Gravelbars on the Drava river between Markovci and Zavrč and possibilities of more effective maintenance measures
- Authors: Mateja KLANEČEK, Igor ČUŠ, Tomaž HOJNIK
- Citation: Acta hydrotechnica, vol. 23, no. 38, pp. 57-76, 2005.
- Abstract: In the paper some characteristics and water-management problems in the section of the Drava River between Ptuj and Zavrč are described. Owing to the change of the water flow regime during low run-off, which is the case after the Formin hydro power plant was put into operation, as well as the reduction of bedload inflow and gravel mining during the maintenance in the section, morphologic changes occurred, bed narrowing being most pronounced because of overgrowth (up to 50% of width) and deepening (locally up to 2.5 m). In the riverbed of the Drava mostly the ecological minimum only is achieved (10 m3/s in the summer season and 5 m3/s in the winter season), a great part of the riverbed is dry, the low gravelbars are overgrowing and consolidating, and the cross section is narrowing. In the narrowing cross sections bed erosion and, to a lower extent, bank erosion are present. On the basis of a comparison of the cross sections the mass- balance of gravel in the treated section is negative, reaching a value of 360,000 m3 of gravel in 25 years, and is not solely a result of natural processes. During the last two maintenance works on the Drava at Borl 36% of complete estimated gravel deficit on the upstream section was removed from one location only. It is obvious that the existing maintenance practice does not bring the wanted results. On the basis of analysis of river processes in the section and some new findings on the connection of elevation of the gravelbars with the overgrowing process some starting points and suggestions for improvements are given.
- Keywords: Drava, gravelbars, gravel mining, morphologic changes, riverbed maintenance, water management
- Full text: a38mk.pdf