Hydroelectric Power Generation - Renewable Energy: Technology, Economics and Environment - page 381

For organisms living in running waters, the flow conditions are especially critical;
many species need specific flow conditions as their habitats. A decrease in the
flow velocity e.g. means a decline in the oxygen and food supply and the sedi-
mentation of fine materials; this often leads to a change in the composition of spe-
cies. At the same time, an appropriate flow for the waters is required for the trans-
port of suspension matter and fine sediments - their sedimentation in the diverted
river reach has similar effects here as in the reservoir.
A low water level in the diverted reaches also carries the risk of critical water
temperatures in summer and winter. If the water is warmed up by strong sun ra-
diation, the oxygen content decreases. The production of too much algae can lead
to an oversaturation with oxygen during the day; once the algae die, the result is
massive oxygen depletion.
Because of the reduced flow, a more or less significant part of the original riv-
erbed is dry. That can lead to a decline in the aggregation of available cover for
fish or spawning sites. If the aquatic habitat is reduced too much in its size, it
normally leads to a quantitative reduction in the number of fish as well as a gen-
eral reduction in the diversity, or to the development of a composition of species
untypical for the habitat.
The reduction in the wetted area can, however, also lead to the development of
new, valuable secondary biotopes. Free sand and gravel banks, for example, be-
come habitats for specialist species such as bottom nesting birds, special beetles,
locusts or spiders - for these species such extreme biotopes are often the last re-
treats.
The negative effects of diversion-type power stations can be limited if instream
flows are fixed in advance to observe ecological requirements. Besides the mini-
mum flow, there are a number of individual possibilities to achieve a composition
of species in a diverted reach, in spite of the relatively low water level, similar to
the river sections that have not been changed. The morphology of the riverbed
plays a key role here.
More recent research has come to the overall conclusion that diversion type
power stations are less damaging for the habitat "running waters" than river power
stations with large reservoirs if they are designed appropriately and with an ecol-
ogically justified minimum water regulation.
Malfunction. If an accident occurs in an operation, lubricants might be released.
If biodegradable lubricants (e.g. lubricant based on vegetable oil) are used, appro-
priate protection mechanisms (e.g. oil separators) are installed, and the lubricants
are stored outside of the area that might be flooded, the risks of the potential envi-
ronmental damage can be minimised. Furthermore, electrical parts of the plant
might burn (e.g. cable) and release a limited amount of toxic pollutants into the
environment, which are, however, not specific for hydroelectric power stations.
Mechanical failures within the machine components in general are not at all harm-
ful for people and the environment - or the danger is limited to a certain small
area. If dams or weirs fail, this can have a large impact on the population and the