Future Aspects of Flood Protection Management in the German Oder Region Concluded from the Flooding in Summer 1997

 

BAERBEL KOPPE

 

Dipl.-Ing.

University of Rostock, Institute for Hydraulic and Coastal Engineering, Philipp-Mueller-Strasse, 23966 Wismar, Germany

Tel.: ++49 - (0)3841 - 753 448, Fax: ++49 - (0)3841 - 753 448
E-mail: bkoppe@bau.uni-rostock.de

 

 

ABSTRACT

In summer 1997 extremely heavy rainfalls in large parts of Eastern Europe resulted in disastrous floods on the river Oder and its upper tributaries in the Czech Republic, in Poland and in Germany. The damage in Poland and the Czech Republic was enor­mous, while in Germany comparatively little damage occurred. This can be put down to the small German area that is endangered by high water levels of the Oder, the relief by breaches in Polish dikes, the available time for preparation after first reports about the catastrophe in the headwaters and the huge personnel, technical and financial efforts to protect the Oder dikes in the Federal State of Brandenburg.

Even if the quelling of the flood disaster at the river Oder speaks for the disaster man­agement in Brandenburg, improvements in flood protection management are necessary. This concerns preventive technical protection measures, as well as pre­ven­tive measures to minimise the damage potential; observation and forecasting of water levels, early warning systems, disaster control measures and transboundary co-ordination of flood protection measures.

Future aspects of the flood protection management in the German Oder region con­cluded from the flooding in summer 1997 will be highlighted in the paper. Special attention is directed to the integration of the population in flood protection measures.

 

Keywords: Flood Disaster - Flood Protection Management - River Oder - Risk Handling

 

INTRODUCTION

Extremely heavy rainfalls in large parts of Eastern Europe resulted in disastrous floods on the river Oder in the Czech Republic, in Poland and in Germany. In the Czech Republic, a third of the territory was hit by the flood and 60 people were killed. In the south of Poland, nearly 7000 km² were flooded and 54 people died. The incurred damages in both countries were estimated to be between ten and fifteen thousand million German Marks (approx. six to nine thousand million US $).

In Germany, although the flood on the river Oder did not take any lives, an area of 60 km² was flooded and the damages amounted to 650 million German Marks (approx. 380 million US $). The comparatively small damages can be put down to the small German area that is endangered by high water levels of the Oder, the relief by breaches in Polish dikes, the available time for preparation after first reports about the catastrophe in the headwaters and the enormous personnel, technical and financial efforts to protect the Oder dikes.

 

METEOROLOGICAL AND HYDROLOGICAL SITUATION AT THE ODER IN SUMMER 1997

Two successive periods of heavy rainfalls in large parts of the Oder catchment area led to the flood during July and August 1997. Continuous rainfalls occurred in the upper Oder region with an average of 150 mm between 4th and 7th July. Maximum values of up to 400 mm appeared at the station Lysa Hora in the Czech Republic. Fur­thermore, the flood situation was worsened by the second period of precipitation between 18th and 21st July, with average rainfalls of 50 mm. The centre of the rain­falls was once more the Czech Republic and the south of Poland with, for example, 164 mm at Lysa Hora. But heavy rainfalls were also noted in the German Oder region.

Such weather situations and the resulting floods are not unusual for the Oder region. But the floods in summer 1997 were exceptional for two reasons: (1) The coincidental repetition of the extreme rainfalls after only two weeks and (2) the complete covering of the whole Oder catchment area with rain more than twice that of the average pre­cipita­tion for the month of July [1].

The flood in summer 1997 therefore has to be evaluated as an extremely rare event. According to the peak water level, it can be classed as HQ₁₅₀ in the affected German Oder region in the Federal State of Brandenburg [2]. In addition, the flood in summer 1997 was exceptional because of the time, (more than two weeks), which the high water levels in the German Oder region lasted.

