LESSONS LEARNED – THE PROCESS OF COMBINING NUMEROUS HYDROSTRATIGRAPHIC MODELS INTO ONE REGIONAL MODEL FOR FUTURE USE IN THE GROUNDWATER ADMINISTRATION

In 1999 a focused groundwater mapping campaign was initiated in Denmark. Several land areas particularly interesting in relation to groundwater, was pointed out prior to that, based on existing groundwater abstraction, and estimated future needs, combined with geologic knowledge. The areas are widely distributed in the entire part of Denmark and have since then been subject for intensive mapping of geology and groundwater by drillings, geophysics, and geological and hydrological modeling. They cover approx. 40% of Denmark. The outcome of the mapping and model building has led to more than 180 hydrostratigraphic layered geological models, typical in size ranges from 400 - 2000 km² and focused on the uppermost 300 m of the soils. So far – so good, but in retrospect, it became clear that we, on a national scale, needed a well-defined model structure, to avoid the many cases seen where numerous models and model generations intersected and overlapped, but were based on different setups (number of layers, modeling approaches etc.) leading to un-even numbers of layers and crossing hydrostratigraphic surfaces.

These lessons learned us that we needed a well-defined but flexible model structure, which had to be used by geological modelers when making hydrostratigraphic models. Without this, models in different areas too often couldn’t be combined or compared, making “cross-border” calculations and decisions very difficult and time consuming.

This talk introduces you to the process from acknowledgement of this very fundamental problem to the solution that has been implemented in Denmark today. From the initial meetings between the EPA, the National Geological Survey, consultants, stakeholders, and modeling software developers, to the definition of a nationwide “maximum stratigraphy” which accommodates the regional geological differences in Denmark, and which are used today when working with hydrostratigraphic modeling and groundwater mapping for the authorities. We’ll investigate challenges and the selection process of the hydrostratigraphic models which have been analyzed and quality checked and finally combined and stitched together into one common web-based public hydrostratigraphic model, the “FOHM-model”, which is now accessed, updated, and extended on the fly, by multiple modelers at the same time.