Coastal Engineer gives presentation on coastal processes at Sharp Park Library


By on Thu, August 26, 2010

Coastal armoring, whether a seawall, riprap boulders or both, often results in a loss of the beach and ultimately, over the long term, can affect the surf zone and the entire environment in that vicinity.
This was one of the many interesting facts mentioned in a presentation by California’s premier coastal engineer and local Pacifica surfer Bob Battalio on August 16th in the Community room at Sharp Park Library. Coastal erosion, sea level rise, and flood control were the focus of discussion.

Pacifica’s coastline has been eroding for thousands of years and will continue to erode into the future as the sea level rises, according to Battalio. Apparently armoring the coast can actually speed up the rate of erosion, although these “active” effects of seawalls are being debated.  While in the short term armoring can stop erosion of the land immediately behind it, experience along California’s coast has shown that erosion continues in front of the engineered structure. As the waves remove sand in front of the structure, engineers and geologists who study coastal processes have discovered that the beach is lost and the wave energy that the beach once absorbed makes the structure and what is behind it more vulnerable.

Battalio used historic photos to explain the erosion process and illustrate how severe the erosion problem has become along Beach Boulevard. Pacifica faces some very important decisions about how to deal with sea rise in the coming years. 

Along most of Pacifica’s coast, private property concerns make managed retreat a very controversial topic. Often a sea wall is put up to protect homes at the cost of losing the beach. But in the long term, the most cost-effective way of dealing with sea level rise in many locations, says Battalio, is managed or planned retreat which allows the shoreline to advance inward over time. Pacifica State Beach at Linda Mar is an example of the successful implementation of managed retreat strategy.

Coastal managers now realize that in many situations attempting to stop erosion through structural or non-structural solutions is a losing battle. According to the United States National Oceanic and Atmospheric Administration, shoreline protection efforts and/or their repeated maintenance will be too costly and ultimately ineffective
The beach at Sharp Park south of Clarendon is one of the only places where Pacifica could allow the beach to migrate inward without threatening private property, says Battalio. In fact, he explained, a sea wall will actually increase the flood risk at south Sharp Park by blocking outflow of rain runoff to the ocean causing Laguna Salada to flood. Hearing this, an audience member expressed surprise that San Francisco and Pacifica would want to build a sea wall to protect a golf course that doesn’t make any money and that would cause the beach to erode.

It will be something to think about in the coming months. Battalio’s informative presentation began an important discussion about the tough decisions that Pacifica residents will need to make about the city’s future along a changing coast.