The recently completed project to prolong the life of the 85 year old wooden culvert siphon that brings irrigation water into Corrales has dramatically transformed the north end of Corrales next to the river. The old barrel stave pipe that delivers water from the east side of the river to the Corrales valley has been threatened by the constantly eroding river bed since about 1974 when Cochiti Dam was built.
The river has washed away about 12 feet of dirt that originally covered the hydraulic siphon when it was laid in 1935. (See Corrales Comment Vol.XXXII, No.16, October 5, 2013 “River Bed’s Drop Disturbs Buried Irrigation Culvert.”) The Middle Rio Grande Conservancy District (MRGCD) studied options for a remedy, deciding to cover it with large rocks, arranged in a long line all the way across the river, forming a low dam that over time is expected to cause river water to drop silt and recover the wooden pipe.
Completed at the end of last month, the effect has been to create a mini-white water rapid as water crashes over the rocks for a drop of about three feet. But it also drastically has changed how people use the area for access to the river’s edge.
One of the most outspoken critics of the project’s results has been Corrales photographer Ken Duckert. In a series of emails last month, he questioned MRGCD Executive Director Mike Hamman about environmental, recreational and esthetic impacts. “I have many friends and family who have access to water delivered through local acequias and appreciate the effort, especially with these periods of drought, to deliver that water,” Ducket “The long-time tradition of farming in Corrales can only exist as long as water continues to flow through the acequias.
“For me, and I know for others, the scope of the project is something none of us were prepared to see. North Beach has always been a very special place because of its accessibility and its grand beach area that provided a rare riverside recreation area.
“Seniors and folks with disabilities had a good chance to experience the river without having to walk a long distance on a trail to access a beach area. Many of these folks just wouldn’t have been able to enjoy the beauty and serenity offered by the North Beach area.
“A few of my friends asked why the wood stave construction was not replaced in this repair. I imagine cost was an issue, but staying with the same 1935 year design and the predictable behavior of the river, isn’t the problem encountered this year going to return sometime soon?”
Duckert expressed concern that the river’s fish would be hindered by the rock dam, such as the endangered silvery minnow. “I've been able to discuss this issue with biologists at the University of New Mexico, and they explained that provisions can be made to provide for fish movement. The construction that I saw would require fish moving upriver to accomplish going over what looked like a four- to six-foot height from the downriver side of the dam. Are these fish shut out of upriver movement until the degradation and flattening of the rock dam you mention occurs?
“I haven't been back to the construction site since my visit last weekend and so haven't seen what plans you have for boaters. As a small business person here, I am concerned about losing the visits to the village from the boating community that used the North Beach site. On mornings during the Balloon Fiesta, I have seen well over 200 kayakers leave from North Beach area. Unless I’m wrong, it would appear that these folks will have to carry their kayaks some distance downriver to access a suitable place to put in the river. I’ve talked with Albuquerque outfitters. They had seen the construction and weren't aware of the scope of the project and were eager to come out to check it out.”
Hamman replied in an October 19 email as follows. “Here are the answers to your questions but first let me describe the purpose and importance of the project. The Corrales Siphon is a critical piece of infrastructure to the Corrales area and serves over 1,000 acres of farm land as well as creating the flowing water people and wildlife enjoy throughout the irrigation season.
“When constructed in 1935, the 5-foot diameter wood stave pipe supported by a timber frame was covered with 12 feet of riverbed. Since the construction of Cochiti Dam in 1974, the river has changed dramatically by narrowing and down cutting to the point that the top of the siphon structure became completely exposed after the high and sustained runoff of 2019. “If you have noticed when at the site, there are very tall cutbanks on both sides of the now very narrow (200 feet wide more or less) river channel and the river is leaving the Corrales bosque high and dry.
“To save this critical infrastructure, the MRGCD needed to act quickly as exposed wood begins to degrade rapidly so a grade control structure was constructed to stabilize the bed at an elevation approximately two feet over the top of the siphon.
“This is standard practice for stabilizing degrading river beds and we expect the federal agencies will be constructing more in this reach to help stabilize the bed elevation between the siphon and Alameda Bridge. Over time, the river will deposit sands and gravel and the beach area will return and perhaps become a much bigger area. Now on to your specific questions.
“1. The MRGCD planned, designed and constructed the project.
“2. There is no requirement for an environmental review as no federal funds were used and the District is exempted from federal 404 requirements given that this is an existing irrigation facility. We did, however, consult the proper federal agencies and they concurred that no formal actions were required.
“3. This is solely an MRGCD project but we did inform the Village of Corrales and the boating community of this project.
“4. The MRGCD left the far end of the rock structure in an ununiform condition and a flatter grade to allow for potential fish passage.
“5. A portage area is being constructed to allow for boaters to take boats around the structure at low flows. Over time, higher flows will flatten and fill in the rock structure so experienced boaters will be able to negotiate the weir. Warning signs and public information will assist boaters as to this potential hazard.
“6. The weir itself is complete but crews are placing fence barriers and other safety features and preparing parking areas.”
Duckert got the following response from UNM Biology Professor Tom Turner. “At low flows like we are experiencing now, the structure functions as a dam. Over time, and as higher flows move over the structure, it is designed to degrade into a riffle and act as a grade control structure to prevent channel incession. There are similar structures in place upstream to prevent head cutting This aggraded section will accumulate sediment behind it, covering the previously exposed siphon.
“Minnows could have a hard time making it over the current rock structure, but over time, they should be able to pass it easily. At this point, we do not anticipate the river to dry in the reach between Angostura Dam and Isleta Dam, so minnows should be able to tolerate the presence of the structure with minimal negative effects.”