Block mattresses are widely used bed protection elements under non-uniform flows. Previous studies show that the turbulence of the flow plays a key role on the instability of the mattress. However, in the available design equations, the turbulence intensity is included as a magnification factor roughly and qualitatively defined. Consequently, the design equations are often used as a rule of thumb, where the engineering criteria of the designer is critical and large safety factor are used. In turbulent non-uniform flows, the available design equations were developed for uniforms flow and the turbulent intensity is included as a magnification factor, usually poorly defined. The stability reduction due to turbulence has been proved by several authors. However, there is not any study in previous literature that investigate the role of velocity fluctuations on block mattress failure. Nevertheless, the literature review showed that an innovative approach, which combines the mean velocity and the turbulence intensity to quantify the flow forces, has been largely study for loose rock by several authors. Following this trend, the option of applying this structure (u ̅+α√k) as a flow quantification on Pilarczyk equation was decided to study. For this purpose, a series of test were done under four different configurations. Two weir heights were used (15 and 18.5cm) and the distances corresponding to 3h and 4h were checked. Four failures were recorded for each configuration for a total of 16 failures. Additionally, a data base was recorded for each configuration where the flow discharge was related to mean velocity and the turbulence intensity. An analysis of the failure mechanism was done by synchronizing the velocity time series with the displacement of the blocks. The results showed that an episode of peak streamwise velocity and downwards (sweep) was present at the failure. However, the analysis of the velocity showed that higher combinations of streamwise velocity and shear stress were present before the failure on almost all the records. Therefore, the streamwise velocity and the induced shear stress cannot solely explain the failure of the block mattress. This conclusion is in line with the work done by Hofland (2005). However, the recorded data did not allow to describe completely the failure mechanism.
The turbulence magnification factor (α) at the stability equation was derived by two different approaches. The first approach was based on the peaks of velocity associated to failure while the second one was described as a fitting parameter. The analysis concluded that the α values were close to 3 for both cases, in line with the expected value from previous studies. Finally, the new developed equation was compared with the original Pilarczyk equation and the modification proposed by the Rock Manual (2007). The comparison shows that the new developed equation described the required thickness of the block more accurately than the available equations. Thus, the results show that the proposed approach described the effect of turbulence accurately on a design equation. Additionally, all the relevant derived conclusions for design propose were summarized in a design guideline.

When sea-going or inland vessels berth along a mooring location they use their bow thruster to manoeuvre. When the induced propeller jet is directed towards a slope it might affect the stability of the slope material and this can lead to damage when the loads are too large.

The objective of this research was to extend and validate a method to determine hydraulic bed loads on slopes induced by bow thrusters and a method to determine the stability of slope material. In order to answer this objective scale model tests are conducted at the test facilities of Deltares. Velocity and stability measurements are performed during multiple test scenarios that contain variations in slope angle, axial distance and pile configuration. From the obtained data of the velocity measurements the time-averaged velocities and the turbulence intensities are determined. For example, the time-averaged slope velocities measured in the scale model that consists of an 1 : 3 slope with an open quay pile configuration and a rough bed (test scenario T10 in the research) are shown in Figure 1. These values are compared to the values according to the Dutch guidelines and a correction factor for the underestimation of the hydraulic bed load on a slope is defined for each test scenario. After that the consequences for a design of a slope protection are evaluated. Furthermore, for the stability tests it is determined what the critical slope velocity is. This is done for multiple criteria of initiation of motion. With these critical slope velocities a stability parameter for the stability relations can be determined that is applicable at situations similar to the scenario tested. These determined stability parameters are compared to the recommended stability parameters and the differences are evaluated. Finally recommendations are formulated for correction factors for the slope velocities induced by bow thrusters and recommendations are formulated for a proposed stability formula by an earlier research.

The main objective of this thesis is to assess the effectiveness of Nature-based Solutions in reducing flood risk in the Galveston Bay by means of wave attenuation. The methodology to answer these questions consists of both literature review and numerical modelling. The wave height reducing capabilities of marsh vegetation, seagrass meadows and oyster reefs are described and assessed quantitatively. Their limitations and optimizations strategies are investigated and applied to the Galveston Bay, Texas.

Downstream of hydraulic structures, the flow is normally of turbulence. This will cause considerable erosions on the gravel bed. To prevent this, block mattress is preferable in many cases. Its effective stabilization and feasibility on construction make it commonly used against scouring problems, protecting underwater pipelines and cables. The currently widely used design formula with dedicated parameters for block mattresses was derived by Pilarczyk. However, it is observed to be partly functioning under non-uniform flow condition, since the turbulence parameter is rather empirical. Therefore the main purpose of this thesis is to optimize the current design formula (Pilarczyk’s) for non-uniform flow condition. In this flow regime, turbulence is of importance for bed material entrainment. Thus this research focused on how to introduce turbulence effect into formula explicitly. To predict the failure of block mattress better, a detailed study on failure mechanism and impact of flow condition over the block mattress edge is necessary.