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River dune predictions : comparison between a parameterized dune model and a cellular automaton dune model

Seuren, J. (2014) River dune predictions : comparison between a parameterized dune model and a cellular automaton dune model.

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Abstract:River dunes are of great importance for the determination of water levels, especially during flood events. They have a large influence on the hydraulic roughness and thereby on water levels. In addition, dune formation could affect the navigability of rivers and propagation of dunes could uncover pipelines or other constructions beneath the river bed. Because fast calculations are essential during an upcoming flood event, there is a need for fast model predictions. The focus of this research is on a parameterized dune model and the cellular automaton dune model (CA model) HR Wallingford is experimenting with. Both models are relatively fast in their calculations but have a fundamentally different approach to predict river dunes. This research reveals the performance of these two models tested under various conditions. The main objective of this research is: “To compare the performance of the cellular automaton dune model and the parameterized dune model for the prediction of dune dimensions, migration rates and sediment transport in equilibrium state, under flume conditions, similar to low-land river situations like the River Rhine (the Netherlands).” The first step in this research was the preparation of the CA model for comparison with the parameterized dune model. A sensitivity analysis provided insight in the behaviour of the input parameters used to adjust the model: A length scale was added by assuming a fixed domain and defining the model parameters in a unit of distance instead of a number of cells. Sediment transport was determined by counting all moving slabs and used to implement a time scale. Finally, the input parameters of the model were linked to the flow characteristics. After these adjustments, the model was calibrated using the same data as used for the calibration of the parameterized dune model. The second step was the comparison of the parameterized dune model and the CA model using a data set containing sixteen experiments. Research has shown that the parameterized dune model is reliable for prediction of dune dimensions, although it seems limited to experiments with a slope between 11*10-4 and 22*10-4. The parameterized dune model overestimates migration with approximately a factor of three. The CA model is tested for the first time in the way as presented in this thesis, by adding time and length scales to the model. Results seem promising and show predictions that are reasonable for five experiments; however in general the predictions are slightly underestimated. The CA model underestimates the migration with approximately a factor of three. In this research a non-dimensional CA model is made dimensional. The model has potential and recommended improvements are: a) linking the shear velocity to flow characteristics and b) adding an equilibrium state.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering and Management MSc (60026)
Link to this item:http://purl.utwente.nl/essays/65037
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