Influence of changing river levels on the groundwater system. A study with the regional groundwater model MORIA (Modelinstrumentarium Rivierenland Actueel).
Influence of changing river levels on the groundwater system
During my internship I focused on the regional groundwater model MORIA that is used by the waterboard Rivierenland. The main trigger for my internship was the accident with the weir near Grave. During the accident a unique situation occurred, with extreme low river levels on the Maas for a longer period. This was a unique opportunity to investigate the influence of the river levels on the adjacent groundwater system. Questions that pop up where, what are the spatial and temporal influences of changing groundwater levels during extremes? Next to these questions there was a special interest in the performance of the MORIA model during these extreme situations. The region Grave-Mook and Weurt was investigated as the area of interest.
To investigate the influence of the river on the groundwater levels, both stationary and dynamic situations are investigated. The stationary influence is determined with the program Menyanthes, and the dynamic situations are modeled with the groundwater model MORIA. With help of statistical analyses the model performance of the MORIA model is investigated during normal river levels, extreme high river levels and extreme low river levels.
The results of the stationary influence with Mentyanthes showed an influence in groundwater levels up to 1700 m from the river Maas. The dyanamic influence for the extreme river levels during the year 2011 showed a possible influence even over 2500 m. For the special case study with the accident with the trust near Grave, an influence between 800 and 1300 m was found. From these results it became clear how the influence distance is determined by the rate of increase or decrease in the river levels. For the MORIA model the statistical performances showed systematic errors in the spatial as in the temporal. Spatial errors are found in the western part of the Maas-Waal kanaal, with systematic over estimations. Temporal errors are found during the winter and summer periods, with systematic overestimations during the winter and underestimations during the summer. The model showed average underestimations of 0.4 m for the groundwater levels near the river during extreme high and low situations. The timing of the model was good with dynamic travel times of 1-3 days for measurement points in the influence zone.
This study quantified the spatial and temporal influence of changing river water levels on the adjacent groundwater levels and the dynamic performance of the MORIA model during extreme situations.