Sea-level rise and the precious commodity of sand

Sea-level rise and the precious commodity of sand
Adam Young, a researcher at Scripps Institution of Oceanography, shared valuable insight with local residents on sea-level rise during a workshop at Encinitas City Hall on May 8. Courtesy photo

ENCINITAS — Humans use more sand than any other natural resource besides air or water. It’s used in concrete and asphalt, which build the world’s buildings and roads. Sand is also needed to make glass. The sand used to construct towns and cities leads to development that then impedes sand’s natural flow from watersheds, diminishing one of its best sources of replenishment.

Ironically, then, humans have contributed to the shortage of a precious resource by using sand to build in places that block it.

In North County, development along the coast has dammed 60 percent of the watershed coming from the eastern mountainous areas like Julian and Mt. Palomar, according to Adam Young, project researcher for Integrative Oceanography Division at Scripps Institution of Oceanography.

“That watershed has the potential to bring sand to these beaches,” Young said during a workshop on sea-level rise at Encinitas City Hall on May 8. Manmade development has greatly inhibited its flow, he added.

Further contributing to the sand shortage are structures like the Oceanside jetties that disrupt the movement of sand north to south in what’s called the Oceanside Littoral Cell.

That means that not as much sand is getting conveyed southward to the beaches of Encinitas and Solana Beach, for example, as it would in the absence of development. Efforts are underway to mitigate the sand-diverting effect of those jetties, which will hopefully improve the north-to-south flow, Young said.

Beach sand also comes from coastal bluffs. By armoring local cliffs with sea walls, we’ve reduced that particular sand source by 40 percent, according to Young. But sea walls could also be useful in protecting against sea-level rise, a phenomenon that has local coastal communities on alert.

According to Crystal Najera, the city of Encinitas has adopted a Climate Change Action Plan that predicts a regional sea-level rise of 5 to 24 inches by 2050 and 17 to 66 inches by 2100. Najera, Climate Action Plan Program Administrator for Encinitas, noted that those predictions stem from analysis performed for the San Diego Regional Coastal Resilience Assessment of 2012.

But as Najera and every other workshop presenter said on May 8, no one knows for certain what the level will be, nor the extent of its impact. “Exactly how much the sea level will rise is based on many varying factors and is very hard to predict with certainty,” Najera wrote in an email correspondence with The Coast News.   

According to Najera, Encinitas has not conducted detailed financial analysis of the potential costs related to sea-level rise for the short or long term, but she wrote that “generally, significant financial impacts are more likely to occur in the later years, 2050-2100.”

Najera also explained that “the city is addressing Sea Level Rise on a project-by-project basis.” She pointed to the recent reconstruction of the Marine Safety Center at Moonlight Beach as an example of a structure designed to protect against rising seas.

One resource Encinitas and other North County beach communities know they need and want is sand. It could protect against the effects of sea-level rise, and it replenishes the sand lost to erosion by El Niño and other factors.

Through state funding, the city of Encinitas is slated to start the Cardiff Beach Living Shoreline Project in September 2018. The plan is to create a dune system on Cardiff State Beach just west of Highway 101 that will provide native dune habitat and act as a buffer against sea-level rise by protecting the roadway from flooding.

In the near future, Encinitas intends to continue managing coastal bluffs and nourishing beaches. Beach nourishment is a euphemism for what is essentially a sand dump. Sand is deposited on beaches to make up for the sand that’s been carried away by the ocean.

Bob Guza, professor emeritus for the Integrative Oceanography Division at Scripps Institution of Oceanography, and his team of researchers have monitored beach elevations — or how high the sand is — at various San Diego County beaches for many years. That sand surveying has provided data to study how effective sand nourishment is.

Guza said the county spent $30 million on beach nourishment in 2012. He believes, however, that it’s an effective practice. His research revealed that the beach nourishments of 2012 kept those beaches wide until the El Niño winter of 2015-2016.

Through a combination of warmer water and strong wind, El Niño causes the sea level “to go on these wild binges,” as Guza put it, that accelerate erosion. While 2015’s El Niño washed away much of the nourishment sand, the added sand “prevented the overwash of Highway 101,” Guza said.

During his workshop presentation, Guza showed a photo of Torrey Pines State Beach, which hasn’t been nourished since 2001. It’s covered in cobbles. He quipped, “The Germans won’t pay to sit on rocks,” which leads to another aspect of sand nourishment: its ability to sustain beach tourism, which brings money into coastal communities.

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