Left: The Rio Grande River at Corrales' Romero Road riverside bosque access in August, 2010. This picture was taken before a fire broke out in June, 2012. The Sandia Mountains loom in the background.The bank has been here long enough that Russian Olive Trees have had a chance to grow to maturity in the middle distance - that has got to be at least ten years!
Note how narrow the gap across the river, and prone to spreading fire from flying sparks.
The river here is showing signs of retrenchment, with the water running about three feet below the bank on the opposite side. This retrenchment process likely started with the completion of Cochiti Dam in 1974, which arrested the yazoo-making process of silt deposition. The dam has only a 100-year lifetime, so this retrenchment likely isn't permanent, but it's likely enough to change the character of the area, with the slow death of the cottonwood trees, unable to rejuvenate due to too-infrequent flooding.
A more-thoughtful approach to managing the bosque is under consideration that may slow or stop these changes:
The U.S. Army Corps of Engineers has proposed another foray into the Corrales Bosque Preserve with heavy equipment to carve out new “backwater channels,” depressions, clearings and re-vegetation efforts using a refreshed pot of federal dollars.
...Much of the modification in those areas would involve Corps contractors excavating depressions down to near groundwater to establish swales where willow could grow. He said the commission “didn’t want to support any wide-area thinning. The idea of applying an eradication program cutting down Russian olives, salt cedar, mulberry and other non-natives in a very wide area was not what we were going to recommend.”
...The Corps’ new proposal begins with a plan to monitor previous work done in phase one at the south end of the preserve and, “using adaptive management process… re-treat exotics, replant and reseed natives throughout in areas where native revegetation does not meet objectives or is inadequate.”
That objective is likely to displease no one, and addresses villagers’ ongoing complaints that the Corps’ work is left abandoned to return to the earlier, undesirable state, overgrown with salt cedar and other invasive species.
...Another part of the plan would re-vegetate about six acres in the burned area near Romero Road, as well as dig backwater channels that would draw water from the river to excavated pools (referred to as “small/deep pools).
That component would also excavate a three- to five-acre depression near the end of Lipe Road at the north end of the preserve.
Two small, backwater channels would also be dug near the Andrews Lane entrance to the bosque leading to a new willow swale adjacent to the shaded fuelbreak there.
The last work plan component, as presented in the packet for the April 22 Village Council meeting, is a project to dig out a five-acre “wetland depression water feature in general area indicated east of Via Oreada Road.”
The Corps’ “bosque restoration” project derives from a realization that the cottonwood forest along the Rio Grande is dying off, primarily due to lack of over-bank flooding that would allow the trees to re-generate. That, in turn, has resulted because earlier Corps projects upriver no longer allow the Rio Grande to flood over its banks to wet the bosque soil so cottonwood seedlings can sprout.
The Corps’ not-well-thought-out engineering to achieve flood control for the Middle Rio Grande Valley with upstream tributary dams created the cottonwood die-off. But it’s not so much that insufficient river water is released from the dams to achieve over-bank flooding into the forest.
Rather, it’s that the dams and other measures disrupted the river’s normal sedimentation patterns. In essence, the Corps’ work over the past six decades has upset the Rio Grande’s riverbed sedimentation balance.
Due to sediment-holding dams upstream and other factors, river flows have been scouring out the riverbed in the Corrales area year after year, decade after decade. As the riverbed goes down in the main flow channel, it carries more water there, leaving less to flood into the bosque.
The hydrology problem not only effectively eliminates prospects for natural cottonwood regeneration, but it significantly increases the threat of wildfires in the bosque. River flows that used to occur across the bosque floor washed away much of the fallen twigs, branches and other flammables. And, importantly, the soaked logs that remained on the forest floor decayed.
Now the tons of dead-and-down wood built up is considered an unacceptable fire hazard.
As cottonwoods have lost dominance in the bosque ecosystem, aggressive non-native species like salt cedar and Siberian elms have invaded.
The Corps has millions of federal dollar to fight back that invasion and to “restore” the bosque all along the Rio Grande from Corrales to Isleta Pueblo. The battle begins in the Corrales Bosque Preserve.
Here’s the battle plan. Since the river can no longer swell to flow over the river banks to flood the bosque, the Corps will dig one or more channels —basically irrigation ditchs— to divert water from the river into the bosque. Called “high flow channels,” these ditches would generally carry water only during peak seasons.
Corps planners have identified what they think are old channels cut by the river itself that would be enhanced by earthmoving equipment to make ditches to bring water to parts of the bosque.
Another tactic is to dig out swales (linear depressions) in some areas, removing earth down to near the water table to encourage vegetation growth there. Similarly, the Corps has proposed excavating ponds that would become seasonal wetlands.
A third maneuver —so far unapproved for the Corrales bosque— would be to carve away the river bank in some parts of the bosque, bulldozing it down a few feet to allow the river to flow into the forest during peak run-off.
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