Ramboll is preparing a site planning scheme for the restoration of the Pärrinkoski rapids for the City of Tampere. The rapids form part of Myllyoja stream in the Peltolammi-Pärrinkoski nature reserve, just 5 km from the city centre.
Protecting the brown trout
The restoration goal is to remove obstacles from the rapids to allow brown trout (Salmo trutta) to migrate up-stream to find suitable spawning grounds. In Finland, brown trout in freshwater south of 67N latitude is considered an endangered species. The construction of waterways that block free-flowing water is one of the main reasons for the current situation and there are several projects underway to restore flowing waters and make them suitable for brown trout.
Protected species and a valuable archeological site
This restoration project is further complicated by both the presence of protected species and its history. The site is home to several protected aquatic moss and macroinvertebrate species, which all need to be taken into account during restoration, when old concrete structures will be from the stream.
The site has also been identified as having archaeological value. There was already a mill by the stream in the 1500s and an old rock bed that was used for the mill house is still visible at the site. This archeological value brings additional requirements to the planning process, when compared to a typical restoration project. A professional archaeologist’s survey will be used in the site planning scheme to find out which man-made structures can be removed and which are going to stay as an echo from the past.
Taking all species and plants into consideration
In addition to the site planning scheme, Ramboll is responsible for conducting a baseline survey of terrestrial vegetation, biotopes, aquatic mosses, Siberian flying squirrels and green shield-mosses at the site. This information is required to ensure that no protected species are harmed during the restoration work.
Due to the several endangered species living in the stream, including aquatic mosses and benthic macroinvertebrates, all restoration measures must be implemented in a careful manner. To prevent releasing any extra-fine particulate material to the stream, the removal of structures and digging of by-passing channels must be planned properly.