Background

Floodplains are part of those ecosystems that offer the most ecosystem services (ES). These ecosystem services are, for example, the flood retention in the floodplain area, the retention of nutrients and pollutants, providing a basis for agriculture and forestry or climate regulation through the storage of carbon in soils and plants - on functional floodplains. But what is a functional floodplain and how can one define its size? Thus far floodplains have been defined on the basis of very large floods, which statistically occur once every 100 years and usually reach the dikes. However, if you look at the ES, for example nutrient retention, that mainly depend on yearly floods, then the extent of smaller floods is important as well. Due to the EU flood directive, all EU countries are obliged to model these more frequent floods. However, the frequent floods are to be understood as floods that statistically occur once in 5 to 25 years, i.e. significantly less than annually but substantially more frequently than the very large flood events. That raises the question: Does it make a difference if you compare the ES of a floodplain with frequent flooding to those of a floodplain with less flooding?