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Hydroelectric power plant in River Glomma

During summer 2018 the final decision was made to build a hydroelectric power plant in Glomma just upstream of Tolga. Let me try to explain what this means for Kvennan Fly Fishing.

A few km upstream of Tolga village a small dam will be constructed. A reservoir will be formed with a capacity of 10.000 m3. From this reservoir a part of Glomma’s water will be drained into a to be excavated tunnel, going all the way down to Eidsfossen (the beginning of the Fly Fishing zone), where the water is spilled back in the river bed again. The difference in altitude between the water outlet at the dam and the Eidsfossen falls is about 88 meter.

The build of this power plant has started in September 2018 and it will be finished during 2021. Total costs involved are 582 million NOK or about 60 million euro. The plant will generate on average 205 GWh per year, enough to provide 10.000 Norwegian households with electricity.

In the tunnel there will be three turbines, each with a maximum capacity of 20 m3/sec. The tunnel will be about 12 km long, and ca 7 meter wide. The power plant will have a maximum capacity of 60 m3/sec. In summer time a minimum flow of 12 m3/s has to remain in the river bed, in winter time minimum flow is 7 m3/sec. Normal summer level in Glomma at Hummelvoll is about 50 m3/s . The minimum flow in the affected river section is 12 m3/s , so the power company, named Eidsiva, can take maximum 38 m3/s into the tunnel. They could use the extra capacity of the reservoir (10.000 m3) to use the maximum capacity (60 m3/s) of the plant. The reservoir would drain with 60 – 38 = 22 m3/s. In 8 minutes the reservoir would be empty. Common sense tells me this is not going to happen very often, and sudden changes in water level in the KFF zone will only happen if it rains a lot. Just like before.
 

The construction of the power plant, dam, tunnel and outlet at Eidsfossen will take about three years. Pollution of Glomma, caused by the build of the dam, seems to be avoided by the use of temporary dams. The biggest part of the job will be the excavation of the tunnel and the build of the machinery in the tunnel. This has no impact on the river.

It’s also good to know what we are talking about, when it comes to the relation between water level and flow. During the last years I have been collecting data, and I found out that a change in water level (at the Hummelvoll measuring point) of 10 cm corresponds with a change in water flow of about 10 m3/s. This 10 cm change at Hummelvoll will give a change of about 4 cm in the Fly Fishing zone at Kvennan camp. The reason for this is simple: Glomma flows faster and the river bed is much wider at the campsite, compared to the rather deep, narrow and slower flowing section at Hummvoll.

The part of Glomma between the dam and the Eidsfossen falls – the so called Tolga zone - is going to be affected badly by the power plant, especially because of the relatively small amount of water in the river bed during mid summer and winter.

But for the Fly Fishing zone not so much will change, I think. The water that was taken out of the river, and into the tunnel, is back in the river again. There can be some small changes in water level when the power plant is in production, but I guess they will not have much impact on the fishing conditions at Kvennan Fly Fishing. There might be a small effect on water temperature – I heard someone say 0,5 degrees Celsius. All in all, this power plant is not improving things, but I am quite confident during the coming years KFF will remain one of the best stretches for fly fishing in famous and beautiful river Glomma.

Hein van Aar, November 2018
 

 
 

contact : kff@kvennan.com

© Hein van Aar