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The restoration of Lake Puurijärvi continues

The largest and most challenging phase of the restoration of Lake Puurijärvi has started. The building of the dam in the south end of the lake and of the almost one kilometer long embankment is in progress. The excavation continues, as well. The work goes on in the south end of the lake for the whole spring and summer. The south end has the scarcest bird population and the work is done so that disturbance for the birds is as small as possible. The restoration is planned to be finished by the end of the autumn.

Photo: tapio Aalto

Changes in plans without jeopardizing the aim of the restoration

By excavation and raising the water level, the purpose is to increase the open water area and stop overgrowth. Because of the river-like nature of the lake and shape of the bottom, the dam in the south end has no effect on the water area of the lake as a whole. The effects diminish in the north end of the lake.

The structures of the restoration work have turned out to be challenging, for example the supporting structures of the embankment in the south end are more difficult than expected. The structures need to be stronger, which will raise the expenses. For economic reasons, the original restoration plan from the early 2000s has been somewhat altered, and a new environmental permit for the changes was given last autumn. The positive attitude of the local landowners has been very important for finding solutions and for the progress of the planning and restoration.

The changes are designed so that the conservational objectives are not compromised. According to the new plan the dam is built as a submerged weir instead of a gate-structure dam. In this case the structure is more acceptable also in the landscape. With the submerged weir the water level will be about 10 cm lower than in the original plan, but the effects of the raise will be roughly the same. In the summer and the dry seasons the water level in the south end of Lake Puurijärvi will be about 90 cm higher. The total excavated water area will be smaller but the areas have been replanned and relocated. In the north end, where the effects of the raise are unsubstantial or very small, the excavated area is about 3 hectares smaller than in the original plan. Furthermore, a part of the embankment is not built and, instead, compensations will be paid to the landowners or the ground level of the fields is raised. Now, the water area of Lake Puurijärvi is about 180 hectares and this is almost doubled after the restoration.

Photo: Tapio Aalto

Published 2014-06-26 at 15:04, updated 2014-06-26 at 15:04