SOME GEOMORPHOLOGICAL AND GEOECOLOGICAL IMPACTS OF THE 2010 EXTREME RAINFALLS IN HUNGARY
DÉNES LÓCZY
ABSTRACT. Some geomorphological and geoecological impacts of the 2010 extreme rainfalls in Hungary. The extreme rainfall events in the unusually wet year of 2010 brought about major changes in the floodplains of several streams in Hungary. On the small watercourses in low mountain or hill environments flash floods were generated. In the floodplains of medium-sized rivers, like the Kapos River in Southern Transdanubia, lasting inundations transformed the landscape. The system of wetlands preceeding the 19th-century river regulation and land drainage measures was restored by natural processes and within a very short time as excess water filled the entire broad valley sections in a shallow layer temporarily, for some weeks, and the former oxbows for several months. The nature conservation value of the river valley increased: reed and sedge beds and the brooding colonies of aquatic birds extended. There are, however, unfavorable impacts as well. Denser wetland vegetation significantly contributes to the organic filling of floodplain landforms. The spreading of invasive plants (allergetic ragweed, Ambrosia artemisiifolia, in the first place) was promoted by the prolonged survival of extensive bare but moist silt surfaces in the floodplain. The long-term effects of this colonization on floodplain communities are unpredictable. A delayed and indirect impact of extreme rainfalls was the breach of a red sludge reservoir near the Ajka alumina plant in October, 2010 and the resulting environmental disaster. After the gradual accumulation of rainwater in the reservoir, the dyke breach happened, released 600-700 thousand m3 of basic (up to pH 13!) sludge over the floodplain of the Torna Stream, a tributary of the Marcal and Rába rivers in an area of ca 40 km2. The emergency mitigation measures (spreading gypsum from power plants to neutralize the strong base) over the layer of red sludge accumulation proved unfortunate as it prevented that the sludge should be washed downstream and diluted. The gypsum crust hindered the natural regeneration of aquatic life. With serious damage to residential buildings, the ecological impacts on the floodplain may not be as long-standing as predicted.
Keywords: flash floods, inundation, red sludge spill, channel and floodplain changes