University of Twente Student Theses


Numerical Assessment of Floating Breakwater Effects at Intertidal Flats

Taufiiqul Hakim, Afif (2023) Numerical Assessment of Floating Breakwater Effects at Intertidal Flats.

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Abstract:Intertidal flats in the Eastern Scheldt, a tidal basin in the southwest of the Netherlands, have been encountering severe erosion issues. One of the intertidal flats subject to erosion in the Eastern Scheldt is Roggenplaat. The erosion in Roggenplaat causes a decrease in the intertidal area. As a consequence, reduces the foraging for various species dependent on the habitats. Multiple measures are available to prevent erosion that could be applied in the Roggenplaat. For instance, nourishment that could be eroding and has a limited lifetime. Another option is conventional breakwaters. Yet, it is not economically attractive, especially in deep water and poor soil conditions. Floating breakwater can potentially protect the intertidal area like Roggenplaat against erosion. This is foreseen based on the wind-generated waves in the Eastern Scheldt that can be handled by a floating breakwater and the availability of deeper water considering the channel-shoal interaction in the Eastern Scheldt. However, even though the floating breakwater has potential, the effects of the floating breakwater on hydrodynamic and morphodynamics under realistic conditions are still not fully understood. Therefore, the current study aims to assess the hydrodynamic and morphodynamic effects of a floating breakwater (FB) under varying wave conditions, FB positions, and slopes on the intertidal flats. In this study, two research phases are undertaken. The first is to understand whether the Delft3D model can be used to reproduce the results of the laboratory experiment by Shimoda et al. (1991) that explored the effect of FB intervention. In the second research phase, various data parameters are derived, including wave conditions, water depths at FB position, channel slopes, and intertidal area slopes inspired by conditions in the Eastern Scheldt. A total of 180 unique combinations of these data parameters are created for the data input of Delft3D simulations. From these simulations, three hydrodynamic parameters, such as wave height, near-bed orbital velocity, and bed shear stress, and three morphodynamic parameters, such as bed load transport, suspended load transport, and cross-sectional erosion area, are used for the interpretation. FB is represented by the transmission coefficient feature (obstacle) in Delft3D for both the first and the second research phases. Based on the results in the first research phase, it was found that Delft3D could not predict the erosion and sedimentation pattern of the three observed cross-sections in the laboratory. Nevertheless, Delft3D was able to reproduce the effects of FB in terms of reducing erosion and sedimentation in the lee side of FB for the three cross-sections. The result in the first research phase gave insight into the effect of using the transmission coefficient to represent FB, which was also used for the second research phase. Furthermore, results in the second research phase showed that FB is less effective as the wave conditions became more extreme. Under mild wave conditions with incident wave height (H0) = 0.40 m and peak wave period (Tp) = 1.7 s as well as H0 = 0.70 and Tp = 2.3 s, hydrodynamic parameters, bed load and suspended load transport were effectively reduced. As a result, erosion could be fully diminished with a 100% reduction. Next, with slightly more extreme wave conditions, H0 = 1.20 m and Tp = 3.0 s, erosion was reduced by 92.7% - 96.4%. Meanwhile, with more energetic wave: H0 = 1.8 m and Tp = 3.8 s, erosion was reduced by 57.4% - 62.6%. The ranges emerged from different water depths at FB position, channel slopes, and intertidal area slopes.
Item Type:Essay (Master)
Deltares, the Netherlands
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering and Management MSc (60026)
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