, Modelling of
undertow by a one-equation turbulence model, Coastal Engineering,
15, 431-458, 1991.
Figure 1: Schematic of important nearshore processes showing how the
incident wave energy that drives the systems evolves as the waves
progress from offshore to the shoreline (top to bottom of the figure).
Wave evolution is grouped into processes occuring seaward of the break
point (denoted ``shoaling'') and those within the surf zone (denoted
``breaking''). In both bases, energy is spread to lower (left) and
higher (right) frequencies. The beach topography provides the bottom
boundary condition for flow, so is important to wave processes. In turn,
the waves move sediment, slowly changing the topography. Wind and tides
may be important in some settings, but are not shown here. (from [
Holman, et al., 1990])
Figure 2: Frequency-cyclic wavenumber (f-K) spectra for an example data
run from the SUPERDUCK experiment. a) spectrum calculated based on a
longshore array of cross-shore velocity sensors. Well-defined peaks are
indicated, with relative energy shown with shading. All gravity waves
must reside between the two curved mode-0 dispersion curves. Shear
waves, the sloping line of energy to the right, show wavenumbers that
are substantially too large to be gravity waves. b) Expected frequency
wavenumber combinations for rapidly growing shear instabilities. The
match between theory and data provides strong support for the shear
wave model of far infragravity motions. (from [ Dodd, et al.,
1992])
Figure 3: Time series of mean locations for the shoreline, inner and
outer bar over a six year period at Duck, NC. Values are averages over
a 400 m longshore extend and over the period of one month. The annual
cycle is apparent in 1986, 1987 and 1990/1. However, the disappearance
of the outer bar in 1988/9 apparently made the inner bar unstable, with
a terrace developing that was hard to distinguish from the shoreline.
Long data sets are invaluable in showing behavior that had not been
previously expected. (from [ Lippmann and Holman, 1993])