Morphological development of the Vecht river due to changes in the weir policy

The Vecht river, located in Overijssel in the eastern part of the Netherlands, has been canalized over time by cutting of meanders, constructing weirs, and covering the banks with revetments. However, recently river management practices started focusing on the environmental wellbeing of the river system, which resulted in the formulation of a new vision and implementation of measures to rebuild the Vecht into a semi-natural river (Helder et al., 2017). Such a semi-natural river can be characterized by a.o. the presence of meanders and clearly visible morphological processes like sedimentation and erosion. The current weir policy that is applied in the Vecht is based on maintaining target water levels. A reversed seasonal water level variation is maintained so that water levels are higher in summer than in winter. The weirs also block the flow of water and sediment. This is non-fitting for semi-natural rivers. Implementation of a discharge controlled weir policy is expected to increase the flow through the river and bring back natural seasonal water level variations. Research about the effect of alternative weir policies on the morphology of rivers is limited (Ni et al., 2021). The objective of this exploratory research is therefore to evaluate the effect of certain changes in the weir policy on the morphology of the Vecht.