Groundwater Level Variation and Deformation in Clays Characteristic to the Helsinki Metropolitan Area

Abstract

The aim of this study was to use various modelling approaches to examine the groundwater level changes and other factors influencing subsidence and soil compaction in clay deposits characteristic to the Helsinki metropolitan area in Finland. The research area is Perkkaa in Espoo, located in the Helsinki metropolitan area in the coastal area of Southern Finland. The surface of the studied area is mostly covered by clay, with a thickness varying between 5 and 15 m. The urban development of the Perkkaa area began in the beginning of the 1970s. The hydrogeological environment in the area has been considerably altered by construction, and it has also led to lowering of the groundwater levels. As a result, there are large deformations, especially on the streets and the yards. Using an available laser scan data, GPS-measurements of the levels of ditches and minor streams, and drilling and geological maps provided by the city of Espoo and Finnish Geological Survey of Finland, it has been possible to create a 3d model of the geological main units in the research area and estimate the depth of the clay deposits. The 3d model was used further to model the changes in the groundwater flow in the research area. On the basis of this study, significant reduction in the groundwater levels are induced by the drainage systems and particularly the underground pipeline systems rather than changes in the recharge in the area due to construction.