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A long-term objective of nearshore
oceanography is to understand the processes shown in the photograph below,
including the evolution of surface gravity waves propagating across the
continental shelf through the shoaling region and surf zone, and the
corresponding inner shelf and breaking-wave driven nearshore circulation,
sediment transport, and subsequent bathymetric change. |
FIGURE 1: Aerial photograph near Black's Beach
in Southern California showing the effect of offshore canyons on surfzone
processes. Alongshore variations in wave height, caused by propagation over the
canyons, result in variation of the surfzone width from about 150 m at the
southern edge of the image to 100 m at the northern edge. The waves propagating
at large oblique angles relative to the shoreline (thin arrows point to wave
crests) are nearly perpendicular to the incident wave direction and may have
reflected from the steep canyon walls (located offshore and south of the
image). The complex, breaking-wave-driven circulation includes converging
alongshore flows and sediment-laden, offshore-directed rip currents that extend
well outside the surf zone (thick arrows).  |
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To attain this
objective, scientists are developing a
nearshore processes community
model. The assumptions and physics underlying the model hypotheses are
tested with field observations, including those obtained in a
suite of experiments conducted on a
barred beach on the gently sloping, wide continental shelf near Duck, North
Carolina. In contrast to the North Carolina coast, many continental shelves
have abrupt irregular bathymetry that causes large gradients in the wave field
outside the surfzone. The steep topography of Scripps and La Jolla Submarine
Canyons in Southern California produces dramatic changes in wave energy over
alongshore distances of only a few hundred m
(FIGURE 2), resulting in
complex
nearshore circulation and
morphological
change. |
