Freezing weather conditions in the winter months have been a fact of life on the Danube since time immemorial, but the months of January and February 2017 saw many countries in the Danube Basin and its tributaries facing an especially bleak situation. Ice drifts appeared and aggregated into ice jams along the entire length of the Danube. Fortunately, contingency measures ensured that no casualties were reported during last year’s event and damage and disruption were kept to a minimum. The event did however highlight the need for the basin-wide development of technical and human resources for sustainable and coordinated ice-management.
Critical situations caused by ice events can result in ice jams and even ice floods. Ice jams occur on rivers when floating ice accumulates at either a natural or man-made feature which impedes its progress downstream. Sometimes called ice dams, these jams can significantly reduce the river’s flow and cause flooding due to the backwater effect. Ice management has therefore become an integral part of flood protection on the Danube. For this reason measures to tackle ice related problems were comprehensively developed and integrated into ICPDR Sub-Basin Level Flood Action Plans in 2009.
Basic features of river ice
The development of ice on rivers is a complex process influenced by air and water temperature. However, other disturbing factors also have an effect. These can include the concentration of chemical substances, groundwater inflow, velocity of the stream, geomorphological shape of the riverbed etc. Due to the limited range of tools available for monitoring ice-related data on the Danube and its tributaries, a streamlined classification system is used. This classification is based on the presence and status of ice movement on the river surface and consist of just two categories: ice drift and ice cover. The classification of the different stages of ice formation is currently not uniform in the Danube River Basin, with different national coding systems in use throughout the region.
Ice drift: this expression is used to describe ice floating on the surface of a river in the form of ice sheets. An ice drift can be calm, moving slowly downstream until it gradually stops at a downstream obstacle, but it can also be turbulent, colliding and tumbling with other ice sheets (floes).
Ice cover: this term is used to describe any fixed ice formation on the river surface. It may be compacted ice of a uniform thickness which is normally found in relatively calm waters, stopped ice drift composed of uniformly distributed floes and frazil, or piled up ice and ice barriers of considerable thickness, depending on the hydraulic conditions at the time the ice cover was formed.
Potential effects of the ice phenomena
Ice on rivers is a direct consequence of weather conditions, primarily sub-zero air temperatures, and the problems of dealing with ice events are confounded by the fact that cold weather spells are unpredictable, occurring at different times from year to year and with different durations and degrees of severity.
In late winter, as air temperatures begin to rise above freezing point, river ice begins to melt. It can disintegrate with little jamming or significant rise in water levels, but in many cases the ice may begin to move and form ice jams. Spring breakup jams are usually very destructive because of the large quantities of ice present. In addition to causing sudden flooding, the ice itself may collide with structures and cause damage.
Ice drift and ice cover can also lead to navigational closures and damage to water regulation structures or bridges. The movement of floating ice can have an adverse impact on man-made structures, natural habitats on the riverbed, riverbanks and floodplains. Driftwood and floating debris accelerate the cumulative process of ice jams. If the movement of ice is obstructed, ice jams can occur, leading to elevated flood water levels.
Special equipment is needed to deal with river ice, especially with human resources and performance capacity often limited during the winter months. Some examples of measures to avoid or mitigate ice jams on rivers are listed below:
Thermal shield: moveable parts on structures, such as sluice gates, are kept warm by means of an internal heating element which keeps its temperature above freezing point. Its effect is limited to securing the operability of the structure it protects.
Oscillation of the water level: it is possible to constantly lift-and-drop the water level in problematic areas in order to shred ice plates and avoid the formation of full surface ice coverage. The effect of this solution is however limited and difficult to control. Intensified ice plate movement can also endanger the operation and stability of the structure in question.
Intervention from the riverbank with machinery: excavators or long cranes can be used to fight ice formation on smaller streams, working from banks, bridge pavements or solid structures. This method involves an element of risk and the riverbanks are usually difficult to access, particularly in Protected Areas.
Blasting with explosives: in former times this was a standard technique for fragmenting large ice plates. The placement of the explosive is carried out using divers or by precision throwing or dropping. This is very dangerous and special permission is required. Seismic effect and potential damage to the riverbed or surrounding structures also need to be taken into account.
Gunfire, bombardment: this is a method of last resort carried out by the army when the waterway is otherwise inaccessible. It carries the same risks as blasting and its effectiveness can be limited; if the section downstream of the jam is not ice free, the ice destroyed will remain in place.
Icebreaker ships: On larger rivers one of the most important tasks is to limit the size and movement of ice plates and at the same time ensure that the deep channel is kept open for navigation. Special icebreaker ships with reinforced hulls and other appropriate equipment are used for this purpose. Although icebreaker deployment is completely random and dependent on weather conditions, with their use often not being required for several winters at a time, costs for regular maintenance of these ships and their skilled crews still need to be covered on an annual basis.
The ICPDR’s first Flood Risk Management Plan in the Danube River Basin District (DFRMP) was endorsed by the Danube Ministers in 2016. The plan includes the project proposal ‘DANube river basin ICE conveyance investigation and icy flood management’ (DANICE). The principle objective of this plan is to create the ‘Danube Basin Ice Management Plan', which will provide long-term ice-management measures for the Danube River Basin.
The project will enable the implementation of real-time monitoring and forecasting for ice formation and its conveyance in the basin. The project will also deliver a national and basin-wide operative resource management and mitigation plan for ice floods and other situations. Harmonization of ice management planning methods and recommendations for standardization throughout the basin are also an integral part of the proposal.
DANICE is the logical follow-up to the so-called ‘DEVICE Danube’ preparatory collaborative project between Hungary, Serbia and Slovakia, which was submitted to the Danube Transnational Programme (DTP) Seed Money Facility (SMF) 1st call in December 2017. The primary objective of “DEVICE Danube” is to lay the groundwork and establish partnerships for DANICE.
The ‘Danube River Basin Enhanced Flood Forecasting Cooperation’ (DAREFFORT) project is another initiative and was submitted to the 2nd call of the Danube Transnational Programme in June 2017. It was selected for subsidy by the Monitoring Committee in May 2018 and kicked off on 1 June 2018. The project will deliver real-time monitoring and forecasting of national water levels and share ice-related information throughout the basin. The key objective of this project will be to further develop existing systems in a comprehensive and compatible way. The project’s partners will collaborate to formulate policy recommendations to be submitted to the ICPDR in support of the development of the Danube Hydrological Information System (DanubeHIS).
The implementation of these two projects will result in the establishment of a flexible and sustainable system for data exchange. Their implementation will provide enhanced ice management in the Danube River Basin and ensure that river authorities are able to cope with all types of extreme weather events, as and when they occur. Both projects have been made possible due to the active support of the EU Strategy for the Danube Region Priority Area 5 (EUSDR PA5) coordination team.
The ICPDR has also published an ‘Ice Report’, compiled by its Flood Protection Expert Group (FP EG) and the Public Participation Expert Group (PP EG). The report contains a comprehensive overview of ice features, past ice events on the Danube, lessons learnt and recommendations for the future. The objective of this document is to disseminate up to date information and stimulate an exchange of ideas and experiences to ensure that the river is able to cope with all types of extreme weather events as and when they occur in these times of global climate change.