Portland State University. Department of Geology.
Curt D. Peterson
Date of Award
Master of Science (M.S.) in Geology
1 online resource (vii, 113 p.)
Beach erosion -- Washington (State), Beach erosion -- Oregon, Subsidences (Earth movements) -- Washington (State), Subsidences (Earth movements) -- Oregon, Subduction zones -- Washington (State), Subduction zones -- Oregon
Beach shoreline retreat induced by coseismic subsidence in the Cascadia subduction zone is an important post-earthquake hazard. Sand on a beach acts as a buffer to wave attack, protecting dunes, bluffs and terraces. The loss of sand from a beach could promote critical erosion of the shoreline. This study was initiated in order to estimate the potential amount of post subsidence shoreline retreat on a regional scale in the Central Cascadia Margin. The study area is a 331 km stretch of coastline from Copalis, Washington to Florence, Oregon. Several erosion models were evaluated, and the Bruun model was selected as the most useful to model shoreline retreat on a regional scale in the Central Cascadia Margin. There are some factors that this model does not address, such as longshore transport of sediment and offshore bottom shape, but for this preliminary study it is useful for estimating regional retreat. The range of parameter input values for the Bruun model include: the depth of closure (h) range from 15 m to 20 m water depth; the cross-shore distance (L) range from 846 m to 5975 m; and the estimated subsidence amount (S) range from O m to 1.5 m. The minimum to maximum range of post-subsidence shoreline retreat is 142 to 531 m in the Columbia River cell, 56 to 128 m in the Cannon Beach cell, 38 to 149 m in the Tillamook cell, 25 to 91 m in the Pacific City cell, 11 to 126 m in the Lincoln City cell, 30 to 147 m in the Otter Rock cell, 0 to 165 m in the Newport cell, 0 to 76 m in the Waldport cell, and 0 m in the Winchester cell. Results of the study suggest that many of the beaches in the study area are at risk of beach and personal property loss. Beach communities could limit the amount of potential damage in these areas through coastal zone planning.
Doyle, Debra Lee, "Beach Response to Subsidence Following a Cascadia Subduction Zone Earthquake Along the Washington-Oregon Coast" (1996). Dissertations and Theses. Paper 5072.
GPR transect on South Jetty Road profile, Florence, Oregon (From Meyers and others, 1996)
Pocket2.pdf (1991 kB)
GPR transect 'A' on Loomis Lake State Park profile, Long Beach Peninsula, Washington (From Meyers and others, 1996)
Pocket3.pdf (183 kB)
GPR transect 'B' on Loomis Lake State Park profile, Long Beach Peninsula, Washington (From Meyers and others, 1996)