ON THE CHARACTERISTICS OF RIVERS IN YUGOSLAVIA

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  • ユーゴスラヴィアの河川
  • ユーゴスラヴィア ノ カセン

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Abstract

This article deals with the characteristics of rivers in Yugoslavia, based on the results of the field survey and the data observed by the Hidrometeorologieal Institutes, F. R. of Yugoslavia.<br> Roughly speaking, the river systems in Yugoslavia are classified into two : the Danube (including the Sava, the Drava, etc.), a long, gentle current, and the Neretva and the Vardar, relatively short, rapid ones. In the karst region, where the two river systems mentioned above are included, many discontinued rivers are found.<br> Seasonal changes of run-of amount of the rivers in Yugoslavia differ very much from those of Japan, which show maximums in the typhoon season in autumn or in the baiu (rainy) season in early summer. In such rivers as the Sava and the Drava: the coefficient of river regime is less than 30, and the level of water becomes higher in April through June due to melting of snow and from November to December by rain-fall. The water level is the lowest in July and August.<br> Because of the high seepage and flowing-out characteristics in the karst regions the run-off ratios of the rivers in Yugoslavia are relatively high, ranging approximately from 60 to 90%; as an extreme case, the Una shows a value of 112%. The velocity of flood-waves in the case of a great flood of the Sava, a tributary of the Danube, was 0.6_??_0.7 m/sec for a distance of 680 km from the river head to Beograd. A similar value, 0.7 m/sec, was obtained for the Drava. The water level changes more widely in the lower course than in the upper course of the Sava. However, the coefficient of river regime is rather small probably because the current velocity is relatively low. In contrast to this, the floodwaves of Japanese rivers generally travel more rapidly at a rate of more than 3 m/sec or even 10 m/sec on some occasions.<br> The water temperature of the Sava is nearly constant in February, being about 1°C both in the upper and lower courses. In August it is 12_??_13°C in the upper course, gradually becomes higher in the lower basin, rising up to 25°C in Beograd. It is found that there is a close relationship between the levels of underground and river waters along the course of the Sava river.

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