Completely constructed river in the lower reach
This river flows into the sea, but is fully harnessed for hydropower production. There are three powerplants built on the river. Thus the river is constructed, dammed and regulated throughout.
Damming creates static pools out of a formerly free-flowing river and destroys the stream ecosystem
A fully constructed river is like a stairway where level steps and steep drops alternate. In this stairway there is horizontal water surface as the step, then a dam and a power plant as the drop to the lower step. The design is such that the water falls through the turbines from a height and runs from one dammed pool to another, harnessing all possible power without the loss of flow.
The potential power of the water increases with the height of the fall and the amount of water. From the direction of the water source, at the plants upper channel, water is pent-up as high as possible by the first dam. Due to the increase in the water level, the original river bank is partly or completely under water. The rapids and other stream areas are covered by the risen water level. With them the spawning and hatching areas for the migratory fish have also disappeared. In addition, other stream-inhabiting organisms have largely disappeared and have been replaced by species that thrive in still waters.
The natural channel is dredged or left dry
The water flows through the turbines of the power plant and is discharged into the lower subchannel. A new artificial channel has been excavated for the central power plant. Due to this, a bigger fall height and a straight, unobstructed flow has been achieved. The old natural channel, which was serpentine and gradual, has been left dry.
Nowadays it only receives water when the volume of water in the system is too high for the powerplant to harness all of it. In the two other power plants the natural river channels were suitable for energy harnessing. However, they too have been altered, cleared and straightened, as the natural stream was too winding and gentle.
Flow discharge and regulation changes the natural flood regime
Water is directed through the power plant turbines to generate electricity. During flooding, for example in spring, excess water is discharged through the flood locks of the power plant, passing the plant and its turbines.
Due to the regulation of flow and the increase of water level, floodplains with the flooded meadow and forest ecosystems have disappeared from the river banks. The annual self-cleaning of the river is out of function. Sediments accumulate above the dam and cannot be transported downstream.
In order to ensure a steady supply of water for all the hydroelectric power plants, water is stored in the upper channel, which acts as a reservoir. A regulated water system works as a machine with many parts. The three power plants at this river form a synchronized chain of powerplants with coordinated water discharge and supply. With the help of this regulation the water level remains constant but the flow rate varies. Water is discharged through the turbines most intensely when the price for electricity is at its highest, for example during day time and in winter months.
Powerplant dams are migration barriers
The dams of hydroelectric powerplants prevent the migration of fish and other river-inhabiting species up- or downstream. In this river, fish migration is facilitated with the help of a technical fish pass (lowest powerplant) and a fish lift (middle powerplant). There is no fish pass on the dam of the upper powerplant.
The technical fishpass of the lowest power plant only partially fulfils its function. The power company directs water through the technical fish pass only from May to November. In winter the fish pass remains dry. Therefore no river-inhabiting species can live or reproduce in it.
Whether or not a fish is able to use the fish pass depends on the species and size of the fish. When swimming upstream the fish orientate towards the strongest flow.
If the fish pass’ flow is lower than the flow from the turbine, fish cannot find their way to the fish pass entrance. When moving downstream the fish cannot navigate. They drift downstream with the water flow. The fish might drift into the power plant and die in the turbines. In addition, young fish on their downstream migration often die in the dammed pool areas, where they are easy prey to pike, seagulls and other predators.
The second powerplant has a fish elevator. Lights and walls direct the fish below the dam into a fish lift basket. The elevator then rises to the upper water section above the dam barrier, simultaneously getting lighter as water pours out of the device. Therefore, the fish lift is limited in providing the solution to the needs of the river-inhabiting organisms.
Naturally reproducing fish populations disappear
Fish that spawn in streams do not reproduce in this river. All streams and rapids have disappeared from the main river channel, thus there are no suitable spawning or breeding areas left. The fish also cannot access the lake or connected rivers further upstream that have suitable spawning areas, because the powerplant dams prevent their migration, either partially or completely. Some trout may find a tributary where they can reproduce. For the reproduction of salmon the tributary is too small.
Since the original, naturally reproducing migratory fish populations have disappeared, fish fry are grown in a fish hatchery and are transported in a truck to be planted in the river system. These stocked fish are usually caught from the lake before they grow big enough to breed. Wild fish populations that are still preserved but weakened are further affected by fishing.
Adult fish migrating upstream are sometimes transported over the dams in trucks.
The journey back to the sea is dangerous for the fish’s offspring. Many die before reaching the sea, with only a fraction surviving the journey through the three power plants without being killed by the turbines or by the predators that are waiting for an easy catch in the dam pools. Sometimes the best way for a young fish to survive is to stay in the headwaters. These fish gradually form a local population. This is an option for brown trout that can adapt their migration behaviour according to the changes in their environment.