INTEGRATION OF SEDIMENTOLOGICAL AND GROUNDWATER FLOW MODELS WITHIN THE VIRTTAANKANGAS ESKER AQUIFER, SOUTHWESTERN FINLAND

A process-based sedimentological model of a subglacial esker associated with repeated, intensively wave-reworked subaqueos fans with prominent fan lobe structures has been established to explain and predict the large-scale structural heterogeneity of the Virttaankangas aquifer in SW Finland. The model provides appropriate scale architecture of the main hydrogeological units of the aquifer that has been integrated with the 60-layer groundwater flow model. A separate 3D hydrogeological model is used only for visualization purposes.

Pseudo-3D GPR survey of the uppermost 20 m of the deposits (supported by reference data from drill hole logs and pit exposures) forms the basis for understanding the internal heterogeneity of the coarse-grained glaciofluvial unit, which is the most important part of the aquifer in terms of groundwater flow and water production. The setting of the GPR survey lines and the resolution of the groundwater flow model (cell size 50 m x 50 m x 2 m in 60 layers) have been optimized for their commensurability with the scale of the observed sedimentological units affecting the groundwater flow.

The synthesis of existing geological and hydrogeological data sets has been used to interpret the dominant sedimentary characteristics of the main aquifer below the GPR record as well as within the marginal areas of the glaciofluvial deposits. This interpretation has been recently supplemented with data from landstreamer-driven shallow seismic reflection survey (HRSR) supported by 3 new reference drill holes.

There is a straight data flow from the new observations to the groundwater flow model that is controlled with the use of the sedimentological model. We conclude that reliable modeling of groundwater flow and application of HRSR surveys have to rely on GPR-based sedimentological models depicting the presence and continuation of the observed structures and units.