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You searched for subject:(Braiding rivers). Showing records 1 – 3 of 3 total matches.

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Universiteit Utrecht

1. Marra, W.A. Dynamic channel network extraction from satellite imagery and dynamics of the Jamuna River.

Degree: 2010, Universiteit Utrecht

Braiding rivers consist of many channels, separated by bars which split at bifurcations and join in confluences. Much is known about these basic elements and their dynamics. However, the nature, direction and effects of propagation of local changes through the entire channel network has barely been studied and is not fully understood. Logically, the evolution of the river planform is the result of development of the individual elements. The link between the two has not yet been made. In this study, a braided river is considered as a network of bifurcations, confluences and channels. The evolution of the braided river is analysed by considering the river as a network and analyse the development of individual elements in this network. A novel methodology was developed to extract detailed channel networks of the river form satellite images (not to be confused with hierarchical stream order networks). Both conventional river properties (i.e. braiding index) as properties derived from network analyses were used to analyse the river network evolution. Furthermore, a weighted braiding index is proposed as a measure for the dominance of a channel, this measure is based on the importance of channels which is derived from the network. Besides changes in network properties, the evolution of the channel pattern is analysed by means of the development of individual bifurcations. Bifurcations in the channel networks at two dates are linked by evaluating the similarity in bifurcation configuration. The bifurcation asymmetry is calculated for every bifurcation, the development of bifurcation asymmetry is calculated for every bifurcation linked between two river networks. The developed methods were designed to be automated and repeatable for the purpose of application to a series of images. These methods were applied to a time series of satellite images of the Jamuna river (Bangladesh) from 1999 - 2004. The network measure `betweenness centrality' maps the importance of all elements in the network. These values of importance are calculated from the local channel geometry, but does not directly relate to the local geometry because the whole up- and downstream configuration of the network is taken into account. Other network measures were not directly useful for river network analysis. An increase of bifurcation asymmetry and a decrease of braiding and weighed braiding index are observed in periods of persistent low discharge and an increase of bifurcation asymmetry and weighed braiding index are observed during high discharge conditions. Due to the large differences in the appearance of the channel pattern during high discharge conditions, the development of bifurcation asymmetry appeared chaotic possibly due to limitation of the current methods used. During the dry season, parts of the river had only one dominant channel, in other words there was no active braiding. Development of bifurcation asymmetry during persistent low water stages caused the formation of a dominant channel and a decrease of… Advisors/Committee Members: Kleinhans, M.G., Addink, E.A..

Subjects/Keywords: Geowetenschappen; Rivers, Braiding, Bifurcation Stability, Morphological Evolution, Remote Sensing, GIS, Neurology, Network Analysis, Jamuna, Bangladesh

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Marra, W. A. (2010). Dynamic channel network extraction from satellite imagery and dynamics of the Jamuna River. (Masters Thesis). Universiteit Utrecht. Retrieved from http://dspace.library.uu.nl:8080/handle/1874/189146

Chicago Manual of Style (16th Edition):

Marra, W A. “Dynamic channel network extraction from satellite imagery and dynamics of the Jamuna River.” 2010. Masters Thesis, Universiteit Utrecht. Accessed November 28, 2020. http://dspace.library.uu.nl:8080/handle/1874/189146.

MLA Handbook (7th Edition):

Marra, W A. “Dynamic channel network extraction from satellite imagery and dynamics of the Jamuna River.” 2010. Web. 28 Nov 2020.

Vancouver:

Marra WA. Dynamic channel network extraction from satellite imagery and dynamics of the Jamuna River. [Internet] [Masters thesis]. Universiteit Utrecht; 2010. [cited 2020 Nov 28]. Available from: http://dspace.library.uu.nl:8080/handle/1874/189146.

