January 13, 2004
14:38
WSPC/101-CEJ
00092
Recent Developments in the Geomorphic Investigation
573
Merrimack River Inlet is a riverine-associated inlet (FitzGerald et al., 2002). The
sediment supply to this inlet is dominated by an influx of fluvial sediment during
late winter and early spring freshets. Bathymetric LIDAR data collected by the
USACE clearly displays ebb-orientated sandwaves and flood-oriented megaripples
(Fig. 4; FitzGerald et al., 2002). Based on the LIDAR information gathered in this
study, sediment transport is determined to be seaward.
SHOALS surveys were collected three times during 1994 at New Pass, Florida
in March, September, and December (Irish and Lillycrop, 1997). The spatial extent
of these surveys varied but in total the channel, ebb delta, and adjacent nearshore
areas were covered. Expansion of the survey area from the navigation channel to
the surrounding areas provided a more complete explanation of the morphological
changes. Not only could the erosion and shoaling within the navigation channel be
explained by the sequential surveys but sand sources and sinks could also be identi-
fied. The SHOALS surveys demonstrate that the cause of shoaling along the north
side of the ebb tidal delta was due primarily to sand influx from longshore sediment
(Fig. 5; Irish and Lillycrop, 1997).
Bathymetric LIDAR surveys have also been applied to the study of the effects
of coastal structures. Preaque Isle in Lake Erie is a 10-km long recurved sand spit
(Mohr, Pope, and McClung, 1999). It has 55 segmented breakwaters to protect it
from erosion (Mohr, Pope, and McClung, 1999). In 1995, a SHOALS survey was
added to the monitoring strategy and extend from the subaerial beach to a depth
of about 7 m (Mohr, Pope, and McClung, 1999). Volume analysis of the SHOALS
surveys showed an accretionary trend between the breakwaters and the shoreline
while there was erosion seaward of the breakwaters. Seaward of the breakwaters
resulted in the seafloor being lowered an average of 0.2 to 0.4 m over the four year
monitoring period (Mohr, Pope, and McClung, 1999).
2.4. High resolution shallow marine seismic surveys
Seismic reflection profiles provide an image of the subsurface and are particularly
useful for delineating sedimentary layers, bedrock outcrops, depth to the acous-
tic basement, and other geological features beneath the sediment-water interface.
Traditionally, seismic surveys have been employed to help determine the stratigra-
phy and evolution of various depositional sequences on the continental shelf and
in nearshore settings such as estuaries, lagoons, and major river channels. In re-
cent years seismic surveys have been utilized at tidal inlets to decipher channel
migrational trends and overall depositional history of the inlet (Buynevich et al.
2001), dredging requirements (FitzGerald and Montello, 1990), and thickness of ebb-
tidal deltas (FitzGerald and Nummedal, 1977). High resolution seismic equipment
produces acoustic waves using a variety of sources including boomer systems, sparker
arrays, or air gun. Depending upon the desired imaging, particular energy outputs
and filtering schemes are used; lower frequencies noise produces greater penetration,
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