Saturday, 12 April 2014

The contemporary research of headwater streams in the midmountain Beskydian landscape

Recently, two new papers assessing the Beskydian headwater steep streams were published in impacted Elsevier journals. Morphological patterns of headwater streams based in flysch bedrock: Examples from the Outer Western Carpathians (Catena) deals with channel-reach morphology (after Montgomery- Buffington system) of local streams: the downstream trends in bankfull parameters and influence of woody debris are discussed and compared to other studies coming out from various landscapes. The role of local forest management is accented, when woody debris are systematically removed from local channels. The second article called Channel-reach morphology controls of headwater streams based in flysch geologic structures: An example from the Outer Western Carpathians, Czech Republic (Geomorphology) deals with sediment supply and transport processes related to resulted channel-reach morphologies estimated by 1D transport model TOMSED (, when also several at-reach parameters are statistically evaluated. The ratio between sediment supply and transport capacity clearly distinguishes some channel-reach morphologies: bedrock-cascades and step-pools are charasteristic for the limited sediment-supply conditions, whereas cascades and step-rapids occur under high sediment supply related to transport capacity. 

The bedrock-cascade channel-reach; the Malá Ráztoka stream

Morphological patterns of headwater streams based in flysch bedrock: Examples from the Outer Western Carpathians
A channel-reach morphology of mountain headwater streams results from the balance between fluvial and hillslope processes. A large dataset (n = 102) of channel-reaches coming out from flysch mid-mountains was evaluated and compared with streams occurring in other environments. Two new channel-reach morphologies were distinguished with respect to their differences in the ratio of sediment supply to transport capacity: bedrock-cascades and step-rapids. The chaining of channel-reach morphologies by gradient criteria and the parameters of channel gradient and bankfull width related to the basin area show similar trends, when compared to other recent studies. By contrast, bankfull depth indicates its independence on increasing basin area. Significant downstream coarsening of bed material occurs only in alluvial stepped-bed morphologies (cascades, step-pools and step-rapids) mainly due to strong slope–channel coupling processes. Moreover, the specific ratio of bankfull width and d90 predicts the interlocking of boulder steps as well as well-developed step-pool morphology. An amount of large woody debris is closely related to the activity of strict local forest management in evaluated channels, as a significant decrease in large woody debris pieces is observed with increasing basin area.

Channel-reach morphology controls of headwater streams based in flysch geologic structures: An example from the Outer Western Carpathians, Czech Republic
A detailed measurement of 93 channel reaches that were classified with an adjusted Montgomery-Buffington (1997) reach-scale system provided comprehensive information of approximately 9 at-a-reach parameters: the channel gradient, the bankfull width, the bankfull depth, d90, the percentage of resistant rocks in the bed sediment, the number of pieces of large woody debris, valley confinement, direct sediment inputs and the presence of fluvial accumulations in the stream channel. In addition, the quantified intensity of sediment transport (i.e. ratio between sediment supply and transport capacity in longitudinal stream profiles) during flood events have been estimated by the one-dimensional bedload transport model (TOMSED), which was validated in two local streams. The principal component analysis of the at-a-reach parameters did not reveal significant groups of channel-reach morphologies; thus, the selected parameters that exclude sediment transport dynamics within stream longitudinal profile cannot reliably distinguish or predict individual channel reach morphologies. Nevertheless, the channel gradient represented the most significant single explanatory variable for stepped-bed morphologies. The addition of bedload transport parameters demonstrated that limited sediment supply streams and streams with limited transport capacities featured different successions of the channel reach morphologies in terms of the channel gradient and, subsequently, the fluvial continuity. The bedrock-cascades and step-pools were significant for the first case, whereas cascade and step-rapid morphology often occurred in higher sediment supply conditions.

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