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).