Many of the major
hydro schemes were built in the 1950's before full ecological
impact was understood and at a time when methods to resolve
the problems were poorly developed.
Threats posed are four fold:
-
Prevention of upstream migration of adults.
-
Prevention of downstream migration of smolts
and kelts.
-
Changes to water chemistry and temperature causing
slow growth.
-
Abstraction,
loss and changes to water flows.
Today the Tay Board works closely with SEPA and Scottish
and Southern Energy (SSE) to ameliorate these problems.
Prevention of upstream migration of adults.
In recent years several Boreland lifts have been
observed to operate inefficiently due to poor flows.
These have now been modified and are more efficient.
At Pitlochry dam salmon were getting trapped behind
the downstream screens. It has been found more efficient
to remove these screens.
On the Gaur
the fish pass had insufficient flows to enable passage. Redesign
and increased flow now enables adult salmon to reach
many miles of potential spawning grounds. In 2007
salmon parr were found above this fish pass for the
very first
time.
Prevention of downstream migration of smolts and kelts.
Studies are currently underway on the Lyon at Stronuich
Dam. It is thought that smolts are having great trouble
finding passage over the dam. see Stronuich
Dam Smolt Trap.
Most turbine intakes are screened to prevent smolts
from being minced. But since the greater flow goes
through the turbines rather than down the fishpass
smolts often get confused. In fact some turbines do
little damage to smolts. It may therefore preferable
to remove the smolt screens!
Changes to water chemistry and temperature causing
slow growth.
Considerable work has be done on this. See the report
What's
gone wrong with the River Lyon? by Dr David Summers.
There is now little doubt that cold water drawn from
the base of dams causes a reduction invertebrate abundance
and slower growth of salmonids.
Abstraction, loss and changes to water flows.
Without question the worst case of over abstraction
is the River Garry. Here 13 miles of a main river are
virtually bone dry. For the full story see the River
Garry Report.
Removing all of the water is the
worse case scenario, but there are many more instances
of reduced flows. These reductions are governed by
compensation flow regimes and freshets. In the past
compensation flows tended to be constant (the same
flow throughout the year) and freshets were random.
Timing of freshets is now the responsibility of SEPA.
It is hoped that freshets can be timed to coincide
with natural spates to better mimick nature and the
Board and SSE are looking at ways of better managing
compensation flows.
As a major company presenting green credentials SSE
must be seen to be acting reposnsibly and in most instances
this is very much the case. The Board continues to
work with SSE to ameliorate problems.
Large existing hydro schemes are now being joined
by a plethera of micro schemes. In each instance it
is the Board's duty to advice on the environmental
impact of such works.
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