Validate results of river bends modelled by Delft3D 4 Suite and D-Flow FM

Student report (2017)

Authors

G. Frölke Civil Engineering & Geosciences

Contributors

Kees Sloff (mentor)
Erik Mosselman (mentor)
Faculty
Civil Engineering & Geosciences, Civil Engineering & Geosciences
Copyright: © 2017 Guus Frölke
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Published Date

31-10-2017

Language

English

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Faculty

Civil Engineering & Geosciences

Abstract

The use of rivers for navigation and the increased human activity along their banks generally requires river control and improvement measures. Most rivers have a natural tendency for continuous change of alignment, e.g. meandering and braiding rivers. Construction of bridges, towns, berths, etc. have required fixation of the river alignment at many places, changing the natural morphology of the rivers. This might lead to bank erosion, erosion around bridge pillars, sedimentation of navigation channels, etc. Adequate measures against this requires a reliable prediction of the morphological changes.
For simulating the morphological effects in bends there are two different major factors involved that have been described by several scientists: bed slope effects and spiral flow. For modelling morphological development of a river bend several tests have been done on two different cases that have been researched in a laboratory flume (Delft Hydraulics Laboratory (DHL) and Laboratory of Fluid Mechanics (LFM)) in the 80s. In this research the effects of the major characteristics on the bed development of the bend are examined. This has been done by varying the different input parameters that have influence on the secondary flow and the bed slope effects. Subsequently the varied input files are used to model the same bend with Delft3D 4 Suite, D-Flow FM with an unstructured grid and D-Flow FM with a structured grid. In this way the differences are shown between the different kinds of modelling of the same input parameters.

The parameters that have been tuned are Ash, Bsh and Csh for the bedload transport factor that is influencing the bed slope effect. The other parameter is Espir that influence the amount of spiral flow in a bend. The last is αcal that is a multiplication factor in the sediment transport formula from Engelund-Hansen in Delft3D 4 Suite. After optimising these parameters it was not possible to reproduce the flume experiments. Reason for this is probably a simplification in the numerical calculation because with similar parameters of Struiksmas modulation [6] in 1985, which reproduce the flume well, it was still not possible.
To improve the reliability of the model it is recommended to study the following aspects:
• Improvement of the inflow boundary conditions, to improve the way in which water and sediment flows into the system.
• Improvement of the numerical modelling, to create a model that can simulate the characteristics of the river bed in a better way.
• Look for test cases which are close to reality to see if the updates in the model are truly simulating the reality.

By improving these points, the morphological changes might be predicted in a better way than it is in the current situation. Also it will be possible to have less crashes during the run of simulations.