certain. However, the Hochstein and Adams model
scenarios but more importantly for scenarios con-
should provide an improved basis for compari-
sidered for possible future implementation where
son of various vessel frequency scenarios. This
field documentation is not possible.
model was subsequently modified by personnel
from the Detroit District to allow input of mea-
Sediment transport
sured ambient velocity distributions, but the
and shoreline erosion
hydraulic calculations remain one dimensional.
The potential for shore damage due to draw-
Treat ing ship effects in two dimensions is impor-
down is a direct function of the ship-induced
tant due to significant variation in ship-induced
change in hydraulic conditions that can initiate
water velocities across a river cross section. This
sediment transport or increase transport rates. For
variation must be accounted for in predicting mag-
sediment transport to occur, near-bottom or
nitudes of sediment transport, turbidity and im-
nearshore water velocities must overcome a sedi-
pacts on biological systems.
ment particle's resistance to motion. Three modes
Data from a prior study on the Kanawha River
of transport of granular bottom sediments have
in West Virginia (Hochstein and Adams 1985a)
been observed during vessel passage (Wuebben
were compared with predicted values, but the re-
et al. 1978a). They are
sults are not presented in two-dimensional form.
Bed load, which is typified by a pattern of
Further, no information is given on river or ship
slowly migrating sand ripples on the river-
characteristics or the location of the sampling
bed;
points, so the feasibility of transferring velocity
Saltation load, the movement of individual
distributions and parameter values developed
grains in a series of small arcs beginning and
there to a Great Lakes connecting channel is un-
ending at the riverbed; and
clear. Lacking a complete, two-dimensional set
Explosive liquefaction, in which bottom sedi-
of field data on the variation of ship-induced water
ment is rapidly suspended due to a rapid
velocities and sediment movement on the St.
change in the soil pore-water pressure gra-
Marys River (which they strongly recommended
dient.
obtaining), the performance of the model cannot
Bed load is the most commonly observed trans-
be definitely assessed. It was, however, calibrated
port mode, with a progression to saltation and
against the available data on ship-generated draw-
liquefaction for events with larger, faster ships.
down and waves. The model was also applied to
For the cohesive sediments that are widely dis-
channels in DuluthSuperior Harbor* and resulted
tributed in the Great Lakes system, disrupted sedi-
in predictions of sediment suspension of the same
ments typically go directly into suspension, where
order of magnitude as the field data of Stortz and
they can remain for extended periods. Hodek et
Sydor (1980).
al. (1986) and Liston and McNabb (1986) made
In summary, the major hydraulic effects of ves-
field measurements of turbidity and light extinc-
sel passage during periods of ice include propel-
tion profiles under both ambient and ship-influ-
ler wash and drawdown and surge. Ship-induced
enced conditions on the St. Marys River. Accord-
waves were found to be quickly damped by an
ing to Hodek et al. (1986), during open-water
ice cover and thus unimportant. In contrast, pro-
periods, turbidity develops due to wind-driven
peller wash and drawdown can be increased due
waves acting on clay bluffs and the nearshore ri-
to the need for greater thrust to overcome the re-
verbed. For waves on the order of 6 in. or more
sistance of ice and the reduction of open cross-
in height, they observed that a high level of tur-
sectional area by the ice. Several models have been
bidity may develop, extending from the shore to
developed for or adapted to the Great Lakes con-
the navigation channel, and no increase in tur-
necting channels for predicting vessel-induced
bidity could be detected during ship passage
drawdown, providing both one-dimensional and
during periods of wind-driven waves. In the ab-
two-dimensional predictions. The two-dimen-
sence of wind-driven waves, they stated that near-
sional approach also considers ship waves and
shore turbidity develops with the passage of each
propeller wash effects. These models provide a
vessel. This topic is discussed further in the sec-
capability to develop system-wide predictions of
tion dealing with biological effects.
vessel effects, not only for existing navigation
As discussed previously, a drawdown and
surge event can cause water movements in all di-
rections, so that sediment transported in one di-
* Personal communication, Don Williams, Detroit Dis-
rection may be offset during an opposing current.
trict, COE.
8
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