2,221 research outputs found
Reservoir sedimentation; a literature survey
No full textA survey of literature is made on reservoir sedimentation, one of the most threatening processes for world-wide reservoir performance. The sedimentation processes, their impacts, and their controlling factors are assessed from a hydraulic engineering point of view with special emphasis on mathematical modelling. The objective of this study is to find the remaining gaps in the understanding of the relevant features, and the needs for further research. The physics of sediment distribution (such as delta formation and density currents) and the present modelling techniques are identified for various types of reservoirs. Attention is also paid to the operational aspects and the environmental impacts of the reservoir on the river-system morphology. Finally the methods to reduce the sediment inflow, to reduce the accumulation, or to remove the deposits are described. Evaluating the state of knowledge it is clear that a large number of physical processes are involved which are not well understood or hard to simulate. Recommended is to develop more comprehensive mathematical models and to do more specific laboratory research.Civil Engineering and Geoscience
DVR toolbox for sediment management in the Rhine delta
No full textThe DVR Toolbox is a modeling system developed to be used as an operational model for long-term morphological assessment of the Rhine branches in the Netherlands (10 to 50 years). The Toolbox consists of a 2D computational core (containing the Delft3D modeling system), a shell that controls input- and output, and a system for time/simulation management. The effects of different processes, e.g. helical flow and sediment sorting, on time-dependent bed topography and dredging-operations can be simulated. It has been designed and optimized to allow for relative short computation times: 40 year simulations for the full delta can be run in less than 1 week. The Toolbox is mostly used to calculate morphological impacts that affect the navigability of the Rhine, and the impact of measures to affect them. It is now also widely used as an official tool to study the impacts of flood-lowering measures in the Room for the River program. Also for future studies in the Rhine River this Toolbox will be widely used.Hydraulic EngineeringCivil Engineering and Geoscience
The method of characteristics applied to analyse 2DH models
No full textTo gain insight into the physical behaviour of 2D hydraulic models (mathematically formulated as a system of partial differential equations), the method of characteristics is used to analyse the propagation of physical meaningful disturbances. These disturbances propagate as wave fronts along bicharacteristics (rays) into the physical solution domain, while carrying the information from initial and boundary conditions. The method is applied to 2DH models for flow on a fixed and a 2DH two-layer model for turbidity currents in a reservoir. Introducing a point disturbance, circular shaped wave fronts develop related to water movement, and a star-shaped wave front related to disturbances in the mobile bed. A transversal wave front, related to vorticity, is formed in all models. An essential difference is shown in the propagation of the wave fronts for subcritical and supercritical flows. The characteristics have been used to define rules for imposing boundary conditions, and to find a stability condition for the two-layer 2D flow. The theory presented in this report is also applicable to other twodimensional engineering problems, and is important for imposing boundary conditions and for using the 2D numerical solution methods.Civil Engineering and Geoscience
Analysis of basic equations for sediment-laden flows
No full textDerivations and analyses of basic equations for I-dimensional sediment-laden flow (concentrations up to about 10% of volume) on a mobile bed are presented . Equations of mass and momentum conservation have been derived by means of a control section as well as by depth integration. Therefore a three-layer approach has been used (i.e., bed layer, bed-load layer, and suspended-load layer). Despite the assumptions of uniform sediment, fixed banks and constant width the derivations can easily be extended for more general models. Analysis of the basic equations b means of the method of characteristics showed that with increasing concentration wave celerities alter, and showed that critical flow occurs at Froude numbers less than unity. A stability analysis of the equations showed that the criterion for occurrence of roll waves in supercritical flow is also modified by the increased concentration. Due to increased concentrations roll waves can occur in sediment-laden flow at lower Froude numbers than in clear water flow.Civil Engineering and Geoscience
Modelling turbidity currents in reservoirs
No full textA two-layer mathematical model is presented for sedimentation in reservoirs where turbidity currents are to be expected. As the model is two-dimensional in plan, the suspended-sediment concentration of the turbulent underflow is described by a depth-integrated form of the convection-diffusion equation originally proposed by Galappatti in 1983. The bed-level variations governing this model are described by a depth-integrated sediment balance. For closure of the model various closure relations are required based on the vertical distribution of flow and sediment of the turbidity current. A semi-empirical model, presented to describe these distributions, is used to quantify boundary shear stresses, suspended-sediment transport rate, and the adaptation scales in Galappatti's equation. Additionally a discussion is given on the applicability of various existing relations for interfacial mixing, as well as on relations for the near-bed sediment concentration. The presented model, and the proposed simplified models deduced from it, can be used for various types of reservoirs and to more conventional computations such as for saline underflows.Civil Engineering and Geoscience
C.J. Koch (1932 - )
No full textBiographical, bibliographical, and literary historiography of Australian author C.J. Koch
Rivierkundige gevolgen van de 'Nieuwe Lek' bij extreme rivierafvoeren
No full textRiver EngineeringHydraulic EngineeringCivil Engineering and Geoscience
Modelling of the bedrock channels of the Mekong River
No full textAdditional master thesis - To mitigate the effects of the hydropower dam development on the Mekong river system, research must be done on the effects of sediment catchment of these dams. With unknown amounts of sediment, stored in the banks and in local bars, all spread over this long bedrock channel, local sediment transports are hard to predict. Especially, in the case of implementation of a dam, the reduction in available sediment and so the sediment transport is difficult to determine. In this research different Delft3D input is tested to model the reduction in sediment transport. The various options were the local change of roughness, change of threshold for sediment reduction for sediment close to non-erodible layers, increasing the density (locally) of sediment, controlling the maximum erosion as percentage of the water depth and the local change of available sediment at the bed. This was all done using two different sediment transport formulations of Wilcock, both for sand-gravel mixtures. The best solution turned out to be the change of the threshold for sediment reduction for sediment close to non-erodible layers. However, disadvantage here, was the inability to change this parameter locally, to be able to determine where sediment buffers in the model are located.Civil Engineering and GeosciencesHydraulic Engineerin
Long-term bed level change in the Dutch Rhine branches and its impacts to water availability
No full textGreen Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Rivers, Ports, Waterways and Dredging Engineerin
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