Council of Science Editors:

Marra WA. Dynamic channel network extraction from satellite imagery and dynamics of the Jamuna River. [Masters Thesis]. Universiteit Utrecht; 2010. Available from: http://dspace.library.uu.nl:8080/handle/1874/189146


Delft University of Technology

2. Nientker, Gustav (author). Porcupines for river training: A study on the near-field effect of porcupines.

Degree: 2018, Delft University of Technology

Braiding rivers are characterised as highly dynamic, and experience annual morphological changes in plan- form. This dynamic nature of the river leads to navigational hindrance and risk of unstable bifurcation points where discharge distributions might switch. In pilot studies, porcupines have shown promising results in re- tarding the flow and cause sediment deposition near river banks to prevent bank erosion. However the aim now becomes to apply the porcupines on a much larger scale to increase the channel roughness and influ- ence discharge distributions of bifurcation points such that the flow is mainly diverted to the channel where the highest discharge is required. This way the main channel receives the largest discharge and therefore sedimentation in these channels is prevented. Currently it is not known how porcupines should be modelled in a numerical model. It is simply assumed that porcupines can be modelled similar to vegetation which is schematised as rigid cylinders with a certain density, drag coefficient and resulting representative roughness. No measurements are available to validate the assumed roughness of porcupines and if the hydro- and mor- phodynamic behaviour, represented by the model, is true. In this thesis laboratory experiments are conducted to assess the near-field hydro- and morphodynamic ef- fect of porcupines and generate more knowledge about their behaviour. Experiments with a concrete bottom give a detailed insight in the hydrodynamic behaviour of porcupines without the interference of bedforms and morphological developments. Experiments with a sediment bottom give more insight in the morpho- logical development and flow patterns over time which clearly influenced the initial hydraulic behaviour. Experiments are conducted in a 12 metre long and 0.8 metre wide flume with a recirculating pump. The wa- ter level, discharge, density of the porcupine field and configuration of the field are systematically varied to identify the dependences on the drag and sedimentation/erosion volumes in the near-field domain of the porcupines. Additionally, general observations are performed, describing the flow structures and sedimenta- tion patterns in and around the porcupine field. From fixed-bed experiments it is observed how the flow is retarded by the presence of porcupines. Flow is pushed around the field in both transverse and vertical direction. Behind the porcupines, longitudinal flow vectors are downward directed and the flow velocity near the bed is significantly reduced. It is observed that staggered porcupine grids help to retard the flow stronger and captures sediment behind the field in wider strokes. Non-staggered grids only work effectively in the line of porcupines. Between those lines barely any retardation is observed and therefore only narrow strokes of sedimentation are observed behind the lines of porcupines. The reduction in flow velocity behind the porcupines is similar to the velocity reductions ob- served in experiments with vegetation. The velocity… Advisors/Committee Members: Uijttewaal, Wim (mentor), Sloff, Kees (graduation committee), Mosselman, Erik (graduation committee), Schuurman, F (graduation committee), Delft University of Technology (degree granting institution).

Subjects/Keywords: Porcupines; Permeable structures; Braiding rivers; River training; Flexible solutions; Laboratory experiment; Bank erosion

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Nientker, G. (. (2018). Porcupines for river training: A study on the near-field effect of porcupines. (Masters Thesis). Delft University of Technology. Retrieved from http://resolver.tudelft.nl/uuid:28298b28-8b7a-4c64-a5be-9561bc1180a5

Chicago Manual of Style (16th Edition):

Nientker, Gustav (author). “Porcupines for river training: A study on the near-field effect of porcupines.” 2018. Masters Thesis, Delft University of Technology. Accessed November 28, 2020. http://resolver.tudelft.nl/uuid:28298b28-8b7a-4c64-a5be-9561bc1180a5.

MLA Handbook (7th Edition):

Nientker, Gustav (author). “Porcupines for river training: A study on the near-field effect of porcupines.” 2018. Web. 28 Nov 2020.

Vancouver:

Nientker G(. Porcupines for river training: A study on the near-field effect of porcupines. [Internet] [Masters thesis]. Delft University of Technology; 2018. [cited 2020 Nov 28]. Available from: http://resolver.tudelft.nl/uuid:28298b28-8b7a-4c64-a5be-9561bc1180a5.

