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

This research is dealing with the Olše River in the Czech part of the Flysch Carpathians. It 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 active Olše R. channel was narrowed from 35 m in 1955 to 24 m in 2010 in the studied reach. In some locations, the original river bed has lowered as much as 2.3 m between the years 1960 and 2003. Morphology of the Olše 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 was affected especially by 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.).
 
The paper has been recently published in Zeitschrift für Geomorphologie.

Cross profiles, water level stage and w during the 100 R.I. discharge (the source of discharge data was provided by Povodí Odry Enterprise, R.I. discharges were derived from the Jablunkov-Olše gauging station) in 1960 (grey colour) and 2003 (black colour) in the studied river reach of the Olše R.: a – 56.163 r. km; b – 57.601 r. km; c – 58.604 r. km; d – 59.773 r. km; e – 63.204 r. km; f – 64.932 r. km; g – 66.064 r. km; h – 67.426; i – 69.850 r. km; vertical axes – elevation (in m a.s.l.); horizontal axes – distance (in m).

Comparison of incision and change of ω from 1960 to 2003 of analysed cross-sections in the Olše R. study reach during the 5, 20, 50 and 100 R.I. discharge.