Is riverbank vegetation important for the estimation of flood water levels?

Freshwater plants are one of the main components of the aquatic ecosystem and significantly influence river processes at different scales, and they are also affected by the river flow (Nikora, 2010; Nepf, 2012). Thus, a proper flood risk management requires to include understanding the processes of mutual interactions (flowbiota), which are still challenging (Nikora, 2010; Nepf, 2012). It is essential to know that such vegetation is a crucial component of the environment, which provides important tool for nature-based solutions for river engineering and management. Considering appropriate placement of plants along the stream, various possibilities for using vegetation as a nature-based solution may include facilitate sediment transport in the channel, control to direct overbank flows, and the reduction of scour and river channel erosion processes (Shields Jr. et al., 2017). However, a proper prediction of processes occurring in rivers with vegetated bank? (e.g., vegetationinduced turbulence) needs sufficient studies of vegetation seasonality due to its dynamic nature. Past approach to the subject of river management (e.g., Ree 1949) did not include the ecological meaning (wildlife habitat) of riverine vegetation and thus, all the actions were focused only on reducing the source of flow resistance by cutting the vegetation to reduce flooding (Nepf, 2012). Hence, current methods should be developed in such a way as to comply with the assumptions of finding the balance in predicting the channel resistance in the presence of vegetation between ecological management and flood control (Nilsson et al. 2005; Nepf, 2012). Flow-biota-sediment interactions, due to continuous vegetation development, are vulnerable to extensive knowledge gaps in the investigation linking the fluid mechanics, biomechanics, ecology and transport processes that prevent a full understanding of these phenomena (Nikora, 2010; Łoboda et al., 2018). To expand knowledge in this research field, the aim of this study is to investigate the effect of riverbank vegetation on the flood water levels, considering various riverbank vegetation coverage due to its variation throughout the annual seasons. For that purpose, the hydrodynamic model Delft3D Flexible Mesh will be used to simulate river flow hydrodynamics on the part of the Meuse river as a case study. This study will investigate various static vegetation scenarios considering seasonal changes in vegetation roughness and their life cycle, e.g., due to leaf loss or plant dying. The main focus will be drawn to short periods including before, during and after the flood event (i.e., period of approximately two weeks; starting two days before the flood event). As Nepf (2012) highlighted, vegetation is not distributed uniformly, which plays an important role in the reach-scale flow resistance. Thus, the proposed study will consider the density of plant coverage on the riverbanks as well as species variety

Benchmark study of numerical model grids to study historic floods of the river Rhine

Up until now, structured curvilinear grids are commonly used for hydraulic modelling. However, this grid type has several disadvantages such as staircase representations along closed boundaries and unnecessary high resolution in sharp inner bends. A so called ‘flexible mesh’ can overcome these limitations, since different shapes of grid cells can be used. However, model performance is not directly clear. Several different grid types are compared based on model performance and computation time. This shows that an unstructured grid with curvilinear grid cells in the summer bed and triangles in the floodplains is the most appropriate mesh for 2DH hydraulic modelling. A curvilinear grid in the summer bed ensures high resolution in the channel cross direction, while less grid cells are needed compared to a complete triangular grid. This has a beneficial effect on computation time