ice from entering locks and flushing ice past
level ice sluice and an under sluice for sand, al-
dams is a major issue on waterways that carry
lowing relatively ice- and sediment-free flow to
winter navigation in the U.S.
enter the diversion canal leading to the intakes.
In addition, a rock-filled jetty and an excavated
basin in front of the ice sluice further reduce the
Ice diversion at hydropower intakes
ice quantities entering the diversion canal
in northern Europe
At the Burfell power plant in Iceland the dis-
(Carstens 1992).
charge of frazil and solid ice may be as great as
Perham (1983) described a fixed concrete shear
55% of the total winter ice and water flow of
boom at the head of the intake canal to the Hrau-
3500 cfs. In addition, the river carries a signifi-
nyjafoss power plant, located downstream of the
cant sand bedload. The three-level intake struc-
Sigalda Reservoir in Iceland. Constructed in 1981,
ture, shown in Figure 24, consists of an upper-
the boom extends to a depth of 13 ft and prevents
frazil from entering the power canal. The frazil is
not sluiced over the adjacent spillway but kept in
the reservoir to promote ice cover formation.*
The boom does not provide a complete solution,
however, since the surface velocity in the 3300-ft-
long canal is too great for an ice cover to form. As
a result, frazil accumulates at the trash racks
located at the canal's downstream end (Frey-
steinsson and Benediktsson 1994).
At the power dam at Rygene, Norway, a 5-
Excavation
26-ft ice flushing gate, located 40 ft upstream of
the intakes, performed poorly, until a redesign
located a new ice sluice gate immediately adja-
cent to a submerged intake. The ice-flushing cap-
acity was also increased at the power plant at
Fiskumfoss, Norway, again by locating a new ice-
Diversion Canal
flushing gate as close to the intakes as possible.
At the Burfell, Rygene and Fiskumfoss power sta-
Gated
Weir
tions, physical model studies helped optimize the
design of the ice diversion structures upstream of
nnel
ay Cha
unw
Side R
the intakes (Carstens 1992).
In contrast, the intake on the Orkla River, at
Bjorset, Norway, has performed poorly, exper-
e
ik
D
iencing severe frazil problems. Flow is diverted
on
al
n
beneath a shear wall, upstream of a control weir,
r
a
Bj
to enter a 7-mile-long rock tunnel. Frazil accumu-
lates on the trash racks, tunnel walls and even at
0
50 m
the downstream surge tank.† The intake's poor
performance may result in part from its location
500 ft upstream of the control weir.
Thjorsa
Floating shear booms upstream of dams
Ice
River
Ice Sluice
Many shear booms designed to divert debris
to collection sites along the shore upstream of
dams are also effective for ice. In addition, any
structure designed to capture or divert debris in
cold regions must consider ice forces in the de-
sign. The shear boom upstream of the Chief
Bed
Joseph Dam, a large-scale structure of this type,
Load
0
5m
Undersluices
Figure 24. Ice sluice at the intake to the Burfell Power
* Personal communication with S. Freysteinsson, May 1994.
Station, Iceland. (After Carstens 1992.)
† Site visit, August 1994.
19
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