Retreat of a coastal bluff in Pacifica, California

The focus of this study is the long-term evolution of a developed coastal bluff. The 1.4-km-long study site is located in Pacifica, California. Historic topographic maps and aerial photographs, geo-referenced within a geographic information system (GIS) framework, were employed to quantitatively characterize bluff retreat distances and rates. The most conservative estimate of bluff retreat for the study site results in an average rate of 0.5 m/yr, with a million cubic meters of sediment lost during a 68-year period. There is no question that the bluffs in Pacifica will continue to evolve. A better understanding of bluff retreat rates and processes for the study site will require data-intensive discovery in the form of committed long-term monitoring. The results herein provide a foundation for those in the decision-management arena.