operated jointly by the New York Power Author-
and OH on the International Section. In addition,
ity (NYPA) and Ontario Hydro (OH). The ice
anchor lines on the forebay boom are equipped
booms and the flow-control measures were
with load cells for continuous force measurement.
The highest forces are found during the early
adopted following massive ice jams that formed
during the first season of operation of the Moses-
stages of the ice-formation period, as an unconsoli-
Saunders Dam in 195859. As a result of the jams,
dated ice cover forms behind the boom. At this
discharge through the power stations on the St.
time, discharge is maintained at the cutback level.
Lawrence was reduced by about 1130 m3/s for
Once the ice cover consolidates and freezes to the
most of the winter, water intakes downstream at
channel sides, the measured boom force falls off,
Montreal were above water, and upstream prop-
indicating that the discharge can be increased. The
erty along Lake Ontario was threatened by flood-
boom load cells are also used to time flow reduc-
ing.
tions during ice cover breakup. Ice management
Flow at the dam is adjusted according to
at Beauharnois increases annual winter hydro-
weather conditions, air and water temperatures,
electric production by an estimated 200 MW
and the location of the edge of the ice cover as it
(Perham and Racicot 1975).
progresses upstream. Although the average cut-
back flow of 6230 m3/s is not significantly lower
Northern Canada: Lake Winnipeg Diversion
than the long-term average January flow of 6510
The Jenpeg Control Structure at a latitude of
54N regulates the outflow from Lake Winnipeg,
m3/s (Table 1), outflow from Lake Ontario during
the early winter can be as high as 8490 m3/s (New
feeding the large hydrostations on the lower
York Power Authority 1970). When the ice cover
Nelson River. These stations have a combined gen-
on Lake St. Lawrence reaches Morrisburg, flow at
erating capacity of about 3600 MW. An ice stabili-
the Moses-Saunders Dam is reduced if air tem-
zation program that includes a flow cutback dur-
perature is at or below 8C, to allow a juxtaposed
ing November is estimated to save Manitoba
ice cover to progress up this higher velocity reach.
Hydro C million annually (Zbigniewicz 1997).
A quality ice cover cannot form in this reach at
In addition to flow control, the program includes
higher air temperatures, even at the cutback dis-
monitoring of weather forecasts, discharges, and
charge (Wigle et al. 1981). As the cover progresses
water levels; surveying ice conditions from the air;
upstream around the Galop Island, where four
and installing an ice boom upstream of the Jenpeg
booms are located, discharge is regulated to main-
forebay each year. When border ice and a high con-
tain surface velocities of about 0.52 m/s (Perham
centration of frazil pans appear upstream of the
1974). When the cover reaches the Iroquois Con-
boom, operators reduce flow from 2550 to 1670
m3/s, which lowers water velocities to about 0.61
trol Structure, the gates are lowered into the
water to promote continued upstream progression
m/s. Additional requirements for flow reduction
towards Ogdensburg, where two additional
are an extended forecast for clear skies, northerly
winds, and air temperatures of 20C or below.
booms are located. Once the ice cover has formed
and stabilized, discharge is returned to seasonal
Because the cutback at Jenpeg reduces the electri-
levels.
cal production on the lower Nelson River Stations
during the peak demand period of December, it
Beauharnois Canal
must be as brief as possible.
Between the International Section and
Montreal, the Beauharnois Canal diverts between
Northern Canada: La Grande River Complex
3960 and 7360 m3/s of the St. Lawrence River dis-
Three powerhouses on the La Grande River
charge through the Hydro Quebec 1600-MW
Complex east of James Bay in Quebec at latitude
53N have a combined generating capacity of
Beauharnois Power Station. In early winter, flow
through the turbines is reduced to about 4530
10,270 MW. In the 48-km-long reach between the
m3/s to allow an ice cover to form behind a series
first two stations, a November flow reduction from
4300 to 1420 m3/s promotes the rapid formation
of six ice booms installed along the 24-km length
of the canal. Operators at Beauharnois have found
of a smooth ice cover. Average water velocity dur-
that the optimum water velocity for the rapid for-
ing the cutback is about 0.61 m/s. In addition to
mation of a smooth ice cover is 0.46 m/s (Perham
field monitoring of air and water temperatures
and Racicot 1975). The timing and duration of the
and water levels, an ice cover prediction model
flow reduction is determined through field moni-
aids operators on the timing and magnitude of the
toring, which is similar to the program of NYPA
flow changes (Drouin and Hausser 1984).
5
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