ОЦІНКИ СТОКОФОРМУЮЧИХ ОПАДІВ ПРИ ФОРМУВАННІ ВИСОКИХ ПАВОДКІВ 1998 ТА 2001 РОКІВ НА РІЧКАХ БАСЕЙНУ ТИСИ (В МЕЖАХ УКРАЇНИ)

Abstract

The purpose of the study is to estimate the effective precipitation during the formation of high floods in 1998 and 2001 on the rivers of the Tisza basin within Ukraine. The flood of November 3-05, 1998 was rainy, the flood of March 3-05, 2001 – snow-rain. The maxima of the studied floods exceeded the average values of the peaks for many years on different rivers by 2.0-3.5 times. To determine the probabilities of exceeding the maximums of floods in 1998 and 2001, series lasting 60-70 years were formed for 18 rivers within the study basin. In 1998, on the rivers of the Tisza basin, the probabilities of annual exceeding the maximum costs are in the range of 1.4-10%. The flood in 2001 did not cover the entire territory of the Tisza basin. In the upper reaches of the Tisza, highs in some cases even exceeded the 1998 highs. In the Latorica and Uzh River basins, 2001 highs were not so rare, with probabilities exceeding 10-35% each year. To estimate the effective precipitation, the runoff coefficients during the 1998 and 2001 floods were defined as the ratio of the water runoff layer of the flood itself (without baseline) to the precipitation layer that fell during the floods in the river basin. For the November 1998 flood, only liquid rainfall was taken into account, and for the March 2001 flood, the amount of rainfall was supplemented by water reserves in the snow, which were within the catchments at the beginning of the flood. The percentage of effective precipitation from total rainfall in November 1998 varies from 35 to 82 %, and during the formation of thaw-rain flood in March 2001 – from 44 to 60 %. The runoff coefficients of the 1998 and 2001 floods depend on the hydrographic characteristics of the studied rivers and their basins. The greater the average weighted slope of the river and the average height of the catchment and the smaller its area, the greater the amount of effective precipitation. The correlations of runoff coefficients from the hydrographic characteristics of the studied rivers and their basins for rain floods in November 1998 are closer than for the snow-rain in March 2001.