Is There Room for Floodplain and River Restoration? Example: Sava River Basin in Croatia

By regulating streams, part of the former floodplains has been converted into agricultural areas, while part of the floodplains, such as forests, natural wet meadows and marshes, have been separated from the streams due to the construction of embankments or river channel straightening. The aim of this work is to find natural and semi-natural habitats in the Sava River Basin in the Republic of Croatia that could be returned to their natural hydrological function for reducing the risk of floods and improving the hydromorphological state of the waters. The basic data used in the conducted analyses are: Flood hazard and risk maps, a digital relief model, hydromorphological monitoring data from more than 200 locations and a vector layer of water bodies defined according to the rules of the Water Framework Directive. The analyses conducted included GIS-based hydrological analyses of defining the streams with a catchment area greater than 10 km2 and using the Vertical Distance to Channel Network tool for natural floodplain definition. By comparing the high probability layer of floods and the defined natural floodplain and the Map of Terrestrial Non- Forest Habitats of the Republic of Croatia (Bardi et al. 2018), areas of potential rehabilitation or restoration areas (without endangering the population and economic activities) were delineated. The analyses carried out showed that the largest compact areas that could be rehabilitated or restored, in sense of restoring riverfloodplain connectivity by removing obstacle like embankment, reconnecting old meanders or flood water storage, are in the Lonja, Česma and Ilova river catchment, then parts of the river Sava floodplain from the stream Strug confluence to the river Orljava confluence.