River Project. Also interviewed was Karen Schlatter, project manager for the institute’s delta program.
Q. Why does this event matter?
Flessa: It may turn out that the volumes that reached the sea are so small that they will have limited ecological benefits. The symbolic value is great — as a reward for everybody’s efforts, and as a reminder that a river reaching the sea is a newsworthy event these days.
Zamora: The difference is that you have fresh water there. The water from the pulse flow will be mixing with seawater brought by the tides. The tides come with marine life, plankton. They can bring larvae of shrimp, even fish.
The tides bring sediments, also. You will have to do some on-the-ground work and remove some of the sediments in the river so the tides can meet the river more often and so the river can travel more downstream.
Q. What about the groundwater levels near the river and the cottonwood and willow seedlings planted in restoration areas?
Flessa: We know that the pulse flow has raised the water table. We know that it reached the prime restoration areas. We know that native vegetation has germinated in those areas (and elsewhere). We know that we have and will have learned a lot. Remember, it’s an experiment: about how we can use water efficiently for Colorado Delta restoration.
Zamora: At our Laguna Grande restoration site, 40 to 50 miles downstream of the dam, we have seen the germination of cottonwoods and willows. They may be an inch, an inch and a half or a couple inches in height. We have got 350 acres that are benefiting from the combination of pulse flow and on-the-ground restoration efforts.
Q. How are the trees doing compared with what you expected? Are they OK with the pulse flow now receding?
Zamora: Three weeks ago, our soil moisture sensor data showed there was more inundation of the soil than we had expected.
Schlatter: With cottonwood and willow seedlings, as the water recedes, the root of that plant can grow fast enough. ... We’ve had a slow enough recession of the pulse flow that the seedlings will survive until we can deliver more water to them.
I was just at the site (Thursday), and I did see some plants that look like they’ve grown since the last time I’ve seen them three weeks ago. And there’s more. The water levels are now going down in the river, but the germination is happening. We have a bunch of volunteers coming out (today) to plant 5,000 more trees.
Q. How will these seedlings make it through the summer?
Zamora: We have water rights to lesser, base flows in the river that will start delivery next week to the delta. The base flow has two components. The water has to irrigate trees we plant, and the water is sent to meander on the river to enhance them.
Schlatter: In just one summer, both cottonwoods and willows can grow up to a meter. In two years, they can grow up to 2 to 3 meters (or a little over 6 to 9 feet). In other restoration sites we have on the delta, we sprayed a mix of seed and water onto 5 acres of prepared land two years ago and 3 acres this year. The ones we did two years ago are 5 meters tall now.
Q. Jennifer, your group struggled for years to get this done. How do you feel?
Pitt: Well, right now there’s no water flowing below Morelos Dam. It’s not like you can say the river is continuously flowing to the gulf. But to the extent that people have had an interest in it, it’s something that feels inherently right about a river reaching the sea.
I can’t tell you if there’s great ecological value represented in this. I don’t expect this is going to have a substantive impact on commercial fisheries or estuary habitat. It’s significant in the cultural understanding of the river reaching its destination. We’ve been missing that connection for a long time.