Water managers have begun the slow, steady process of allowing stretches of the Rio Grande to go dry through south-central New Mexico.
The U.S. Bureau of Reclamation on Monday began throttling back releases from El Vado Reservoir on the Chama River. By this morning, flows in the San Acacia stretch of the river, between Socorro and Elephant Butte Reservoir, could begin drying up, said Bureau of Reclamation hydrologist Carolyn Donnelly.
The carefully choreographed reductions in flow are timed to meet requirements to keep water in the river through the middle of June, so endangered Rio Grande silvery minnows can spawn.
After June 15, the minnow-driven river operating rules allow the federal agencies managing the river to slowly allow it to dry in a process that begins south of Socorro and could eventually see drying of large stretches all the way north to the Belen-Los Lunas area.
The drying is permitted under the law in drought years. In 2012, Rio Grande runoff at San Marcial in southern Socorro County is projected to be 21 percent of the long term average.
In a process repeated in most recent dry years on the river, crews from the U.S. Fish and Wildlife Service will be poised to move in and rescue minnows that are stranded in river pools as the Rio Grande dries, said the agency’s fish biologist, Jason Remshardt.
Rescued fish will be moved up or downstream to areas where the river remains wet, Remshardt explained.
The federal Endangered Species Act requires the Fish and Wildlife Service and the Bureau of Reclamation to take the steps to prevent the extinction of the minnow. Once widespread from northern New Mexico to the Gulf of Mexico, the fish is now gone from most of the river other than central New Mexico and a stretch in Texas where silvery minnows were recently reintroduced.
Although the pre-development Rio Grande frequently went dry during dry years, the river valley in those days included large wetland areas that provided a refuge for the fish, from which it could return to the river once flows resumed. The modern system of levees and dams has eliminated those refuges, Remshardt said. That is why the Fish and Wildlife Service tries to keep some stretches of the river wet as a refuge for the endangered minnow, while stepping in to rescue fish stranded in reaches that go dry, Remshardt explained.
Over the course of the summer, the river will be allowed to dry through Socorro and Valencia counties, but the operating rules require flows to be maintained through Albuquerque.
While the river itself will dry, irrigation water will for now continue to flow through the Middle Rio Grande Conservancy District’s ditches paralleling the river, district hydrologist David Gensler said Friday. But Gensler is trying to marshal his shrinking supplies against the possibility of an early irrigation cutoff as a result of the drought.
Gensler has already warned farmers that the district’s supplies for irrigation this year could be exhausted by the middle of August. And if the summer rains are not productive, there could be shortfalls even sooner, he said.
“If it doesn’t rain, it’s going to be tough to get all the way to the middle of August,” he said.
— This article appeared on page A1 of the Albuquerque Journal