The average temperature in the county of Trøndelag is 1,5 centigrades warmer than in it was back in 1960. The effects on our salmon rivers are becoming more and more obvious. Climate change have caused more extreme weather; more torrential rain and more drought, and this has been particularly noticeable since 1990. Increased temperatures cause the snow to melt earlier in the winter, and often there can be several snow melts during the same winter. This being a fact, it is useful for those considering booking a fishing trip on the Orkla to be aware of the hydropower regulation of the river, and how this affects the waterflow.
Waterflow and water temperature may hugely affect the behaviour of the salmon. Salmon fishers will first and foremost worry about there being enough water, so that the fish can easily enter the rivers and run upstream. Low water might cause salmon to hold in the estuary, and the salmon already in the river will become stationary and shy.
The hydropower regulation of the Orkla
Early in the season, melting snow will feed the river sufficiently, whereas later in the summer one must rely upon rain. For the Orkla the situation is different than for many other rivers. In the period 1978 – 1985, Orkla was regulated for the production of hydropower. 5 hydroelectric power stations are in operation along the river, and several controlled reservoirs ensure a stable supply of water to the turbines. The operator of the hydropower production, Kraftverkene i Orkla (KVO), are obliged to sustain a minimum waterflow of 20 m3/sec below the Bjørset dam. KVO can obtain this by letting water from the reservoirs through the Brattset and/or the Grana power station.
The Granasjøen reservoir, with the dam in the foreground
After 15 years of operating Aunan Lodge, our experience is that 20 m3/sec is enough water for the salmon to enter the Orkla and swim upstream. The set minimum water flow on the Orkla makes for exciting fishing at most of the 18 pools on the Aunan Lodge beat. Some of our pools, like Litjmoen, Bruholt and Gorsetøya, Gamshølen and Skjelsenghølen, are actually at their most productive on low water. Other less fortunate salmon rivers struggle with hydropower regimes with levels of mandatory minimum water flow that are too low for the salmon to migrate upriver. And, of course, rivers without hydropower production reservoirs at all, are depending on nature alone for water, and might get almost totally dried out during periods of prolonged drought.
The outlet of the Grana power station runs into the Korshølen pool at Aunan Lodge, and is therefore influencing 13 of the 18 pools on our beat. When in operation, the normal water flow through the power station is 12 – 20 m3/sec. The water comes from the Granasjøen reservoir. The intake is located at the bottom of the lake, which means that the water temperature is close to 4 centigrades. When the Grana power station is in operation during the summer, the water temperature in the river downstream from the outlet will be colder than it would be under natural conditions. It’s believed that the salmon is most active when the water temperature is between 8 and 14 centigrades, and that the ideal temperature for fishing is between 10 and 12. During cold periods of the season, electricity production at the Grana power station could cause the water temperature in the river to be lower than ideal, whereas during warm and dry summer days it could represent a cooling relief for a river that otherwise would hold temperatures between 15 – 20 centigrades.
A nice catch in Korshølen, with the outlet of the Grana power station in the top right corner
Most salmon anglers have experienced the frustration of being sat on the riverbank, staring at a river that is not fishable, either due to low and warm water flowing with weeds, or a highly flooded river with chocolate brown water. KVO’s reservoirs in the mountains collect snow melt and rain, making the fishery less vulnerable for the extreme weather that we’ll be seeing more of in the future.
But there will be exceptions, and the 2018 season was indeed one of those. The average temperature for the whole of Norway for the period of May till July was the highest that has ever been measured. Because of the extreme conditions, the authorities granted KVO a reduced minimum water flow of 10 m3/sec for a period. It was still fishable at this height, and we caught several salmon at Aunan after the reduced water flow came into effect. But with the drought continuing for another 3 weeks, the conditions eventually became dire. Thankfully it never became so critical that the fishing had to be closed. This event in 2018 is the only time during 30 years of hydropower production on the Orkla that the minimum water flow had to be reduced like that, and hopefully it will be long till next time.
The Bjørset dam (intake for the Svorkmo power station), located approximately 15 km downstream from Aunan.
So what’s the ideal water level that you should wish for when visiting the Orkla and Aunan Lodge? There is no single answer to that question. Early in the season we at Aunan Lodge would prefer the river not to be too big and cold, as this will slow the fish going past the outlet of the Svorkmo power station. For Aunan Lodge and other fisheries on the upper river, this was painfully felt in the 2012 season, with a cold spring and late snow melt. We do wish for a marked flood in the spring, as this is important for the smolt to leave the river successfully, but we prefer this flood to have finished during the second half of May, so that the water temperatur will exceed 7 centigrades well in time before the 1st of June. The average water flow at Aunan Lodge throughout the fishing season has been around 50 m3/sec the last 10 years (a bit more in June and August, and a bit less in July), and this is a good allround water flow for the Aunan Lodge salmon beat. But if you ask our guides, they’ll be more concerned about the water level not becoming too static over time, as it is the changes in water flow that make the fish move and hence become more likely too take.
Hourly updates on water levels on different places on the river are published on the Orkla river board’s web site. The readings from the Syrstad gauge is the most relevant for the situation at Aunan, as there are no major tributaries or power stations between Aunan Lodge and the Bjørset dam.
The Aunan Lodge beat is 5,5 km long with 18 different pools. This offers a variation that very few Norwegian salmon fishing lodges can match. A mix of pools that fishes well on different water levels is very valuable in a time where the weather is going to be more and more unpredictable. Combine this with a guaranteed and sufficient minimum water level, and the risk of having your trip partly or totally spoiled because of water conditions is heavily reduced.