University of Twente Student Theses


Modelling of morphological development in the Vecht river due to changes in the weir policy

Haastregt, A.V. van (2023) Modelling of morphological development in the Vecht river due to changes in the weir policy.

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Abstract:The River Vecht, located in the eastern part of the Netherlands, has previously been canalized by cutting of meanders and constructing weirs. However, in the past thirty years a new vision has been formulated and measures have been taken to rebuild the Vecht into a semi-natural river as a result of river management practices focusing on the environmental wellbeing of the river system. The current weir policy that is applied in the Vecht is based on maintaining target water levels. This is non-fitting for a semi-natural river, since weirs block the flow of water and sediment. It was expected that an alternative discharge controlled weir policy could increase the flow through the river. To investigate the impact of such a discharge controlled weir policy, several alternative weir policies were set up and their effect on the morphology of the Vecht was evaluated based on morphological model simulations. The effect of the alternative weir policies on the morphology was compared to a reference scenario in which the current weir policy was applied. Four scenarios were simulated for a period of 50 years with a 1D SOBEK 3 model of the Vecht. For all scenarios several morphological patterns were found, consisting of local deposition peaks upstream of the weirs, while both local and large-scale erosion were found downstream of the weirs. Also downstream propagating erosion and deposition waves were observed, which were partially blocked by weirs. A decrease in large-scale deposition upstream of the most upstream weir was found when comparing the alternatives to the reference scenario. Downstream of the weirs a large-scale decrease in erosion was found. While the local patterns and propagation of erosion/deposition waves agree with the existing literature, the large-scale change to increased deposition downstream of weirs differs from earlier research, where an overall decreased bed level was predicted. This difference can be caused by various factors, but more research is required to pinpoint what exactly causes this different outcome. Therefore it is unsure whether a discharge controlled weir policy contributes to the achievement of a semi-natural Vecht.
Item Type:Essay (Master)
Waterschap Drents Overijsselse Delta
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering and Management MSc (60026)
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