Study Offers Ways to Stem Silt Pouring Into Lagoon

Armed with mountains of data collected over months of surveys and complex hydrological studies, an engineer here is completing a plan to stem the choking tide of silt pouring into Buena Vista Lagoon.

Engineer June Applegate said the study, to be released by the end of the month, will recommend a combination of measures expected to reduce erosion of the lagoon’s watershed and substantially curb the volume of sediment swept into the wetland via Buena Vista Creek.

An official with the state Coastal Conservancy, which financed the yearlong, $52,500 study, praised Applegate’s findings and predicted her solutions would serve as “an important model for other north San Diego lagoons, all of which are severely threatened by erosion and sedimentation.”

But in other corners--the City of Vista, for example--the proposal has generated some grumbling.

“The way this (study) looks, the City of Vista would be carrying the whole darn burden for the project, in terms of land lost, maintenance and possibly financing,” said Joe Karrer, Vista’s director of public works. “We’re not real excited about that, considering the lagoon is in Carlsbad and Oceanside--miles from Vista.”

Karrer’s complaints center on the study’s recommendation that six detention basins--large holding ponds designed to slow the velocity of water flowing downstream--be built in Vista, the source of most of the erosion. In all, those basins would consume about 17 acres of land, some of which is slated for commercial development.

“They’re trying to put one of these things on the only piece of commercial land we’ve got left,” Karrer said. “We’ve got plans for that land, plans that will bring in revenue that this city needs to get sewers and other services to our people. We can’t sacrifice those plans in the interest of nature.”

And so, Karrer said, “We’re simply not going to agree to do anything unless some big changes are made.”

While sympathetic to Vista’s financial troubles, Applegate and other officials note the recommended measures carry benefits for the inland city. They say detention basins that slow the speed of water and reduce the load of silt deposited in the lagoon also would reduce the potential for flooding in downtown Vista.

“That’s one carrot, but another is that these recommendations could turn that creek into a really beautiful, green, visual corridor for the city--a real amenity,” Applegate said. “That’s a lot nicer than a concrete ditch, and it’s an asset that will enhance property values.”

As for the cost, the Coastal Conservancy is likely to shoulder a portion of the burden, with Vista, Carlsbad and Oceanside contributing a share.

“It’s not like Vista is going to get saddled with all of this just because 70% of the watershed is in their city,” said Alyse Jacobson, manager of the conservancy’s Resource Enhancement Program. “I have no doubt that we’ll continue to fund this project and perhaps offer extra help to Vista.”

Buena Vista, the only fresh-water lagoon in Southern California, has long been plagued by sedimentation problems, caused by poor grading practices and severe erosion of the creek channel by high-speed water flow. While Carlsbad, Vista and Oceanside all have relatively restrictive grading ordinances on the books, enforcement has been lax.

The siltation problem is considered so serious a threat to the health of the lagoon that the nonprofit Buena Vista Lagoon Foundation operates an “erosion control hot line,” urging residents to be on the lookout for rivers of silt running into the lagoon from development sites. Upon receiving a call, volunteers staffing the line call the responsible city and demand an investigation.

In 1983, the state Department of Fish and Game financed a $1 million dredging project at Buena Vista, removing nearly 175,000 cubic yards of silt. Dredging is effective but is a costly and temporary solution, Applegate said.

“The lagoon is a very efficient sediment trap, meaning 90% of the silt that goes in there stays (rather than flowing out to sea),” Applegate said. “So the focus of any effective solution has to be on the sediment source--the watershed.”

The engineer’s study includes six major recommendations for reducing siltation that winds up in the lagoon, smothering its plants and jeopardizing its fish population. In order of effectiveness, they are:

- Modification of the Buena Vista Creek channel. This step suggests widening the channel to 40 feet, constructing rock structures to reduce the steepness of the stream-bed grade and planting vegetation in and along the creek. These measures all would reduce the speed of the water and consequently the amount of silt swept downstream.

- Construction of six detention basins. The basins, or holding ponds, would contain water behind 5-foot-high dams, releasing it slowly through an 18-inch pipe.

- Improved enforcement of grading ordinances. Applegate recommends a campaign to educate developers about effective erosion-control measures to keep silt on construction sites.

- Construction of two sedimentation basins. These are moderately useful “last minute traps” to catch some sediment just before it drops into the lagoon.

- Lagoon modifications. These may include installing a moveable weir--or floating dam--at the lagoon’s mouth to allow more sediment to wash out to sea and dredging a deep channel on the lagoon floor to encourage water, and the sediment it carries, to move at high speed toward the ocean.

- Dredging of the lagoon. Even with improved erosion control measures, some dredging of the lagoon will be necessary in the future.

After the study is released, it will be available for public review for three weeks. Then a public hearing will be held and the three cities involved, along with the Coastal Conservancy, will consider how to accomplish the recommendations.