After checking the smolt traps I had a close look at some of the water abstraction issues in the upper Truim catchment. At present the Truim has a defined compensation flow of 0.68m3/sec. This consists of the residual flow in the upper Truim supplemented when required a short distance downstream with additional water from the Cuaich aqueduct.
The Cuaich aqueduct is an open concrete channel which can be seen from the A9. It flows from the Cuaich power station carrying water from the upper Cuaich catchment itself plus the water piped through the hill from the reservoir in the upper Tromie. At Dalwhinnie the aqueduct flows into a pipe which carries the water under the road into Loch Ericht. This water is of course completely lost to the Spey catchment as Loch Ericht is part of the Tay system.
A short video of the aqueduct and the abstraction can be seen here. I couldn’t say what the flow was down the aqueduct today but volume diverted back into the Spey via the Truim compensation was tiny in comparison to the total volume flowing into the Tay catchment.
The most controversial aspect of the Scottish & Southern Energy (SSE) proposal for the Garry Tummel scheme is undoubtedly the proposed switch in the Truim from compensation flow to Hands of Flow (HoF). HoF means that once the flow drops below a certain point abstraction stops with no additional compensation. The implications of this are huge with a potential reduction in the upper mainstem low water flow at Invertruim of 26%. Even as far downstream as Delfur the impact will be equivalent to a 3%+ reduction in the low water flow! Expect to hear more on this issue in the coming weeks.
Readers may not be fully aware of the implications of the current review of the Garry Tummel scheme which involves the re-watering of the River Garry in the Tay catchment. The entire upper Spey suffers from abstraction with Spey Dam and the two primary upper tributaries mentioned below also heavily abstracted. SSE’s proposal involves taking even more water from the Spey so that they can afford to reintroduce a flow into the Garry without losing any renewable generation capacity. The proposal is based on taking additional Spey water by reducing the Tromie compensation flow plus the considerable volume they will gain by stopping completely the Truim compensation flow. Both the Truim and Tromie are important spawning and nursery tributaries of the Spey, supporting salmon throughout their length, unlike the upper Garry which is unlikely ever to. I should say that in general the SSE works in the upper Spey are operated to a high standard, there are worse examples!
My main interest today was to have a look at the Allt an Sluie, a now dry tributary of the Truim which it used to join just downstream of the Dalwhinnie Distillery. The Sluie was dammed as part of the SSE hydro scheme with all the flow at the dam diverted into the Tay via Loch Ericht.
Just above the SSE dam there is another weir and offtake which I believe is the distillery water supply.
Upstream of the dams the habitat was good with improving spawning gravels further upstream.
The average width of the Sluie above the dams was about 5m decreasing in an upstream direction. The banks in the lower reaches were very heavily grazed; there must be a high deer population in the area. There was some remnant birch woodland on the slopes but there was absolutely no new regeneration.
I wanted to find the upper limit of fish access – that involved a fair walk. Eventually I came across an impassable waterfall but the burn was only about 2m wide at this point and it is unlikely that salmon ever made it this far upstream.
Were salmon ever present in the lower Sluie? Almost certainly so, the habitat is good and similar sized burns in the upper Spey support salmon populations. The effective total abstraction of the Sluie represents a loss, albeit minor, to the Spey salmon habitat resource. Restoration of even the minimum required EU flow into the Sluie wasn’t even considered in the SSE proposal, nor it would seem by SEPA.
It was mission accomplished today, there were two aims; establish whether there were any waterfalls in the lower reaches that would make the Sluie naturally inaccessible and the assess the quality of the habitat. Answers: no and pretty good.