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Numerieke simulatie van hydraulische en morfodynamische processen in nevengeul/hoofdgeul-systemen: inzicht in effecten van ontwerpparameters nevengeulen

Schuurman, P.K. (2012) Numerieke simulatie van hydraulische en morfodynamische processen in nevengeul/hoofdgeul-systemen: inzicht in effecten van ontwerpparameters nevengeulen.

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Abstract:In the Netherlands, in the last few years, side channels are constructed, with the aim to create nature and/or more space for a river in times of high water (e.g. in the context of PKB Room for the River). Side channels are secondary streams (up to several kilometers) which flow more or less parallel to a river through the floodplain of that river. The construction of a secondary channel has an impact on hydrodynamic and morphological processes in the secondary channel, the floodplain and the river itself. There is a threefold reason for the research. First, Rijkswaterstaat wants to obtain advice on the construction of side channels to minimize future efforts in terms of management and maintenance. It is also desirable from the science point of view to gain more insight into the effect of currents on the floodplain morphodynamics in and around secondary channels. Thirdly, the research institute Deltares wants to know whether it is possible to implement a secondary channel in the existing Duurzame Vaardiepte Rijndelta model (DVR model; Sustainable Navigation Depth for the Rhine Delta) as the DVR model is a useful tool to predict hydro-and morphodynamic changes in the Rhine branches. This study aims to advice on modelling of secondary channels and design parameters for the construction of secondary channels, in order minimize management and maintenance efforts by preventing sedimentation/erosion problems. From a literature review it appears that there is a need to understand the morphodynamic effects of the secondary channel design parameters like bifurcation angle, the location of branching in the groyne embayment, side channel width, side channel depth, and inflow barrier. The effects on sediment movement of these four design parameters are determined in the adjusted DVR model, by modelling the extremes. It is assumed that the management and maintenance efforts are proportional with the dredging volume. With regard to the design parameters, the model simulations resulted in four interesting insights. First, a higher discharge abstraction leads to an increase in management and maintenance efforts in terms of sediment transfer. In addition, choices in bifurcation angle and side channel width have a higher impact on the amount of dredging volume, compared to the other two modelled parameters in this research. A larger bifurcation angle or a smaller side channel width, leads to a substantially smaller amount of dredging volume. Moreover, it is shown that some of the current rules of thumb regarding secondary channel dimensions are unnecessary, namely: maximum withdrawal thresholds, and maximum sedimentation heights. The basic rules on minimum navigable depth and maximum dredging volumes are conclusive. The study also showed that there is no best approach to model a discharge curve stationary. The two main disadvantages of modelling with a stationary approach are: the lack of understanding of the morphodynamic behaviour just outside the banks of the secondary channel, and lack of wash effects. Further research can focus on the influence of suspended transport, detailed three-dimensional model simulations from the in- and outflow location of the side channel, and the model method itself
Item Type:Essay (Master)
Clients:
Deltares
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering and Management MSc (60026)
Link to this item:http://purl.utwente.nl/essays/62192
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