the St. Marys, St. Clair and Detroit Rivers using
that very slow water level variations due to long-
aerial photos, Corps of Engineers permit data and
term seasonal changes may result in such low
site visits. He estimated the total value of private
loading rates that plastic deformation within the
shoreline structures at that time to be on the or-
ice or at the ice/structure interface can occur. This
der of million (1976 dollars). A probabilistic
will result in very low vertical forces being ap-
approach was employed that consisted of char-
plied to the structure.
acterizing the ice conditions, on a reach-by-reach
In addition, ice conditions were monitored at
basis, that occur naturally and under several
several sites. In contrast to periods with naviga-
schemes of winter navigation. On the basis of these
tion in ice, active, shore-parallel cracks were largely
ice conditions and the channel characteristics
absent. During the 1979-80 closed period one site
within each reach, two probability estimates were
had a grounded crack only during a survey in
made: the probability of the occurrence of ice
late January, and a second site showed an active
damage and its probable severity. Damage val-
crack only during a survey in late February. Dur-
ues were calculated in terms of replacement cost.
ing the 1980-81 field season, no active cracks were
Although the results of this study are hard to
observed. Arrays of pins were set in the ice across
summarize since they provide maximum poten-
active cracks evident at the close of the naviga-
tial damage costs as a function of various levels
tion season, but no measurable changes in the
of probability, it was concluded that there was a
relative locations of these pins were detected dur-
90% probability that the annual ice damage costs
ing the closed season, except near the dock expe-
for the three rivers should not exceed
||content||
.275 mil-
riencing uplift in March. At this location the shore
lion without navigation, .28 million with the
parallel crack opened 1.5 in., but no lateral move-
traditional season (navigation to December 15th)
ment was noted. Apparently the water level fluc-
and .05 million with year-round navigation. If
tuations during these two field seasons were not
damage mitigation measures were implemented,
large or frequent enough to develop the continu-
it was felt that these year-round damages could
ous, open, shore-parallel cracks evident during
be reduced to
||content||
.65 million.
all previous field seasons with navigation in ice.
On the St. Marys River, Wuebben (1981a,c,
On the St. Lawrence Seaway a study was con-
1983b) reported the results of shore structure moni-
ducted to determine the nature and extent of any
toring during two winter periods with essentially
damage to shore structures during the winter sea-
no commercial shipping. During the period from
son to serve as a database in the event that the
15 January to 24 March 1980 there were only eight
navigation season was extended there (Palm
passages (all by icebreakers), and from 31 Decem-
1977a,b, Palm and Cutter 1978). As part of that
ber 1980 to 24 March 1981 there were nine pas-
study they inventoried 5675 structures within the
sages (all icebreakers except for one tanker). Un-
U.S. portion of the seaway and categorized them
der the program, docks were repeatedly observed
according to function, type of construction, his-
and photographed throughout the two winters,
torical and cultural significance, and potential for
and four river areas were selected for detailed
damage due to ice.
monitoring based on a high potential for dam-
Damage potential criteria were based on the
age during years with winter navigation. At these
distance from the navigation channel, the pres-
sites, points on the structures were repeatedly sur-
ence of sharp turns and the conditions of an in-
veyed to document any displacement of their com-
dividual structure. Structures closer than 300 yards
from the channel or near turns sharper than 10
ponents.
Visits immediately following the close of navi-
were considered susceptible to damage. Structure
gation showed some damage due to both hori-
types included both shore protection measures
zontal and vertical forces, but their condition at
and facilities for recreational boating. Overall they
that time was used as a basis for future compari-
determined that 3247 should not be impacted, 135
sons. No structural displacements were measured
might require minor additional maintenance, 177
in either closed season, except for one dock that
could be subject to moderate damage and 54 could
was documented to have had piles uplifted a maxi-
be severely impacted. Of 26 historic or culturally
mum of 5 in. following the passage of a convoy
significant structures, 4 were considered suscep-
of one tanker and four icebreakers on 3 March
tible to damage.
1981. Apparently the natural water level varia-
They also conducted repeated surveys of 18
tions were not sufficient to cause noticeable dam-
structures to check for any vertical or horizontal
age during either period. Hodek et al. (1986) noted
displacement. During the first winter season 6 of
19
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