Influence of the Rhine widening in Maienfeld / Bad Ragaz on local groundwater levels

In 2005, the governments of the cantons of St.Gallen and Graubünden as well as the Fürstentum Liechtenstein and Vorarlberg adopted the Alpine Rhine development concept. One of its measures is the river widening of the Rhine in Maienfeld / Bad Ragaz. This is a revitalization project to compensate for the ecological and hydraulic engineering deficits in this section. Over a length of three kilometers, the Alpine Rhine is widened alternately. This is to prevent a further deepening of the bed and lowering of the groundwater, while the flood safety is still guaranteed.

A 3D groundwater flow modelling was carried out to assess the influence of the river expansion on the local groundwater conditions. The 2D runoff model mesh was integrated into the existing, calibrated 2D groundwater model Alpenrhein from TK CONSULT AG and expanded into a 3D model. The water levels of the Alpine Rhine were determined by a 2D runoff modelling and integrated into the groundwater model. The modelling for the actual, future and construction state enables the evaluation of the effects of varying parameters such as bed altitude, bed permeability and channel width on the groundwater situation. Thus, changes of the groundwater level that are too large compared to the natural fluctuations can be avoided. The critical situation during floods was examined in most detail. Based on the results, it was possible to determine the best scenario in a way that the effects on the groundwater level during the construction phase and in the final state remain within an acceptable range.