Vízügyi Közlemények, Az 1998. évi árvíz, 2003 (különszám)

I. kötet: Az 1998. évi árvíz - Váradi József: Bevezető

INTRODUCTION During a period as brief as 28 months only, between the 6

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h of November, 1998, and the 6

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h of March, 2001, four abnormal flood waves have passed down the River Tisza. At the same time the undrained runoff, which has swamped large areas, the floods, which have wrought havoc on minor streams, and cyanide pollution with the dire consequences thereof on the rivers Szamos and Tisza have taxed the capacity of the emergency control organisation of the Hungarian water agency. There are a number of hydrologic criteria, in tenns of which a particular flood could be classified "abnormal", like the depth, intensity or area pattern of the triggering rainfall, its time of occurrence, the resulting rate of runoff, the water level, the stage-discharge relationship, the shares of the discharge conveyed in the main channel and the flood bed, the rate of rise, simultaneous flood waves on the tributaries, the rate of flood wave travel, the flood volume, the water load imposed on the defences, to name some of these. The flood waves during the 1998-2001 period could well be regarded abnormal in terms of several of the aforementioned parameters. For instance, on the Tivadar gauge on the River Tisza, the former HHW mark was surpassed in 1998 and 2001 alike, with a total rise of 149 cm. On the Middle-Tisza former records were also surpassed on two occasions by a total of 132 cm on the Szolnok gauge (65 cm in 1999 and further 67 cm in the year 2000.) In November, 1998 — after a calm period of almost three decades — abnormal flood alert had to be announced along the River Tisza for 12 days, over 450 km length. The length of alerted defences grew to 1.605 km. The total length of defences, for which some degree of alert was announced, was 2.223 km during the flood. The daily workforce employed on emergency operations culminated at 9.800. In 1999 the first alert was announced on the 23

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d of February for the River Fekete Körös. To illustrate the rate of rise it should be noted that within 24 hours the water level has surpassed the 3

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d degree alter stage and by the 4

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h of March over 1.000 km of defences had to be alerted. On the 11

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h of March alert was announced for 2.700 km, i.e., for 96 % of all defences in the Tisza Valley. Extremely high flood levels have required great efforts to prevent the flood from overtopping the defences. Along the Tisza defences the water level was for 22 days above the highest mark on record thus far. Between the 13

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h of March and the 2

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d of April, 1999, abnormal flood alert was maintained for a total of 20 days along several defence sections. The largest daily workforce employed on emergency operations was 8.254, including 3.418 on the payroll of the water agency. Abnormal alert was announced for 16 of the 91 drainage districts in Hungary after the 6

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h of March, 1999. This was the first occasion ever that a state of emergency and abnormal alert had to be announced for coping with undrained runoff. The state of emergency was maintained for 1

7 days. The total area inundated was second in size only to that registered in 1940-41. Undrained runoff has flooded a total of 420 thousand hectares, 220 thousand in the districts for which emergency was announced. The workforce employed on drainage operations was larger than 2.300. Flooding has jeopardised 435 communities in which close to 8.800 buildings suffered damage. Over 1 million people were at risk.