Reconstruction of 2D riverbed topography from scarce data. Case studies: Atrato River (Colombia) and Waal River (The Netherlands)
Henok Endale Abebe
WSE-HERBD-11.02 April, 2011
Reconstruction of 2D riverbed topography from Scarce data. Case studies: Atrato River (Colombia) and Waal River (The Netherlands).
Master of Science Thesis by HenokEndale Abebe Mentors
Dr. Alessandra Crosato (UNESCO-IHE) Dr. Erik Mosselman (Deltares)
Examination committee Prof. Dano Roelvink (UNESCO-IHE) Prof. Maximo Paviani (External) Dr. Alessandra Crosato (UNESCO-IHE)
This research is done for the partial fulfilment of requirements for the Master of Science degree at the UNESCO-IHE Institute for Water Education, Delft, the Netherlands
The findings, interpretations and conclusions expressed in this study do neither necessarily reflect the views of the UNESCO-IHE Institute for Water Education, nor of the individual members of the MSc committee, nor of their respective employers.
Dedicated to my Family
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Reconstruction of riverbed topography from scarce data.
AbstractDifferent numerical models have been developed to analyze morphodynamic evolution of rivers. However, the functionality of these models is challenged due to lack of accurate bathymetric data. The current practice to overcome this shortcoming is the use of simple interpolation techniques to draw the bed topography where the data are missing, however these methods are inaccurate (Schäppi, et al.,2010). This research investigates whether the use of simple physics-based morphodynamic model MIANDRAS and GIS interpolation techniques allow for reconstruction of riverbed topography when data are scarce. The study is done to two meandering rivers. The first one is the Waal River (the Netherlands), which has detailed measured bathymetry. The other one is the Atrato River (Colombia), which ischaracterized by scarce measured bathymetric. Since the Waal River has detailed bathymetry, the performance of each technique is evaluated on this river with the aim of making generalization on the results so that they can be used later for the Atrato River. In case of GIS interpolation techniques (Kriging and Spline), different scenarios are analyzed with different quantity of bed levels. The data aresynthesized by making several sailing tracks and centreline, each one simulating a single-beam eco-sound bathymetric survey and the cross-sections are designed as a function of river sinuosity and width. The results show that, when data are scarce GIS interpolation (Kriging and Spline) tends to smooth out bars and pools, whereas these are great relevance for identification of river navigability.Furthermore, compare to other method Ordinary Kriging interpolation method gave better result. Similarly the performance of MIANDRAS for reconstruction of riverbed topography was analyzed in Waal River. The model MIANDRAS computes the 2D equilibrium bed topography, including steady alternate bars and point bars, while only requiring the knowledge of a few cross-sections. The results suggest that, whenthe data are scarce MIANDRAS could be one of the means for the reconstruction of riverbed topography. Furthermore, MIANDRAS could be used in planning detail bathymetric survey because it assists in identifying the location of pool and bars which are great relevance of bathymetric survey. All the experience gained from Waal River is used for reconstruction of Atrato River (Montano reach) bedtopography. However, due to data limitation the bed was reconstructed with a lot of assumption which might affect the accuracy of the each methods used. In general the experience gained from the Waal River is summarized in such a way to be used for reconstruction of the whole reach of Atrato River. Application of MIANDRAS for reconstruction of riverbed topography is a new method so that it would be...