The Sierra Club has taken a stand supporting removal of Rindge Dam, so Malibu chapter members trekked to the site Sunday for a first-hand look.
The 100-foot-high concrete dam in Malibu Canyon, 2-1/2 miles from the ocean, was built in the 1920s to provide irrigation water but no longer serves that purpose because it is completely silted up.
“The dam doesn’t provide flood control, it’s just a waterfall,” commented Jim Edmondson, executive director of California Trout, explaining the ecological impact of the dam.
Malibu Creek contains the southernmost run of steelhead trout in North America — an estimated 10 to 75 fish — only in the 2-1/2 miles below Rindge Dam. Before the dam was constructed, an estimated population of 1,000 steelhead spawned in the 100-square-mile watershed of Malibu Creek. Last fall, the federal government listed the Southern steelhead as an endangered species.
Steelhead, named for their steel-blue coloring, are actually rainbow trout with a life cycle similar to that of a salmon. Born and reared in fresh water, as juveniles they migrate to estuaries, adjust to saltwater and then move on to the ocean. After spending one to three years foraging on the food sources of the Pacific Ocean, the adults return to their home rivers upstream to reproduce. Unlike salmon, steelhead do not necessarily die after spawning and may make the journey more than once.
“It’s the granddaddy of all the rainbow trout on this planet,” Edmondson said. DNA tests show the species to be more than 10,000 years old, the world’s most ancient rainbow trout. They have adapted to near-desert conditions. While most trout thrive in 68-degree water, the steelhead in Malibu Creek live in water that reaches 78 degrees in summer.
Rep. Brad Sherman spearheaded a 1998 appropriation of $100,000 to study the feasibility of removing Rindge Dam. In 1995, the Bureau of Reclamation completed a feasibility study. According to that study, excavating and backfilling the beaches would cost $17 million; excavating and backfilling the canyon would cost $12 million; and notching the dam would cost $3.5 million.
The dam holds one million cubic yards of sediment, of which 65 percent is suitable for beach fill. However, the silt levels need to be taken down slowly. “By notching, the dam is dismantled bit by bit, row by row, over 10 years,” Edmondson said. “You would take nine feet a year. It may take maybe 15 to 20 years of work.”
The concrete and rebar of the dam wall would be trucked out. Then in winter, the sediment would be washed down and deposited on the beach, without filling in the lagoon or creek, Edmondson said. “The U.S. Army Corps of Engineers, who would be responsible for the work, would do a sediment transport analysis.”
If the sediment is taken away too quickly, the trout eggs will be smothered, defeating the purpose of getting rid of the dam. “If the sedimentation is released [too quickly], then this would impact the lagoon. We don’t want to hurt any living things or anybody. We don’t want to fill up the lagoon,” Edmondson said. “But the fish are trapped in the worst possible place in Malibu creek. We want to get them out of there and up into the upper reaches of the creek. It’s in the upper seeplets and brush-covered tributaries that they thrive.”
Edmondson says he believes the issue has been “mischaracterized” and that logic tells us when the dam filled up in 15 years, the system carries a lot of sediment that would have moved through the creek without the dam.
“My sense was that they [Sierra Club members] saw the wisdom, function and logic of removing the dam to create a functioning river system again,” Edmondson said.
Marcia Hanscomb, executive committee member of Sierra Club Angeles Chapter, said their task force will meet to get everyone’s opinion, but that she feels the dam must come down.
“The solution that Caltrout has offered may be the best,” she said. “For historical purposes, it makes perfect sense to retain the 90-foot spillway and remove the dam. We like to find solutions that please everyone.”