Del Playa Drive’s erosion-plagued cliffs have been receding as quickly as 15 inches per year from natural and man-made causes, according to geological studies and environmental documents dating back to the mid-1970s.
The eroding blufftops have threatened DP homes since the day they were built. However, while many causes of the erosion have been identified – most notably the relentless pounding of the Pacific Ocean – solutions to the problem have been scarce.
In 1981, a group of DP property owners convinced the county to look into creating a Del Playa seawall maintenance district. Using public funds, the purpose of the district would be to construct and maintain a 3,686-foot seawall out of large vertical timbers.
The wall was intended to diffuse much of the ocean waves’ energy and slow the rate of bluff erosion. The county generated an environmental impact report in 1981 to assess the feasibility of the wall and introduce the project to the public. Despite a favorable review, some residents opposed construction of the wall, citing its possible ineffectiveness and unsightly appearance. Others opposed the taxes that would be needed to fund its construction.
The report acknowledged that the DP erosion problem needed to be addressed, but that a wooden seawall was not the only solution.
“If no corrective remedial actions are taken to stem or slow the sea cliff retreat along the site, a loss of an undetermined amount of land (on the order of 12 inches per year or more) and an undetermined number of residential structures would occur. Loss of fronts of some residential structures could occur within 5 to 10 years,” the report said.
Due to resident opposition, the wall was not built, but the project was revived in 1988 when some property owners sought to privatize the project and build the wall only in front of their properties. However, according to transcripts of public comment contained in the environmental impact report, some residents and researchers suspected that leaving gaps in the seawall would actually concentrate the wave energy in the gaps, causing greater cliff destruction in those areas.
The proposal had significant opposition from owners of properties that would be situated behind wall gaps. The project was stalled again until 1992, when the details of the wall’s coverage were revised. The proposal was again turned down until 1996, when the wall was planned to cover all private properties. This was met with opposition from a significant number of residents who did not want any part of the wall.
Like many parts of the California coast, the lower portion of the 35-foot cliffs is made of a rock called shale. The shale is part of the Sisquoc formation, a large layer of rock that underlies much of the ground in Santa Barbara. Even the toughest rocks would be eroded by ocean waves, but shale is especially soft and crumbles when hit by breakers.
The rate of cliff erosion has been studied in Isla Vista for many years, with one of the earlier studies done in 1975 by William Cottonaro. His findings were published in California Geology – a journal devoted to geological science research – and detailed how fast the bluff line was receding in I.V. between 1967 and 1973.
Cottonaro found that the cliff does not recede at a uniform rate; rather, some areas of the cliff erode more quickly than others. The slowest rate of erosion found in the one-mile section of coast studied was less than two inches per year, while the fastest was over 15 inches per year. The average rate was 8.5 inches per year.
“A sea cliff is not a permanent land form,” Cottonaro wrote. “Rather than a smooth steady process, cliff erosion is intermittent, depending wholly on a number of varying conditions.”
Some of those varying conditions depend on the ocean waves, but others depend on how people deal with cliff erosion. Adding grass or other plants may seem like a good idea to help secure the soil, but Cottonaro found these efforts are mostly fruitless.
“The heavy stalk and leaves of the ice plant, however, with its ability to overhang a bluff make it unsuitable for sea cliff landscaping,” Cottonaro wrote. “Shortrooted grass is also ineffective in securing the soil near the edge of the bluff because land slippage in this area occurs deep beneath the holding capacity of such root systems.”
Geology Professor Robert Norris was also involved with research on the coast and published a 1990 report on cliff erosion in California Geology.
Norris found that the required watering of grass or ice plants worsens erosion by washing away parts of the cliff. This is not a trivial effect, as Norris found that the addition of lawns on the cliff’s edge actually caused the overall rate of erosion to increase substantially.
Norris stated that even drought-resistant plants may not be helpful because their root systems can split the rock into pieces, which can be washed away. Adding drainage pipes that extend from the cliff face can also cause increased erosion if they leak or if water collects around the outside of the pipe. Also, rainwater and wind-driven ocean spray can cause the cliff to crumble.
“Groundwater seeping from a cliff face may cause another type of non-marine erosion called spring sapping,” Norris wrote. “People and animals also affect sea cliff erosion. For example, foot trails up steep cliffs result in increased erosion.”
Despite all of these non-marine factors, Norris estimated that over half of the erosion is caused by the ocean waves directly.
Some of Norris’ work also described why building seawalls so often garners negative public opinion.
“State and local government agencies involved in zoning and building safety usually do not approve construction of sea walls and other protective structures because these structures occupy beach space, are usually unsightly, require continuing maintenance, and hinder beach access,” Norris wrote.