During construction of breakwaters, adverse weather conditions can result in damage, in the form of reshaping and loss of material to the open work fronts of the structure. Based on literature research, analysis of work methods, analysis of damage to older breakwater projects and interviews, it was deduced that during construction, the open work fronts of the submerged core section, emerged core section and underlayer section are in particular prone to the following damage mechanisms: - Reshaping of the submerged core due to head-on and oblique wave attack - Reshaping of the emerged core due to head-on and oblique wave attack - Reshaping of the underlayer due to head-on and oblique wave attack. - Mixing of rock material of different sections. - Overwash of dislocated material. When a damage event occurs, construction is delayed as repair works are needed. This delay increases the probability of encountering unfavourable conditions in the remaining construction time. Such positive feedback complicates any quantitative risk assessment. The main objective of this thesis was to investigate the feasibility of a computational model with which risks related to the construction phase of rubble mound breakwaters in sea-state conditions can be assessed. By simulating the construction process in time with a fully probabilistic process-based model, the financial risk due to storm-induced damage during construction can be assessed. Due to the stochastic behaviour of the parameters used in the building process simulation, the simulation outcome itself is characterized by a stochastic behaviour. To calculate the financial risk, the simulation is run multiple times like a Monte Carlo simulation. Quantitative damage calculations in the model were performed using methods reported in the relevant literature. However, currently available literature did not cover all damage mechanisms or the full extent of it. For these damage mechanisms, some newly developed methods were introduced. The damage profiles predicted by these methods turned out to be in excellent agreement with data from an older breakwater project. This older breakwater project was used as a reference case to test the model and analyses its performance. Furthermore, a sensitivity analysis on the breakwater parameters showed that the nominal diameter of the core and underlayer material and the start date of construction works have the strongest sensitivity on the financial risk.

The reach of the Magdalena River around the city of Barrancabermeja experiences large issues concerning its navigability since the construction of the Yondó Bridge. The purpose of this study is to investigate possible causes of this poor navigability and to come up with an improvement to the current situation. The influence of bars and scour holes around bridge piles are seen as hypothetical problem causes. A bar mode analysis shows that, for the examined river section, the river contains one alternate bar over the years. It is plausible that the construction of the bridge has induced changes in flow conditions in such way that the original alternate bar started to erode and eventually totally disappeared. Therefore, it is highly possible that the construction of the bridge forms the main reason for the shift of the thalweg. The scour holes around the piers of the Yondó Bridge that were approximated by the empirical method of Melville and Coleman. These scour holes are incorporated in the Delft3D-model to assess their influence by adapting the initial bed elevation profile. From the model simulation it turns out that the presence of the holes does result in more erosion in the vicinity of the bridge.

Three possible solutions (null-solution, groynes and guide bunds) have been weighed using Multi-Criteria Analysis. Based on this analysis the guide bunds appeared to be the most suitable solution. The structure was implemented in the Delft3D-model and some additional simulations proved that the effect of this structure on the hydro and morphodynamic conditions in the river is twofold. First, the guide bunds improve the distribution of the flow over the cross section of the river. More flow is forced through the right side and indeed the flow velocities turn out to be higher at that location. Moreover, the flow velocities on the left side decrease, as expected. However, the structure has an opposing effect on the cumulative erosion and sedimentation. More sedimentation takes place at the right side of the channel, whereas the left side of the channel gets deeper. It can be concluded that the best way to improve the situation in Barrancabermeja, is the construction of a guide bund structure in the vicinity of the Yondó Bridge. However, more detailed (physical) model tests should be performed to gain better insight in the effect of the guide bunds.