With
co-operation with our colleague Assoc. Prof. Dr. Zdeněk Máčka from Masaryk
University, we published article about effect of hydraulics of regulated and
re-naturalized channels on grain-size parameters in Science of the Total Environment multidisciplinary journal.
The grain-size characteristics obtained on 68 gravel bars were confronted with modelled flow hydraulics and information obtained by fluvial-geomorphic mapping along 14.0-km river reach of the Bečva River (Outer Western Carpathian Mts., Czech Republic). The studied channel reach is presently characterized by several distinctive sections: for a long time (ca. 100 years) regulated single channel sections with artificial bank stabilizations incised several meters in the floodplain and by contrast, multi-thread channel patterns of two sections, which have witnessed retrograde development after large floods in 1997 and 2010.
The grain-size characteristics obtained on 68 gravel bars were confronted with modelled flow hydraulics and information obtained by fluvial-geomorphic mapping along 14.0-km river reach of the Bečva River (Outer Western Carpathian Mts., Czech Republic). The studied channel reach is presently characterized by several distinctive sections: for a long time (ca. 100 years) regulated single channel sections with artificial bank stabilizations incised several meters in the floodplain and by contrast, multi-thread channel patterns of two sections, which have witnessed retrograde development after large floods in 1997 and 2010.
The mapping
of sediment (dis)connectivity brought important findings about the character of
sediment flux in the studied reach, which were confronted with simulated
cross-sectional hydraulics. We demonstrated that in the case of a high occurrence
of lateral sediment inputs (tributaries, bank failures) and longitudinal
sediment flux disconnectivities (weirs or boulder ramps), the assessment of the
longitudinal distance, bar grain size and simulated hydraulics submerging bars
did not produce any clear relationships. Although the sections with re-naturalized
multi-thread patterns showed distinctive hydraulic variables (i.e., larger
wetted width or lower unit stream power), we did not observe direct relationships
with their bar sediment sizes. This implies that for complex fluvial systems of
multi-thread rivers as the transition reaches connecting mountainous and
lowland areas, even those in unconfined valley settings out of the primary
sediment sources, additional factors (i.e., effect of bank failures and
especially tributaries as sediment inputs, weirs or boulder ramps as sediment
flux disconnectivities) beyond local flow hydraulics and distance from the main
sediment sources contribute to better explanation of the downstream evolution of
grain-size patterns.
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| View of the Bečva River channelized (managed) single channel sections (A, C, E) and retrogradually developed (re-naturalized) multi-thread channel sections (B, D). |
