Ponding water that seeps below Seacoast Drive homes and condos after a sand replenishment project has roused residents and beachgoers.
But environmental workers are worried, too—that the sand could move south and block the mouth of the Tijuana River.
If the sand stopped flow of the river, said the manager of the Tijuana Slough National Wildlife Refuge, it could threaten endangered species and other wildlife in the Tijuana River Valley.
“It’s like your circulatory system,” said Brian Collins, the refuge manager. “You don’t want it blocked. It causes a heart attack. Or like asthma. You want to be able to breathe, and my analogy is you want the water to be able to go in and out."
The potential closure is especially worrisome as threatened and endangered bird species like the Light-Footed Clapper Rail are expected to begin their breeding and nesting seasons this month.
“I’ve seen raptors and other birds already flying around near the pier with nesting material already,” Collins said.
SANDAG, the regional planning agency, brought 450,000 cubic yards of sand to Imperial Beach in October as part of the Regional Beach Sand Project.
According to project engineers from Moffatt & Nichol, once the sand dissipates, the material may move as far north as the mouth of San Diego Harbor and as far south as the U.S.-Mexico border.
SANDAG has not answered repeated phone calls for comment on these concerns.
The City of Imperial Beach declined to state its position until the city could have more conversations with estuary staff.
"My reaction is to get their thoughts directly and go from there," said City Manager Gary Brown. "The estuary has had blockage problems at this river mouth for years so I'm not sure how this is any different than it's been for a long time."
Collins, a U.S. Fish and Wildlife Service employee, said sand has closed the river mouth twice in recent history–once in 1984 and partially in 2010.
Warm waters during a 1983 El Niño generated extreme sea levels and storms that flooded areas of the city near the estuary and ocean.
Damage caused by those storms contributed to the closure of the Tijuana River the following year, said a study by Joy Zedler published by the Ecological Society of America.
From April to December 1984, a lack of tidal flushing decimated cordgrass. As a result, the endangered light-fooled clapper rail lost its nesting habitat, food and protection from prey.
“This salt marsh-dependent bird either died or emigrated when nontidal conditions altered their habitat,” the study stated.
Closing river flow can cause water to be too salty or too fresh. The result can be a lack of oxygen or nutrients in the water, pollution and eventually a die-off of plant and animal species, said estuary researcher Jeff Crooks.
“The bird population just crashed after that; they recovered, but it took some time,” he said.
The estuary, specifically the Oneonta slough near Seacoast Drive homes, hosts the second-largest population of the Light-Footed Clapper Rail in the world, Crooks said.
Support to respond if sand stops river flow is much different from 1984, Collins said.
The area received National Wildlife Refuge federal protection in 1981, and in 1984 there was no Visitor Center or on-site staff and less monitoring.
Today estuary staff can tell if the river is blocked with instruments that give real-time indications of salinity, tidal flow, water and dissolved oxygen levels and more.
Once permits are approved and heavy equipment is in place, the river could be reopened within a matter of days, Crooks said.
When a large winter storm pushed sand into the river’s path in 2010, crews using heavy equipment were able to clear the way within a matter of days, Collins said.
If sand disrupted or stopped flow of the river tomorrow, Collins said, a plan is in place to call the Army Corps of Engineers and San Diego Regional Water Quality Control Board and request emergency permits, but the estuary doesn’t have the money to carry out the dredging work, Collins said.
“At this stage, we’re cautiously keeping an eye on it, and if we do think we’re going to have a problem with it, we’ll pursue discussions with SANDAG, [because] our budget is not enough to do anything right now,” he said.
Estuary management also would need to call state regulators since threatened or endangered species may be impacted.
“It’s possible you could have least terns and snowy plovers nest near the project site,” Collins said.
In the past, the river mouth has naturally moved or closed, and sediment from across the 1,750-square-mile watershed replenished local beaches, Collins said.
But dams and other man-made action have changed the river’s characteristics, polluted the water and taken away much of California’s coastal wetlands.
“It’s very difficult to let it do that now for all sorts of different reasons,” Crooks said. “The water isn’t clean and it needs to be flushed out, and because of what we're managing for now, it needs to be open.”
The Tijuana River National Estuarine Research Reserve is the largest remaining coastal wetland in Southern California, providing habitat to endangered species and more than 370 species of birds, so the critical habitat cannot afford closures that may have naturally occurred in the past.
Since the Tijuana estuary is so unique, though a closure would be unfortunate, it may provide valuable research data, he said.
Using Jet Skis, GPS devices and other instruments, Scripps Institution of Oceanography professor Bob Guza studies how sand is distributed on San Diego beaches and teaches courses on how waves and sand interact at the coast.
Like Collins and Crooks, Guza thinks there is a potential for sand to close the river mouth. A chance exists flooding could occur upstream if the mouth is closed, and a chance water will find another way to the ocean or punch through the sand and reopen the river mouth if there is heavy river flow.
Predicting whether that happens is like predicting the weather a month ahead of time, Guza said.
“You can’t make a prediction any more than you can make a prediction about what the temperature’s going to be in a few months,” he said. “The distance is not so far that it’s impossible. It’s close enough, and that’s a lot of sand. 450,000 cubic yards is a lot of sand.
“Is it going to clog the mouth? I don’t think it will actually—but that’s speculation.”
Guza said he and graduate students have been on the beach in IB to quickly monitor the recent replenishment project but can only make fairly simple observations: The sand is moving, no big storms have moved the sand very far away and the beach is wider.
Only thorough monitoring—to observe where sand moves after it hits the shore and disappears under the waves after a replenishment project—can that question be answered.
And that requires time and money, Guza said. In most instances, that money goes to sand, not research.
Even if sand closed the mouth of the river next month, where the sand came from cannot be proven without studies like the kind Guza is conducting in Solana Beach and Cardiff, one of eight beaches to receive replenishment as part of the Regional Beach Sand Project.
“If it happens, we won’t know for sure what caused it because nobody’s making the detailed observations,” he said.