Sediment Transport in Headwater Streams of the Carpathian Flysch Belt: Its Nature and Recent Effects of Human Interventions

The paper summarizes results of both empirical and modelling research of bedload transport in headwater streams of the Czech part of the Western Carpathians. Flysch lithology (i.e. alternation of less resistant claystones and sandstones) affects bedload transport parameters in view of relatively fine-sized sediment supply resulting in low flow resistance of channels. Flood competence method (Q20 flood) and marked particle displacement method (up to Q1–2 flow) was applied to determine critical conditions for the incipient motion of grains in channel bed. The beginning of bedload transport in flysch headwaters under lower values of critical conditions when compared to other regions was confirmed by application of the criteria of unit stream power and unit discharge. The simulated values of bedload transport intensity (1D transport model TOMSED) during a high-magnitude flood in both supply-limited and transport-limited headwaters are significantly lower than it was observed in torrents of the Alpine environment. In relation to unsuitable contemporary watershed management affecting the sediment transport (large check-dams, removing of large wood from local channels), trends of accelerated incision are observed in most headwater streams as well as in lower-gradient piedmountain gravel-bed rivers of the Flysch Belt of the Western Carpathians. Approaches of contemporary local watershed management are presented and some recommendations for the maintenance of channel stability predisposed by soft lithology (e.g. application of artificial step-pool sequences, management of woody debris in channels) are proposed.