Beach Morphology Monitoring Program

Beach Profiles - Seaside

Beach profiles provide important information concerning the temporal (time) and spatial (cross-shore) variability of the shape of a section of beach.  The information derived from these 'repeated' surveys provide a measure of the response of the beach to variations in the offshore wave energy (e.g. winter versus summer wave conditions), which is reflected in accretion of the beach during the summer and erosion in winter.  These data also contain important information on how the beach responds to major storms, such as the extreme 1997-98 and 1998-99 winters, in the form of dune or bluff erosion (i.e. how much dune or bluff retreat occurred), data that is extremely useful when designating hazard zones along the coast.  Beach profile data provided in the figure below have been surveyed on a quarterly basis since fall 1997 by staff from the Washington Department of Ecology as part of the Southwest Washington Coastal Erosion Study.  These surveys were carried out using a Trimble RTK-DGPS surveying system.  Since October 2005, surveys undertaken along the Clatsop Plains have been carried out by DOGAMI staff.

Excursion distance analysis (EDA) extends the usefulness of conventional beach profile data by capturing the response of the beach at different contour elevations across the beach over time, and as a result reflects a 'time stack' of how the beach is changing.  Markers in the figures below reflect when surveys of the beach were undertaken.  The orientation of the line provides an important clue as to how the beach is responding.  For example, lines that deviate right of the zero line indicate that the beach is accreting, while lines and points left of the zero line indicate erosion.  Depending on the frequency with which the surveys have been carried out, such plots can highlight the seasonal response of beach between summer and winter, as well as any longer term evidence of coastal change.  The four lower plots reflect contours of greater interest due to their proximity to the dune toe (e.g. the 6.0 m and 5.0 m contour) or to Mean High High Water mark (e.g. the 3.0 m contour).  The fall 1997 survey data have been used in the four lower plots as a baseline since this reflects the first comprehensive survey of the shape and position of the beach.