The current flood risk assessment framework in the Netherlands aims at ensuring a nation-wide protection level with a long-term vision. It assumes that future river bed level changes will not pose negative effects on flood safety and it adopts a fixed-bed assumption. However, the river bed level shows a strong spatial and temporal variability, where bed aggradation trends could lead to higher water levels in the future. Recent measurements in the Dutch Rhine have shown both bed degradation and aggradation in different river sections along the lower river domain. This raises questions to what implications does future river bed level changes have on flood safety in the Netherlands and whether the current fixed-bed assumption has adverse connotations to it.

The objective of this MSc thesis is to study the impact of river bed level changes on flood safety in the Netherlands. To achieve this, a framework for incorporating large-scale bed level changes into flood risk assessments is developed and applied under the current Dutch context. The implications on the long-term and short-term flood safety are analyzed separately, as fundamentally different approaches and uncertainties relate to the flood safety standards derivation and for the periodic safety assessment in the Netherlands.

In the long-term, I propose to incorporate morphodynamic modelling scenarios into the flood safety standards derivation process to account for future bed level changes and their long-term uncertainties. Modelling scenarios should include future river discharge, sea level rise, river maintenance and the evolution of river bifurcations, as they represent main drivers in the long-term river bed response in the Netherlands. Based on existing long-term morphodynamic modelling studies of the Rhine River, it is estimated that the extreme water levels decrease over the upper Waal, but increase over the lower Waal by 0.15 m and 0.30 m in 2050 and 2100, respectively. These scenarios consider that river dredging is not maintained after 2025.

In the short term, I propose to incorporate the analysis of the recent river bed level behaviour into the safety assessment process to account for its uncertainty in the near future. Based on yearly bed level measurements in the Waal from 2005 to 2020, decreasing and increasing water level trends have been identified in the upper and lower Waal, respectively, with increments in the order of 0.05 m. This is small in absolute terms, but significant compared to the accuracy level of the hydraulic loads used in the safety assessment process. As a consequence, these increments can have important economical implications on dike reinforcement programs.

In summary, this thesis provides a framework incorporating large-scale river bed level changes into the current flood risk assessment framework in the Netherlands. Furthermore, it quantifies the impacts of bed level variability on flood safety in the Waal River. In general, the fixed-bed assumption in the current flood safety framework is a conservative, or safe, assumption for the hydraulic loads’ calculation in the upper Waal. However, it may underestimate the future hydraulic loads in the lower Waal and impose adverse conditions on flood safety.

Predicting and modelling meandering river migration is necessary for river engineering, land development, and risk assessment. One chaotic process that makes predicting the migration more difficult is the cutoff of a river bend, which is the subject of this report. This report describes the research process and results of a study on overbank flood effects on chute and neck cutoffs in single-thread meandering alluvial rivers. The following research question is addressed in this report: “What is the relationship between the duration of overbank flooding and the formation of chute versus neck cutoffs?”. The relationships between the overbank flood shear stress and the frequency of chute versus neck cutoffs, and between the soil type of the floodplain and the frequency of chute versus neck cutoffs are evaluated.

An overbank flood exceeds the bankfull limit of a river, flowing over the floodplain. When a river bend is cut off, two cutoff types are visually distinguished: neck cutoffs and chute cutoffs. Cutoffs of both types were analysed in four rivers in the United States of America: Cheyenne River in North Dakota, Powder River in Wyoming and Montana, Pearl River in Mississippi, and Trinity River in Texas. These rivers have a chute cutoff regime, a mixed cutoff regime, and two neck cutoff regimes, respectively.

For these four rivers satellite imagery on Google Earth Pro was combined with measurements from USGS measurement stations and soil data from SoilWeb. The bankfull river discharge was converted to bankfull river depth to calculate the overbank flood heights and the overbank flood shear stresses acting on the floodplain during floods. Subtraction of the critical shear stresses of the soils resulted in residual shear stresses. These were combined with the corresponding flood durations to calculate the flood impulses of each flood.

The floods associated with chute cutoffs showed larger overbank flood shear stresses than those for neck cutoffs. Rivers with steeper slopes seem to be more prone to a chute cutoff regime than rivers with gentler slopes. The soils in which chute cutoffs were formed contained high sand percentages, while the neck cutoffs occurred in a wider range of soil types. The overbank floods creating chute cutoffs exerted larger residual shear stresses for shorter durations, as opposed to smaller residual shear stresses for longer durations of floods associated with neck cutoffs. The overbank flood impulses associated with chute cutoffs show a larger range and higher values, but are on average not significantly different to those of neck cutoffs.

The processes related to river bend cutoffs are very complex and not entirely understood yet and more research is needed on a local and a greater scale. The formulation of general relationships for chaotic events such as cutoffs will improve the prediction and modelling of meandering rivers. This will be increasingly useful, especially now with more extreme weather events and river floods all over the world.

Sediments play a crucial role in civil engineering branches like delta and river flood risk management and in maintaining natural ecosystems. Changes in the availability of sediment can have a major impact on all of these. It is therefore crucial to understand how sediment load in a source-to-sink system behaves in changing environments. Studies quantifying these behaviors often do not span further than a few decades to a hundred years. Carbon emissions will likely have an effect on our climate on the much larger scale of millennia. Humans have begun to plan and adapt their behavior to mitigate climate change by way of greenification of urban areas and replacing traditional agricultural practices by more sustainable alternatives. This study looks at the influence of climate change and different anthropogenic land use changes on the sediment load of the river Rhine by integrating tectonics, sea-level and precipitation change, and land use change for the coming 10,000 years using Badlands. This is done by utilizing a scenario-based approach. The essential role of topsoil dynamics, and a lack thereof in traditional landscape evolution models, such as Badlands, was identified. Using a general scale of topsoil and bedrock erodibilities calibrated to produce realistic sediment load in the Rhine, we found that any implementation of more sustainable land use like agroforestry is predicted to decrease the sediment load of the Rhine in most climate change scenarios, agreeing with similar studies that focused on short-term modeling. Implementing non-uniform precipitation change resulted in significantly different outcomes than using a uniform approximation, so it is advised to implement region-based precipitation change. Furthermore, Badlands has shown impressive versatility and adaptability, and shows potential to be used for the growing demand of studies that focus on predicting future influences of different processes in light of climate change using a holistic process-based approach.