Ice dams and backwaters as hydrological risk phenomena – case study: the Bistrita River, upstream of the Izvorul Muntelui Lake (Romania)

During the last 20 years, Romanian territory witnessed a recurrence of high-risk hydrologic phenomena. From this point of view, the floods and droughts are particularly noteworthy. Most of the rivers registered historic record levels, while droughts appear even in the mountainous hydrographic networks. Despite the fact that the frequency of rainfall increased during the same time-span, droughts are increasingly present since most of the precipitations are torrential in nature. It is precisely these precipitations of a torrential character that generate flood phenomena. Because Romania harbours a significant number of dams, especially in the mountainous sector, an increase in the number of backwater flooding is noticed. The only phenomenon which manifests itself with some regularity is to be found upstream of the Izvorul Muntelui Lake, on the valley of the River. Various natural and, particularly, anthropic causes favour the formation of ice-dams and Bistrita the flooding of the settlements upstream of the tail of the Izvorul Muntelui Lake. In most cases, the flooding was caused by backwater phenomenon (1–3 m). The overspills are due to ice-dams or the congestion of ice-floes along the course of the Bistrita. The building of houses on the minor bed, and the presence of bridges with the substructure embedded in the mid-channel, have favoured the generation of some of the most spectacular ice-dam ever formed on the river courses of the Carpathians. During winter, a significant contribution to the much-increased discharge levels of the Bistrita River is made by föhn phenomenon present in the upper sector of the river (the Vatra Dornei Depression). Unfortunately, during the last few years, the phenomenon occurs almost yearly, and the damage inflicted is considerable. The Flood Recovery Innovation and Response III 167 www.witpress.com, ISSN 1743-3541 (on-line) WIT Transactions on Ecology and The Environment, Vol 159, © 201 WIT Press 2 doi:10.2495/FRIAR120141 floods caused by the backwater behind the ice-dams are unique in Romanian territory. The maximum thickness of the ice-dams can reach 6 m.