On Minimum Flow.
There are a lot of calculations and theories for minimum flow. Calculations from Statkraft show a nearly non existing minimum flow because they don´t want to give water to biological diversity. To their mind the river shall be optimized for Water Power Production disregarding recreation and tourism in the valley. An example is that Statkraft suggests a minimum flow of 3 % of the annual mean flow of Rinna and Bulu in their revision document for Surna, for the revision of the Folla-Vindöla Regulation. It is clear that if minimum flow is not quantified and real the need for a minimum flow in Surna will be ignored. Surna was regulated 1968 and the conditions were given 1962, and the river was appointed a National Salmon River by the Norwegian Parliament year 2003.
Fiskeraksjonen has chosen the Montana Method (or the Tennants Method) to determine the minimum and flushing flow for Surna, i.e. 30 % minimum flow over the year and 200 % flushing flow in two weeks, of the annual mean flow [1] [2]. Rather than sitting at a desk theorizing on minimum flow Fiskeraksjonen have used the statistics of Tennant in the Montana Method. No river section is the same next year and our calculations would only be valid for a short time duration. A sentence at court gave 33 %, a minimum flow of 15 m/s of the total annual mean flow of 45 m/s at Trollheimen power station.
‘Well, I arrived at them just, from a lot of experience looking at different
flows and what I felt were good flows. I always like to look at a 10% because
I think that's a danger to most any stream I've seen. When you get 10% or
below you're in serious trouble. It's a short-term survival habitat situation
usually, at best, and I color it red because I see red when I observe a flow
less than that and a third always looks like a pretty good flow and two-thirds
always looked real good, but instead of using 33.333 and 66-2/3, I rounded
it off at 30% and 60%. (from Eiser, Allen A, 1972. Tennant comment).’
Refs.
2. Fiskeraksjonens brev_20170520.pdf