Hidrológiai Közlöny, 2017 (97. évfolyam)
2017 / 3. szám - MANAGING ENVIRONMENTAL RISKS - FLOOD PROTECTION EXPERIENCES AND COOPERATION IN THE DANUBE RIVER BASIN - Gombás Károly - Balatonyi László: Extremities in winter season - outlook for mitigation measures
Extremities in winter season - outlook for mitigation measures Károly Gombás* and László Balatonyi** * Head of Regional Technical Service Group, North-Transdanubian Water Directorate (ÉDUVIZIG), Győr, Hungary; EU SDR PA5 Environmental Risks, HU coordinator; Chairman of ICPDR Flood Protection Expert Group. Email: gombas.karoly@eduvizig.hu ** Head of the Department for Flood Protection, General Directorate of Water Management (OVF). Budapest, Márvány utca 1/D, Hungary; E-mail: balatonyi.laszlo@ovf.hu Abstract The increased frequency of the appearance of icy conditions is a potential consequence of the climate extremities that have been experienced recently. There are many possible field measures to avoid the adverse effects of the ice transport or conglomeration. One of those is the fluvial ice-breaking with ice-breaking ships where appropriate conditions are present - like in the Danube River. Despite the locally favourable impacts the effective mitigation measures are based on mutually accepted basin-wide masterplans and cooperation of the interdepended countries in the catchment. "Several initiatives are known currently and EU SDR PA5 is willing to support the activities to receive funding. Keywords Icy flood hazard, ice phenomena, ice breaker, ice forecast, mitigation measures, Danube basin, water scarcity, mitigation measures ______________________________________________________________________________________________________________________81_ INTRODUCTION The following article will discuss the potential flood protection measures related to the winter season and draws up the basin-wide development opportunities for mitigation measures related to frozen conditions. Special attention is necessary on catchment level to maintain the awareness and preparedness against the hazards and risks of ice conveyance on rivers. DESCRIPTION OF THE CONCERNED ISSUES Ice is a special type of water scarcity and the due effects are less predictable. The climate change/alteration scenario analyses point out generally that the hydrologic extremities will be more frequent in future. In publicities commonly the global warming related floods and drought events are highlighted as potential scenarios. Although the other end of the temperature scale could result in comparable devastating consequences - in among much worse circumstances to fight against them. The „lower end” is the freezing zone and icy condition, where permanent ice cover, ice jams and ice floods can appear on the rivers, endangering the hazard areas with inundation and erosion by the overwhelming force of mass movement. Picture 1. Frozen dam, Rába River, Nick, Hungary in 2012 (Photo: ©ÉDUVIZIG) The ice transport and permanent ice cover on rivers itself blocks navigation, harms water regulation structures and occupies their operation. In certain cases the whole structure could be covered with ice like it happened just 5 years ago at the Nick dam on the Rába River (Picture 1). The natural dilatation of the ice cover and especially the impulse of the floating ice plates can remarkably effects the manmade structures and the natural habitats in the riverbed, along the banks and extensively in the floodplain. Under permanent low temperature the ice plates are growing constantly and freezing to each other. The driftwood and floating debris accelerate the cumulating process. If the ice conveyance is obstructed, ice jams can occur e.g. at shallow sections, bridges or low radius bends which can lead to elevated flood water levels peaking way above the normal conditions. Even if the discharge is low, the backwater effect of the ice barrier appears quite suddenly and immediate actions are needed to avoid inundation and/or structural failures. The worst case scenario seems to be having an encumbered section and an approaching flood wave from upstream. The increased and continuous monitoring of the conditions is very important but difficult. Airborne survey or satellite images provide the best perspectives but they cannot replace the manmade visual observations. Moreover the icy conditions could hinder the water level remote sensing and that need to be provided as well. In 2012 in the Upper-Danube floodplain the field investigation was the most adequate data collection activity (Picture 2). Picture 2. Ice monitoring at Dunakiliti, Hungary in 2012 (Photo: ©ÉDUVIZIG)
