port equations developed for gravity-driven flows
their criteria, they used data on ship-induced ve-
could be applied to these calculated velocity dis-
locities as well as the results of 34 measurements
tributions. This assumption may not be strictly
of directional sediment transport. This allowed
correct but definitely necessary given the state of
quantitative prediction of net transport and di-
the art.
rection for sand-sized materials, but their actual
For two sites on the St. Marys River, they pre-
damage criteria were largely qualitative in na-
dicted velocities, bed loads and suspended sedi-
ture. Their basis for prediction of cohesive sedi-
ment concentrations for several vessel classes.
ment transport is unclear. They classified the po-
They did not attempt to discriminate between
tential for damage into three categories. None to
events causing or not causing a level of unaccept-
light refers to inconsequential movement, mod-
able transport, but they did compare vessel ef-
erate damage implies light transport as bedload,
fects in terms of kinetic energy density (one-half
while severe damage is defined as a condition
of the square of net ship-induced velocity). It is
where sediment is suspended and soils sustain-
not clear how the kinetic energy of individual ship
ing shallow-rooted organics may be displaced.
passages can be summed to provide a season-long
As mentioned earlier, they found little sediment
estimate of the potential for sediment movement,
transport for drawdown events less than 6 in. in
but it is used here to compare the cumulative ef-
magnitude and concluded that damage could be
fects of different fleet mixes and navigation sea-
effectively minimized by controlling vessel speed
son durations.
to prevent larger events.
In general, they found downbound vessel pas-
sage to be more damaging, since ships are typi-
Field studies of shoreline recession
cally loaded passing downbound and light pass-
The first field study of shore damage in con-
ing upbound. In comparing the relative effects
nection with winter navigation on the Great Lakes
of ships in open water, a continuous broken ice
was conducted by the Detroit District on the St.
cover and sheet ice, they concluded that propel-
Marys River beginning in 1972 (USACE 1974). In
ler wash effects also increase in that order since
that study they measured waves and water level
increasing propeller thrust would be required to
fluctuations at four sites and repeatedly surveyed
maintain speed. They also concluded that the
shoreline profiles at 12 sites. They observed no
newer, 1000-ft vessels had a potential for dam-
gouging of shorelines due to ice shoving and in-
age four to nine times higher than smaller exist-
stead felt that the shore ice formations served as
ing vessels due to higher horsepower, twin pro-
protection against damage.
pellers and greater possible draft. The lower num-
During a survey period from November 1972
ber represents open-water sailing, the latter with
to March 1973 they noted little or no change in
a solid ice sheet.
the measured shore profiles. A subsequent June
In developing a damage criterion for vessel-
survey indicated some erosion at most sites, with
induced drawdown, Wuebben et al. (1984) adapt-
a maximum recession of about 2.5 ft for two sites
ed non-scouring velocity criteria from the open-
on Lake Nicolet but more typically 0.5 ft or less.
channel-flow literature for the various classes of
They observed that waves generated by small craft,
soils found in the Great Lakes connecting chan-
particularly cruisers, were generally higher and
nels. Since drawdown is the ship effect that can
apparently more damaging than those generated
be predicted with the best accuracy, these scour
by commercial vessels. Sites found to be experi-
criteria were then correlated to field data on the
encing significant erosion were near Mission Point,
maximum ship-induced velocities caused by given
Frechette Point, Six Mile Point, Nine Mile Point,
levels of drawdown. This allowed the use of a
the north shore of Neebish Island and upstream
one-dimensional drawdown model to compare
of Johnson's Point.
the significance of various channel, vessel size
Their conclusions were that erosion of the shore-
and speed scenarios and to predict reaches along
lines occurs during the traditional navigation sea-
the river where the erosion potential was high.
son but is minor during the extended season pe-
Hodek et al. (1986) based their damage crite-
riod. Further, they concluded that less than 5000
ria on the level of drawdown and velocity distur-
ft of shoreline is subject to significant erosion and
bance, the magnitude of surge, soil conditions and
that high water levels (which occurred during the
shore geometry. They also indicated that the de-
study) are the most significant cause of erosion.
velopment of shorefast, grounded ice would serve
A follow-up study by the consulting firm of
as a barrier to shoreline damage. In developing
Dalton, Dalton, Little and Newport, Inc. (1975)
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