 

SHORT TERM PROTECTION WORKS IN THE GERMAN ODER REGION IN SUMMER 1997

The main problem for maintaining the Oder dikes in Germany, which are approxi­mately 167 km long, was the long duration of the flood. Not one of the dikes in Ger­many was inundated, despite the fact that in some places of the "Oderbruch" north of Frank­furt/Oder, the water almost reached the dike-crest.

Most of the so-called homogenous dikes are built of sandy and clayey soil. A large part of the dikes were built 250 years ago when the low-lying area Oderbruch was drained. Since then they have been heightened a few times. The structure of the dikes is not known in detail, because of their old age and their rebuilding. Normally, no safety measures like drainage or filters on the inner side of the dikes have been im­plemented. There­fore the dikes can only withstand high water levels temporarily. They lose their stability by means of erosion / suffusion and seeping water.

The Ziltendorfer Niederung, a low-lying area south of Frankfurt, was flooded after two breaches in the Oder dike. The inundated area had a size of 60 km², 2,000 people had to be evacuated and 300 houses were damaged.

In the Oderbruch, a low-lying area extending approximately 1,000 km², an inunda­tion was prevented by an enormous personnel, technical and financial effort. In this area, up to 20,000 inhabitants were endangered by the flood and 8,000 people tem­porarily left their homes.

In particular, three dike-sections sheltering the Oderbruch were badly affected. The operation at the dikes ran for nearly two weeks day and night. Because of the weak­ness of the dikes, only light vehicles could enter the dike-roads. At some sections of the dike, the supply with sandbags was only possible by helicopter. About 200 weak points had to be provided with sandbags in the Oderbruch alone. Nearly the whole dike-line of the lower Oderbruch was protected with ring dikes.

The operation was carried out with the assistance of more than 15,000 members of the German Armed Forces, 4,300 members of the Federal Border Police, 2,100 fire­men and -women, 7,000 members of technical relief organisations, 1,500 policemen and -women, 1,000 members of aid organisations, 430 employees of the regional environmental authori­ties and numerous volunteers. More than 60 helicopters, 1,400 trucks, 200 bulldozers and 80 boats were in use. To secure the dikes, 8.5 million sandbags, approximately 10,000 m² of geomembranes, 66,000 m² of geotextiles and 2,000 fascicles were needed [3]. It was the biggest civil action in the history of the German Armed Forces.

 

FUTURE ASPECTS OF FLOOD PROTECTION MANAGEMENT CONCLUDED FROM THE ODER FLOODING IN SUMMER 1997

Technical flood protection measures can never provide overall, but only restricted safety. If the water level or the load exceeds the design criteria, the construction will fail. The flood protection management consists not only of preventive technical pro­tec­tion measures, but also of the analysis and the minimisation of the damage potential, the observation and forecasting of water levels, early warning systems and disaster control measures. The precondition for effective flood protection manage­ment is an awareness on the part of the authorities and the popula­tion of flood endangerment. The integration of the threat of flooding in political and social life in low-lying areas would improve the state of readiness in the event of an emergency.

Not just the right, but the most probable moment for improvements in flood protec­tion management is the time after a flood disaster. The memory of the endan­germent is fresh and the quality of the protection measures can be assessed. The following text looks at future aspects of preventive technical protection measures, the reactivation of flood plains, transboundary co-operation for flood protection management and concepts of disaster control in the German Oder region.

 

PREVENTIVE TECHNICAL FLOOD PROTECTION MEASURES

The reconstruction of breaches and badly-damaged dike sections in the Ziltendorfer Niederung and in the Oderbruch were finished in November 1997. The protection against wintry floods was therefore installed in time. In all, 9 km of dike line were either completely destroyed or seriously weakened by either hydraulic base and slope failure or by soil erosion. The costs of reconstruction or repair of these stretches were put at 36.5 million German Marks (approx. 21.5 million US $).

The strengthening of large parts of the Oder dikes in the Federal State of Branden­burg, especially of the dikes in the Oderbruch, shall be concluded by the year 2005. The costs are estimated at 230 million German Marks (approx. 135 million US $). In the period 2006 to 2020, up to 270 million German Marks (approx. 160 million US $) will once more be spent on preventive technical flood protection in Brandenburg [4].

