South of Sweden, 2-4 May 2006
One of CCB’s prioritised working areas is protection of the naturally spawning Baltic Salmon. The salmon live in the Baltic Sea but go up in rivers to spawn. Their migration however, is obstructed in many rivers by hydropower dams. To solve this problem fish passages are built around the dams. It is difficult to construct a well functioning fish passage: of around 500 fish passages in the Southern parts of Sweden between one third and one fourth of them do not work at all and half of them are functioning poorly.
During 3 days in May 2006, 7 salmon experts within the CCB network were invited to participate in a study trip to rivers holding naturally spawning populations of the Baltic Salmon in the South of Sweden. The purpose of the trip was to see solutions that actually work.
The most common passage is the fish ladder, which also is the cheapest option. The disadvantage with the ladder is that no other fish than salmon can pass it. Constructed channels that resemble natural meandering streams with rocky bottoms are another type of passage. One big advantage with this solution is that other fish than salmon can use them for migration. To construct a channel is however much more expensive than the fish ladder.
Despite what passage is used there are several aspects to consider making it work properly. In the passage the water flows more slowly compared to the outflow from the floodgate. As the fish follows the water with the highest velocity it has difficulties in finding the passage. Another problem is that there has to be enough water in the passages for the fish to pass. Releasing water into the passages means a cut in profit for the owner of a hydropower plant. In Sweden, legislation says that 5 % of the yearly river water flow has to be released to fish passages. That amount of water is often not enough for the fish.
In the Alma River a great solution has been found to the two problems mentioned above. First, the channel is built near the outflow from the floodgates so it is easy for the fish to find. Second, the 5 % water released from the dam is being used as efficiently as possible. At the top of the channel there is a hydraulic pump that is regulating the water flow. During the time of migration for the salmon the water flow is increased from 200 litres per second to 500 litres per second. Every 14 days the flow is increased further to 1 500 litres per second. During the most intense migration the flow of 1 500 litres per second occurs every 5 days. The fish thus has to queue up in front of the dam site for some time before it is permitted upstream.
The cost for this kind of solution is higher than the ordinary passages, approximately 218 000 EUR, and it requires a better control. What solution is the best then – both from an ecological and economic perspective? Mats Hebrand, leading expert in the field says: there are no fixed solutions, adjustments must be made for every waters and every season.
The problems for the fish are not over even though a good solution is found for migration upstream. They have to migrate downstream also. The fish do not find the passages on their way downstream and end up in the turbines of the dams. Very few survive this. At the end of the day the most preferable solution would therefore be to remove the dams.