Incident wave spectrum. The incident wave spectrum for Yaquina Bay was
generated using a TMA spectral shape (with a spectral peakedness parameter,
γ = 8), cosnnα directional distribution (with nn = 30), Hmo = 12.5 m, Tp = 20 sec,
and αm = 55 deg (from the Southwest) on the offshore grid. The nearshore grid
was forced with the output spectrum at a depth of 47 m from the offshore grid.
These incident conditions represent extreme high wave conditions from a storm
in 1999.
Current field. The current field for Yaquina Bay was generated using the
tidal circulation model ADCIRC. The current field output from ADCIRC was
interpolated onto the STWAVE grid using SMS as described in Chapter 5. The
ebb and flood current fields are plotted in Figures 17 and 18 for the area near the
jetty tips. The current fields show not only the tidal current through the entrance,
but also a longshore current toward the north generated by strong alongshore
storm winds. Representative nearshore tide levels of -0.90 m (at peak ebb) and
0.61 m (at peak flood) from ADCIRC were applied in STWAVE.
Results
The wave height contours in Figures 20 and 21 show that the waves in the
nearshore in this extreme storm event are breaking due to depth limitations (note
gradient in the wave height contours). The 1.5-m higher water level on flood
accounts for the larger wave heights during flood than during ebb (generally,
larger wave heights are expected on ebb due to wave-current interaction, unless
the wave heights are depth limited, as they are in this example). Figure 22
(generated in SMS) shows the difference in wave height (flood minus ebb) for
this example. The red/orange contours show areas where the wave height is 1.5
to 2 m higher on flood (at the jetty tips). The blue contours show areas where the
wave height is 0.5 to 1.0 m higher on ebb (in the interior channel, where the
water depth is greater and the current stronger).
61
Chapter 6 Example Applications
Previous Page
