It is a common sight to see chunks of sand breaking off of the bluffs and falling down to the beaches around Santa Barbara and Isla Vista. What is not common are houses on Del Playa being evacuated because the bluff that once supported it has crumbled away.
The erosion of the California coastline is the inevitable result of natural processes. However, climate change has resulted in less sand on beaches and more powerful El Niños, causing the coastline to erode even faster.
Where does all the sand come from, and where does it all go? It comes from sediment that flows down freshwater sources, such as rivers or rain, and that is then deposited on beaches. Beaches then lose sand to the ocean.
In a recent study by the U.S. Geological Survey (USGS), scientists found that the 2015-16 El Niño event was the strongest El Niño event in the last 150 years. By calculating coastal change and using water and water-level statistics, scientists were able to compare changes in the California coastline due to El Niños over time. Their latest projections suggest that future El Niños will continue to be extreme.
According to USGS researcher and lead author of the study Patrick Barnard, beaches in California are sediment-starved because there has not been enough rain to replenish their sand supplies.
UCSB marine scientist David Hubbard, who contributed to the study, explained why beaches were so affected by the El Niño.
“When you have a five-year drought, not much sediment is coming to the coast, and with an El Niño that increases the amount of sediment you lose, the beaches are gonna get narrower,” Hubbard said.
This event is a preview to future El Niño events, which are projected to increase in strength. When asked what can be done in terms of beach recovery after such events, Barnard stressed the importance of maintaining sand volume on beaches. When beaches have more sand, they are more resistant to El Niño events. Beaches are the first line of defense and can slow cliff retreat.
According to Hubbard, these are the moments in which plenty of coastal hazards and flooding occur, and understanding these events will help us understand the ecological challenges that are coming.
“Southern California beaches have lost 50 percent of their sediment supply, and a lot of that sand supply has been lost because people put dams on rivers and creeks,” Hubbard said. “If the interest is in having healthy beaches, which also helps protect the coast from erosion, one of the things that would help is restoring sand supply to the coast.”
Using the Matilija Dam in Ventura County as an example of restoring sand supply, Hubbard said that it no longer provides any flood control and it does not supply any water to agriculture or drinking water because it is full of sediment.
“There’s been an effort to take the dam out and restore natural hydrological functions to the watershed and to let the sediment get back down to the coast where it would make the beaches wider and restore the ecosystem,” Hubbard said.