Channel bed adjustment to over bankfull discharge magnitudes of the flysch gravel -bed stream - case study from the channelized reach of the Ole River (Czech Republic)

摘要

The rivers draining the Czech part of the Flysch Carpathians have deeply incised their beds over the last 60 years. This paper focuses on the Olse River in the Czech part of the Flysch Carpathians and summarises the results of the increased kinetic energy of flowing water of contemporary channel based on the analyse of hydraulic parameters of channel. The comparison of geodetic measurements from 1960 and 2003 was used together with the assessment of aerial photos from 1950s and present. The average width of the studied reach of the active Olse R. channel narrowed from 35 m in 1955 to 24 m in 2010. In some locations, the original river bed has lowered as much as 2.3 m between the years 1960 and 2003. Morphology of the Olse River channel has accelerated these erosion processes. The main reason for this is an adjustment of water flow dynamics. The unit stream power and hydraulic radius values have increased two to three times from 1960 to 2003 for 5, 20, 50 and 100-recurrence interval discharge. Incision of channel greater than 0.10-0.21m in the studied period may reflect change in cross-sectional geometry and lower than 0.10-0.21m may reflect other factors such as sediment disruption operating in the basin (e.g. with land-use changes, gravel mining etc.).