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Analysis of flow processes at the downstream side of various river measures using 1D- and 2D flow models

Clements, Michiel (2016) Analysis of flow processes at the downstream side of various river measures using 1D- and 2D flow models.

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Abstract:After implementation of river measures in sub-critical flow, the water level upstream of the measure decreases. However, at the downstream boundary of these measures the water level tends to increase. This is observed as a local peak. In this research the existence of this peak is investigated. This is undertaken by introducing two schematized river measures: a widening measure and a deepening measure. The focus was mainly on the downstream side of these measures. It is shown that the flow processes that cause the peak at the downstream boundary of the both measures can be explained by the Bernoulli equation. Bernoulli states that when the flow decelerates, the water level increases. In sub-critical flow, the effects of the river measures are only experienced upstream. Implementing the deepening measure, no changes thus occur far downstream of this measure. When going from that point in upstream direction, the flow decelerates since the river profile expands. Bernoulli explains that due to this deceleration the water level increases in upstream direction. A similar process occurs at the downstream side of the schematized widening measure. However, at the downstream boundary of the measure, the lateral change of the river profile causes lateral flow velocities towards the axis of the river. This has a significant influence on the shape of the peak. Furthermore, turbulence tends to be an important flow process and has an increasing effect on the peak. There is also an analysis undertaken on the used grid size in flow models. Regarding the deepening measure, using a smaller grid size then length of the step in the bed, no significant changes occur. However, using a larger grid than this length results in a smaller peak and should therefore not be used. Regarding the lateral flow constriction, when a grid size is used that is smaller than 1 * db/dx, no significant change occurs. When using a larger grid size the peak is overestimated. Besides the schematized flow constrictions, the real world case ‘Scheller- and Oldeneler Buitenwaarden’ near Zwolle is used. This project concerns the construction of a side-channel. Using the analysis of the schematized flow constrictions, it is attempted to reduce the peak downstream of the side channel. It is shown that adapting the mouth of the side channel such that the lateral flow velocities are reduced also reduces the size of the peak. It is furthermore shown that increasing the roughness that causes a local decrease of the water (the Bernoulli effect in opposite direction) only has an enlarging effect on the peak.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering and Management MSc (60026)
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