Small series on ’Nyheter’ with the themes shelter, food and warmth in free English.

13.01.2017 22:38

Why minimum water – the river has been dry before and the salmon survived?


A river has floods when it is natural, mainly spring floods, a dynamic variation of different flows. Residues are flushed, bottom is vitalized, turned and ventilated and there are cavities between gravel and stone. There is a coupling between river and ground water so ground water can flow up into the river and a low river can flow through cavities in the gravel. The biological productive surface is large in the cavities and the water temperature is moderated. Young salmon hide during lack of water in the cavities.

When a river is regulated floods are damped and temperature changed. The damped floods cannot turn rooks and gravel enough and cavities are filled with sand and sediment - the volume of residuals, gravel and sediment are larger from the catchment than the river transport capacity can handle. The young salmon has nowhere to hide during a draught or sudden water cut and runs aground and die.

The water temperature is changed. In Surna the power production water is taken from the bottom of the dam and flows down a cold dark tunnel in the mountain instead as surface water being heated, shined upon and produce biomass. The spring comes a month later below the power station which can be devastating when the salmon fry comes up from the gravel to actively feed. The difference between spawning surface in autumn and bio-productive surface in winter can be large, the bio-surface can be very small and spawning surfaces with eggs can freeze or dry out.     

To overcome a rivers lack of cavities, and avoid that young salmon and eggs run aground, freeze or dry out, the regulation can release minimum water. Compensation is made for the lack of biological productive surface in the cavities so some bio-production is present. The minimum water gives a smaller bio-productive surface than in a natural river and the regulated rivers biological capacity is reduced. Minimum flow creating a bio-productive surface must be present in a regulated river for biological production and diversity.

The large question is how much water the regulation shall release, how much water is needed to keep enough natural processes, diversity and salmon. For Surna Statkraft suggests in the revision document a minimum water of 3.5 %, or 0.25 m³/s of the regulated yearly mean flow 7.2 m³/s from Rinna and Bulu. A court judged for ‘Overskjonn’ 33 % as minimum flow, 15 m³/s of the natural yearly mean flow 45 m³/s alongside the Trollheim Power Station. The Montana Method (Tennant Method) suggests a minimum of 30 % of the yearly mean flow, fil2_140929.pdf (5,6 MB) .

In principle Statkraft suggest no minimum water, their calculation has out of the blue boundary conditions. An example is that Statkraft suggests the minimum water to be measured down at Lösetli where tributaries make the criteria for minimum water up at Rinna Dam mostly met, . To ignore minimum water is nothing new in the power industry, . The advertising of Statkraft states that they take biological responsibility but in the end when Statkraft applies for revision there is no real minimum water in their documents and they take no responsibility for biological diversity and salmon in Surna.

Is 3.5 % minimum water legal?

Why this difference in advertising and production? Is the advertising just to give the production department peace and quiet, as a keeper, to fool about Statkrafts environmental devastation?

Put your money where your mouth is.


Fig 1. Picture from Fiskeraksjonens hearing document on gravel and cavities at Pellhölen in Surna. fil2_140929.pdf (5,6 MB)


Fig 2. The stone is lifted and the cavities are shown filled in with sand and silt.

Swedish version:



A river shall provide nutrition and remove residues.


Beside that a natural river shall provide a biological surface it shall also provide nutrition for the biomass. The most important in this food chain is the coupling in the river corridor between river and catchment. In flood the river retrieves leafs, branches and minerals that decompose in the river to nutrients for plants, insects and salmon. It is a never ending story where nutrients from the catchment are decomposed and absorbed by the river, biomass is produced and residues are washed out into the sea, and the river endorses biological diversity.        

In a regulated river the potential energy that should have produced biomass is transformed to electrical power, floods are held back in a dam for power generation. The coupling between catchment and river in the corridor must be maintained so the bio-production has access to nutrients, so mixed salmon populations can exist in the river.

In Surna the unregulated part can follow a natural variation of the water flow, so the river shore receives nutrients and is not leached by varying water without rain from driving power in the station. However, the regulation must help with water on top of the minimum water to create a spring flood, so Surna becomes thoroughly flushed and nutrients are supplied after the winter fallow.

When flow from the unregulated part shall contribute to a flood the power plant cannot adapt the power production flow, amount of power water is run to touch the minimum flow criteria of the regulated and unregulated water together to save water in the dam. The minimum flow shall be constant and the contribution to floods from the unregulated river real, the river has flow variations that keep natural processes and biological diversity. Large floods will happen when the dam is already filled but they are not sufficient to keep diversity, statistics on salmon and the silted cavities verify (see pictures 1 and 2 in previous article). A varying river flow is a must to get nutrients, to support natural processes and maintain biological diversity.  

