Abstract:
Because of highly dissipative conditions and strong alongshore gradients in foreshore
beach morphology, wave run-up data collected along the central Oregon coast during
February 1996 stand in contrast to run-up data currently available in the literature. During
a single data run lasting approximately 90 min, the significant vertical run-up elevation
varied by a factor of 2 along the 1.6 km study site, ranging from 26 to 61% of the offshore
significant wave height, and was found to be linearly dependent on the local foreshore
beach slope that varied by a factor of 5. Run-up motions on this high-energy dissipative
beach were dominated by infragravity (low frequency) energy with peak periods of
approximately 230 s. Incident band energy levels were 2.5 to 3 orders of magnitude lower
than the low-frequency spectral peaks and typically 96% of the run-up variance was in
the infragravity band. A broad region of the run-up spectra exhibited an ƒ¯⁴ roll off,
typical of saturation, extending to frequencies lower than observed in previous studies.
The run-up spectra were dependent on beach slope with spectra for steeper foreshore
slopes shifted toward higher frequencies than spectra for shallower foreshore slopes. At
infragravity frequencies, run-up motions were coherent over alongshore length scales in
excess of 1 km, significantly greater than decorrelation length scales on moderate to
reflective beaches.
