Jouko Laitinen, CEO at Navitas Kehitys Oy, says that Maveplan produced the plans that enabled Navitas, which was in charge of the project, and project manager Jaakko Lappalainen to invite bids from professionals in various fields. Maveplan expert Lauri Keskitalo: Some starting points for the design of Ämmäkoski. Typically, when designing a fish pass, the amount of flow to be diverted is relatively small and drives the design. In the case of Ämmäkoski, the grove-like environment of the area and the space needed for a reasonably usable pass, as well as the protection of the flying squirrel trees in the area, imposed constraints on the size of the fish pass and the amount of flow that could be diverted. The longitudinal gradient of the bypass had to be made sufficiently gentle, but there was little space available for meandering. In addition, in the lower part of the fish pass, on the grove side, the terrain rose across the pass. The fish pass was commissioned at the end of November 2022 and Jouko Laitinen says that all Maveplan’s plans have been fulfilled. There were some variables during construction, but there was no need to change the design of the fish pass. The implementation has required expertise from the designers and implementers. Jouko Laitinen says that a good outcome is the result of cooperation between several parties. The fish pass should be considered as a whole and its core function was to act as natural migration and spawning rapids for rapids fish. From a technical point of view, the gradient and the target flow rate of the fish pass have been achieved as planned and have served their purpose. It was a major fish pass project in Finland, and even in the Nordic countries. The restoration project involved the construction of a submerged weir and a channel approximately 170 metres long and 10 metres wide bypassing the gate-structure dam. The flow rate in the Ämmäkoski was increased from half a cubic metre to 10 cubic metres per second all year round. The design work was based on field surveys and studies on the reproduction of stream fish in Ämmäkoski Rapids. The construction of the fish pass and the restoration of the rapids increased the area of the rapids by thousands of square metres, allowing salmonids to spawn and their young to survive and rapids fish to rise from the south of Varkaus far upstream into the watercourse above the rapids. The census of the Ämmäkoski spawning grounds has proven that the water body also functions correctly from the point of view of nature, as evidenced by the WWF Finland’s Luontolive fish cam. Recreational fishermen have also taken over the rapids, and the restored rapids and the entire Kämäri park area have come to life in other ways. Jouko Laitinen is pleased to see how the site has developed into a recreational area as a whole. It has become an important fishing, tourism and environmental destination for Varkaus. According to Jouko Laitinen, the restored Ämmäkoski rapids have been received very positively. Maveplan expert Lauri Keskitalo on the result:

• The streambed was dimensioned according to the regulated lower and upper limits of the Unnukka Lake for a flow range of 2.6 to 4.7 m³/s.
• A balanced entirety was achieved in terms of width, water depth, flow velocity and space requirements for the side slopes of the streambed.
• The length of the streambed was maximised by placing the neck of the streambed as far as possible from the mouth of the northern bay.
• At the mouth of the bay, construction conditions were favourable and the shallow bay was converted into a rapids area.

The planned follow-up works cannot be carried out during the winter because of the spawning grounds, but the finishing work on the rapids will continue in the summer of 2024. The CEO of Navitas Kehitys Oy is satisfied with the progress of the whole project, from design to final outcome. Jouko Laitinen praises Maveplan for producing an expert plan that was easy to follow and which was also implemented in practice. The water flows as designed at the planned points and, above all, the underwater function of the streambed is natural and functional.

“It was a pleasure to be a designer on this project. The members of the project group were united in their view of the importance and significance of the Ämmäkoski fish pass.” – Our expert Lauri Keskitalo

More on the topic: Navitas Kehitys Oy, basic information on the project WWF Finland’s fish webcam recording Yle news on the opening of the fish pass Images: Navitas Kehitys Oy