Flow Control to Manage River Ice
ANDREW M. TUTHILL
During the midwinter period, flow control at
INTRODUCTION
dams can smooth and maintain the newly formed
Winter flow control can reduce ice problems
ice cover for the benefit of winter hydroelectric
on rivers and waterways, benefiting the hydro-
production and ice jam flood control. Following
electric and navigation industries, and reducing
ice cover formation, gradual increases in flow
the threat of ice jam flooding. Winter flow regu-
smooth the underside of the ice cover, reducing
lation can also reduce ice interference with the
hydraulic resistance and ice-related head losses at
operation of locks and dams and mitigate ice
the intakes. Once a stable freezeup cover has
problems upstream and downstream of water
formed, hydroelectric projects often return to their
storage reservoirs. More recently, the interrela-
open-water generating capacity without adverse
tionships among flow regulation, ice processes,
effects.
and winter fish habitat have gained increasing
Where ice jam flood potential exists, project
attention.
operators may try to minimize rapid fluctuations
Flow reductions during critical early winter
in stage and discharge that could break up the
periods can speed the formation of a juxtaposed
midwinter ice cover. However, this practice often
ice cover, decreasing the open water area for frazil
conflicts with hydroelectric operations, where
ice production, and reducing the occurrence of
large daily fluctuations may be required to meet
freezeup ice jams and hanging dams. An addi-
peak demands. In some situations, a hydroelec-
tional benefit is that a juxtaposed cover is rela-
tric diversion may be great enough to reduce
tively smooth, offering less resistance to flow than
the ice conveyance capacity of a river reach and
the rougher, "shoved" ice cover that might form
actually contribute to ice jamming. The winter
in the absence of flow control. During the last
pool level of water supply and flood control res-
three or four decades, many hydroelectric produc-
ervoirs can affect the location and extent of
ers in the northern U.S., Canada, and northern
freezeup ice jams on tributary streams.
Europe have regulated flow during critical early
Passing brash ice and flows at navigation
winter periods to reduce ice-related head losses,
projects while maintaining minimum pool levels
at substantial economic gains. In addition to maxi-
presents additional operational challenges. Dur-
mizing winter hydroelectric production, projects
ing midwinter breakups, passing ice without
may control outflow to reduce the occurrence of
damaging river structures or threatening naviga-
freezeup ice jams and related flooding. The suc-
tion is an important operational issue. Finally,
cessful performance of ice retention booms may
maintaining minimum channel depths for navi-
also depend on flow reductions during critical
gation and providing water supply and in-stream
periods. Finally, the rapid formation of a smooth
flow requirements for fish during low-flow peri-
ice cover can benefit winter navigation by mini-
ods are important midwinter flow-control issues.
mizing frazil ice production and ice cover thick-
Flow control can influence the timing and
ness, thus reducing ice interference with naviga-
sequence of final river breakup and subsequent
tion projects such as locks and dams.
ice jams. The upstream pool level at a dam at the
Go back to contents pg
Previous Page
