One of the less well known impacts of dams and weirs is the interruption of the downstream transport of gravel that occurs in every river naturally inhabited by salmon. This is very apparent in the Allt Bhran, a tributary of the River Tromie, which was dammed and dried when the hydro scheme was built in the 1930/40s. There is a large pool upstream of the abstraction weir which acts as a settling pond for all the gravel that moves downstream during spate conditions. Every now and again the hydro company excavate the gravels and deposit them on the downstream side of the weir. This was done last year but there is a now a large bund of river gravel on the banks of the river downstream of the weir.
Duncan and myself went up there today to try and quantify the amount involved. Neither of us are quantity surveyors but we took some rough measurements of the bund and came up with a figure of about 1800 tonnes. The bund was much larger last year but the part nearest the weir has been washed downstream during flood events. The remainder is likely to remain there as it is too far from the channel. This gravel is an important part of the Bhran and Tromie ecosystem and we are currently figuring out the best strategy to return it back to the river.
The Bhran upstream of the weir looked very good today. Every time I see it I am more certain that it will be an excellent spawning burn if sufficient flows are restored.
On the way down the glen we stopped for a blether with the Glen Tromie gamekeeper. He reported that he had seen several salmon redds well up the Allt na Feinnich, which is the furthest upstream unabstracted tributary of the Tromie. I had walked a short distance up the Feinnich last spring after having mistaken it for the Allt Fearna, a heavily abstracted tributary which joins on the same side a short distance upstream. These snippets of info from the keepers on the ground are very useful. We will be surveying the Tromie in detail this summer and will include sites on the Feinnich to establish have far upstream salmon are present.
Hearing that salmon spawn in the Feinnich highlights the potential significance of the much larger Allt Bhran as a spawning and nursery tributary. Surviving here long enough to witness salmon spawning in the upper Bhran is now my interim career target!