New Shoals Pose Boat Danger at Harbor : Storms: Runoff creates buildup at mouth of Ballona Creek, just three months after Corps of Engineers cleared area.

Runoff from recent heavy storms has deposited so much sediment at the mouth of Ballona Creek that Los Angeles County officials have been forced to close nearly half of the south entrance to Marina del Rey harbor to boating.

The rapid buildup of sandy sediment has created potentially dangerous shoals, prompting authorities last week to install orange buoys warning boaters to avoid the area closest to the mouth of the creek.

Ironically, the closure was ordered only three months after the U.S. Army Corps of Engineers spent nearly $400,000 to knock down shoals that were choking off much of the adjacent south entrance to the marina channel.

The temporary measure was intended to buy time while county and federal officials decide how to dredge and dispose of bottom sediments that are contaminated with toxic metals.

After initial tests last year, the U.S. Environmental Protection Agency concluded that the sediment, which contains varying levels of lead, copper, zinc, chromium and nickel, is too toxic to be dumped offshore. If no other solution can be found, the material may have to be sent to a toxic waste site--at great expense.

County officials had thought the knockdown operation would allow them to keep the south entrance open through much of this year’s boating season while alternative methods for disposal of the sediment are considered.

But Marina del Rey Harbor Master Joe Manusia told the county Small Craft Harbor Commission last week that the recent buildup of sediment has reduced the depth of the water in the south entrance channel to seven feet at the lowest tide, three feet less than necessary for safe operation of many sailboats.

After the temporary knockdown was completed in November, the Corps of Engineers had measured the south entrance’s depth at more than 15 feet.

Manusia told the commission he thought that the winter storms and tides would make the channel deeper but that instead the sediment has piled up where Ballona Creek enters Santa Monica Bay.

“It’s built up and I don’t believe it’s going anywhere,” he said.

Manusia, who took depth readings last week using a measuring pole, said he was “surprised that a shoal would grow that rapidly.”

After taking the measurements, he ordered placement of the buoys closing 250 feet of the 600-foot-wide south entrance. The harbor master advised boaters to “stay as far away as you can” from the buoys that warn of the shoaling.

“This sounds . . . like we’ve got a serious problem,” said Commission Chairman Herbert J. Strickstein. In the past, Strickstein has warned that the county risks incurring the wrath of boaters if a solution is not found to the sediment problem that is narrowing the harbor entrance.

Commissioner Carole Stevens called it “absolutely ludicrous (that) we just finished a knockdown and now we’re back in the same situation again.”

Stan Wisniewski, deputy director of the county Department of Beaches and Harbors, said the sediment problem has been aggravated by the recent storms.

Ballona Creek is by far the largest flood control channel entering Santa Monica Bay and it has been carrying a vast amount of material this winter, including partly treated sewage, because of heavy rains.

Wisniewski said the county will ask the Corps of Engineers to conduct a study of the harbor entrance to determine if design changes are needed. In addition, he said, the corps intends to request $2.1 million in the next federal budget for the dredging project.

In the meantime, the federal agency plans to use electronic equipment to measure the depth of the entrance channel this week and will sample the toxicity of the sediment again this month.

“Where to put the material? That’s the biggest question right now,” said Mo Chang, chief of the Navigation Section for the Corps of Engineers. “The key is the disposal site.”

County officials have previously said that it will be “very problematic and very costly” if an estimated 320,000 cubic yards of sediment has to be dredged, dried, and hauled to a toxic waste site.