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Upper stage plane bed in the Netherlands

Daggenvoorde, R.J. (2016) Upper stage plane bed in the Netherlands.

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Abstract:The Netherlands is vulnerable to flooding, both from the rivers and the sea. To counter these threats the Dutch protect themselves with dikes and other flood protection measures. These protective measures are designed to withstand a design water level. To be able to predict the design water levels the processes determining the water levels need to be understood. Amongst others bed roughness is an important factor determining the water depth. So it is important to know the form of the river bed. Upper Stage Plane Bed (USPB) is a river bed form. When USPB is present at the bottom of a river, the river bed is less rough compared to dunes and ripples. The presence of USPB in a river in the Netherlands during design discharge is expected to reduce the design water levels up to 0.5 meter. Whether USPB in the Netherlands develops under design conditions is still unknown and is the focus of this study. The study comprehends two mayor parts. The first part focusses on finding the location with the most USPB favourable conditions and the second part uses a dune evolution model in order to predict dune evolution under design discharge. The USPB-index has been formulated to find the most probable location for USPB in the Netherlands. This index is based upon the Froude and Suspension numbers along with a threshold which is based upon observations of dunes and plane beds. The index allows comparing different locations to each other on their probability to develop USPB. The lower the USPB-index the more likely the location is to develop USPB and when the index drops below zero, USPB is expected to develop. This index indicated the IJssel near Kampen as the most probable location for USPB to develop in the Netherlands, with the river Lek near Tienhoven-Lopik as the second location. The second part of this study applied the model of Van Duin (2015) on the IJssel near Kampen and the Lek near Tienhoven-Lopik. By performing three calibrations the model could be applied on river scale. The morphological module of the model has been calibrated upon equilibrium dune heights in flume experiments (Coleman et al., 2005; Naqshband et al., 2014c), the calibration led to a Nash-Sutcliffe-coefficient (NS-value) of 0.69. Secondly the hydrodynamic module was calibrated on a river scale, aiming to reproduce the observed dune heights in the Waal in 2002-2003 (Sieben, 2004), resulting in an NS-value of 0.3. The morphological module did not need to be calibrated again since it is standardized for different water depths (applicable on flume and river scale). The third calibration aimed to correctly reproduce the moment when the bed form in a simulation changes from dunes to a plane bed. This has been done by changing the step-length-model such that the conditions when USPB is present have an UPSB-index below zero. This step-length-model is within the morphological module of the model and could be changed without influencing the resulting dune heights. The fully calibrated model showed that the IJssel near Kampen did develop USPB. In the river Lek near Tienhoven-Lopik dunes remained present during the design discharge wave. So, within the Netherlands, USPB is only expected to occur in the river IJssel near Kampen. Due to the lack of data on the transition to USPB in both flumes and rivers this transition to USPB is calibrated upon observations of dunes and plane beds, instead of the transition itself. To cover this and other uncertainties further research is needed. The transition to USPB needs to be validated by field observations or flume experiments and the calibrated model needs to be validated for other rivers than the Waal. These follow-up-studies can lead to enough knowledge to be able to use the beneficial water level reducing effect of this plane bed when designing flood protection measures.
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/71629
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