Environmental Engineering Reference
In-Depth Information
is so abundant during the flood, the turbines run continuously at full capacity,
generating a large amount of electricity every day. On the other hand, because of
the increased water volume in the river, the head at the individual power stations
is reduced; hence they produce less energy per unit of water. Furthermore, by this
continuous production, some of the regulatory capacity of hydroelectricity is lost.
The special - and also financially highly priced - feature of hydropower, to bal-
ance out the daily variations in electricity demand by instantaneously adjusting
production, is mostly absent during the flood. A rather complicated task at this
time of year for hydroelectric engineers is to keep the water level along the river
within the limits specified by their power plant operation licences. Every licence
for running a hydroelectricity plant states exactly, how high or low the water table
may be above its dam (Holm 1991, pp. 116-120) - during flood times, these limits
are even more difficult to keep than during the rest of the year.
The most dreaded event during the spring flood, for hydroelectric engineers and
other river-dwellers alike, is the formation of an 'ice dam', that is, the conglom-
eration of ice floes across the river, jamming its flow and causing the water up-
stream to rise. The water level during flood times is already exceptionally high,
but when an ice dam forms and accumulates sufficient further ice floes, the water
can rise to a level that inundates and damages not only roads and auxiliary build-
ings like barns and saunas, but also people's homes. Ice dams are prone to form on
shallow river stretches with rocks close to the surface, like in rapids and on par-
ticularly narrow points along its course. Furthermore, they can occur when an up-
stream section of the river has already discharged its ice cover, while there is still
solid ice on a downstream part, so that the floes get stuck on the edge of the per-
sisting ice crust. This used to happen only rarely on the Kemi River, because its
upstream sections lie northwards and north-eastwards from the downstream river,
in colder regions thus, where the spring flood would set in later. Since the con-
struction of hydroelectric infrastructure on the river, however, the latter kind of ice
dam has become a real threat, because the ice cover does not readily leave the
pools upstream of the power stations, where the current is slow. Thus, the power
company tends to get blamed for many damages associated with the spring flood
and ice dams. Arguably, during spring the river controls the hydroelectricity engi-
neers more than they control the river, as their main occupation seems to consist
of averting damages to their infrastructure and public image.
Such rather concrete threats are not the only factors limiting the hydroelectric-
ity engineers' grip on the river. Changing climate patterns, for instance, make the
reliance on data that has been collected over the decades less meaningful. Obser-
vations from the past are unlikely to be indicative of what happens in the future.
Mild winters, wet summers and various unpredictable and extreme weather events
are prone to considerably change how the river is - and can be - dealt with. This
results in more of an 'experimenting' with the river, than a well thought out man-
aging of it. For instance, it is projected that in the near future, precipitation in late
autumn will increasingly be in the form of rain - instead of snow - which enlarges
the river's volume. At this time of year, however, the reservoirs throughout the
watershed are usually full to the brim, because they are anticipated to store as
much water as possible for the winter. Therefore, there will be the risk of an 'au-
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