WP5 - Groundwater Dynamics

Objectives
1. To develop appropriate hydrogeological and geophysical methods for locating aquifer systems at outflow boundaries and quantifying the diffuse submarine groundwater discharge to Ringkøbing Fjord and the North Sea.

2. To map the freshwater – saltwater interface in the eastern part of the survey area.

3. To integrate the information and data obtained from hydrological and geophysical investigations into a numerical groundwater model.

Work content

Task 1: SkyTEM survey
A SkyTEM survey has been conducted in the western side of the catchment over Ringkøbing lagoon, revealing extremely detailed information on the hydrogeological setting by application of novel methodology developed at Aarhus University. The survey provides a highly detailed picture of the salinity distribution in the area, showing that the hydrological setting is to a large degree governed by a heterogenous geology. The results of the survey is currently used as the basis for further hydrological studies of the area as well as refining existing hydrological models.

Task 2: Mapping of saltwater-freshwater dynamics in Ringkøbing Fjord
Measurements on the shallow groundwater system below the Ringkøbing Fjord have been carried out using several tracers and methods; (1) water (seepage meter), (2) temperature, (3) Salinity, and (4) stable isotopes. The campaigns have been carried out in spring, summer, fall, and winter. Furthermore the location of the saltwater-freshwater interface has been locally mapped using EM31 in collaboration with Andrew Binley.

Task 3: Numerical modelling
A 2D density-dependent flow and transport model has been used to investigate (i) the effect of the presence of Ringkøbing fjord on the large-scale saltwater intrusion pattern and the discharge from Skjern river catchment to the fjord and the sea and (ii) on the local scale, transience in the interaction between the shallow aquifer and fjord including movement of the saltwater-freshwater interface and discharge.