Devil's Gate Sediment Removal Next Week Far Cry from "Big Dig," But Crucial, Says County Public Works Director

Goal is to prevent flooding, says Mark Pestrella

Published : Thursday, September 14, 2017 | 5:40 AM

Call it the “Little Dig,” if you must.

Los Angeles County Department of Public Works heavy machinery is scheduled to begin removing thousands of cubic yards of sediment and debris washed down from higher elevations by earlier storms and lodged immediately in front of Devil’s Gate Dam as early as Monday.

The work is expected to take about one month to complete, a County flyer distributed to nearby residents said.

According to the new head of the Los Angeles County Department of Public Works, this interim cleanup is not comparable to or intended to replace the court-contested “Big Dig” project, a County Board of Supervisors-approved plan to haul away 2.4 million cubic yards of sediment and debris that would take five years and use as many as 425 trucks a day. That project is temporarily on hold after a judge ruled its final environmental impact report was deficient.

Mark Pestrella, P.E., Director of the County of Los Angeles Department of Public Works

But a cleanup really needs to happen now, County Public Works Director Mark Pestrella said Wednesday.

Arroyo Seco Foundation Managing Director Tim Brick, who opposes the “Big Dig” and whose organization sued the County in an effort to stop it, told the Pasadena Star-News that he approves of this interim cleanup, which he pointed out at 4,000 cubic yards is less than 1 percent of what County plans call for in the Big Dig project.

Pestrella said Wednesday the removal process is “a coping mechanism, given the state of affairs with respect to the reservoir.”

While the removal is part of regular and ongoing scheduled maintenance at Devil’s Gate, Pestrell said “this is not a normal activity, because normally, we would have not have the reservoir in the state of condition that it’s in currently, so we came up with a routine that we felt gave us some operability. It is in no way a fix or the ideal scenario for the reservoir currently to be operated in.”

Pestrella said that the County’s planned large sediment removal, currently wending its way in and out of Los Angeles County courtrooms, “would put us in a position which we would do minimal removal within the reservoir itself. We wouldn’t be even near the valve system, and we wouldn’t be taking these kinds of really not optimal activities.”

The regular removal measures have a sense of urgency now, says Pestrella, given not only the debris mass from large storms of last winter but the rising number of weather emergencies throughout the country, such as the recent hurricanes in Texas and Florida.

“Frankly, we dodged a bullet for about 5 years now,” Pestrella said.

The Houston hurricane could also be a preview of what Southern California could eventually come to face, posits Pestrella, who said, “ I think it’s a preview of what’s happened in respect to climate change, and we know that in our jurisdictional area within the Los Angeles County area, we expect more severe rain events, which does concern us. We have been seeing more intense sediment depositing off of the San Gabriel Mountains, and this is one of the facilities that protect the public from that sediment and mudflow. So it is critical that we get this reservoir cleared for lots of reasons, one of them is a direct nexus to, yes, climate change, with increased heat, and drier weather during the dry months and more intense rainfall during the storm season.”

In addition to the effect of climate change on the amount of rain falling locally, Pestrella said he is also concerned specifically on what scenarios a major storm and a clogged dam system could create locally.

“If we were to have the Houston scenario occur here, you would be talking all of the downstream communities along the Los Angeles River being threatened by flooding,” he said. “If you know the area, that would be something we don’t hope for, but we have to plan for it. There are well over 200,000 people along the river that are in what we call ‘flood zone areas,’ so no dam operator ever wants to lose control of their facility because it has a cascading effect, if you will, on the larger downstream community.”

As Pestrella mused, “I’ve been in the business for 30 years and it’s been my experience that it takes basically one to three years for people to forget that it even rains in Southern California, and then on top of that, that there are hazards associated with rainfall. The classic scenario is people forget that they are supposed to drive a certain way in the rain, right? Well, more significant is people forget that there are people that live within a mile of our dam, and not even know that there’s a dam or even maybe a neighborhood away from the dam, that does not know that that’s a dam there.”

Continued Pestrella, “I think that the residents and the people that drive the 210 freeway don’t normally realise that (the Devil’s Gate Dam) is a facility built to protect the lower portions of Los Angeles and South Pasadena, and all the communities along the way there, so our job is very difficult because it’s not a scenario that occurs very often, much like an earthquake. I do think there’s a whole generation that has grown up that doesn’t understand that LA has been flooded many times and we have experienced severe rain events through the years. 1968, 1969, 1978 were huge years, and the 1938 rain year is the mother of all flood years. We had multiple events that occurred simultaneously that flooded the entire Los Angeles basin. That was the reason for building the system that we are trying to maintain now.”

The flood scenario that Pestrella conjures is not a pretty one.

“The low-lying areas over in Long Beach, and Southeast Los Angeles, Compton, Watts, North Long Beach, Lakewood, are all lower lying areas. If you had a breakout event, what you would expect is that those areas would in 7 feet of water around homes, and access would be cut off in terms of being able to drive through the area easily,” he said.

“The 110 freeway is driving this scenario,” Pestrella continued, saying, “so you would have access issues there. The mountain areas, the uphill areas would be, and continue to be, highly erosive areas, so you would expect severe mudflow events occurring especially in very recently burnt areas within five years, where you would see mudflow make its way to the streets and actually in local homes. In Los Angeles, the flood control system relies on the streets, and it also drains these areas, so when it gets overwhelmed, then what you have is you have a lot of traffic water in the low lying areas of Los Angeles, and again everything just south of the 10 Freeway or the 60 Freeway.”

Pestrella credits the original designers of the City’s flood control system as being forward thinking, saying, “I think it’s really a testament to the maintenance and operation and also, the thinking by the community leaders in the 30s and 40s, who decided they’ve had enough of this kind of flooding and so they built a system that keeps us flood free.”

“What you have,” Pestrella explained, “is a system that maintains LA county free from flood hazards and also provides 1/3 of the drinking water supply for Los Angeles, and people forget that, too. We capture all that water, and we we put it back in the groundwater for our drinking water supply every year, so it’s a dual system and it also provides recreation so there’s like a lot of benefits out of the system, but it’s got to be maintained.”

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