Hydrological studies at the Gravity Station Metasahovi in Finland
Abstract
The recovery of global and regional variations in gravity from observations with a superconducting gravimeter requires modelling of local gravity effects. The importance of monitoring the hydrological conditions at the gravity station is demonstrated. Examples for years 1994-2000 are presented, observed by the superconducting gravimeter T020 at the station Metsahovi, Finland. The total view including terrain modelling, precipitation measurements, properties of snow cover and groundwater levels observed by access tubes in the vicinity is shown. The gravimeter stands on a small hill, on crystalline bedrock, which is exposed for a distance of 15-20 m around the gravimeter. After removing known effects on gravity, such as tides, polar motion and air-pressure, the residual curve clearly shows a correlation with the observed groundwater level. This means that the level of the groundwater indicates the variations in water storage in bedrock and/or in the soil of the surrounding terrain. Heavy local precipitation has been observed to have an immediate influence on gravity probably through soil moisture. The observations gave the impetus to investigate the local recharge and discharge mechanism. In order to model the effect of soil moisture, soil thickness up to a distance 100 m will be mapped during the summer 2000.
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