ERDC/CHL CHETN-I-67
June 2003
Tedious Creek Small Craft Harbor:
CGWAVE Model Comparisons Between
Existing and Authorized Breakwater
Configurations
by Michael J. Briggs, Barbara P. Donnell, Zeki Demirbilek, and Robert D. Carver
model comparisons between existing and authorized breakwater configurations at Tedious Creek,
MD. The numerical model CGWAVE was used to predict wave heights and directions inside the
harbor to determine if there are any significant differences between the two configurations.
BACKGROUND: Tedious Creek is a small estuary on the eastern shore of Chesapeake Bay in
Dorchester County, MD (Figure 1). It provides anchorage to more than 100 commercial and
recreational vessels. The primary anchorages are the county boat dock (CD) and the public piers
(PP), both on the south shore. Because of its orientation, storm waves may cause substantial
damage.
In 1994, the U.S. Army Engineer District, Baltimore, and the U.S. Army Engineer Research and
Development Center (ERDC), Coastal and Hydraulics Laboratory (CHL) conducted hydrodynamic
model investigations to determine if the proposed breakwater would have any adverse navigation or
environmental effects. An analytical model and the RMA2 numerical model were used in the design
to optimize the gap width and breakwater alignments. The Baltimore District wrote a Section 107,
Feasibility Report and Integrated Environmental Assessment in March 1995 suggesting that a
breakwater could provide a cost-effective solution. The authorized project design included a
breakwater gap of 91 m (300 ft) for the main channel. An additional gap was included midway along
the length of both north and south sides of the new breakwater to improve water circulation and
quality.
The existing as-built breakwater differed in geometry from the plans tested in 1994 because of
foundation problems encountered during construction in 1997. As a result, the north breakwater was
shorter with a 30-m- (100-ft-) wider gap (i.e., 122-m (400-ft) gap) in the main entrance. Because of
local concerns, a monitoring effort was initiated in 2001 to test the hypothesis that (a) the existing
as-built gap will provide a functional harbor from the standpoint of wave attenuation, circulation,
sedimentation, and wetland impacts, (b) the 1997 improvements are structurally sound, (c) the
numerical models accurately predict prototype performance, (d) navigation and the environment will
not be adversely impacted by sedimentation from the improvements, and (e) local wetland areas are
not adversely impacted. Wave data are being collected in FY03 as part of the Monitoring Completed
Navigation Projects (MCNP) Program. Numerical model results will be compared with these field
data.
CGWAVE MODEL SETUP: CGWAVE is a general purpose, state-of-the-art wave prediction
model based on the mild slope equation that is used to model waves in harbors, open coasts, inlets,
islands, and fixed and floating structures. It includes the effects of wave refraction, diffraction, and
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