Groundwater Modelling - A Geophysical Approach

A regional groundwater model covering a 375 km2 large Danish island is established on the basis of 1D interpretation of geophysical datasets including almost 3.000 electromagnetic TDEM soundings. The model is based on 13 layers with downward increasing thickness and initial model parameters were determined on a presumed statistical dependence between electric resistivity and hydraulic conductivity. <br> <br>During the last decade, geophysical methods for groundwater purposes have been intensively developed and applied in Denmark as electric and electromagnetic methods measuring the subsurface resistivity distribution have shown most suitable for Danish conditions. <br> <br>The modelling strategy is based on a relationship between geophysical models and the hydraulic properties of the geological sediments. The actual case has proven a relationship between the electrical resistivity and hydraulic conductivity, though for some sediment-/rock-types with some uncertainty. As expected, interpretation difficulties are connected with transferring the geophysical information (resistivity from 1D interpretation of TDEM-soundings) to hydrogeological information. However, by combining electrical resistivity with borehole information, a model that yields a good representation of the aquifer properties can be defined. <br>Conclusively, a significant advantage can be achieved by including geophysical surveys when setting up regional groundwater models.