Artificial retention of beaches in California: Current extent, public opinion and influence on backshore morphology

Artificially retained beaches form where the alongshore movement of littoral drift is detained by the presence of man-made structures within the coastal zone. It has long been recognized that there are numerous artificially retained beaches within the state of California that have modified the shoreline, but the full extent to which engineered structures have shaped present-day beaches has not previously been investigated. The importance of understanding the role that retained beaches play in expanding total recreational area and buffering the backshore from erosion is increasingly important as engineered sediment retention is considered as a coastal management strategy.;This study has catalogued and described the retention effectiveness of 211 man-made structures along the 1,760 km open-ocean coastline of California. Measurements of the area of sandy beach retained by each of these structures reveal that 15 million m², more than 18% of California's total exposed sandy beach area, is presently retained in and behind fillet or salient beaches associated with man-made structures. A survey of frequent beach users has revealed the extent to which these retained beaches have influenced coastal residents and shaped their opinions about engineered retention as an erosion control measure.;An investigation of the relationship between beach widths and cliff slopes has quantified the dissipative role of beaches by measuring the denudation of low relief cliffs and bluffs in the presence of a range of beach widths, both naturally and artificially retained. A deeper knowledge of this relationship is critical to considering the role that artificially retained beaches could play in reducing the marine erosion of developed backshore areas.;By using a combination of traditional and non-traditional approaches, this study has addressed the influence that artificially retained beaches have upon the total extent of sandy beach area within the state, on patterns of back-beach erosion and on coastal residents. The results of this work advance our understanding of the role that engineered structures have in shaping coastal processes and answer questions about the types of roles that these structures may play in the future.