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Oregon Beach and Shoreline Mapping and Analysis Program: Pacific Northwest Estuaries and Shores

Beach Morphology Monitoring Program

 

Beach Profiles - Alsea Spit 3

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 were derived from LIDAR topographic data flown by the USGS and NASA in October 1997 (pre EL Nio), April 1998 (post EL Nio), and September 2002, while more recent data have been measured using a Trimble 5700/5800 RTK-DGPS surveying system.

 

 

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 six lower plots reflect contours of greater interest due to their proximity to the dune or bluff face and toe (e.g. the 7.0 m, 6.0 m and 5.0 m contour) or to Mean High High Water mark (e.g. the 3.0 m contour).  The 1997 data have been used in the six lower plots as a baseline since this reflects the first comprehensive survey of the shape and position of the beach.