What do the proposals mean?
Though in principle welcomed, the flow proposed
for the River Garry would still just be a very modest
attempt
at restoring the river. The proposed flows in the Garry represent
something known in hydrological jargon as the Q90
flow, i.e. a low flow which would be exceeded 90% of the year in the absence of hydro. (There is apparently some debate in SEPA that the software used to estimate this may be underestimating what actually happens in this locality.) This basically means the flow which is predicted
to occur on the 36th driest day of an average year.
It is, therefore, very much a drought flow.
Of course these represent the Q90 flows at the points of abstraction on the Garry, but because abstraction also occurs from the tributaries of the Garry for some distance downstream, the proposed flow will quickly become less than the natural Q90 flow, especially below the confluence of what should be a major tributary, the Anndeir. So, while
even the proposed flow would be capable of maintaining a considerable
population of juvenile salmon, it is likely that it will be below optimum, getting progressively less so on moving downstream. No flow has been proposed in the tributaries, some of which are considerable streams in their own right.
A further issue is that it is likely that adult salmon
would not be capable of pushing far up to spawn.
Unless a provision is made to allow higher flows
for a period in the autumn, then these proposals
may not be sufficient to fully re-establish a self-sustaining
salmon population. Furthermore, salmon might only
be expected to use the river up to the lower intake,
as there is no provision to allow salmon to ascend
beyond there, or more importantly to prevent smolts
from ending up in the diversion if they did.
Of course there will also be implications for
the River Spey. Very small benefits will accrue from the partial re-watering
of streams at Dalwhinnie, but these would need
to be balanced against any negative effects of
reducing the flow on the Tromie. On the basis
of data presented by the National River Flow Archive, at the Q95 flow,
this would amount to a reduction of nearly 1/8th
of the flow
in the Spey where the
Tromie joins.
The effects of this will have to be considered not only on fish and fishing but in terms of the wider environment. For example, the Tromie meets the Spey at the Insh Marshes which is “one of the most important wetlands in Europe” according to the RSPB and has been designated an EU Special Area of Conservation. This would presumably require an appropriate assessment under
the EU
Habitats Directive.
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Scottish and Southern Energy have not proposed any artificial spates as
these would require a reduction in electricity
generation. Without higher flows in the autumn salmon
might not be able to spawn the full length of the river.
Scottish and Southern Energy's proposals do not include some of the significant tributaries of the Garry which are also overabstracted. This is the Geallaidh.
This is the Anndeir, a large tributary reduced to a trickle.
Downstream of the Anndeir confluence the proposed flow will still be much less than a natural summer low flow
And on the Spey.......
It is proposed that the compensation flow in the Tromie, a Spey tributary, be cut by 40%.
However, a lot of water is already diverted from the headwaters of the River Spey at Spey Dam to the west coast to make aluminium.
For most of the time the compensation flow below Spey Dam is much lower than it would naturally be. The Tromie compensation flow was agreed to offset this.
The Tromie joins the Spey in the middle of the Insh Marshes which is both a European Special Area of Conservation and Special Protection Area. Already affected by abstraction, in a drought SSE's proposals would reduce the inflow to the marshes by 1/8th.
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