Tay District Salmon Fisheries Board

Protecting and Improving The Tay System

Threats to migratory species: Hydro Schemes

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.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. 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 mimic 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 responsibly 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 plethora of micro schemes. In each instance it is the Board's duty to advice on the environmental impact of such works.