The first large hydro-electric scheme
in Scotland was built in the 1890s.
The establishment of the North of Scotland
Hydro-electric Board in 1943 led to a succession of new
schemes in the following 30 years.
Now there is a renewed interest in
developing hydro-electric power, stimulated by Government
incentives to achieve a higher proportion of energy from
renewable sources.
The effect of a hydro-electric scheme
on fish depends on: the site, the type of scheme, and the
design of its various elements and how they are constructed
and operated.
There are four main types: run of river,
storage, pump-storage, and catchment transfer.
The potential effects on fish are from:
obstructions in the river, damage from turbines, pollution,
transfer of water between catchments, and other changes in
hydrology.
Generators of electricity are required
to, "avoid, so far as possible, causing injury to fisheries
or to the stocks of fish in any waters" (Schedule 9 of the
Electricity Act 1989).
Obstructions
Weirs and impounding dams may obstruct
the passage of salmon or other fish unless an effective
fish pass is provided.
Temporary obstructions may also occur during
the construction of a scheme (e.g. building of coffer dams
or culverts on temporary roads) and the needs of fish must
be considered.
Turbines and tailrace
Depending on the design of a turbine,
fish passing through it may be killed or injured from
changes in pressure or by being struck by turbine blades.
It may therefore be necessary to provide
screens at the intake to keep fish out.
Screens may also be necessary at the
downstream end of a tailrace to prevent fish entering
it.
Pollution
Fish may be adversely affected by
pollution arising during the construction and operation of
a scheme.
Constructors and operators are required to
meet strict standards to prevent such pollution
occurring.
Catchment transfer
As well as the hydrological effects of
catchment transfer, fish can gain access to previously
uninhabited watercourses via the tunnel used to transfer
water.
Water-borne infection too can be
transferred.
Salmon are thought to recognize chemical
attractants in their home waters, so catchment transfer
also has the potential to mislead fish up a 'wrong'
tributary.
Changes in hydrology
Hydro-electric schemes change the
hydrology within the area of the development, and, in cases
of catchment transfer, beyond it.
These changes include:
- In run of river schemes there is
usually a large reduction of flow in the river channel
between the water intake and the discharge from the
power station.
This may also occur downstream from the
impounding dam of a storage scheme.
If a sufficient residual flow is not
provided, the stocks of fish in these areas will be
lost or significantly reduced and the passage of
migratory salmon will be prevented.
A required residual flow is usually
called a 'compensation flow'.
- If a stretch of river is dammed,
the resulting reservoir may create a new fishery for
trout or other freshwater fish, but may destroy fish
spawning grounds or nursery areas.
In storage schemes, depending on the
pattern of generation, the flow downstream of the power
station may fluctuate markedly and this could adversely
affect fish or fisheries.
The water level in the reservoir may
also fluctuate, affecting fish stocks.
- Catchment transfers can result in
substantial changes in flow in the affected catchments
with consequential effects on fish or fisheries.
- There are other indirect effects,
such as changes in sediment transport which can alter
the character of a river bed, which in turn may affect
fish stocks.
Further information on hydro-electricity, and renewable
energy in general can be found on the Scottish Executive
Business
and Industry - Energy Webpages