applications, the local wave generation (represented by the source terms) is often
an essential process, increasing the wave height near shore and altering wave
directions.
Example 3: Wave Propagation at Yaquina Bay
Entrance, OR
The final example is based on a field site, Yaquina Bay Entrance, OR. The
nearshore bathymetry at Yaquina is complex because of the presence of the
entrance channel, rock reefs, and jetties. Tidal currents at the entrance exceed
1.5 m/sec, and the tidal range is greater than 2 m. The wave climate off the
Oregon coast is severe with observed deepwater wave heights exceeding 12 m.
The north Yaquina jetty was repaired in 1988 and has experienced progressive
loss of the head of the jetty since 1996 (approximately 110 m of jetty length has
been lost). Quantitative information about waves at the entrance was required to
support structure redesign and to evaluate navigability. More information about
the Yaquina Bay Entrance north jetty is given by Hughes et al. (1995).
The nearest wave gauge to Yaquina Bay is a National Data Buoy Center
buoy located 35 km off the coast in a depth of 130 m. It is not practical to
transform the measured waves from the buoy to the entrance at fine resolution.
Although high resolution (25 m) is required in the nearshore to define the reefs
and entrance channel, coarser resolution is sufficient offshore (where high-
resolution bathymetry is not available). For this application, a fine nearshore grid
was nested with a coarse offshore grid. The offshore grid has a resolution of
250 m with 125 cells across the shore and 253 cells along the shore. The grid
extends from an offshore depth of 130 m (at the buoy location) to a nearshore
depth of 47 m. NOAA bathymetry was used. Both the offshore and nearshore
grids were aligned with the nearshore contours (x-axis at 350 deg counterclock-
wise from west), so no rotation of the spectra was required between offshore and
nearshore simulations. Measured heights, periods, and directions from the
offshore buoy were then transformed across the offshore grid (including wind
input, but excluding currents and tide variations). Output spectra were saved in
the most landward column and used as the input spectra for the nearshore grid.
The nearshore model runs are described in the following paragraphs.
Model input
Model parameters. Figure 19 shows the bathymetry contours within the
STWAVE nearshore modeling domain selected for the Yaquina Bay Entrance.
The offshore boundary location is selected at an approximate depth of 47 m.
This depth is chosen because the bottom contours are fairly straight and parallel
at this depth (out of the influence of the ebb shoal). The lateral boundaries of the
domain are positioned away from the influence of the entrance, to areas of fairly
straight and parallel depth contours. A 25-m grid cell spacing is selected to
resolve the reefs and entrance bathymetry. To cover the domain with 25-m
resolution requires 188 cells across the shore (NI) and 236 cells alongshore (NJ).
59
Chapter 6 Example Applications
Previous Page
