Applying GIS to assess the vulnerability of the Päijänne water-conveyance tunnel in Finland

Using GIS, relevant hydrogeological, geological and technical data on the Paijanne Tunnel in Finland were assembled with regional environmental datasets for spatial analysis of vulnerability and environmental risk. This 120-km rock tunnel conveys potable water to the Helsinki metropolitan area. It is connected to local groundwater circulation through fractures and, consequently, it is at risk from contaminant transport. The observed heterogeneity in the occurrence of superficial deposits, in fracturing in the rock mass and in hydraulic activity are used to recommend alternatives for (1) focusing the assessment and eventual protective measures; and (2) for delineating the recommended zone of caution for protection of tunnel water. Central criteria in identifying vulnerable locations are the spatial distribution of interlinked highly localized groundwater inflows measured inside the tunnel and the iteratively interpreted fracture zones. Among the relevant considerations for assessing risk are the large volume of flow in the tunnel, the irregular distribution of potentially hazardous human activities, and the interplay of natural and human-influenced factors. The study demonstrates a visual and expressive approach using GIS to support sound land-use planning and water resource protection, based on the geology and taking into account of the dynamics of the underground construction.