How large shall a spring flood be so the river can vitalize the bottom, absorb nutrients from the river corridor and flush out residues? The Montana Method states at least 200 % of the yearly mean flow to turn stones and gravel, and to retrieve nutrients from the corridor. For Surna that is 120 m³/s and the spring flood has historically continued a minimum of two weeks.

A river has over time a constant sum of energy, it looks like it does. In a natural river most potential energy goes to restructure the river bottom and create cavities, get nutrients and flush residuals. When potential energy is transformed to electricity it becomes less energy over for the natural river. The Power Industry argues that you can modernize to get both more salmon and more electrical power, it is called a vin/vin situation and requires that energy is mystically supplied. It is a lie, we learn in school that perpetual mobile machines do not exist. Energy must always be taken from somewhere, transformed from one type to another with loss, taken from the natural rivers potential energy and transformed to electricity.

To read: Ward_and_Stanford_1983.pdf (155,5 kB)

Serial_disc_conc_1995.pdf (1 MB)

Swedish version:



About heat for cold-blooded (ectothermal) animals in the river.


We continue the little series on ’Nyheter’ with the themes shelter, food and warmth, or biological productive surface, nutrient and water temperature (see above).

The water temperature is as important as a bio-productive surface and nutrient in the river, it gives naturally a species spread. Salmon, other animals and plants have adjusted to the temperature variations that the river had for hundreds of years, over spring, summer, autumn and winter, and each phase in their development has the corresponding demand for temperature [3]. When the temperature is changed in the river biological productivity and diversity is reduced, and salmon populations can succumb. Animals are cold-blooded or ectothermal, the body has at rest the same temperature as the water and the water temperature limit their maximum effort. In higher temperatures fish metabolism is limited by time, otherwise the fish and their reproductive glands come into oxygen dept. The salmon shall save energy during its travel up the river to spawn but high water temperature gives high metabolism at rest [4].       

In a regulated river the temperature is extra important in the spring so the river gets a sufficient long growth period, most of the growth is experienced the first haft of the summer. Scientists consider that a river in Scandinavia needs at least 100 days over 7° C, with a double water temperature in between. Especially when the salmon fry comes up from the gravel to actively feed nutrients must have been produced after the winter fallow and it shall be warm enough so the cold-blooded fry can perform. Scientists recognize that the river then needs a water temperature of at least 8° C [5, 7 and 10].

When Surna was regulated water was taken from above the Trollheim Power Station and the tributary Vindöla, and regulated via Follsjö Dam [6]. The power production water, tapped from the bottom of Follsjö Dam, is in the spring about 3° C colder than the water from above the station. The water from above is considered to hold a natural temperature and is alike the water from the surface of Follsjö Dam [7, 8]. Surna is regulated to over half the water from the catchment, the part that comes from the high mountains of Trollheimen and has most potential energy. The power production water goes through a tunnel in the mountain where it after the outlet of the power station is mixed with the unregulated water from above. Measurement series during middle summer shows a temperature difference of 5° C between the power production water and the unregulated water, in September the temperature from bottom of Follsjö Dam is equal to the above and warmer to about a month later. In the winter the mixed water below the station is about 1.5° C and the above near 0° C, see below figure. Above the station the lack of water hinder salmon to reach their natural spawning and growing environment in Sunna with Lomunda and Tiåa, and spawning surfaces can freeze and dry out during the winter.  

There are many phases in the salmons life history that require a specific temperature range. We shall consider when the salmon fry comes up from the gravel to feed, the temperature criteria is a threshold value and simple to assess. Calculations give that most fries comes up from the gravel below the station the first week in June [9], above some weeks later [10]. Our task is simple, to see if the water temperature below the power station has increased to 8° C the first week in June. We observed that there were a lot of fries in Faksnes, we stamped in the gravel and it crept around our feet. Since 1997 the fries are gone, Follsjö Dam is drained in the spring and the power production water is colder as it contains more melted water than before 1997.   


The vertical dark red line in the figure represents June 4, or the first week in June, and is added to facilitate [8]. We can see that the water temperature below the station is about 6° C the first week in June and devastating for the salmon. It is obvious why the salmon has disappeared below the power station, the revision must get it back. Surna is appointed a National Salmon River by the Norwegian Parliament - Stortinget. 



  1. Varför minivatten – älven var ju torrlagd förr och laxen överlevde?
  2. En älv skall tillhandahålla näring och avlägsna restprodukter.
  3. Grunddata om laxen
  4. Brett1_1_NEW.pdf
  5. Jensen et al 1989 Temp initial feeding.pdf
  6. Konsesjon_Trollheim_Kraftverk.pdf
  7. temperatur_Follsjö.pdf (1345528)
  8. Sintef3.pdf (30264532)
  9. Sintef_1.pdf
  10. Initial_Feeding_Time_of_Atlantic_Salmon_20151028-16936-luwhw6.pdf (430813)

Swedish version:



An in depth document in Norwegian can be seen in fil2_140929.pdf