Council of Science Editors:

Nientker G(. Porcupines for river training: A study on the near-field effect of porcupines. [Masters Thesis]. Delft University of Technology; 2018. Available from: http://resolver.tudelft.nl/uuid:28298b28-8b7a-4c64-a5be-9561bc1180a5

3. Baral, Bishnu Raj. Numerical modelling of braiding processes in gravel-bed rivers.

Degree: PhD, 2018, Queen Mary, University of London

Gravel bed braided rivers are distinctive natural environments that provide a wide range of key environmental, economic and recreational services. There is, however, a growing concern that over the twentieth century, an increasing number of braided rivers have metamorphosed into wandering or single thread channels, representing a loss of key habitats, geodiversity and amenity. While in some situations, shifts in channel pattern may be unambiguously linked to abrupt changes in flow or sediment supply, the lack of a theoretical basis underpinning the development and maintenance of braiding makes identification of the cause and effect of channel metamorphosis hazardous. A growing body of research has suggested that the transition between channel patterns may depend on the poorly understood interaction between the flow regime, sediment supply and vegetation colonisation. Such interactions are governed by critical thresholds, due to changes in flow resistance and bank strength associated with the distribution, form and intensity of vegetation colonisation. Subtle changes in flow or sediment supply that promote vegetation growth or indeed remove it through inundation or attrition. This can lead to complex non-linear shifts in the balance of forces that govern sediment transport and bedform morphodynamics, ultimately resulting in one-way changes in channel morphology. There is, therefore, a critical need to develop a quantitative understanding of these feedbacks in order to design sustainable river management programmes that seek to optimize the ecological and socio-economic benefits these rivers offer. During the last three decades, significant advances in the understanding of the morphodynamics of braided rivers have been made through a combination of field and physical experimentation. More recently, the emerging field of numerical modelling has created a new avenue to investigate the processes that govern channel dynamics. While this methodology offers significant promise through the construction of virtual experiments that examine the spectrum of drivers and responses of river systems, such models require careful and critical evaluation before they can be used to guide management practice. The wider goal of this research is to explore the application of a numerical modelling to investigate the feedbacks associated with the development and maintenance of braiding. Specifically, the state-of-the-art numerical model, BASEMENT, was used to examine channel responses to steady, and unsteady flow regimes, with and without the representation of vegetation. The research focuses on four main contributions: 1. The development of a systematic framework to quantify the evolving form and processes of braided rivers that can be used as part of a comprehensive approach to model validation. 2. Simulation of braiding development and maintenance using BASEMENT under steady flow conditions. Model simulations based on the natural prototype of the braided River Feshie were used to examine the sensitivity of emergent channel morphologies to…

Subjects/Keywords: Braiding processes; Gravel-bed rivers; Numerical modelling; Unsteady flow; Vegetation; BASEMENT

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Baral, B. R. (2018). Numerical modelling of braiding processes in gravel-bed rivers. (Doctoral Dissertation). Queen Mary, University of London. Retrieved from http://qmro.qmul.ac.uk/xmlui/handle/123456789/44686 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.766212

Chicago Manual of Style (16th Edition):

Baral, Bishnu Raj. “Numerical modelling of braiding processes in gravel-bed rivers.” 2018. Doctoral Dissertation, Queen Mary, University of London. Accessed November 28, 2020. http://qmro.qmul.ac.uk/xmlui/handle/123456789/44686 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.766212.

MLA Handbook (7th Edition):

Baral, Bishnu Raj. “Numerical modelling of braiding processes in gravel-bed rivers.” 2018. Web. 28 Nov 2020.

Vancouver:

Baral BR. Numerical modelling of braiding processes in gravel-bed rivers. [Internet] [Doctoral dissertation]. Queen Mary, University of London; 2018. [cited 2020 Nov 28]. Available from: http://qmro.qmul.ac.uk/xmlui/handle/123456789/44686 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.766212.

Council of Science Editors:

Baral BR. Numerical modelling of braiding processes in gravel-bed rivers. [Doctoral Dissertation]. Queen Mary, University of London; 2018. Available from: http://qmro.qmul.ac.uk/xmlui/handle/123456789/44686 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.766212

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