Scientists tracking movement of sand

CARDIFF-BY-THE-SEA — Millions of dollars have been spent on local beach replenishment projects. 

But where does that sand go? And once in place, will it stop beach erosion for years to come?

Researchers hope the answers to these questions can be found in piles of sand that were recently dumped on Cardiff State Beach. With a mixture of old and new technology, they’re tracking what happens to the sand over the next few months as winter waves push it offshore, according to Bob Guza, a research scientist with the Scripps Institute of Oceanography.

To do this, Guza and his team set up shop in early November alongside Cardiff State Beach in a storage container, where they’ll be until mid-February. Mounted about 20 feet above the container, a laser scanner borrowed from the Army Corps of Engineers, shoots invisible beams seven times a second at all hours to record how sand levels have changed on a wave-by-wave basis.

“A lot of money has gone to placing sand for beach nourishments throughout the years,” said Guza, who called sand “his life’s work” as he motions towards the waves crashing on the beach.

“Yet not enough emphasis has been put on monitoring where the sand moves to,” Guza said.

When the Scripps project is complete, researchers expect to have a better understanding of how tides and waves affect sand transportation. This knowledge could help engineers decide where to deposit sand in the event of future beach nourishments.

At a cost of $22.5 million, a separate SANDAG project deposited 1.4 million cubic yards of sand on eight local beaches from September to December to shore up sand-starved beaches to protect homes and infrastructure. Plus, the sand is expected to widen beaches, giving tourists more reason to pay San Diego a visit.

SANDAG will check up on sand they’ve deposited in three months or so. But Scripps’ research will be more in-depth, gauging in real time where the sand was transported to and what type of swells moved it.

“We’re not going to understand the behavior of beaches and surf zones anytime in the near future using only computers,” Guza said. “Our computers are not powerful enough, and our understanding, independent of computers, is not large enough. Therefore, if we want to understand these things, we have to observe them.”

In addition to the laser scanner, researchers are mapping the surf zone and ocean floor by driving jet skis equipped with depth finders over the areas during high tide.

At low tide, (even at night) they employ hand-push carts and all-terrain vehicles that have GPS. Guza noted efforts were made to notify all law enforcement agencies of nighttime riding, but because it looks suspicious, they’ve had guns pulled on them at least once.

Research from a similar 2001 SANDAG beach replenishment project suggests that sand dumped on the beach is carried offshore by larger waves in the fall and winter. Then the sand gets thrust back onto the beach in the spring and summer when gentler surf laps onto the shore.

Currently unknown, this project will shed light on the amount of sand that returns to the beach, how long it will remain there and under what circumstances. These variables include wave size and direction as well as tides, according to Guza.

“This is one small part of whether we should do beach nourishments,” Guza said, referring to surfers, fishermen, restaurant and homeowners with property near the beach.

“There are more vested interests pushing and pulling at beach nourishments than you can shake a stick at.”

But the results from the Cardiff State Beach study won’t necessarily be applicable to all beaches in San Diego County.

“By studying this beach, will we learning everything about all beaches? No,” Guza said. “Will we only learn only about this beach by studying this beach? No.”

So far, researchers know some of the sand that was at Cardiff State Beach is migrating south toward Fletcher Cove. But Guza cautioned that results might not be released for several years, as the data requires heavy analysis. But given trends, Guza believes the information is only going to become more valuable.

“Our beaches are in a world of hurt,” Guza said. “We don’t have to do anything. But if we don’t, there won’t be a beach here. It could be 50 years, and it could be 100. I’m not sure. But the writing on the wall is crystal clear.”

Flood control, not waves, is the biggest contributor to beach erosion. Dams block off river sediment from flowing to the ocean; seawalls and cliff armoring, which are designed to protect homes, will continue to add to sand loss.

And for the last 80 years, large construction jobs dredged large quantities of sand onto San Diego’s shores. But Guza said those are increasingly rare.

Taking these factors together, Guza said beach nourishments might be deemed necessary. For one, jobs and tax revenue are tied to sand. California’s beaches generate $14 billion in revenue annually, according to a study from the Public Research Institute at San Francisco State University.

“Think about 50 years from now, when we maybe have to make some of these decisions,” Guza said. “We will either have a history that we’ve developed by observing our beaches over 50 years, and how nourishments affected and didn’t affect the beaches, or we won’t.”

With recent advances in technology, Guza said there’s much to learn from the present at Cardiff State Beach. But the past is worth looking at, too.

“As well as trying to understand what’s happening now — with an eye to the future — we’re going backwards in time to try and establish from old surveys dating back to the 1930s what the beaches were like then,” Guza said. “We want a trajectory.”