The dikes on the Oder were repaired according to the principle of the "3-zone-dike". The whole of the dike body was not renewed, providing the damage and the founda­tion al­lowed it. The central part remained as a supporting body. The waterside foot of the dike was removed, so as to bind the sealant which needed to be applied to the highly impermeable bottom. This minimises the seepage in the dike and with it the danger of slope failure and inner erosion. The dam is drained by a landward porous load filter, which also provides protection against hydraulic base failure. The previous embank­ment gradients, which ranged from 1:1.5 to 1:2, were reduced to 1:3 and the dike crest was made wider, so as to improve the stability of the construction. The larger width of the dike crest will also enable an increase in the height of the dike at a later date. Previous arrangements with the Polish government are necessary to height­en the German Oder dikes.

 

REACTIVATION OF FLOOD PLAINS AND TRANSBOUNDARY CO-ORDINATION FOR FLOOD PROTECTION MANAGEMENT

In Germany, the possibilities for the reactivation of flood plains are limited. A large number of existing flood plains were drained and populated during the last centuries. Nowadays only 280 km² of flood plains, including the already available polders in the "Nationalpark Unteres Odertal" (Downstream Oder Valley National Park), could be reactivated from the original amount of 3,000 km². In all, about 650 million m³ of water could be stored in the German flood plains at the Oder in future. In comparison with the planned retention areas, the flooded Ziltendorfer Niederung took 150 million m³ and lowered the water level in Frankfurt/Oder for two days by up to 0.75 m [4].

The flooded lowlands of the Ziltendorfer Niederung were repopulated again. During the flooding some politicians were already promising the inhabitants of the low-lying area that they would be able to go back. This rendered any further discussion of a resettlement policy impossible. In any case, resettlement of this kind would have been a very difficult task. Now, there are some restrictions for building in low-lying areas, like the ban on installing any kind of oil heating. A real flood-proof architecture and use of buildings has not been demanded up to now.

For better flood protection management at the Oder, transboundary concepts of retention and improvements in run-off conditions and flood warning systems on a long-term basis are essential. The concepts must include the whole catchment area of the Oder covering 110,000 km². The largest part of it is in Poland, only 6 % is in the Czech Republic and 5 % in Germany.

An efficient reduction of the flood crest cannot be achieved without substantial reten­tion measures contributed to by the water management in the Polish catchment area. First steps in transboundary co-operation were made shortly after the flood-disaster in September 1997 [2], but the discussions have been very difficult up to now [4]. A main problem is the conflicting opinion of Polish and German authorities about river control works at the Oder. The Polish government want to facilitate the navigation of container ships of the Europe class on the Oder, whereas the German authorities for flood protection management fear an increasing velocity of the flood crest and there­fore a shortening of the early warning time and a heightening of the peak water levels from these measures. Further discussions on this theme will be necessary.

Other aims of transboundary co-operation for flood protection management are im­provements in the water level measurement and in the forecasting system to extend the early warning time and to get better quality information. During the flooding in 1997, the forecasting of water levels was very difficult. Most of the water level gauges in the Czech Republic and in Poland were swept away by the currents. In addi­tion, different rainfall-runoff-models are in use in the three countries, so that the exchange and comparison of results is still problematic.

 

CONCEPTS OF DISASTER CONTROL

In the State of Brandenburg, the district administrators are responsible for disaster control measures. If several districts are affected by a catastrophe like in summer 1997, the Minister of the Interior will be the superior disaster control authority for co-ordinating the measures in the different districts. The protection of the Oderbruch lowlands which were hardly affected was a great success and speaks for the disaster management in Brandenburg. The co-ordination of different organisations with differ­ent command-structures was absolutely essential for the successful outcome.

The events in summer 1997 proved that only the teamwork of highly equipped organi­sations like the Federal Army, the Federal Border Guard, the Technical Relief Organisation and the telecommunication service together with meteorological and hydrological experts and with local fire brigades can handle a catastrophe of this dimension. In addition, the large number of highly motivated volunteers was a great help.

