Author(s): Hauer Christoph; Schober Bernhard; Habersack Helmut
Keywords: River widening; Flood protection; Meso-habitat modelling
Abstract: The catastrophic flood events of the years 2002 and 2005 in Central Europe showed clearly the necessity to act in terms of flood protection. The meaning of floodplain areas and the errors in land use management of the past became obvious by the occurred extraordinary discharges. Unfortunately a high use pressure exists in the surrounding of rivers and the important floodplain areas are blocked in most European countries. Within this work the results of a study of an Austrian River are presented, which exactly exhibits the described problems. In August 2002 a thousand-year flood occurred at the Lower Austria Kamp River. The flood wave damaged 2304 building in the catchment area and caused huge sociologic and economic losses. The destruction on building, road- and railway dams was estimated with 145 Mil. € around this Danube River tributary. Based on the specific geomorphic situation (narrow valley) with average overbank width of 125 m only few flood protection and river restoration concepts were possible. Apart from the construction of flood protection dams, river widenings were seen as possible measures and were established in some reaches of the Kamp River in 2003. This work presents the results of a hydraulic- and morphological monitoring of one of these river widenings (village Kammern) from 2003 – 2005. It was possible, combined with meso-habitat modelling, to evaluate the measure concerning to flood protection and ecological demands of the European Water Framework Directive (WFD). This integrated approach allows to define decisive parameters (Qbf, shear stress, dm, WUAs) for a sustainable management of river widenings. Further a hydrodynamic – numerical sensitive analysis was implemented in this work for Cross section enlargement in different reaches of the Kamp River. The modelling of statistical defined flood events (HQ200 – HQ1) showed that the maximum reduction of the water surface level was the highest in the upper reaches (bed slope=0. 006). This improvement for flood protection occurred only within the range of the measure. Contrary to these results river widening in the lowland reach (bed slope = 0. 0007) exhibited a smaller reduction of water surface elevation, but the effects of the measure were found 3 times longer than the widening length in upstream direction. Based on the monitored aggradation processes of Kammern between 2003 and 2005 different scenarios of bed level rising were developed and included in the numerical sensitive analysis. As example for 500 case studies the results for a onehundred year flood are presented in this paper showing the effects of aggradation on vm and τ. In summary it can be said, that this complex matrix of different “widening” szenarios concerning to different river morphologies with the implementation of aggradation processes can be seen as useful tool for sustainable river restoration.