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?
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.
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.
Above the gorge the gradient flattened out and the habitat improved.
The SSE intake is a greedy structure swallowing all the flow except for some seepage below one of the sluice gates.
Upstream of the intake the habitat is excellent with a constantly varying succession of pools, glides, runs and riffles – perfect salmon habitat.
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.