Impact limiting dredging and regulation works on the fluvial processes of the Upper Ob

Abstract

The analysis focuses on a  fragment of  a  braided river with numerous bars and islands, considerable bed load transport and predominance of  lateral erosion over bed erosion. Navigation conditions are analysed in relation to hydrological regime and ice phenomena. The prevailing hydromorphologic conditions of  the Upper Ob render navigation difficult. In order to improve navigation conditions, navigational beacons are established, dredging is carried out and channels are straightened. The works were most intensive in the 70s’ and the 80s’ of  the 20th century. At that time the depth of  the channel increased from 110 to 145 cm as a  result of  extractig 60,000 m3 of  bed load over 1 km long waterway reach, erecting lateral barrages and  constructing groins. Due to the reconstruction of  the channel, water transport increased to 5 M tonnes per year. In the 90s’ of  the 20th century the extraction of  bed load reduced to 20,000-30,000 m3 per 1 km of a channel, which, in turn, reduced the depth of the channel to less than 110 cm. In order to maintain navigation on shoals (oblique bars) dredging is carried out on selected waterways (arms of  the river) where hydromorphologic conditions are believed to most favourable. Furthermore, the article discusses the conditions for selecting optimal waterways.