Modelling the effects of the Maaswerken on the drinking water production near Roosteren, The Netherlands.

Abstract

The provision of safe drinking water is of significant importance for a countries social and economic development (Cotruvo et al, 2019). As a constant monitoring of chemical components and microorganisms is not possible, adequate risk analyses, modelling and management are crucial (Ministry of Infrastructure and the Environment, 2014). This study presents the effects of lowering the riverbank of an inside bend of the Meuse river at the Roosteren drinking water production site of drinking water company WML (Waterleiding Maatschappij Limburg). This production site contains 5 shallow wells that partly abstract Meuse water through the riverbank (wells 9, 10, 11, 12 & 13). In the future, the inside riverbank in the study area will be lowered due to the Maaswerken project to provide the Meuse with more space during high discharges. As a result of this travel times of infiltrated river water towards the shallow wells can change, implying a change of microbiological and chemical risks for drinking water production. This study uses the regional groundwater model IBRAHYM to execute the initial model (present situation) and three modelling scenarios (low, median, high discharge after lowering riverbank). To examine the effects of the Maaswerken iMODFLOW is used to compute flow paths and travel times. The results show that during a median discharge minimal changes in travel time occur, as the Meuse wells are not abstracting Meuse water from the area where the Meuse moved inland after lowering of the riverbank. Furthermore, the high and low discharge scenarios after lowering the riverbank show largest and smallest spread in travel time distributions, due to changes in distance from Meuse to the wells. The high discharge scenario contains Meuse water with a travel time of <60 days for all Meuse wells, implying microbiological risks are at hand. Meuse wells 10 & 11 even contain Meuse water with a travel time of <60 days in all modelling scenarios, posing a microbiological risk. For the determination of the chemical risk, the ratio of abstracted Meuse water and phreatic water is required. It is advised to replace the Meuse wells further away from the Meuse, as these wells can be out of operation for 120 days or more per year due to the preservation of water quality after lowering of the riverbank. Additionally, wells 10 & 11 should be replaced as these are exposed to erosive processes due to inundation during high discharges, thereby affecting their physical stability.