OBJECTIVES
Wave energy tends to concentrate after a shoal because of wave refraction
and diffraction processes. The degree of wave energy concentration, however,
depends on wave conditions, shoal geometry, and ambient water depth. In
a previous study at Virginia coast, we found that waves coming from NNE
do concentrate after the Sandbridge shoal. For the three shoals along the
border of Maryland and Delaware coasts, a similar situation may or may
not occur because of the unique bathymetry, shoal geometry, and wave conditions.
One of the study goals is to check out the original natural responses.
When a shoal is flatten (by dredging), the degree of wave energy concentration
would be altered. We have proved that if only a small amount of dredging
(on the order of 106 m3), the influence would be
insignificant because of the huge size of the selected shoals. We will
proceed one step further and study if there is any accumulated effect for
a continuous dredging with an amount on the order of 107 - 108
m3.
Storm surges, driven by strong winds, can help tremendously on the build
up of destructive breaking waves. As a rule of thumb, the more shallow
the water, the more the storm surge. The shoals only have a limited area
of shallow water, and thus, the influence on storm surge would be small.
When a substantial amount of sand was removed, however, the influence should
be checked, and that is another goal of this study.
The grain size of bottom sediment may affect the selection of habitation
for benthic organisms because they prefer to stay in area with more fine
sediments. Numerical model studies of the combination of tidal current,
wave, and benthic boundary dynamics can reveal where the agitation force
(bed shear stress) is small, and thus, favorable for fine sediments to
deposit. On the other hand, it can also tell where the agitation force
is always strong, and thus, only coarse sediment can stay. A map of agitating
force may be correlated with the habitation. If this idea can be proved
successful, then we can provide a possible change of habitations caused
by the change of agitating forces, which can be affected by the dredging.
FUND AGENCY: Minerals Management
Service
FUNDING PERIOD: 6/24/97 - 6/30/98
PIs: Jerome P.-Y. Maa, Sung-chan Kim, Woody Hobbs