In most current dike assessments only the stationary water levels are investigated in the assessment of the stability of the inner slope, while there are differences for all kind of dikes between the stationary and transient pore water pressures and therefore in the stability. This results in a conservative probability of failure, while determination of a probability of failure should not be conservative but should be as realistic as possible. When time dependency is included in a calculation, an average flood duration is used, while the flood duration is highly variable. The following research question is defined to address the problem: “What is the influence of the flood duration on slope stability and in what degree affects the flood duration the design?” The degree of influence of time dependency on the pore water pressures and slope stability depends on dike characteristics, flood wave characteristics and the delay in failure. The basis for answering the research question is the software SEEP/W to model the time dependent pore water pressures and the software SLOPE/W to calculate the safety factor for the stability of the inner slope. In the research theoretical dike are used and there is focused on the flood waves in the Rhine and Meuse. A correlation analysis is performed to get insight in the contribution of different flood wave shape variables to the safety factor. And a probabilistic analysis is performed using transient and stationary water levels to know the differences in probability of failure between taking the shape of a flood wave into account or not. In both probabilistic analyses is varied in the permeability and the strength of the material; the shape of the flood waves is varied in the transient analysis. In this way the contribution of the flood to the probability of failure can be quantified. Dike characteristics The differences in pore water pressure are especially large for dikes that consist of an impermeable material such as clay. When only the subsoil consists of clay, larger differences are expected than when only the dike body consist of clay. However, large differences in pore water pressures do not necessary lead to large differences in the safety factor. The largest differences in safety factor are obtained when uplifting of the hinterland takes place during the stationary state and/ or during the passage of a flood wave. A transient calculation is therefore most useful for dikes with an aquifer and a thin (thinner than 5 m) weak (low POP values) hinterland. Flood wave characteristics The differences in safety factor during a permanent water level and the passage of a flood wave are large when no stationary conditions are reached during the passage of a flood wave. This is the case for high and short flood waves. Both in the Rhine and Meuse, the amount of short waves (< 7days) is high, which increases the influence of a time dependent calculation. Also, the importance of a time dependent calculation increases when the response to the increased pore water pressures is delayed caused by the permeability of the material. The influence of the height of a flood wave on the stability increases when the soil is permeable. Delay in failure Time dependency causes failure of the embankment to not occur simultaneously with the maximum wave height. The flood wave is decisive for the dike failure, but the permeability and the strength of the dike determines the moment of failure. Influence on design Taking time dependency into account leads to higher safety factors and lower probabilities of failure with exception for dikes that consist completely out of sand. For these types of dikes, the probability of failure and safety factors are the same order of magnitude. This could affect the design, because the dikes are safer when time dependency is considered. The strength of the material is the largest contributor to the distribution of safety factors and therefore to the probability of failure (60-95%). Whereas the contribution of the permeability to the probability of failure is small (2-12%), the variation in the height and duration of a flood wave contribute for 2-20% to the probability of failure. In a permeable dike this contribution is mainly determined by the height of a flood wave, while in an impermeable dike the duration of a flood wave is of importance. Considering the influence of time in stability probabilities of failure, this research proved that probabilities of failure taking the duration into account differ significantly from stationary calculations. It is therefore useful to take time dependency into account when determining the correct safety factor for impermeable dikes, but it is not useful in determining the correct safety factor for permeable dikes, because a stationary calculation is sufficient. In clay dikes it is useful to take the variation in height and duration into account, while for a sand dike it is sufficient to only consider the variation in height of a flood wave. When the variation of the duration of a flood wave is not considered, it is recommended to use a representative duration of a flood wave; that results in the same total probability of failure as when the variation of the duration is included. At Lobith the duration of the representative flood wave varies from 13 - 16 days. At Borgharen the representative duration varies between the 10 – 11 days for different dike types.

Jakarta is heavily subjected to land subsidence. Due to this subsidence, the city is sinking further to under sea level. This has influence on the flood safety, both from an extreme sea event as an extreme rainfall event. The major cause of the subsidence is assumed to be the groundwater extraction, which takes place due to a lack of piped water. To reduce subsidence, the groundwater extraction must stop. It is concluded that this would not be feasible in the short term and scenarios are made on how subsidence will continue in the next years.

To ensure flood safety, measurements have to be taken. Research has already been carried out for West Jakarta, but this report focuses on solutions for East Jakarta. Four different solutions are developed to ensure flood safety. The first is to heighten the coastal dike and the flood defences along the river with the same level as the relative subsidence. To accomplish this, high flood defences should be constructed in the densely populated areas along the rivers. A spatial analysis is performed to come to a cost estimation model for the necessary land acquisition for three types of flood defences. These designs are combined to come to a cost efficient design. Another way to ensure flood safety is to close off the rivers and to pump the water into sea. In this case heightening of the flood defences along the rivers is not necessary. To reduce the peak discharges and thus the needed pumping capacity, a retention lake should be built. This can be done inland, but it is concluded that this will not be a cost efficient solution. A more cost efficient solution is to construct an offshore retention lake. This can be done by building an outer sea dike. In this case, the rivers will flow into the retention lake, which is maintained at a given water level. The pumping capacity needed to ensure flood safety depends on the size of the lake. An optimum has to be found to come to the most cost efficient design. In this study it was concluded that the most cost efficient solution is to not make a retention lake at all, but install pumps with sufficient capacity instead to handle the peak discharge. To reduce the pumping capacity, tidal gates can be constructed at the river mouths. A great advantage of this solution is that an amount of pumps can be constructed to deal with mild subsidence rates and more pumps can be built when concluded that subsidence rates turn out to be larger. In this way an adaptive solution is created.