FLOODPLAIN MANAGEMENT IN HUNGARY

Dénes Lóczy, Institute of Environmental Sciences, University of Pécs, Hungary

Abstract

Floods along major rivers the Danube and the Tisza are naturally recurring phenomena in Hungary. Since an overwhelming majority of river discharge is collected from the encircling mountain ranges, the hydrometeorological situation in the Alps and in the Carpathians are decisive controls of flood hazard. For centuries floodplain management has focused on the reduction of flood hazard and on the transformation of floodplains from seminatural wetlands to agricultural land. Flood hazard, however, was even aggravated by flow regulation, which narrowed down the once extensive floodplains to floodways between dykes. The primary feature of floodplains in Hungary is their almost complete separation from the river which shaped them. For more than 150 years river and floodplain have only been connected during the short spells of floods and over the rest of the year only through groundwater flow. Now levee formation is restricted to narrow strips between flood-control dykes. The sedimentation rate in the active floodplain is particularly high along the Tisza, a typical lowland river rich in suspended sediment, and its tributaries. Sometimes even settlements were inundated during floods because their environs were gradually silted up to higher elevations. Naural sediment transport has even increased over the past 150 years due to urbanization and intensified erosion in the upper catchment area.
Flood hazard, however, is not the only danger to floodplain environments. Protected floodplains are now mostly under cultivation. Coupled with weather extremes (exceptionally low precipitation), the lowering of the groundwater table often causes the desiccation of the floodplain. This was the case in the Szigetköz, the Upper Danube alluvial fan, where a diversion canal built in 1992 conducted water to the Gabčíkovo Hydropower Plant in Slovakia. Water supply to the Old Danube channel and the maintenance of groundwater level in the active floodplain could only be ensured by an underwater weir in 1994. The natural floodplain microtopography if preserved does not only contribute to geomorphic diversity but can also be beneficial from the viewpoint of water supply. For, instance along the Drava River (border river with Croatia) large-scale plans for water recharge began to be implemented.
In addition to hydrological, sedimentological and geoecological investigations, the geomorphological research can also be relevant for floodplain management through
- the historical reconstruction of pre-regulation river channels and assemblage of floodplain landforms to be utilized in water recharge schemes;
- estimation of water storage capabilities of floodplain deposits and soils;
- modelling erosion and deposition processes in the floodplain in periods of extreme weather (both inundations and droughts);
- predicting the impact of long-term cultivation on floodplain topography.