Repairs currently under way to Mission Bay Channel’s south jetty should weather the most violent storms likely to descend upon the shore, according to those involved in its design and build. The south jetty was severely damaged by a series of storms associated with El Niño events in the early 1990s, was repaired in 1997 and was later damaged again.

Photo by: Jack Innis

Modern design and building techniques produce stouter jetties than in the 1940s, when the existing three-jetty system was created. Back then, crane operators simply stacked boulders atop one another until the specified height was reached.

New jetties are wider, sport less-steep sides and gain strength from interlocking boulders.

Mission Bay Channel south jetty specifications call for an estimated 800 boulders, weighing between 8 and 24 tons each, to be piled in a specific sequence to repair the seaward 200 feet of Mission Bay Channel’s south jetty, according to the U.S. Army Corps of Engineers. Approximately 10,000 tons of small boulders form the backbone or interior of the jetty.

“(Stacking new boulders on) existing stones from the jetty that was wiped out, there’s a pretty good footprint for the base to sit on,” said Ron Allard, Connolly-Pacific Co. project manager. “These boulders will stay in place.”

Construction crews from the Long Beach-based firm completed the backbone phase Nov. 13. The second phase involves the precise stacking of large boulders to create what is called an armor layer, which involves precise placement of boulders up to 24 metric tons.

Watching the crane operator at work is like watching a game of Tetris being played out with a 260-foot high crane.

“Everything is built in a lock and key system,” Allard said. “Instead of just throwing everything out there, each rock is carefully placed on the three stones underneath it. Every stone is sitting on two or three stones.”

Army Corps of Engineers spokesman Greg Fuderer said the new concept in jetty construction is not something an engineer can precisely pencil out in a design studio; it’s more of an on-site construction method.

“The crane operator has a couple of spotters out on the jetty telling him where to place the stones,” Fuderer said. “He also has a couple of guys on the barge, and what they’ll do is look for the rock that best fits.

“The crane operator may have to turn it or grab it from another angle so that a different end is pointing down, but the idea is to put the jetty together like a three-dimensional jigsaw puzzle -- so the jetty strengthens itself by how the rocks are laid down,” Fuderer explained.

Careful boulder selection and placement are easy, compared to what comes next. The large boulders don’t always fit into their intended openings, as envisioned by helpers on the barge.

“We’ll flip them over and turn them different ways to do whatever we can to fit each rock into the hole, to lock it into position so it doesn’t move,” Allard said. “It’s finesse work and it’s nerve wracking, especially in swell conditions.”

Since the crane sits atop a barge and the barge is affected by the movement of ocean swells, it’s not unusual for the crane bucket to swing 10 to 15 feet or more.

“You can get a boulder in place to drop and, all of a sudden, the swell moves you around and you miss the hole,” Allard said. “You just have to grab it and set it down again.”

When the project wraps up -- by the end of December, unless ocean swells cause too many delays -- the tip of Mission Bay Channel’s south jetty will be brought back to original length and height by stacking a total of 24,000 metric tons of boulders.

The jetty tip will be wider at the base, since new specifications call for a 2.5:1 slope compared to the previous 1.5:1 slope. The greater slope helps waves roll up the jetty face and lessens the amount of direct impact the structure is forced to absorb.

All boulders in this project were mined from the Connolly-Pacific Co. quarry at the East End of Santa Catalina Island. Barges haul the material directly to Mission Bay, and the journey takes approximately nine hours.

Recreational boaters are advised to use caution and be aware of possible marine construction activity near the mouth of Mission Bay Channel.

“The boating public has been fairly cooperative, so far,” Allard said. “Some guys obviously aren’t aware of marine laws and regulations and others come too close to gawk.

“We’ve handed out flyers to local shops, lifeguards and kayak clubs to give people a heads up,” he added. “We just want everyone to respect the fact that the barge isn’t just sitting there by itself: There’s an anchoring system that keeps it in place. So, keep outside the buoys that mark the edge of the system.”

Funding for the project comes from the American Recovery and Reinvestment Act, signed into law by President Obama last Feb. 17. The act is intended to help jumpstart the economy out of a deep, prolonged recession by addressing long-neglected challenges, according to the Small Business Administration.

The $2.289 million jetty repair project came from $184 million in American Recovery and Reinvestment Act funds given to the Army Corps of Engineers’ Los Angeles district.

The same funding pool will pay for most of a separate project to dredge Mission Bay Channel. That contract will be awarded in December, with work beginning in January, according to Fuderer.

The jetty repair project includes installation of a navigation light tower near the tip of the jetty to replace the one knocked over by storms. The Corps of Engineers will work with a local Coast Guard Aids to Navigation team to determine the height and exact placement of the tower.

The Mission Bay jetty system includes three jetties. The north and middle jetties create Mission Bay Channel. The small south jetty across from Dog Beach in Ocean Beach helps contain water within the San Diego River estuary.