GEOHAZARDS IN THE RJECINA VALLEY IN THE PAST AND PRESENT

The Rjecina (length 18.7 km) is the most important watercourse in the Croatian Littoral area. Its source, located at the foot of the Gorski Kotar mountains, is a karst spring which drains groundwater from a spacious karst hinterland and has been used in water supply for a hundred years. In the central section of the watercourse, there are a dam and a reservoir, so the Rjecina water is utilized for power generation as well. Its river mouth is located in the very center of the town Rijeka, and has been used for ship docking for centuries. The Rjecina watercourse has markedly torrential characteristics, with large discharge fluctuations, which has periodically caused flooding and significant damages along the river bed, particularly in the river mouth area, where a settlement has been located since antiquity. More reliable flood data originates from the 18 century onwards, and is mostly kept at the State Archives in Rijeka. The authors of the paper presented all significant catastrophic events related to the Rjecina in a systematic, chronological manner. The same approach was applied to the presentation of the civil works carried out for purposes of flood protection, from the relocation of a river bed segment at the river mouth to the river bed regulation in the central section of the watercourse. The performed works were so successful that there has been no more flooding in Rijeka's center after their completion in 1908. However, recent investigations show that the danger has not been fully averted. Namely, the valley part from the reservoir Valici to the canyon start is characterized by the most significant hazard from instability occurrence in the greater Rijeka area, where a series of unfavourable circumstances could cause backfilling of the Rjecina river bed, a break in the natural dam and a water wave propagation all the way down to the river mouth.