Rob Mayeda made the point that:

Seawalls are often used to protect structures from the ocean onslaught of storm driven surf. These artificial barriers have been shown to focus the ocean energy in areas around the sides of the seawall structure.

Examiner.com: Crumbling coastline: Pacifica’s problems nothing new to the California coast by Rob Mayeda

See Rob Mayeda’s personal blog All Things Weather All The Time.

(NOTE: This post is part of my coverage of the cliff erosion and collapse at 330 Esplanade Ave, Pacifica. For a complete chronology and links to many photos see Evacuation underway at 330 Esplanade.)