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

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Hidrológiai Közlöny (Hungarian Journal of Hydrology) 2017. 97. évf. 3. sz.

The hard winter conditions are not easy to handle due to the freezing circumstances and low temperature, so special equipment is needed. Also human resources are limited to be utilized and the performance capacity is far less than in the summer. Because of the modest focus on the topic, the knowledge about handling such ice cases is disappearing even on professional level. May the skills are reserved somewhere, the number and availability of the experienced crew is disappearing, causing loss of the personal impressions that could be utilized in a havaria situation.

An effective - but in the same time the least natural - way of avoiding such problems of ice is to artificially correct the centreline of the river and the floodplain. It means to excavate and rebuild the banks or deploy hard coverage (bank protection), clean and reshape the riverbed. Due to the nowadays horizontal engineering perspective which considers the Water Framework Directive and other eco- friendly regulations, the utilization of such measures are applied only if any alternative possibilities have no effect and the activity is a must. Anyhow, properly considering the ice hazard is a very important aspect at the design phase of any water management structure.

In order to maintain the flood protection level some of the possible measures to avoid ice jam on rivers are listed below:- Thermal shield: Utilized on structures to temper moveable parts like a sluice gate. The protected component has internal heating assemblies which keeps its’ temperature above the freezing point. It has only local effect and the aim is to secure the function/operability of the structure. The electric consumption and the cost of the solution is matter of the size of the structure. In special cases the warming could be carried out by manpower as well.- Oscillation of the water level: In case of having a water level influencing structure in the problematic area, it is possible to constantly lift-and-drop the water level in order to avoid the forming of the full surface ice coverage or shredding the plates. This solution eases the upstream conditions as far as the backwater effect still plays a role but the impact is limited and not controlled. The intensified ice plate conveyance could endanger the structure operation and the stability as well.- Intervention from the banks with machinery: Only on smaller streams from banks, bridge pavements or solid structures it is possible to execute measures with excavators or long cranes. As the ice core develops the effectiveness of such activities decreases. It is quite dangerous in general and the river banks usually hard to be reached, particularly those sections which are subject of protection measures.- Blasting with explosives: Formerly it was an applied routine to use explosives in order to fragment the large ice plates. The location of the detonation determines the effect of the method so the placement of the explosive shall be carried out by divers

or by (precise) throwing, dropping. It is very dangerous not just because of the shrapnels thrown out by an explosion but also the handling of the explosive materials. Special permissions and qualifications have to be obtained. An extraordinary placement activity is demonstrated on Picture J.The utilization has to take in account the seismic effect and the potential demolish of the riverbed or structures around. Despite the complicated circumstances are, it is a feasible solution at certain segments.- Gunfire, bombardment: Special treatment of river sections where there is no other tools could be utilized. Needs military intervention.- Ice breaker ships: On larger rivers one of the most important tasks is to keep on the conveyance of the ice plates and in the same time provide a sufficient route for navigation. Both of these goals could be served with special icebreaker ships with reinforced hulls and other appropriate equipment. There are different types of boats and technics to slice the ice plates or the massive surface ice cover. The effectiveness of the measure based on the thickness and the location of the boats, so pre-arrangements are necessary. From downstream to upstream the boats can operate the best. The fleet need to be maintained to avoid turning obsolete nevertheless the usage is quite random in time depending on the weather conditions.

Picture 3. Placing explosives at former Kossuth Bridge, Budapest, 1956 (Source: Kor-képek 1956 - MTI 2006)

INTERNATIONAL ASPECTS OF ICE MANAGEMENT

The international aspects of the ice phenomenon are similar to other water related hazards and the effects could go beyond national borders. The observation is a key issue to frequently exchange base data for forecasting. The backwater effect influences the water levels in the upstream country and an intensive ice flow could create devastating situation in a downstream country. The development of the ice-formations is key information and the ice input from the tributaries could play important role for adequate preparatory actions. Preforming an action in the national territory might be less effective than an internationally coordinated operation.

In general we can say that Hungary does have an ice protection regulation with all the neighbouring countries regarding the major border intersecting water courses. The