However, there were some problems. It was partly difficult to convince the people of the gravity of the flooding, despite the fact that in the Czech Republic and in Poland there had already been fatal casualties. In the Ziltendorfer Niederung the danger was not initially taken seriously by the population and warnings to leave the area were ignored. The evacuation was therefore eventually a rush and only absolute essentials could be saved.

The precondition for effective flood protection management is an awareness on the part of the population of flood endangerment. Maps of endangered areas and leaflets with detailed information about flood protection management, possible failures of technical protection measures, precautions to minimise flood damages and the appropriate behaviour in the event of a flood warning should therefore be published. Additional ways to inform people about the endangerment by flooding are illustrated books and films about protection measures and flood disasters. For this purpose, the Institute for Hydraulic and Coastal Engineering at the University of Rostock produced a video about the flooding on the river Oder in 1997 in Germany [5].

For a functional early warning system, not only must every endangered person receive the information in time, but everyone must also trust in it. The more different authorities issue the warning in different ways and maybe different words but with exactly the same content, the more likely the population is to accept it. Local dignitar­ies like may­ors or fire chiefs could be integrated into the transfer of warnings. Often they are in the same situation as those addressed and they can convince the peo­ple of the necessity of seemingly unpleasant measures, more easily than someone in authority who is not personally known.

The strengthening of local flood protection organisations might be a promising way to obtain a cost-effective and sustainable improvement of flood disaster management. The scope of duties of these organisations could be the installation and maintenance of local alarm facilities, the maintenance of technical equipment like emergency gen­era­tors and pumps, the elaboration of an emergency measurement catalogue, and the realisation of regular emergency exercises. The supervision of these measures could be organised by a state organisation; in the State of Brandenburg this could be the Environmental Agency of the State.

The main advantages of local flood protection organisations are:

 

l        emergency plans adjusted to local needs

l        large number of highly motivated and skilled helpers with good knowledge of the area

l        awareness of the endangerment by flooding to the population

l        widespread knowledge of the possibilities to protect life and goods in the event of flooding

l        improvement of early warning communication

l        small financial expenses for a significant improvement in flood protection man­agement

 

CONCLUSIONS

Improvements in technical flood protection measures can raise the degree of safety, but nevertheless they provide only restricted protection and they are very cost-inten­sive. To defuse the endangerment by flooding in the Oder region, the Czech, Polish and German authorities must co-operate. Above all, the reactivation of former flood plains in the Polish catchment area could lower the flood crest signifi­cantly. In addi­tion, improvements in the measurement and forecasting of water levels must be made together.

Effective flood protection management in cost and safety levels should also inte­grate local organisations. They will contribute a large number of highly motivated and skilled helpers with a good knowledge of the area and will ensure the awareness in the population of endangerment by flooding. In addition, early warning communi­cation will be improved.

 

REFERENCES

[1]	GEB, M.; SIELAND-CORADAZZI, H.		1997		"Anmerkungen zum Oder-Hochwasser-Regen im Juli 1997: Ein Sommerereignis wie es im Buche steht?" Beilage zum Nordhemisphaerischen Klimabericht Juli 1997. Meteorologisches Institut FU Berlin.
[2]	DVWK		1997		"Expertengespraech : Reaktivierung der Uberflutungs-aue: 12-Punkte Katalog". Wasser & Boden, vol. 49, 12 / 1997
[3]	DEUTSCHER BUNDESTAG		1997		"Abschlussbericht zur Hochwasserkatastrophe an der Oder". Deutscher Bundestag.
[4]	MUNR		1998		"Pressemitteilung 22.07.1998". Ministerium fuer Um­welt, Naturschutz und Raumordnung Land Branden­burg.
[5]	KOPPE, B.; JUERGENS,M.W.		1998		"The flooding on the river Oder in the summer of 1997 between Ratzdorf and Hohensaaten", documentary videotape in German and English. Institut fuer Wasserbau, Universitaet Rostock.