A hydrogeological analysis of the Kleine Beerze creek using two different groundwater modelling techniques
A set of new model instruments ("Nederlands Hydrologisch Instrumentarium") is developed in the Netherlands by the research institute Deltares to create groundwater models on a national and regional scale. These model instruments are based on the finite volumes modelling principle. However, many institutes in the Netherlands are using their own models based on the finite elements model principle. The objective of this study is to find the influence of these different modelling principles on predicted groundwater distributions. In addition, the influence several measures on groundwater flow is analysed for both the finite elements and finite volumes model principles. Research is carried out for the Kleine Beerze catchment in the south of the Netherlands. Water board "De Dommel" uses a finite elements model for this catchment. In addition, the Feldbiss fault is dissecting the catchment, which might have a strong influence on groundwater distribution. The water board is planning to restore the natural creek flow of the Kleine Beerze creek (a tributary of the Dommel). Other proposed measures are reduction of groundwater abstraction and redesigning pipe drainage underneath agricultural fields.
To analyse the hydrogeological structure of the catchment and the influence of the different modelling concepts on this, two models are used. The modelling environment Flairs (based on the finite elements method) is used by the water board to develop a model for the Kleine Beerze catchment. A Modflow model of the Kleine Beerze catchment is constructed by using the conceptual model approach in the GMS (Groundwater Modelling System) modelling environment.
The results of this study show a groundwater head of 33 m in the south and 13 m in the north of the catchment. The Feldbiss acts as a barrier to horizontal groundwater flow, causing groundwater head changes up to 25 cm compared to a situation without the fault. Reduced groundwater abstraction by 50 %, at the wells near Vessum, increases the heads surrounding the wells by 1 m. The two model concepts show similar results for the water management measures. Therefore, the choice for using the Flairs or Modflow model will not influence any management decisions made by the water board. There are some advantages of the Modflow model compared to the Flairs model. Because of these advantages it is recommended for water board "De Dommel" to make the transition towards using Modflow models.