More Concrete Slabs Wash Down Santa Monica Canyon Channel

Concrete slabs wash down the Santa Monica Canyon Channel Sunday morning. Photos: Courtesy of Sharon Kilbride

By Laurel Busby

News & Information Editor

(This article was updated on Sept. 15.)

Concrete slabs, which L.A. County Public Works employees stacked on the side of Santa Monica Canyon Channel during the first week of September, washed down the waterway during the Sept. 6 rainstorm.

“When the creek was filling up, there was [a] big rumbling down here on the west end, and the concrete is coming down the channel that they left inside the creek, causing blockages down by Short St.,” said The Canyon Alliance Board Member Sharon Kilbride in an email to county and city officials.

Initially, the inflatable dam that siphons water to Hyperion Water Reclamation Plant appeared to be damaged to Kilbride, and she communicated this concern to City Councilmember Traci Park’s office and Jason Rietze, the L.A. County Public Works civil engineer who was overseeing the concrete removal project.

The segment of the channel system that diverts water from the ocean to Hyperion Water Reclamation Plant for treatment.

After receiving her email, Rietze sent a crew to the area, but he said that the number of slabs that came loose had not caused a problem.

“The vast majority of the stockpiled material was still in the same condition as Friday, [Sept. 4],” he said in an email. “There were a few small pieces of concrete washed downstream. The city’s low flow diversion is designed to capture low flows not storm flows. So the storm flow was bypassing the low flow diversion as designed and the water was flowing out to the ocean.  We will continue to remove the stockpiled [concrete] on Tuesday.”

The day after receiving Rietze’s update, Kilbride sent him and other officials pictures showing the buildup of concrete in the creek and the segment of the inflatable dam that appeared damaged to her.

“Please note in the photos west of the interceptor [inflatable dam] heading toward the beach, there’s huge piles of slab that washed down from the rains yesterday so I hate to say it, but a lot of the piles that were staged did in fact make it down to the end of the creek,” Kilbride told Rietze, “Make sure your crews remove the debris from this area.”

A pileup of concrete slabs that moved down the Santa Monica Canyon Channel during Sunday’s rainstorm.

According to Arus Grigoryan, senior field deputy for City Councilmember Traci Park, L.A. Sanitation “informed us that the inflatable dam was placed in the down position for the storm. An assessment of any potential damage will be conducted [on Sept. 9] once it is raised back up and operational. Additionally, LA County has notified us of their ongoing work and confirmed that they will ensure the dam is protected throughout the process.”

On Tuesday, Elizabeth Vazquez, the public information officer for Public Works, said that the dam had not been damaged during the storm.

The loose concrete slabs that washed down the creek are part of a Public Works project intended to remove a layer of concrete that was installed in the channel in the 1970s. Hundreds of slabs of this concrete overlay came loose during a Feb. 16 storm and clogged the channel. That loose concrete was removed, but more concrete overlay remained in place in other parts of the channel.

Piles of concrete overlay slabs lining the Santa Monica Canyon Channel at Amalfi and East Channel.

To better prepare for anticipated heavy rain this fall and winter due to El Niño, Public Works began a project to remove the remaining overlay on Aug. 27. The staging area is located at Amalfi and East Channel, which held piles of concrete slabs during early September.

Unfortunately, some of those slabs were washed into the channel by the Sept 6 rain.

“That concrete should’ve been removed before the storm because if the rain got heavier, all that concrete would’ve washed down to Channel Lane where there’s a dip and it would’ve collected, causing the water to make a blockage and then splash over the walls … potentially flooding homes,” Kilbride said via text on Sunday.

In her initial email to officials, Kilbride requested that they ensure that all of the concrete stacks in the channel be removed and that the workflow be changed to prevent piles of concrete from being left in the channel in future.

“Could you please make sure whoever’s in charge of this project follows protocol, and removes the cement from the channel before any heavy rains to avoid more damage to our infrastructure and potential flooding of the storm control channel in our community?,” she said. “To me, this is common sense.”

Soon afterwards,, Rietze emailed Kilbride and other officials with his reasoning for not removing the concrete slabs before the rain. He also promised to remove them more quickly in the future.

“We were not anticipating enough rain to move any material downstream,” he said. “We are actively working to remove the material. All the stockpiled material within the channel will be removed this coming week. We are also renting additional trucks to ensure we can we remove the stockpiled material in an efficient manner going forward.”

For questions regarding this project, contact Public Works Civil Engineer Jason Rietze at (626) 819-1922 or email him at JRietze@dpw.lacounty.gov during weekday work hours. For after-hours assistance, contact LA County Public Works 24-hour Dispatch Center at (800) 675-HELP (4357).

The diversion that normally siphons water to Hyperion was hit by the concrete slabs this morning.