Introduction

Floodplain vegetation is intrinsically dynamic due to the nature of the rivers hydrology and resulting morphological changes in interaction with vegetation during high flows. When rivers can freely move along with their dynamic discharge patterns, also patterns of vegetation dynamics can be observed . During high flow vegetation patches may be removed by the water and new bare sandbars may appear where vegetation growth recommences . However, in trained rivers where levees and groynes limit the movement of the river and dams regulate the discharge, vegetation is normally not set back in a natural manner, resulting in a steady increase in the amount of vegetation, mainly floodplain forests .
In embanked rivers with a limited discharge capacity, the overall hydraulic roughness of vegetation in the floodplains determines flood levels . Over the last fifty years two observed developments have increased the need for a good understanding of the developments of floodplain vegetation: (1) A shift from agriculture as the dominant land-use in the floodplain to a synergy between increase in discharge capacity and a trend for nature rehabilitation that has led to more dynamic floodplain vegetation patterns in space and time. An example is the change shown in Figure 1. (2) Higher flood forecasts have led to the need for a stricter management of margins of cultivated areas and unmanaged natural government properties. As a result of these two developments the floodplain vegetation has become more dynamic and increased the nature vs floods dilemma. This has led to proposed strategies like room for the river (Klijn et al 2018) and cyclic rejuvenation (Baptist et al 2004).