Allt Bhran habitat survey and electrofishing update

Polly and myself surveyed the Allt Bhran today whilst the electrofishing team were out surveying in the Livet and other Avon tributaries. The electrofishing team  found some good results from the Livet including almost 500 salmon fry from a 11m long section in the right bank channel where the river split at a mature island. 81 salmon parr were found in the same section, excellent for a site of 130m2. Phenomenal trout fry densities continue to be found in almost all the trout burns or the upper reaches of the larger streams.

Back to the Allt Bhran which is effectively a dry riverbed, a sacrifice to the Tromie hydro scheme in the 1930s. Why survey then? Well included in the SSE plan to put water back into the Perthshire River Garry is the proposal to reduce the compensation flow in the Tromie. Reinstatement of a minimum flow down the Bhran is an option offered as part of the proposal, although that would only be at the expense of further reductions in compensation flow in the upper Tromie. The middle reaches of the Allt Bhran flow through a rocky gorge and we needed to find out if there were any impassable obstacles, i.e. waterfalls, that would render the burn impassable to migratory fish.

The Bhran is a fairly sizeable burn with a mean width today of over 5m upstream of the SSE intake. If rewatered adequately would the Bhran provide any worthwhile salmon habitat?

When the hydro scheme was constructed a weir was erected in the lower Bhran to prevent access for salmon tempted tyo run the Bhran during the rare spillage events at the intake.

When the hydro scheme was constructed a weir was erected in the lower Bhran to prevent access for salmon tempted to run during the rare spillage events at the intake. Spills at the dam are fleeting events with any flow below the intake running away very quickly leaving any fish that may have ascended high and dry, or stranded in pools where they would soon succumb.

A short distance upstream of the salmon barrier there are a succession of small waterfalls. Difficult to envisage how they would look with a decent flow but none looked to be impassable.

Typical small waterfall in lower reaches of the Bhran

Small waterfalls typical of those found in lower reaches of the Allt Bhran

The gorge section of the Bhran extended over about 1km with small patches of mixed juvenile habitat between. Smolt production from this sort of habitat would be modest.

One of the more challenging bedrock cascades in the gorge. Only passable under medium flow conditions at least.

One of the more challenging bedrock cascades in the gorge. We figured that it would only be passable under medium flow conditions at least.

Above the gorge the gradient flattened out and the habitat improved.

Good mixed fry/parr habitat upstream of the gorge - just lacking proper flow

Good mixed fry/parr habitat upstream of the gorge – just lacking proper flow

The SSE intake is a greedy structure swallowing all the flow except for some seepage below one of the sluice gates.

This is where the entire flow in the Bhran disappears down a pipe.

This is where the entire flow in the Bhran disappears into a pipe although at present it will return to the Spey via Loch an’t Seallich – all the water in the loch is currently required for the compensation flow.

Upstream of the intake the habitat is excellent with a constantly varying succession of pools, glides, runs and riffles – perfect salmon habitat.

Nice riffle in the upper Bhran

Nice riffle in the upper Bhran, smolt production from up here could be good.

Would the Allt Bhran provide much useful habitat if it was rewatered? We thought so but the benefits would only be realised if the fish were able to get above the intake weir. That would require a fish pass and smolt screens. None of the waterfalls/cascades in the gorge looked totally impassable, certainly none were on the scale of many seen in the upper Feshie recently, and fish get over these.

It will be interesting to see how this situation develops.

 

 

 

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.